Invercargill-Sql/plans/phase-6-unified-query-api.md

Phase 6: Unified Query API

Overview

This phase refactors the query system to provide a unified API for both entity queries and projection queries. The current Query<T> class will become an abstract base class, with EntityQuery<T> handling entity-specific logic and ProjectionQuery<TProjection> adapted to extend the same base.

Goals

1. Create an abstract Query<T> base class with shared state and common methods
2. Extract current Query<T> functionality into EntityQuery<T>
3. Adapt ProjectionQuery<TProjection> to extend Query<T>
4. Update OrmSession.query<T>() to return the appropriate query type based on type registration
5. Standardize return types on ImmutableLot<T> (which extends Lot<T> extends Enumerable<T>)

Current Architecture

┌─────────────────┐     ┌─────────────────────────┐
│    Query<T>     │     │ ProjectionQuery<TProj>  │
│   (concrete)    │     │      (concrete)         │
├─────────────────┤     ├─────────────────────────┤
│ _session        │     │ _query_session          │
│ _filter: Expr?  │     │ _query_definition       │
│ _orderings      │     │ _query_sql_builder      │
│ _limit: int?    │     │ _where_clauses          │
│ _offset: int?   │     │ _order_by_clauses       │
├─────────────────┤     │ _limit_value: int64?    │
│ where()         │     │ _offset_value: int64?   │
│ where_expr()    │     │ _use_or                 │
│ order_by()      │     ├─────────────────────────┤
│ order_by_desc() │     │ where()                 │
│ limit()         │     │ or_where()              │
│ offset()        │     │ order_by()              │
│ materialise()   │     │ order_by_desc()         │
│ materialise_    │     │ limit()                 │
│   async()       │     │ offset()                │
│ first()         │     │ materialise()           │
│ first_async()   │     │ materialise_async()     │
└─────────────────┘     │ first()                 │
                        │ first_async()           │
                        │ to_sql()                │
                        └─────────────────────────┘

Proposed Architecture

                    ┌───────────────────────────┐
                    │     Query<T> (abstract)   │
                    ├───────────────────────────┤
                    │ #_session: OrmSession     │
                    │ #_orderings: Vector<...>  │
                    │ #_limit: int64?           │
                    │ #_offset: int64?          │
                    │ #_use_or: bool            │
                    ├───────────────────────────┤
                    │ where(expr): Query<T>     │
                    │ or_where(expr): Query<T>  │
                    │ order_by(expr): Query<T>  │
                    │ order_by_desc(): Query<T> │
                    │ limit(count): Query<T>    │
                    │ offset(count): Query<T>   │
                    │ materialise(): Immutable  │
                    │   Lot<T>                  │
                    │ materialise_async(): ...  │
                    │ first(): T?               │
                    │ first_async(): T?         │
                    │ to_sql(): string          │
                    │ where_expr(e): Query<T>   │
                    ├───────────────────────────┤
                    │ #build_sql(): string      │
                    │ #get_combined_where()     │
                    └─────────────┬─────────────┘
                                  │
                ┌─────────────────┴─────────────────┐
                │                                   │
┌───────────────┴───────────────┐   ┌───────────────┴───────────────┐
│   EntityQuery<T> (concrete)   │   │ ProjectionQuery<T> (concrete) │
├───────────────────────────────┤   ├───────────────────────────────┤
│ -_filter: Expression?         │   │ -_query_definition            │
│ -_where_clauses: Vector<...>  │   │ -_query_sql_builder           │
│                               │   │ -_where_clauses: Vector<...>  │
├───────────────────────────────┤   ├───────────────────────────────┤
│ #build_sql(): string          │   │ #build_sql(): string          │
│ #get_combined_where()         │   │ #get_combined_where()         │
│ +where_expr(e): EntityQuery<T>│   │ +where_expr(): throws error   │
└───────────────────────────────┘   └───────────────────────────────┘

Implementation Details

1. Abstract Query Base Class

File: src/orm/query.vala

using Invercargill.DataStructures;
using Invercargill.Expressions;

namespace InvercargillSql.Orm {
    
    /**
     * Abstract base class for all queries.
     * 
     * Query<T> provides a fluent interface for building database queries.
     * Subclasses implement specific query execution strategies for entities
     * and projections.
     */
    public abstract class Query<T> : Object {
        
        // Shared state - protected for subclass access
        protected OrmSession _session;
        protected Vector<OrderByClause> _orderings;
        protected int64? _limit;
        protected int64? _offset;
        protected bool _use_or;
        protected Vector<string> _where_clauses;
        
        /**
         * Creates a new Query for the given session.
         */
        protected Query(OrmSession session) {
            _session = session;
            _orderings = new Vector<OrderByClause>();
            _where_clauses = new Vector<string>();
            _limit = null;
            _offset = null;
            _use_or = false;
        }
        
        // === Fluent query builders ===
        
        public virtual Query<T> where(string expression) {
            _where_clauses.add(expression);
            return this;
        }
        
        public virtual Query<T> or_where(string expression) {
            _use_or = true;
            _where_clauses.add(expression);
            return this;
        }
        
        public abstract Query<T> where_expr(Expression expression);
        
        public Query<T> order_by(string expression) {
            _orderings.add(new OrderByClause(expression, false));
            return this;
        }
        
        public Query<T> order_by_desc(string expression) {
            _orderings.add(new OrderByClause(expression, true));
            return this;
        }
        
        public Query<T> limit(int64 count) {
            _limit = count;
            return this;
        }
        
        public Query<T> offset(int64 count) {
            _offset = count;
            return this;
        }
        
        // === Execution methods ===
        
        /**
         * Executes the query and returns results.
         */
        public abstract Invercargill.ImmutableLot<T> materialise() throws SqlError;
        
        /**
         * Executes the query asynchronously.
         */
        public abstract async Invercargill.ImmutableLot<T> materialise_async() throws SqlError;
        
        /**
         * Returns the first result or null.
         */
        public virtual T? first() throws SqlError {
            _limit = 1;
            var results = materialise();
            if (results.length > 0) {
                return results.first();
            }
            return null;
        }
        
        /**
         * Returns the first result asynchronously.
         */
        public virtual async T? first_async() throws SqlError {
            _limit = 1;
            var results = yield materialise_async();
            if (results.length > 0) {
                return results.first();
            }
            return null;
        }
        
        /**
         * Returns the SQL for this query.
         */
        public abstract string to_sql();
        
        // === Protected helpers ===
        
        protected string? get_combined_where() {
            if (_where_clauses.length == 0) {
                return null;
            }
            
            if (_where_clauses.length == 1) {
                return _where_clauses.get(0);
            }
            
            var combined = new StringBuilder();
            string connector = _use_or ? " || " : " && ";
            
            bool first = true;
            foreach (var clause in _where_clauses) {
                if (!first) {
                    combined.append(connector);
                }
                combined.append("(");
                combined.append(clause);
                combined.append(")");
                first = false;
            }
            
            return combined.str;
        }
    }
}

2. EntityQuery Implementation

File: src/orm/entity-query.vala (new file)

using Invercargill.DataStructures;
using Invercargill.Expressions;
using InvercargillSql.Dialects;
using InvercargillSql.Expressions;

namespace InvercargillSql.Orm {
    
    /**
     * Query implementation for entity types.
     * 
     * EntityQuery<T> handles queries for registered entity types,
     * using EntityMapper for materialization and ExpressionToSqlVisitor
     * for WHERE clause generation.
     */
    public class EntityQuery<T> : Query<T> {
        
        private Expression? _filter;
        
        internal EntityQuery(OrmSession session) {
            base(session);
            _filter = null;
        }
        
        public override Query<T> where(string expression) {
            // Parse string to Expression and store
            _filter = ExpressionParser.parse(expression);
            _where_clauses.add(expression);
            return this;
        }
        
        public override Query<T> or_where(string expression) {
            // For EntityQuery, combine with existing filter using OR
            var new_filter = ExpressionParser.parse(expression);
            if (_filter != null) {
                _filter = new BinaryExpression(
                    _filter, 
                    new_filter, 
                    BinaryOperator.OR
                );
            } else {
                _filter = new_filter;
            }
            _use_or = true;
            _where_clauses.add(expression);
            return this;
        }
        
        public override Query<T> where_expr(Expression expression) {
            _filter = expression;
            return this;
        }
        
        public override Invercargill.ImmutableLot<T> materialise() throws SqlError {
            var mapper = _session.get_mapper<T>();
            var dialect = _session.get_dialect();
            
            // Build SQL
            var sql = build_select_sql(mapper, dialect);
            var command = _session.get_connection().create_command(sql);
            
            // Add parameters if filter exists
            if (_filter != null) {
                var visitor = new ExpressionToSqlVisitor(dialect, mapper);
                _filter.accept(visitor);
                
                var parameters = visitor.get_parameters();
                var param_names = visitor.get_parameter_names();
                var param_array = parameters.to_array();
                var name_array = param_names.to_array();
                
                for (int i = 0; i < param_array.length && i < name_array.length; i++) {
                    command.with_parameter<Invercargill.Element>(name_array[i], param_array[i]);
                }
            }
            
            // Execute and materialize
            var results = command.execute_query();
            var entities = new Vector<T>();
            
            foreach (var row in results) {
                try {
                    var entity = mapper.materialise(row);
                    entities.add(entity);
                } catch (Error e) {
                    throw new SqlError.GENERAL_ERROR(
                        "Failed to materialize entity: %s".printf(e.message)
                    );
                }
            }
            
            return entities.to_immutable_buffer();
        }
        
        public override async Invercargill.ImmutableLot<T> materialise_async() throws SqlError {
            var mapper = _session.get_mapper<T>();
            var dialect = _session.get_dialect();
            
            var sql = build_select_sql(mapper, dialect);
            var command = _session.get_connection().create_command(sql);
            
            if (_filter != null) {
                var visitor = new ExpressionToSqlVisitor(dialect, mapper);
                _filter.accept(visitor);
                
                var parameters = visitor.get_parameters();
                var param_names = visitor.get_parameter_names();
                var param_array = parameters.to_array();
                var name_array = param_names.to_array();
                
                for (int i = 0; i < param_array.length && i < name_array.length; i++) {
                    command.with_parameter<Invercargill.Element>(name_array[i], param_array[i]);
                }
            }
            
            var results = yield command.execute_query_async();
            var entities = new Vector<T>();
            
            foreach (var row in results) {
                try {
                    var entity = mapper.materialise(row);
                    entities.add(entity);
                } catch (Error e) {
                    throw new SqlError.GENERAL_ERROR(
                        "Failed to materialize entity: %s".printf(e.message)
                    );
                }
            }
            
            return entities.to_immutable_buffer();
        }
        
        public override string to_sql() {
            try {
                var mapper = _session.get_mapper<T>();
                var dialect = _session.get_dialect();
                return build_select_sql(mapper, dialect);
            } catch (SqlError e) {
                return "-- Error building SQL: %s".printf(e.message);
            }
        }
        
        private string build_select_sql(EntityMapper<T> mapper, SqlDialect dialect) {
            var sql = new StringBuilder();
            sql.append("SELECT * FROM ");
            sql.append(mapper.table_name);
            
            // WHERE clause
            if (_filter != null) {
                var visitor = new ExpressionToSqlVisitor(dialect, mapper);
                _filter.accept(visitor);
                sql.append(" WHERE ");
                sql.append(visitor.get_sql());
            }
            
            // ORDER BY
            if (_orderings.length > 0) {
                sql.append(" ORDER BY ");
                bool first = true;
                foreach (var ordering in _orderings) {
                    if (!first) {
                        sql.append(", ");
                    }
                    sql.append(ordering.expression);
                    if (ordering.descending) {
                        sql.append(" DESC");
                    }
                    first = false;
                }
            }
            
            // LIMIT/OFFSET
            if (_limit != null) {
                sql.append_printf(" LIMIT %lld", _limit);
            }
            if (_offset != null) {
                sql.append_printf(" OFFSET %lld", _offset);
            }
            
            return sql.str;
        }
    }
}

3. Updated ProjectionQuery

File: src/orm/projections/projection-query.vala

Key changes:

• Extend Query<TProjection> instead of Object
• Change _limit_value/_offset_value to use base class _limit/_offset
• Change _order_by_clauses to use base class _orderings
• Change _where_clauses to use base class _where_clauses
• Change _use_or to use base class _use_or
• Implement where_expr() to throw an error (projections use string-based where)

• Change return types to ImmutableLot<TProjection>

  public class ProjectionQuery<TProjection> : Query<TProjection> {
      
  private ProjectionDefinition _query_definition;
  private ProjectionSqlBuilder _query_sql_builder;
      
  internal ProjectionQuery(
      OrmSession session, 
      ProjectionDefinition definition,
      ProjectionSqlBuilder sql_builder
  ) {
      base(session);  // Initialize base class
      _query_definition = definition;
      _query_sql_builder = sql_builder;
  }
      
  // where() and or_where() use base class implementation
      
  public override Query<TProjection> where_expr(Expression expression) {
      // Projections don't support Expression-based where clauses
      // because they need to translate through the projection definition
      throw new SqlError.GENERAL_ERROR(
          "ProjectionQuery does not support where_expr(). Use where() with a string expression instead."
      );
  }
      
  public override Invercargill.ImmutableLot<TProjection> materialise() throws SqlError {
      string? where_expr = get_combined_where();
          
      BuiltQuery built = _query_sql_builder.build_with_split(
          where_expr,
          _orderings,  // Use base class field
          _limit,      // Use base class field
          _offset      // Use base class field
      );
          
      string sql = built.sql;
      var connection = _session.get_connection();  // Use base class session
      var command = connection.create_command(sql);
      var results = command.execute_query();
          
      var mapper = new ProjectionMapper<TProjection>(_query_definition);
          
      try {
          var vector = mapper.map_all(results);
          return vector.to_immutable_buffer();
      } catch (ProjectionError e) {
          throw new SqlError.GENERAL_ERROR(
              @"Failed to materialize projection: $(e.message)"
          );
      }
  }
      
  // Similar changes for materialise_async(), first(), first_async()
      
  public override string to_sql() {
      string? where_expr = get_combined_where();
          
      BuiltQuery built = _query_sql_builder.build_with_split(
          where_expr,
          _orderings,
          _limit,
          _offset
      );
          
      return built.sql;
  }
  }
  

4. Updated OrmSession

File: src/orm/orm-session.vala

/**
 * Creates a new query for type T.
 * 
 * Returns EntityQuery<T> if T is a registered entity type.
 * Returns ProjectionQuery<T> if T is a registered projection type.
 * 
 * @return A new Query<T> instance appropriate for type T
 * @throws SqlError if T is neither a registered entity nor projection
 */
public Query<T> query<T>() throws SqlError {
    var type = typeof(T);
    
    // Check if it's a registered entity
    if (_mappers.contains(type)) {
        return new EntityQuery<T>(this);
    }
    
    // Check if it's a registered projection
    var projection_def = projection_registry.get(type);
    if (projection_def != null) {
        var sql_builder = new ProjectionSqlBuilder(projection_def, _dialect);
        return new ProjectionQuery<T>(this, projection_def, sql_builder);
    }
    
    throw new SqlError.GENERAL_ERROR(
        "Type %s is not registered as an entity or projection".printf(type.name())
    );
}

/**
 * Gets the SQL dialect for internal use.
 */
internal SqlDialect get_dialect() {
    return _dialect;
}

5. OrmSession API Changes

The following methods become internal or are removed:

Method	Change
execute_query<T>(Query<T>)	Remove - logic moved to EntityQuery
execute_query_async<T>(Query<T>)	Remove - logic moved to EntityQuery
query_projection<T>()	Deprecate - use query<T>() instead
get_connection()	Keep as internal
get_dialect()	Add as internal

Migration Guide

For Entity Queries

Before:

var users = session.query<User>()
    .where("age > 18")
    .materialise();

After:

// Same API, but now returns ImmutableLot<User>
var users = session.query<User>()
    .where("age > 18")
    .materialise();

For Projection Queries

Before:

var stats = session.query_projection<UserOrderStats>()
    .where("user_id > 100")
    .materialise();

After:

// Use query<T>() instead of query_projection<T>()
var stats = session.query<UserOrderStats>()
    .where("user_id > 100")
    .materialise();

New Unified Features

Both query types now support:

// or_where() now available on both
var results = session.query<User>()
    .where("age > 18")
    .or_where("name == 'Admin'")
    .materialise();

// to_sql() now available on both
string sql = session.query<User>()
    .where("age > 18")
    .to_sql();

Implementation Checklist

• Create abstract Query<T> base class in src/orm/query.vala
• Create EntityQuery<T> in src/orm/entity-query.vala
• Update ProjectionQuery<TProjection> to extend Query<T>
• Update OrmSession.query<T>() to dispatch to correct type
• Add get_dialect() method to OrmSession
• Remove execute_query<T>() and execute_query_async<T>() from OrmSession
• Deprecate query_projection<T>() (keep for backward compatibility)
• Update src/meson.build to include new entity-query.vala
• Update tests to use unified API
• Update documentation

Testing Strategy

1. Unit Tests for EntityQuery

   • Test where(), or_where(), where_expr()
   • Test order_by(), order_by_desc()
   • Test limit(), offset()
   • Test materialise(), materialise_async()
   • Test first(), first_async()
   • Test to_sql()

2. Unit Tests for ProjectionQuery

   • Same tests as EntityQuery
   • Test that where_expr() throws appropriate error

3. Integration Tests for OrmSession.query()

   • Test dispatch to EntityQuery for registered entities
   • Test dispatch to ProjectionQuery for registered projections
   • Test error for unregistered types

4. Backward Compatibility Tests

   • Ensure existing entity query tests pass
   • Ensure existing projection query tests pass

Risks and Mitigations

Risk	Mitigation
Breaking existing code	Keep query_projection<T>() as deprecated method
Type inference issues	Ensure return type is Query<T> not concrete type
ImmutableLot conversion	Use to_immutable_buffer() extension method
Expression handling in EntityQuery	Reuse existing ExpressionToSqlVisitor

Files Changed

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File	Change
src/orm/query.vala	Convert to abstract class
src/orm/entity-query.vala	New file
src/orm/projections/projection-query.vala	Extend Query
src/orm/orm-session.vala	Update query() dispatch
src/meson.build	Add entity-query.vala
src/tests/orm-test.vala	Update tests
src/tests/projection-test.vala	Update tests