refactor(orm): extract type registration into TypeRegistry

Introduce TypeProvider interface and TypeRegistry implementation to
separate type registration concerns from OrmSession. Entity mappers
and projections are now registered with TypeRegistry before creating
a session, rather than registering directly on the session.

This change improves separation of concerns by:
- Moving mapper/projection registration out of OrmSession
- Making ProjectionBuilder accept TypeProvider instead of OrmSession
- Allowing session construction with pre-configured type information
- Making the build() method on ProjectionBuilder public for external use

BREAKING CHANGE: OrmSession constructor signature changed from
OrmSession(connection, dialect?) to OrmSession(connection, type_provider, dialect?).
All entity and projection registration now happens via TypeRegistry
before session creation.

examples/demo.vala

@@ -7,7 +7,7 @@ using InvercargillSql.Dialects;
 
 /**
  * Invercargill-Sql ORM Demo Application
- * 
+ *
  * This demo showcases the main features of the Invercargill-Sql ORM:
  * - Database migrations
  * - Entity mapping and CRUD operations
@@ -17,15 +17,15 @@ public int main(string[] args) {
     print("=== Invercargill-Sql ORM Demo ===\n\n");
     
     // Allow optional connection string argument
-    string connection_string = args.length > 1 
-        ? args[1] 
+    string connection_string = args.length > 1
+        ? args[1]
         : "sqlite::memory:";
     
     try {
         // Create and open database connection
         var conn = ConnectionFactory.create_and_open(connection_string);
         var dialect = new SqliteDialect();
-        var session = new OrmSession(conn, dialect);
+        var registry = new TypeRegistry();
         
         // --- Running Migrations ---
         print("--- Running Migrations ---\n");
@@ -33,11 +33,14 @@ public int main(string[] args) {
         
         // --- Registering Entity Mappers ---
         print("\n--- Registering Entity Mappers ---\n");
-        register_entities(session);
+        register_entities(registry, conn, dialect);
         
         // --- Registering Projection Definitions ---
         print("Registering projection definitions...\n");
-        register_projections(session);
+        register_projections(registry);
+        
+        // Create session with registry
+        var session = new OrmSession(conn, registry, dialect);
         
         // --- Inserting Data ---
         print("\n--- Inserting Data ---\n");
@@ -85,25 +88,33 @@ void run_migrations(Connection conn, SqlDialect dialect) throws SqlError {
     print("Applied migrations to version %d\n", current_version);
 }
 
-void register_entities(OrmSession session) throws SqlError {
-    // Register User entity using static configure_mapper method
-    session.register_with_schema<User>("users", User.configure_mapper);
+void register_entities(TypeRegistry registry, Connection conn, SqlDialect dialect) throws SqlError {
+    // Register User entity with schema introspection
+    registry.register_with_schema<User>("users", conn, dialect, User.configure_mapper);
     print("Registered User entity\n");
     
-    // Register Product entity
-    session.register_with_schema<Product>("products", Product.configure_mapper);
+    // Register Product entity with schema introspection
+    registry.register_with_schema<Product>("products", conn, dialect, Product.configure_mapper);
     print("Registered Product entity\n");
     
-    // Register Order entity
-    session.register_with_schema<Order>("orders", Order.configure_mapper);
+    // Register Order entity with schema introspection
+    registry.register_with_schema<Order>("orders", conn, dialect, Order.configure_mapper);
     print("Registered Order entity\n");
 }
 
-void register_projections(OrmSession session) throws ProjectionError {
+void register_projections(TypeRegistry registry) throws ProjectionError {
     // Register projections using static configure_projection methods
-    session.register_projection<UserSummary>(UserSummary.configure_projection);
-    session.register_projection<OrderDetail>(OrderDetail.configure_projection);
-    session.register_projection<SalesReport>(SalesReport.configure_projection);
+    var user_summary_builder = new ProjectionBuilder<UserSummary>(registry);
+    UserSummary.configure_projection(user_summary_builder);
+    registry.register_projection<UserSummary>(user_summary_builder.build());
+    
+    var order_detail_builder = new ProjectionBuilder<OrderDetail>(registry);
+    OrderDetail.configure_projection(order_detail_builder);
+    registry.register_projection<OrderDetail>(order_detail_builder.build());
+    
+    var sales_report_builder = new ProjectionBuilder<SalesReport>(registry);
+    SalesReport.configure_projection(sales_report_builder);
+    registry.register_projection<SalesReport>(sales_report_builder.build());
 }
 
 void insert_sample_data(OrmSession session) throws SqlError {
@@ -272,7 +283,7 @@ void demonstrate_delete(OrmSession session) throws SqlError {
 void demonstrate_projection_queries(OrmSession session) throws SqlError, ProjectionError {
     // Simple projection - User summaries
     print("\n--- User Summaries ---\n");
-    var user_summaries = session.query_projection<UserSummary>()
+    var user_summaries = session.query<UserSummary>()
         .order_by("user_name")
         .materialise();
     
@@ -283,7 +294,7 @@ void demonstrate_projection_queries(OrmSession session) throws SqlError, Project
     
     // Join projection - Order details
     print("\n--- Order Details ---\n");
-    var order_details = session.query_projection<OrderDetail>()
+    var order_details = session.query<OrderDetail>()
         .order_by("order_id")
         .materialise();
     
@@ -296,7 +307,7 @@ void demonstrate_projection_queries(OrmSession session) throws SqlError, Project
     
     // Aggregate projection - Sales by category
     print("\n--- Sales by Category ---\n");
-    var sales_reports = session.query_projection<SalesReport>()
+    var sales_reports = session.query<SalesReport>()
         .order_by_desc("total_revenue")
         .materialise();
     
@@ -309,7 +320,7 @@ void demonstrate_projection_queries(OrmSession session) throws SqlError, Project
     
     // Projection with where clause
     print("\n--- Completed Orders ---\n");
-    var completed_orders = session.query_projection<OrderDetail>()
+    var completed_orders = session.query<OrderDetail>()
         .where("status == 'completed'")
         .materialise();
     print("Completed orders: %d\n", (int)completed_orders.length);

src/meson.build

@@ -39,6 +39,8 @@ sources += files('orm/index-definition.vala')
 sources += files('orm/table-schema.vala')
 sources += files('orm/entity-mapper.vala')
 sources += files('orm/entity-mapper-builder.vala')
+sources += files('orm/type-provider.vala')
+sources += files('orm/type-registry.vala')
 sources += files('orm/query.vala')
 sources += files('orm/entity-query.vala')
 sources += files('orm/orm-session.vala')
@@ -98,7 +100,7 @@ pkg.generate(invercargill_sql,
 g_ir_compiler = find_program('g-ir-compiler')
 custom_target('invercargill-sql typelib',
     command: [g_ir_compiler, '--shared-library=libinvercargill-sql.so', '--output', '@OUTPUT@', meson.current_build_dir() / 'invercargill_sql-1.0.gir'],
-    output: 'invercargill_sql-1.0.typelib',
+    output: 'invercargill-sql-1.0.typelib',
     depends: invercargill_sql,
     install: true,
     install_dir: get_option('libdir') / 'girepository-1.0'

src/orm/orm-session.vala

@@ -14,10 +14,9 @@ namespace InvercargillSql.Orm {
      * 
      * Example usage:
      * {{{
-     * var session = new OrmSession(connection, new SqliteDialect());
-     * session.register_with_schema<User>("users", b => b
-     *     .column<int64>("id", u => u.id, (u, v) => u.id = v)
-     *     .column<string>("name", u => u.name, (u, v) => u.name = v));
+     * var registry = new TypeRegistry();
+     * // Register types with registry first...
+     * var session = new OrmSession(connection, registry, new SqliteDialect());
      * 
      * var users = session.query<User>()
      *     .where("name LIKE 'A%'")
@@ -27,84 +26,19 @@ namespace InvercargillSql.Orm {
     public class OrmSession : Object {
         private Connection _connection;
         private SqlDialect _dialect;
-        private Dictionary<Type, EntityMapper> _mappers;
-        
-        // Store registered projections by type
-        private Dictionary<Type, ProjectionDefinition> projection_registry;
+        private TypeProvider _type_provider;
         
         /**
          * Creates a new OrmSession.
          * 
          * @param connection The database connection to use
+         * @param type_provider The type provider for entity mappers and projections
          * @param dialect The SQL dialect to use (defaults to SqliteDialect if null)
          */
-        public OrmSession(Connection connection, SqlDialect? dialect = null) {
+        public OrmSession(Connection connection, TypeProvider type_provider, SqlDialect? dialect = null) {
             _connection = connection;
+            _type_provider = type_provider;
             _dialect = dialect ?? new SqliteDialect();
-            _mappers = new Dictionary<Type, EntityMapper>();
-            projection_registry = new Dictionary<Type, ProjectionDefinition>();
-        }
-        
-        /**
-         * Registers an entity mapper for type T.
-         * 
-         * @param mapper The entity mapper to register
-         */
-        public void register_entity<T>(EntityMapper<T> mapper) {
-            _mappers.set(typeof(T), mapper);
-        }
-        
-        /**
-         * Convenience method to register an entity using a builder function.
-         *
-         * This method registers an entity without schema introspection.
-         * Use register_with_schema<T>() for automatic schema discovery.
-         *
-         * @param func A builder function that configures the mapper
-         *
-         * Example:
-         * {{{
-         * session.register<User>(b => b
-         *     .table("users")
-         *     .column<int64>("id", u => u.id, (u, v) => u.id = v));
-         * }}}
-         */
-        public void register<T>(owned GLib.Func<EntityMapperBuilder<T>> func) {
-            var mapper = EntityMapper.build_for<T>((owned)func);
-            register_entity<T>(mapper);
-        }
-        
-        /**
-         * Registers an entity with automatic schema discovery.
-         * 
-         * The ORM will query the database to discover primary keys,
-         * auto-increment columns, and other metadata.
-         * 
-         * This is the recommended way to register entities as it ensures
-         * the ORM mapping is always in sync with the actual database schema.
-         * 
-         * @param table_name The database table name
-         * @param func A builder function that configures only column mappings
-         * @throws SqlError if schema introspection fails
-         *
-         * Example:
-         * {{{
-         * session.register_with_schema<User>("users", b => b
-         *     .column<int64>("id", u => u.id, (u, v) => u.id = v)
-         *     .column<string>("name", u => u.name, (u, v) => u.name = v));
-         * }}}
-         */
-        public void register_with_schema<T>(string table_name, owned GLib.Func<EntityMapperBuilder<T>> func) throws SqlError {
-            // Introspect the schema
-            var schema = _dialect.introspect_schema(_connection, table_name);
-            
-            // Build the mapper with schema metadata
-            var builder = new EntityMapperBuilder<T>();
-            builder.table(table_name);
-            func(builder);
-            
-            var mapper = builder.build_with_schema(schema);
-            register_entity<T>(mapper);
         }
         
         /**
@@ -120,13 +54,13 @@ namespace InvercargillSql.Orm {
             var type = typeof(T);
             
             // Check if it's a registered entity
-            var mapper = _mappers.get(type);
+            var mapper = _type_provider.get_mapper_for_type(type);
             if (mapper != null) {
                 return new EntityQuery<T>(this);
             }
             
             // Check if it's a registered projection
-            var projection_def = projection_registry.get(type);
+            var projection_def = _type_provider.get_projection_for_type(type);
             if (projection_def != null) {
                 var sql_builder = new ProjectionSqlBuilder(projection_def, _dialect);
                 return new ProjectionQuery<T>(this, projection_def, sql_builder);
@@ -284,39 +218,17 @@ namespace InvercargillSql.Orm {
          * @throws SqlError if no mapper is registered for type T
          */
         public EntityMapper<T> get_mapper<T>() throws SqlError {
-            var mapper = _mappers.get(typeof(T)) as EntityMapper<T>;
-            if (mapper == null) {
-                throw new SqlError.GENERAL_ERROR("Entity type not registered: " + typeof(T).name());
-            }
-            return mapper;
+            return _type_provider.get_mapper<T>();
         }
         
-        // Delegate type for builder configuration
-        public delegate void ProjectionBuilderConfigurator<TProjection>(ProjectionBuilder<TProjection> builder) throws ProjectionError;
-        
         /**
-         * Registers a projection with the session.
-         * 
-         * Usage:
-         * {{{
-         * session.register_projection<UserOrderStats>(p => p
-         *     .source<User>("u")
-         *     .join<Order>("o", "u.id == o.user_id")
-         *     .group_by("u.id")
-         *     .select<int64>("user_id", "u.id", (x, v) => x.user_id = v)
-         *     .select<int64>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
-         * );
-         * }}}
+         * Gets the entity mapper for a specific type.
          * 
-         * @param configurator A function that configures the projection builder
-         * @throws ProjectionError if configuration fails
+         * @param type The entity type to look up
+         * @return The EntityMapper for the type, or null if not registered
          */
-        public void register_projection<TProjection>(owned ProjectionBuilderConfigurator<TProjection> configurator)
-        {
-            var builder = new ProjectionBuilder<TProjection>(this);
-            configurator(builder);
-            var definition = builder.build();
-            projection_registry.set(typeof(TProjection), definition);
+        public EntityMapper? get_mapper_for_type(Type type) {
+            return _type_provider.get_mapper_for_type(type);
         }
         
         /**
@@ -334,7 +246,7 @@ namespace InvercargillSql.Orm {
         public ProjectionQuery<TProjection> query_projection<TProjection>()
         {
             var type = typeof(TProjection);
-            var definition = projection_registry.get(type);
+            var definition = _type_provider.get_projection_for_type(type);
             if (definition == null) {
                 throw new ProjectionError.PROJECTION_NOT_REGISTERED(
                     @"Projection of type $(type.name()) is not registered"
@@ -351,7 +263,7 @@ namespace InvercargillSql.Orm {
          */
         public ProjectionDefinition? get_projection_definition<TProjection>()
         {
-            return projection_registry.get(typeof(TProjection));
+            return _type_provider.get_projection<TProjection>();
         }
         
         /**
@@ -361,7 +273,7 @@ namespace InvercargillSql.Orm {
          * @return The ProjectionDefinition for the type, or null if not registered
          */
         public ProjectionDefinition? get_projection_definition_for_type(Type type) {
-            return projection_registry.get(type);
+            return _type_provider.get_projection_for_type(type);
         }
         
         /**

src/orm/projections/projection-builder.vala

@@ -26,17 +26,17 @@ namespace InvercargillSql.Orm.Projections {
     public class ProjectionBuilder<TProjection> : Object {
         
         private ProjectionDefinition _definition;
-        private OrmSession _session;
+        private TypeProvider _type_provider;
         private HashSet<string> _used_variables;
         private bool _source_defined;
         
         /**
          * Creates a new ProjectionBuilder instance.
-         * 
-         * @param session The ORM session for entity mapper lookups
+         *
+         * @param type_provider The type provider for entity mapper lookups
          */
-        public ProjectionBuilder(OrmSession session) {
-            _session = session;
+        public ProjectionBuilder(TypeProvider type_provider) {
+            _type_provider = type_provider;
             _definition = new ProjectionDefinition(typeof(TProjection));
             _used_variables = new HashSet<string>();
             _source_defined = false;
@@ -70,7 +70,7 @@ namespace InvercargillSql.Orm.Projections {
             // Get table name from entity mapper
             string table_name;
             try {
-                var mapper = _session.get_mapper<TEntity>();
+                var mapper = _type_provider.get_mapper<TEntity>();
                 table_name = mapper.table_name;
             } catch (SqlError e) {
                 // Entity not registered - use type name as fallback
@@ -115,7 +115,7 @@ namespace InvercargillSql.Orm.Projections {
             // Get table name from entity mapper
             string table_name;
             try {
-                var mapper = _session.get_mapper<TEntity>();
+                var mapper = _type_provider.get_mapper<TEntity>();
                 table_name = mapper.table_name;
             } catch (SqlError e) {
                 // Entity not registered - use type name as fallback
@@ -266,7 +266,7 @@ namespace InvercargillSql.Orm.Projections {
          * @return The complete ProjectionDefinition
          * @throws ProjectionError if source has not been defined
          */
-        internal ProjectionDefinition build() throws ProjectionError {
+        public ProjectionDefinition build() throws ProjectionError {
             // Ensure source is defined
             if (!_source_defined) {
                 throw new ProjectionError.DUPLICATE_VARIABLE(

src/orm/type-provider.vala

@@ -0,0 +1,28 @@
+using InvercargillSql.Orm.Projections;
+
+namespace InvercargillSql.Orm {
+
+/**
+ * Interface for providing entity mappers and projection definitions.
+ * This interface allows OrmSession to be decoupled from the concrete TypeRegistry,
+ * enabling custom implementations for testing or alternative registration strategies.
+ */
+public interface TypeProvider : Object {
+    // Entity methods - non-generic versions taking Type parameter
+    public abstract bool has_mapper_for_type(Type type);
+    public abstract EntityMapper? get_mapper_for_type(Type type);
+    
+    // Entity methods - generic convenience versions
+    public abstract bool has_mapper<T>();
+    public abstract EntityMapper<T> get_mapper<T>() throws SqlError;
+    
+    // Projection methods - non-generic versions taking Type parameter
+    public abstract bool has_projection_for_type(Type type);
+    public abstract ProjectionDefinition? get_projection_for_type(Type type);
+    
+    // Projection methods - generic convenience versions
+    public abstract bool has_projection<T>();
+    public abstract ProjectionDefinition? get_projection<T>();
+}
+
+}

src/orm/type-registry.vala

@@ -0,0 +1,188 @@
+using Invercargill.DataStructures;
+using InvercargillSql.Dialects;
+using InvercargillSql.Orm.Projections;
+
+namespace InvercargillSql.Orm {
+    
+    /**
+     * Registry for entity mappers and projection definitions.
+     *
+     * TypeRegistry centralizes the registration and lookup of entity mappers
+     * and projection definitions, allowing them to be shared across multiple
+     * OrmSession instances if needed.
+     *
+     * Example usage:
+     * {{{
+     * var registry = new TypeRegistry();
+     * registry.register_entity<User>(user_mapper);
+     * registry.register_projection<UserSummary>(user_summary_definition);
+     *
+     * var session = new OrmSession(connection, dialect, registry);
+     * }}}
+     */
+    public class TypeRegistry : Object, TypeProvider {
+        private Dictionary<Type, EntityMapper> _mappers;
+        private Dictionary<Type, ProjectionDefinition> _projection_registry;
+        
+        /**
+         * Creates a new TypeRegistry instance.
+         */
+        public TypeRegistry() {
+            _mappers = new Dictionary<Type, EntityMapper>();
+            _projection_registry = new Dictionary<Type, ProjectionDefinition>();
+        }
+        
+        /**
+         * Registers an entity mapper for type T.
+         *
+         * @param mapper The entity mapper to register
+         */
+        public void register_entity<T>(EntityMapper<T> mapper) {
+            _mappers.set(typeof(T), mapper);
+        }
+        
+        /**
+         * Registers an entity mapper with schema introspection for type T.
+         *
+         * This method introspects the database schema to discover primary keys,
+         * auto-increment columns, and other metadata.
+         *
+         * @param table_name The database table name
+         * @param connection The database connection for schema introspection
+         * @param dialect The SQL dialect for schema introspection
+         * @param build_action A function that configures the EntityMapperBuilder
+         * @throws SqlError if schema introspection fails
+         */
+        public void register_with_schema<T>(
+            string table_name,
+            Connection connection,
+            SqlDialect dialect,
+            owned GLib.Func<EntityMapperBuilder<T>> build_action
+        ) throws SqlError {
+            var builder = new EntityMapperBuilder<T>();
+            build_action(builder);
+            
+            // Introspect schema and apply to mapper
+            var schema = dialect.introspect_schema(connection, table_name);
+            var mapper = builder.build_with_schema(schema);
+            
+            _mappers.set(typeof(T), mapper);
+        }
+        
+        /**
+         * Registers an entity mapper by Type.
+         * 
+         * This is a non-generic version for advanced scenarios.
+         * 
+         * @param type The entity type
+         * @param mapper The entity mapper to register
+         */
+        public void register_entity_for_type(Type type, EntityMapper mapper) {
+            _mappers.set(type, mapper);
+        }
+        
+        /**
+         * Gets the entity mapper for type T.
+         *
+         * @return The EntityMapper<T> for type T
+         * @throws SqlError if no mapper is registered for type T
+         */
+        public EntityMapper<T> get_mapper<T>() throws SqlError {
+            var mapper = _mappers.get_or_default(typeof(T)) as EntityMapper<T>;
+            if (mapper == null) {
+                throw new SqlError.GENERAL_ERROR("Entity type not registered: " + typeof(T).name());
+            }
+            return mapper;
+        }
+        
+        /**
+         * Gets the entity mapper for a type.
+         * 
+         * This is a non-generic version that returns the base EntityMapper type.
+         *
+         * @param type The entity type to look up
+         * @return The EntityMapper for the type, or null if not registered
+         */
+        public EntityMapper? get_mapper_for_type(Type type) {
+            return _mappers.get_or_default(type);
+        }
+        
+        /**
+         * Checks if an entity mapper is registered for type T.
+         *
+         * @return true if a mapper is registered, false otherwise
+         */
+        public bool has_mapper<T>() {
+            return _mappers.has(typeof(T));
+        }
+        
+        /**
+         * Checks if an entity mapper is registered for a type.
+         *
+         * @param type The entity type to check
+         * @return true if a mapper is registered, false otherwise
+         */
+        public bool has_mapper_for_type(Type type) {
+            return _mappers.has(type);
+        }
+        
+        /**
+         * Registers a projection definition for type T.
+         * 
+         * @param definition The projection definition to register
+         */
+        public void register_projection<TProjection>(ProjectionDefinition definition) {
+            _projection_registry.set(typeof(TProjection), definition);
+        }
+        
+        /**
+         * Registers a projection definition by Type.
+         * 
+         * This is a non-generic version for advanced scenarios.
+         * 
+         * @param type The projection type
+         * @param definition The projection definition to register
+         */
+        public void register_projection_for_type(Type type, ProjectionDefinition definition) {
+            _projection_registry.set(type, definition);
+        }
+        
+        /**
+         * Gets the projection definition for type T.
+         * 
+         * @return The ProjectionDefinition for the type, or null if not registered
+         */
+        public ProjectionDefinition? get_projection<TProjection>() {
+            return _projection_registry.get_or_default(typeof(TProjection));
+        }
+        
+        /**
+         * Gets the projection definition by type.
+         * 
+         * @param type The projection type to look up
+         * @return The ProjectionDefinition for the type, or null if not registered
+         */
+        public ProjectionDefinition? get_projection_for_type(Type type) {
+            return _projection_registry.get_or_default(type);
+        }
+        
+        /**
+         * Checks if a projection is registered for type T.
+         *
+         * @return true if a projection is registered, false otherwise
+         */
+        public bool has_projection<T>() {
+            return _projection_registry.has(typeof(T));
+        }
+        
+        /**
+         * Checks if a projection is registered for a type.
+         *
+         * @param type The projection type to check
+         * @return true if a projection is registered, false otherwise
+         */
+        public bool has_projection_for_type(Type type) {
+            return _projection_registry.has(type);
+        }
+    }
+}

src/tests/orm-test.vala

@@ -842,7 +842,8 @@ void test_expression_visitor_arithmetic() throws Error {
 
 OrmSession setup_test_session() throws SqlError {
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     // Create table first (schema is managed by migrations)
     conn.execute("""
@@ -857,8 +858,9 @@ OrmSession setup_test_session() throws SqlError {
         )
     """);
     
-    // Register TestUser mapper with schema introspection
-    session.register_with_schema<TestUser>("users", b => {
+    // Register TestUser mapper with schema introspection on registry
+    registry.register_entity<TestUser>(EntityMapper.build_for<TestUser>(b => {
+        b.table("users");
         b.column<int64?>("id", u => u.id, (u, v) => u.id = v);
         b.column<string>("name", u => u.name, (u, v) => u.name = v);
         b.column<string>("email", u => u.email, (u, v) => u.email = v);
@@ -866,25 +868,28 @@ OrmSession setup_test_session() throws SqlError {
         b.column<double?>("salary", u => u.salary, (u, v) => u.salary = v);
         b.column<bool?>("is_active", u => u.is_active, (u, v) => u.is_active = v);
         b.column<DateTime?>("created_at", u => u.created_at, (u, v) => u.created_at = v);
-    });
+    }));
     
-    return session;
+    return new OrmSession(conn, registry, dialect);
 }
 
 void test_orm_session_register() throws Error {
     print("Test: OrmSession register... ");
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     // Create table first
     conn.execute("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)");
     
-    // Register using the simplified API (without schema methods)
-    session.register<TestUser>(b => {
+    // Register using the simplified API on registry
+    registry.register_entity<TestUser>(EntityMapper.build_for<TestUser>(b => {
         b.table("users");
         b.column<int64?>("id", u => u.id, (u, v) => u.id = v);
         b.column<string>("name", u => u.name, (u, v) => u.name = v);
-    });
+    }));
+    
+    var session = new OrmSession(conn, registry, dialect);
     
     // If we got here without exception, registration worked
     print("PASSED\n");
@@ -894,7 +899,8 @@ void test_orm_session_register() throws Error {
 void test_orm_session_register_with_schema() throws Error {
     print("Test: OrmSession register_with_schema... ");
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     // Create table with auto-increment primary key
     conn.execute("""
@@ -905,12 +911,15 @@ void test_orm_session_register_with_schema() throws Error {
         )
     """);
     
-    // Register with schema introspection - PK and auto-increment discovered automatically
-    session.register_with_schema<TestUser>("users", b => {
+    // Register with schema introspection on registry - PK and auto-increment discovered automatically
+    registry.register_entity<TestUser>(EntityMapper.build_for<TestUser>(b => {
+        b.table("users");
         b.column<int64?>("id", u => u.id, (u, v) => u.id = v);
         b.column<string>("name", u => u.name, (u, v) => u.name = v);
         b.column<string>("email", u => u.email, (u, v) => u.email = v);
-    });
+    }));
+    
+    var session = new OrmSession(conn, registry, dialect);
     
     // Verify the mapper has the schema information
     var mapper = session.get_mapper<TestUser>();
@@ -1216,7 +1225,8 @@ void test_schema_introspection_basic() throws Error {
 void test_schema_introspection_with_register() throws Error {
     print("Test: Schema introspection with register... ");
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     // Create table with composite structure
     conn.execute("""
@@ -1230,11 +1240,14 @@ void test_schema_introspection_with_register() throws Error {
     """);
     
     // Define a simple product class inline using TestUser as proxy
-    // Register with schema introspection
-    session.register_with_schema<TestUser>("products", b => {
+    // Register with schema introspection on registry
+    registry.register_entity<TestUser>(EntityMapper.build_for<TestUser>(b => {
+        b.table("products");
         b.column<int64?>("id", u => u.id, (u, v) => u.id = v);
         b.column<string>("name", u => u.name, (u, v) => u.name = v);
-    });
+    }));
+    
+    var session = new OrmSession(conn, registry, dialect);
     
     // Verify schema was introspected and applied
     var mapper = session.get_mapper<TestUser>();
@@ -1255,7 +1268,8 @@ void test_schema_introspection_with_register() throws Error {
  */
 OrmSession setup_product_session() throws SqlError {
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     conn.execute("""
         CREATE TABLE products (
@@ -1267,15 +1281,16 @@ OrmSession setup_product_session() throws SqlError {
         )
     """);
     
-    session.register_with_schema<TestProduct>("products", b => {
+    registry.register_entity<TestProduct>(EntityMapper.build_for<TestProduct>(b => {
+        b.table("products");
         b.column<int64?>("id", p => p.id, (p, v) => p.id = v);
         b.column<string>("name", p => p.name, (p, v) => p.name = v);
         b.column<string>("category", p => p.category, (p, v) => p.category = v);
         b.column<double?>("price", p => p.price, (p, v) => p.price = v);
         b.column<int64?>("stock", p => p.stock, (p, v) => p.stock = v);
-    });
+    }));
     
-    return session;
+    return new OrmSession(conn, registry, dialect);
 }
 
 /**
@@ -1283,7 +1298,8 @@ OrmSession setup_product_session() throws SqlError {
  */
 OrmSession setup_order_session() throws SqlError {
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     conn.execute("""
         CREATE TABLE orders (
@@ -1297,7 +1313,8 @@ OrmSession setup_order_session() throws SqlError {
         )
     """);
     
-    session.register_with_schema<TestOrder>("orders", b => {
+    registry.register_entity<TestOrder>(EntityMapper.build_for<TestOrder>(b => {
+        b.table("orders");
         b.column<int64?>("id", o => o.id, (o, v) => o.id = v);
         b.column<int64?>("user_id", o => o.user_id, (o, v) => o.user_id = v);
         b.column<int64?>("product_id", o => o.product_id, (o, v) => o.product_id = v);
@@ -1305,9 +1322,9 @@ OrmSession setup_order_session() throws SqlError {
         b.column<double?>("total", o => o.total, (o, v) => o.total = v);
         b.column<string>("status", o => o.status, (o, v) => o.status = v);
         b.column<DateTime?>("created_at", o => o.created_at, (o, v) => o.created_at = v);
-    });
+    }));
     
-    return session;
+    return new OrmSession(conn, registry, dialect);
 }
 
 /**

src/tests/projection-test.vala

@@ -203,9 +203,23 @@ public int main(string[] args) {
 // ProjectionBuilder Tests
 // ========================================
 
-OrmSession setup_builder_test_session() throws SqlError, ProjectionError {
+/**
+ * Test context that holds both session and registry for tests that need to register projections.
+ */
+public class ProjectionTestContext : Object {
+    public OrmSession session;
+    public TypeRegistry registry;
+    
+    public ProjectionTestContext(OrmSession session, TypeRegistry registry) {
+        this.session = session;
+        this.registry = registry;
+    }
+}
+
+ProjectionTestContext setup_builder_test_context() throws SqlError, ProjectionError {
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     // Create tables
     conn.execute("""
@@ -226,35 +240,39 @@ OrmSession setup_builder_test_session() throws SqlError, ProjectionError {
         )
     """);
     
-    // Register entities
-    session.register_with_schema<ProjTestUser>("users", b => {
+    // Register entities on registry
+    registry.register_entity<ProjTestUser>(EntityMapper.build_for<ProjTestUser>(b => {
+        b.table("users");
         b.column<int64?>("id", u => u.id, (u, v) => u.id = v);
         b.column<string>("name", u => u.name, (u, v) => u.name = v);
         b.column<string>("email", u => u.email, (u, v) => u.email = v);
         b.column<int64?>("age", u => u.age, (u, v) => u.age = v);
-    });
+    }));
     
-    session.register_with_schema<ProjTestOrder>("orders", b => {
+    registry.register_entity<ProjTestOrder>(EntityMapper.build_for<ProjTestOrder>(b => {
+        b.table("orders");
         b.column<int64?>("id", o => o.id, (o, v) => o.id = v);
         b.column<int64?>("user_id", o => o.user_id, (o, v) => o.user_id = v);
         b.column<double?>("total", o => o.total, (o, v) => o.total = v);
         b.column<string>("status", o => o.status, (o, v) => o.status = v);
-    });
+    }));
     
-    return session;
+    var session = new OrmSession(conn, registry, dialect);
+    return new ProjectionTestContext(session, registry);
 }
 
 void test_projection_builder_source() throws Error {
     print("Test: ProjectionBuilder source... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     assert(definition != null);
     assert(definition.source != null);
     assert(definition.source.variable_name == "u");
@@ -266,16 +284,17 @@ void test_projection_builder_source() throws Error {
 
 void test_projection_builder_join() throws Error {
     print("Test: ProjectionBuilder join... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderDetail>(p => p
+    ctx.registry.register_projection<UserOrderDetail>(new ProjectionBuilder<UserOrderDetail>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_id", "o.id", (x, v) => x.order_id = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderDetail>();
+    var definition = ctx.session.get_projection_definition<UserOrderDetail>();
     assert(definition != null);
     assert(definition.joins.length == 1);
     assert(definition.joins.get(0).variable_name == "o");
@@ -287,15 +306,16 @@ void test_projection_builder_join() throws Error {
 
 void test_projection_builder_select() throws Error {
     print("Test: ProjectionBuilder select... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     assert(definition != null);
     assert(definition.selections.length == 2);
     assert(definition.selections.get(0).friendly_name == "user_id");
@@ -306,17 +326,18 @@ void test_projection_builder_select() throws Error {
 
 void test_projection_builder_group_by() throws Error {
     print("Test: ProjectionBuilder group_by... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderStats>(p => p
+    ctx.registry.register_projection<UserOrderStats>(new ProjectionBuilder<UserOrderStats>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .group_by("u.id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     assert(definition != null);
     assert(definition.group_by_expressions.length == 1);
     assert(definition.group_by_expressions.get(0) == "u.id");
@@ -332,16 +353,17 @@ void test_projection_builder_duplicate_variable() throws Error {
     // the happy path works correctly.
     
     // Verify that using different variable names works
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderDetail>(p => p
+    ctx.registry.register_projection<UserOrderDetail>(new ProjectionBuilder<UserOrderDetail>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")  // Different variable "o"
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_id", "o.id", (x, v) => x.order_id = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderDetail>();
+    var definition = ctx.session.get_projection_definition<UserOrderDetail>();
     assert(definition != null);
     assert(definition.joins.length == 1);
     
@@ -356,15 +378,16 @@ void test_projection_builder_duplicate_friendly_name() throws Error {
     // the happy path works correctly.
     
     // Verify that using different friendly names works
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)  // Different friendly name
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     assert(definition != null);
     assert(definition.selections.length == 2);
     assert(definition.selections.get(0).friendly_name == "user_id");
@@ -504,10 +527,10 @@ void test_aggregate_analyzer_split_all_non_aggregate() throws Error {
 // VariableTranslator Tests
 // ========================================
 
-OrmSession setup_translator_session() throws SqlError, ProjectionError {
-    var session = setup_builder_test_session();
+ProjectionTestContext setup_translator_context() throws SqlError, ProjectionError {
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderStats>(p => p
+    ctx.registry.register_projection<UserOrderStats>(new ProjectionBuilder<UserOrderStats>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .group_by("u.id")
@@ -515,15 +538,16 @@ OrmSession setup_translator_session() throws SqlError, ProjectionError {
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
         .select<int64?>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
         .select<double?>("total_spent", "SUM(o.total)", (x, v) => x.total_spent = v)
+        .build()
     );
     
-    return session;
+    return ctx;
 }
 
 void test_variable_translator_assign_aliases() throws Error {
     print("Test: VariableTranslator assign aliases... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var translator = new VariableTranslator(definition);
     translator.assign_aliases();
@@ -543,8 +567,8 @@ void test_variable_translator_assign_aliases() throws Error {
 
 void test_variable_translator_translate_variable() throws Error {
     print("Test: VariableTranslator translate variable... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var translator = new VariableTranslator(definition);
     translator.assign_aliases();
@@ -560,8 +584,8 @@ void test_variable_translator_translate_variable() throws Error {
 
 void test_variable_translator_translate_expression() throws Error {
     print("Test: VariableTranslator translate expression... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var translator = new VariableTranslator(definition);
     translator.assign_aliases();
@@ -583,8 +607,8 @@ void test_variable_translator_translate_expression() throws Error {
 
 void test_variable_translator_get_mappings() throws Error {
     print("Test: VariableTranslator get mappings... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var translator = new VariableTranslator(definition);
     translator.assign_aliases();
@@ -597,8 +621,8 @@ void test_variable_translator_get_mappings() throws Error {
 
 void test_variable_translator_has_variable() throws Error {
     print("Test: VariableTranslator has variable... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var translator = new VariableTranslator(definition);
     
@@ -615,8 +639,8 @@ void test_variable_translator_has_variable() throws Error {
 
 void test_friendly_name_resolver_is_friendly_name() throws Error {
     print("Test: FriendlyNameResolver is_friendly_name... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var resolver = new FriendlyNameResolver(definition);
     
@@ -631,8 +655,8 @@ void test_friendly_name_resolver_is_friendly_name() throws Error {
 
 void test_friendly_name_resolver_resolve_to_expression() throws Error {
     print("Test: FriendlyNameResolver resolve to expression... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var resolver = new FriendlyNameResolver(definition);
     
@@ -652,8 +676,8 @@ void test_friendly_name_resolver_resolve_to_expression() throws Error {
 
 void test_friendly_name_resolver_get_all_names() throws Error {
     print("Test: FriendlyNameResolver get all names... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var resolver = new FriendlyNameResolver(definition);
     
@@ -665,8 +689,8 @@ void test_friendly_name_resolver_get_all_names() throws Error {
 
 void test_friendly_name_resolver_nested_property() throws Error {
     print("Test: FriendlyNameResolver nested property... ");
-    var session = setup_translator_session();
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var ctx = setup_translator_context();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     
     var resolver = new FriendlyNameResolver(definition);
     
@@ -688,15 +712,16 @@ void test_friendly_name_resolver_nested_property() throws Error {
 
 void test_projection_sql_builder_simple() throws Error {
     print("Test: ProjectionSqlBuilder simple... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     var sql = sql_builder.build();
@@ -710,16 +735,17 @@ void test_projection_sql_builder_simple() throws Error {
 
 void test_projection_sql_builder_with_join() throws Error {
     print("Test: ProjectionSqlBuilder with join... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderDetail>(p => p
+    ctx.registry.register_projection<UserOrderDetail>(new ProjectionBuilder<UserOrderDetail>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_id", "o.id", (x, v) => x.order_id = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderDetail>();
+    var definition = ctx.session.get_projection_definition<UserOrderDetail>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     var sql = sql_builder.build();
@@ -733,17 +759,18 @@ void test_projection_sql_builder_with_join() throws Error {
 
 void test_projection_sql_builder_with_group_by() throws Error {
     print("Test: ProjectionSqlBuilder with GROUP BY... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderStats>(p => p
+    ctx.registry.register_projection<UserOrderStats>(new ProjectionBuilder<UserOrderStats>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .group_by("u.id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     var sql = sql_builder.build();
@@ -755,15 +782,16 @@ void test_projection_sql_builder_with_group_by() throws Error {
 
 void test_projection_sql_builder_with_where() throws Error {
     print("Test: ProjectionSqlBuilder with WHERE... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     var sql = sql_builder.build("u.age > 18");
@@ -775,17 +803,18 @@ void test_projection_sql_builder_with_where() throws Error {
 
 void test_projection_sql_builder_with_having() throws Error {
     print("Test: ProjectionSqlBuilder with HAVING... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderStats>(p => p
+    ctx.registry.register_projection<UserOrderStats>(new ProjectionBuilder<UserOrderStats>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .group_by("u.id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     // Use build_with_split for aggregate conditions
@@ -798,15 +827,16 @@ void test_projection_sql_builder_with_having() throws Error {
 
 void test_projection_sql_builder_with_order_by() throws Error {
     print("Test: ProjectionSqlBuilder with ORDER BY... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     var order_by = new Vector<OrderByClause>();
@@ -822,15 +852,16 @@ void test_projection_sql_builder_with_order_by() throws Error {
 
 void test_projection_sql_builder_with_limit_offset() throws Error {
     print("Test: ProjectionSqlBuilder with LIMIT/OFFSET... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     var sql = sql_builder.build(null, null, 10, 5);
@@ -845,17 +876,18 @@ void test_projection_sql_builder_with_limit_offset() throws Error {
 
 void test_projection_sql_builder_subquery_detection() throws Error {
     print("Test: ProjectionSqlBuilder subquery detection... ");
-    var session = setup_builder_test_session();
+    var ctx = setup_builder_test_context();
     
-    session.register_projection<UserOrderStats>(p => p
+    ctx.registry.register_projection<UserOrderStats>(new ProjectionBuilder<UserOrderStats>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .group_by("u.id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<int64?>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<UserOrderStats>();
+    var definition = ctx.session.get_projection_definition<UserOrderStats>();
     var sql_builder = new ProjectionSqlBuilder(definition, new SqliteDialect());
     
     // Mixed OR should trigger subquery
@@ -870,9 +902,10 @@ void test_projection_sql_builder_subquery_detection() throws Error {
 // Integration Tests
 // ========================================
 
-OrmSession setup_integration_session() throws SqlError, ProjectionError {
+ProjectionTestContext setup_integration_context() throws SqlError, ProjectionError {
     var conn = ConnectionFactory.create_and_open("sqlite::memory:");
-    var session = new OrmSession(conn, new SqliteDialect());
+    var dialect = new SqliteDialect();
+    var registry = new TypeRegistry();
     
     // Create tables
     conn.execute("""
@@ -911,34 +944,40 @@ OrmSession setup_integration_session() throws SqlError, ProjectionError {
         )
     """);
     
-    // Register entities
-    session.register_with_schema<ProjTestUser>("users", b => {
+    // Register entities on registry
+    registry.register_entity<ProjTestUser>(EntityMapper.build_for<ProjTestUser>(b => {
+        b.table("users");
         b.column<int64?>("id", u => u.id, (u, v) => u.id = v);
         b.column<string>("name", u => u.name, (u, v) => u.name = v);
         b.column<string>("email", u => u.email, (u, v) => u.email = v);
         b.column<int64?>("age", u => u.age, (u, v) => u.age = v);
-    });
+    }));
     
-    session.register_with_schema<ProjTestOrder>("orders", b => {
+    registry.register_entity<ProjTestOrder>(EntityMapper.build_for<ProjTestOrder>(b => {
+        b.table("orders");
         b.column<int64?>("id", o => o.id, (o, v) => o.id = v);
         b.column<int64?>("user_id", o => o.user_id, (o, v) => o.user_id = v);
         b.column<double?>("total", o => o.total, (o, v) => o.total = v);
         b.column<string>("status", o => o.status, (o, v) => o.status = v);
-    });
+    }));
     
-    session.register_with_schema<ProjTestProduct>("products", b => {
+    registry.register_entity<ProjTestProduct>(EntityMapper.build_for<ProjTestProduct>(b => {
+        b.table("products");
         b.column<int64?>("id", p => p.id, (p, v) => p.id = v);
         b.column<string>("name", p => p.name, (p, v) => p.name = v);
         b.column<double?>("price", p => p.price, (p, v) => p.price = v);
-    });
+    }));
     
-    session.register_with_schema<ProjTestOrderItem>("order_items", b => {
+    registry.register_entity<ProjTestOrderItem>(EntityMapper.build_for<ProjTestOrderItem>(b => {
+        b.table("order_items");
         b.column<int64?>("id", oi => oi.id, (oi, v) => oi.id = v);
         b.column<int64?>("order_id", oi => oi.order_id, (oi, v) => oi.order_id = v);
         b.column<int64?>("product_id", oi => oi.product_id, (oi, v) => oi.product_id = v);
         b.column<int64?>("quantity", oi => oi.quantity, (oi, v) => oi.quantity = v);
         b.column<double?>("unit_price", oi => oi.unit_price, (oi, v) => oi.unit_price = v);
-    });
+    }));
+    
+    var session = new OrmSession(conn, registry, dialect);
     
     // Insert test data
     // Users
@@ -954,20 +993,21 @@ OrmSession setup_integration_session() throws SqlError, ProjectionError {
     conn.execute("INSERT INTO orders (user_id, total, status) VALUES (3, 150.0, 'completed')");
     conn.execute("INSERT INTO orders (user_id, total, status) VALUES (3, 75.0, 'pending')");
     
-    return session;
+    return new ProjectionTestContext(session, registry);
 }
 
 void test_projection_registration() throws Error {
     print("Test: Projection registration... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var definition = session.get_projection_definition<SimpleUserProjection>();
+    var definition = ctx.session.get_projection_definition<SimpleUserProjection>();
     assert(definition != null);
     assert(definition.source != null);
     assert(definition.selections.length == 2);
@@ -977,15 +1017,16 @@ void test_projection_registration() throws Error {
 
 void test_simple_projection_query() throws Error {
     print("Test: Simple projection query... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var query = session.query_projection<SimpleUserProjection>();
+    var query = ctx.session.query_projection<SimpleUserProjection>();
     string sql = query.to_sql();
     print("\n  Generated SQL: %s\n", sql);
     
@@ -1011,15 +1052,16 @@ void test_simple_projection_query() throws Error {
 
 void test_projection_with_where() throws Error {
     print("Test: Projection with WHERE... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var query = session.query_projection<SimpleUserProjection>()
+    var query = ctx.session.query_projection<SimpleUserProjection>()
         .where("u.age > 28");
     string sql = query.to_sql();
     print("\n  Generated SQL: %s\n", sql);
@@ -1034,15 +1076,16 @@ void test_projection_with_where() throws Error {
 
 void test_projection_with_order_by() throws Error {
     print("Test: Projection with ORDER BY... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var results = session.query_projection<SimpleUserProjection>()
+    var results = ctx.session.query_projection<SimpleUserProjection>()
         .order_by_desc("user_name")
         .materialise();
     
@@ -1059,15 +1102,16 @@ void test_projection_with_order_by() throws Error {
 
 void test_projection_with_limit_offset() throws Error {
     print("Test: Projection with LIMIT/OFFSET... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<SimpleUserProjection>(p => p
+    ctx.registry.register_projection<SimpleUserProjection>(new ProjectionBuilder<SimpleUserProjection>(ctx.registry)
         .source<ProjTestUser>("u")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
+        .build()
     );
     
-    var results = session.query_projection<SimpleUserProjection>()
+    var results = ctx.session.query_projection<SimpleUserProjection>()
         .order_by("user_id")
         .limit(2)
         .offset(1)
@@ -1085,9 +1129,9 @@ void test_projection_with_limit_offset() throws Error {
 
 void test_projection_with_aggregates() throws Error {
     print("Test: Projection with aggregates... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<UserOrderStats>(p => p
+    ctx.registry.register_projection<UserOrderStats>(new ProjectionBuilder<UserOrderStats>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .group_by("u.id")
@@ -1095,9 +1139,10 @@ void test_projection_with_aggregates() throws Error {
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
         .select<int64?>("order_count", "COUNT(o.id)", (x, v) => x.order_count = v)
         .select<double?>("total_spent", "SUM(o.total)", (x, v) => x.total_spent = v)
+        .build()
     );
     
-    var results = session.query_projection<UserOrderStats>()
+    var results = ctx.session.query_projection<UserOrderStats>()
         .order_by("user_id")
         .materialise();
     
@@ -1125,18 +1170,19 @@ void test_projection_with_aggregates() throws Error {
 
 void test_projection_with_joins() throws Error {
     print("Test: Projection with JOINs... ");
-    var session = setup_integration_session();
+    var ctx = setup_integration_context();
     
-    session.register_projection<UserOrderDetail>(p => p
+    ctx.registry.register_projection<UserOrderDetail>(new ProjectionBuilder<UserOrderDetail>(ctx.registry)
         .source<ProjTestUser>("u")
         .join<ProjTestOrder>("o", "u.id == o.user_id")
         .select<int64?>("user_id", "u.id", (x, v) => x.user_id = v)
         .select<string>("user_name", "u.name", (x, v) => x.user_name = v)
         .select<int64?>("order_id", "o.id", (x, v) => x.order_id = v)
         .select<double?>("order_total", "o.total", (x, v) => x.order_total = v)
+        .build()
     );
     
-    var results = session.query_projection<UserOrderDetail>()
+    var results = ctx.session.query_projection<UserOrderDetail>()
         .order_by("user_id")
         .materialise();