Add support for querable functions

src/EFCore.Relational/Extensions/RelationalEntityTypeBuilderExtensions.cs

@@ -264,6 +264,37 @@ public static bool CanSetSchema(
             return entityTypeBuilder.CanSetAnnotation(RelationalAnnotationNames.Schema, schema, fromDataAnnotation);
         }
 
+        /// <summary>
+        ///     Configures the entity as a result of a queryable function.  Prevents a table from being created for this entity.
+        /// </summary>
+        /// <param name="entityTypeBuilder"> The builder for the entity type being configured. </param>
+        /// <returns> The same builder instance so that multiple calls can be chained. </returns>
+        public static EntityTypeBuilder ToQueryableFunctionResultType(
+            [NotNull] this EntityTypeBuilder entityTypeBuilder)
+        {
+            Check.NotNull(entityTypeBuilder, nameof(entityTypeBuilder));
+
+            entityTypeBuilder.Metadata.SetAnnotation(RelationalAnnotationNames.QueryableFunctionResultType, null);
+
+            return entityTypeBuilder;
+        }
+
+        /// <summary>
+        ///     Configures the entity as a result of a queryable function.  Prevents a table from being created for this entity.
+        /// </summary>
+        /// <param name="entityTypeBuilder"> The builder for the entity type being configured. </param>
+        /// <returns> The same builder instance so that multiple calls can be chained. </returns>
+        public static EntityTypeBuilder<TEntity> ToQueryableFunctionResultType<TEntity>(
+            [NotNull] this EntityTypeBuilder<TEntity> entityTypeBuilder)
+             where TEntity : class
+        {
+            Check.NotNull(entityTypeBuilder, nameof(entityTypeBuilder));
+
+            entityTypeBuilder.Metadata.SetAnnotation(RelationalAnnotationNames.QueryableFunctionResultType, null);
+
+            return entityTypeBuilder;
+        }
+
         /// <summary>
         ///     Configures the view that the entity type maps to when targeting a relational database.
         /// </summary>

src/EFCore.Relational/Extensions/RelationalEntityTypeExtensions.cs

@@ -292,6 +292,9 @@ public static bool IsIgnoredByMigrations([NotNull] this IEntityType entityType)
                 return true;
             }
 
+            if (entityType.FindAnnotation(RelationalAnnotationNames.QueryableFunctionResultType) != null)
+                return true;
+
             var viewDefinition = entityType.FindAnnotation(RelationalAnnotationNames.ViewDefinition);
             if (viewDefinition == null)
             {

src/EFCore.Relational/Infrastructure/EntityFrameworkRelationalServicesBuilder.cs

@@ -169,6 +169,7 @@ public override EntityFrameworkServicesBuilder TryAddCoreServices()
             TryAdd<IQueryTranslationPreprocessorFactory, RelationalQueryTranslationPreprocessorFactory>();
             TryAdd<IRelationalParameterBasedQueryTranslationPostprocessorFactory, RelationalParameterBasedQueryTranslationPostprocessorFactory>();
             TryAdd<IRelationalQueryStringFactory, RelationalQueryStringFactory>();
+            TryAdd<INavigationExpandingExpressionVisitorFactory, RelationalNavigationExpandingExpressionVisitorFactory>();
 
             ServiceCollectionMap.GetInfrastructure()
                 .AddDependencySingleton<RelationalSqlGenerationHelperDependencies>()

src/EFCore.Relational/Infrastructure/RelationalModelValidator.cs

@@ -80,7 +80,17 @@ protected virtual void ValidateDbFunctions(
                         RelationalStrings.DbFunctionNameEmpty(methodInfo.DisplayName()));
                 }
 
-                if (dbFunction.TypeMapping == null)
+                if (dbFunction.IsIQueryable)
+                {
+                    if(model.FindEntityType(dbFunction.MethodInfo.ReturnType.GetGenericArguments()[0]) == null)
+                    { 
+                        throw new InvalidOperationException(
+                            RelationalStrings.DbFunctionInvalidReturnType(
+                                methodInfo.DisplayName(),
+                                methodInfo.ReturnType.ShortDisplayName()));
+                    }
+                }
+                else if (dbFunction.TypeMapping == null)
                 {
                     throw new InvalidOperationException(
                         RelationalStrings.DbFunctionInvalidReturnType(

src/EFCore.Relational/Metadata/IDbFunction.cs

@@ -34,6 +34,11 @@ public interface IDbFunction
         /// </summary>
         MethodInfo MethodInfo { get; }
 
+        /// <summary>
+        ///     Whether this method returns IQueryable
+        /// </summary>
+        bool IsIQueryable { get; }
+
         /// <summary>
         ///     The configured store type string
         /// </summary>

src/EFCore.Relational/Metadata/Internal/DbFunction.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Linq.Expressions;
 using System.Reflection;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Diagnostics;
@@ -75,6 +76,19 @@ public DbFunction(
                         methodInfo.DisplayName(), methodInfo.ReturnType.ShortDisplayName()));
             }
 
+            if (methodInfo.ReturnType.IsGenericType
+                && methodInfo.ReturnType.GetGenericTypeDefinition() == typeof(IQueryable<>))
+            {
+                IsIQueryable = true;
+
+                //todo - if the generic argument is not usuable as an entitytype should we throw here?  IE IQueryable<int>
+                //the built in entitytype will throw is the type is not a class
+                if (model.FindEntityType(methodInfo.ReturnType.GetGenericArguments()[0]) == null)
+                {
+                    model.AddEntityType(methodInfo.ReturnType.GetGenericArguments()[0]).SetAnnotation(RelationalAnnotationNames.QueryableFunctionResultType, null);
+                }
+            }
+
             MethodInfo = methodInfo;
 
             _model = model;
@@ -310,6 +324,14 @@ public virtual Func<IReadOnlyCollection<SqlExpression>, SqlExpression> Translati
             set => SetTranslation(value, ConfigurationSource.Explicit);
         }
 
+        /// <summary>
+        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+        ///     any release. You should only use it directly in your code with extreme caution and knowing that
+        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+        /// </summary>
+        public virtual bool IsIQueryable { get; }
+
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
         ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
@@ -345,7 +367,27 @@ private void UpdateTranslationConfigurationSource(ConfigurationSource configurat
         public static DbFunction FindDbFunction(
             [NotNull] IModel model,
             [NotNull] MethodInfo methodInfo)
-            => model[BuildAnnotationName(methodInfo)] as DbFunction;
+        {
+            var dbFunction = model[BuildAnnotationName(methodInfo)] as DbFunction;
+
+            if(dbFunction == null
+                && methodInfo.GetParameters().Any(p => p.ParameterType.IsGenericType && p.ParameterType.GetGenericTypeDefinition() == typeof(Expression<>)))
+            {
+                var parameters = methodInfo.GetParameters().Select(p => p.ParameterType.IsGenericType
+                                        && p.ParameterType.GetGenericTypeDefinition() == typeof(Expression<>)
+                                        && p.ParameterType.GetGenericArguments()[0].GetGenericTypeDefinition() == typeof(Func<>)
+                                    ? p.ParameterType.GetGenericArguments()[0].GetGenericArguments()[0]
+                                    : p.ParameterType).ToArray();
+
+                var nonExpressionMethod = methodInfo.DeclaringType.GetMethod(methodInfo.Name, parameters);
+
+                dbFunction =  nonExpressionMethod != null
+                                ? model[BuildAnnotationName(nonExpressionMethod)] as DbFunction
+                                : null;
+            }
+
+            return dbFunction;
+        }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

src/EFCore.Relational/Metadata/RelationalAnnotationNames.cs

@@ -98,5 +98,10 @@ public static class RelationalAnnotationNames
         ///     The definition of a database view.
         /// </summary>
         public const string ViewDefinition = Prefix + "ViewDefinition";
+
+        /// <summary>
+        ///     The definition of a Queryable Function Result Type.
+        /// </summary>
+        public const string QueryableFunctionResultType = Prefix + "QueryableFunctionResultType";
     }
 }

src/EFCore.Relational/Properties/RelationalStrings.resx

@@ -435,6 +435,12 @@
   <data name="DbFunctionInvalidInstanceType" xml:space="preserve">
     <value>The DbFunction '{function}' defined on type '{type}' must be either a static method or an instance method defined on a DbContext subclass. Instance methods on other types are not supported.</value>
   </data>
+  <data name="DbFunctionCantProjectIQueryable" xml:space="preserve">
+    <value>Queryable Db Functions used in projections cannot return IQueryable.  IQueryable must be converted to a collection type such as List or Array.</value>
+  </data>
+  <data name="DbFunctionProjectedCollectionMustHavePK" xml:space="preserve">
+    <value>Return type of a queryable function '{functionName}' which is used in a projected collection must define a primary key.</value>
+  </data>
   <data name="ConflictingAmbientTransaction" xml:space="preserve">
     <value>An ambient transaction has been detected. The ambient transaction needs to be completed before beginning a transaction on this connection.</value>
   </data>

src/EFCore.Relational/Query/ISqlExpressionFactory.cs

@@ -141,5 +141,6 @@ SqlFunctionExpression Function(
         SelectExpression Select([CanBeNull] SqlExpression projection);
         SelectExpression Select([NotNull] IEntityType entityType);
         SelectExpression Select([NotNull] IEntityType entityType, [NotNull] string sql, [NotNull] Expression sqlArguments);
+		SelectExpression Select([NotNull] IEntityType entityType, [NotNull] SqlFunctionExpression expression);
     }
 }

src/EFCore.Relational/Query/Internal/NullSemanticsRewritingExpressionVisitor.cs

@@ -656,6 +656,13 @@ protected override Expression VisitSqlFunction(SqlFunctionExpression sqlFunction
             return sqlFunctionExpression.Update(newInstance, newArguments);
         }
 
+        protected override Expression VisitQueryableSqlFunctionExpression(QuerableSqlFunctionExpression queryableFunctionExpression)
+        {
+            Check.NotNull(queryableFunctionExpression, nameof(queryableFunctionExpression));
+
+            return queryableFunctionExpression;
+        }
+
         protected override Expression VisitSqlParameter(SqlParameterExpression sqlParameterExpression)
         {
             Check.NotNull(sqlParameterExpression, nameof(sqlParameterExpression));

src/EFCore.Relational/Query/Internal/RelationalNavigationExpandingExpressionVisitor.cs

@@ -0,0 +1,27 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Diagnostics.CodeAnalysis;
+using System.Linq.Expressions;
+
+namespace Microsoft.EntityFrameworkCore.Query.Internal
+{
+    public class RelationalNavigationExpandingExpressionVisitor : NavigationExpandingExpressionVisitor
+    {
+        public RelationalNavigationExpandingExpressionVisitor(
+            [NotNull] QueryCompilationContext queryCompilationContext,
+            [NotNull] IEvaluatableExpressionFilter evaluatableExpressionFilter)
+            : base(queryCompilationContext, evaluatableExpressionFilter)
+        {
+        }
+
+        protected override Expression VisitMethodCall(MethodCallExpression methodCallExpression)
+        {
+            var dbFunction = QueryCompilationContext.Model.FindDbFunction(methodCallExpression.Method);
+
+            return dbFunction?.IsIQueryable == true
+                ? CreateNavigationExpansionExpression(methodCallExpression, QueryCompilationContext.Model.FindEntityType(dbFunction.MethodInfo.ReturnType.GetGenericArguments()[0]))
+                : base.VisitMethodCall(methodCallExpression);
+        }
+    }
+}

src/EFCore.Relational/Query/Internal/RelationalNavigationExpandingExpressionVisitorFactory.cs

@@ -0,0 +1,14 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.EntityFrameworkCore.Query.Internal
+{
+    public class RelationalNavigationExpandingExpressionVisitorFactory : INavigationExpandingExpressionVisitorFactory
+    {
+        public virtual NavigationExpandingExpressionVisitor Create(
+            QueryCompilationContext queryCompilationContext, IEvaluatableExpressionFilter evaluatableExpressionFilter)
+        {
+            return new RelationalNavigationExpandingExpressionVisitor(queryCompilationContext, evaluatableExpressionFilter);
+        }
+    }
+}

src/EFCore.Relational/Query/Internal/RelationalProjectionBindingExpressionVisitor.cs

@@ -9,6 +9,7 @@
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Metadata;
 using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
 using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.EntityFrameworkCore.Utilities;
@@ -22,6 +23,7 @@ public class RelationalProjectionBindingExpressionVisitor : ExpressionVisitor
 
         private SelectExpression _selectExpression;
         private bool _clientEval;
+        private readonly IModel _model;
 
         private readonly IDictionary<ProjectionMember, Expression> _projectionMapping
             = new Dictionary<ProjectionMember, Expression>();
@@ -30,10 +32,12 @@ private readonly IDictionary<ProjectionMember, Expression> _projectionMapping
 
         public RelationalProjectionBindingExpressionVisitor(
             [NotNull] RelationalQueryableMethodTranslatingExpressionVisitor queryableMethodTranslatingExpressionVisitor,
-            [NotNull] RelationalSqlTranslatingExpressionVisitor sqlTranslatingExpressionVisitor)
+            [NotNull] RelationalSqlTranslatingExpressionVisitor sqlTranslatingExpressionVisitor,
+            [NotNull] IModel model)
         {
             _queryableMethodTranslatingExpressionVisitor = queryableMethodTranslatingExpressionVisitor;
             _sqlTranslator = sqlTranslatingExpressionVisitor;
+            _model = model;
         }
 
         public virtual Expression Translate([NotNull] SelectExpression selectExpression, [NotNull] Expression expression)
@@ -242,6 +246,11 @@ protected override Expression VisitNew(NewExpression newExpression)
                 return null;
             }
 
+            if (newExpression.Arguments.Any(arg => arg is MethodCallExpression methodCallExp && _model.FindDbFunction(methodCallExp.Method)?.IsIQueryable == true))
+            {
+                throw new InvalidOperationException(RelationalStrings.DbFunctionCantProjectIQueryable());
+            }
+
             var newArguments = new Expression[newExpression.Arguments.Count];
             for (var i = 0; i < newArguments.Length; i++)
             {

src/EFCore.Relational/Query/Internal/RelationalQueryTranslationPreprocessorFactory.cs

@@ -21,20 +21,23 @@ public class RelationalQueryTranslationPreprocessorFactory : IQueryTranslationPr
     {
         private readonly QueryTranslationPreprocessorDependencies _dependencies;
         private readonly RelationalQueryTranslationPreprocessorDependencies _relationalDependencies;
+        private readonly INavigationExpandingExpressionVisitorFactory _navigationExpandingExpressionVisitorFactory;
 
         public RelationalQueryTranslationPreprocessorFactory(
             [NotNull] QueryTranslationPreprocessorDependencies dependencies,
-            [NotNull] RelationalQueryTranslationPreprocessorDependencies relationalDependencies)
+            [NotNull] RelationalQueryTranslationPreprocessorDependencies relationalDependencies,
+            [NotNull] INavigationExpandingExpressionVisitorFactory navigationExpandingExpressionVisitorFactory)
         {
             _dependencies = dependencies;
             _relationalDependencies = relationalDependencies;
+            _navigationExpandingExpressionVisitorFactory = navigationExpandingExpressionVisitorFactory;
         }
 
         public virtual QueryTranslationPreprocessor Create(QueryCompilationContext queryCompilationContext)
         {
             Check.NotNull(queryCompilationContext, nameof(queryCompilationContext));
 
-            return new RelationalQueryTranslationPreprocessor(_dependencies, _relationalDependencies, queryCompilationContext);
+            return new RelationalQueryTranslationPreprocessor(_dependencies, _relationalDependencies, queryCompilationContext, _navigationExpandingExpressionVisitorFactory);
         }
     }
 }

src/EFCore.Relational/Query/NullabilityBasedSqlProcessingExpressionVisitor.cs

@@ -371,6 +371,9 @@ protected override Expression VisitProjection(ProjectionExpression projectionExp
                 VisitInternal<SqlExpression>(projectionExpression.Expression).ResultExpression);
         }
 
+        protected override Expression VisitQueryableSqlFunctionExpression(QuerableSqlFunctionExpression queryableFunctionExpression)
+            => Check.NotNull(queryableFunctionExpression, nameof(queryableFunctionExpression));
+
         protected override Expression VisitRowNumber(RowNumberExpression rowNumberExpression)
         {
             Check.NotNull(rowNumberExpression, nameof(rowNumberExpression));

src/EFCore.Relational/Query/QuerySqlGenerator.cs

@@ -270,6 +270,17 @@ protected override Expression VisitSqlFunction(SqlFunctionExpression sqlFunction
             return sqlFunctionExpression;
         }
 
+        protected override Expression VisitQueryableSqlFunctionExpression(QuerableSqlFunctionExpression queryableFunctionExpression)
+        {
+            Visit(queryableFunctionExpression.SqlFunctionExpression);
+
+            _relationalCommandBuilder
+                .Append(AliasSeparator)
+                .Append(_sqlGenerationHelper.DelimitIdentifier(queryableFunctionExpression.Alias));
+
+            return queryableFunctionExpression;
+        }
+
         protected override Expression VisitColumn(ColumnExpression columnExpression)
         {
             Check.NotNull(columnExpression, nameof(columnExpression));