Initial implementation of lazy-loading and entities with constructors

Parts of issues #3342, #240, #10509, #3797

The main things here are:
- Support for injecting values into parameterized entity constructors
  - Property values are injected if the parameter type and name matches
  - The current DbContext as DbContext or a derived DbContext type
  - A service from the internal or external service provider
  - A delegate to a method of a service
  - The IEntityType for the entity
- Use of the above to inject lazy loading capabilities into entities

For lazy loading, either the ILazyLoader service can be injected directly, or a delegate can be injected if the entity class cannot take a dependency on the EF assembly--see the examples below.

Currently all constructor injection is done by convention.

Remaining work includes:
- API/attributes to configure the constructor binding
- Allow factory to be used instead of using the constructor directly. (Functional already, but no API or convention to configure it.)
- Allow property injection for services
- Configuration of which entities/properties should be lazy loaded and which should not

### Examples

In this example EF will use the private constructor passing in values from the database when creating entity instances. (Note that it is assumed that _blogId has been configured as the key.)

```C#
public class Blog
{
    private int _blogId;

    // This constructor used by EF Core
    private Blog(
        int blogId,
        string title,
        int? monthlyRevenue)
    {
        _blogId = blogId;
        Title = title;
        MonthlyRevenue = monthlyRevenue;
    }

    public Blog(
        string title,
        int? monthlyRevenue = null)
        : this(0, title, monthlyRevenue)
    {
    }

    public string Title { get; }
    public int? MonthlyRevenue { get; set; }
}
```

In this example, EF will inject the ILazyLoader instance, which is then used to enable lazy-loading on navigation properties. Note that the navigation properties must have backing fields and all access by EF will go through the backing fields to prevent EF triggering lazy loading itself.

```C#
public class LazyBlog
{
    private readonly ILazyLoader _loader;
    private ICollection<LazyPost> _lazyPosts = new List<LazyPost>();

    public LazyBlog()
    {
    }

    private LazyBlog(ILazyLoader loader)
    {
        _loader = loader;
    }

    public int Id { get; set; }

    public ICollection<LazyPost> LazyPosts
        => _loader.Load(this, ref _lazyPosts);
}

public class LazyPost
{
    private readonly ILazyLoader _loader;
    private LazyBlog _lazyBlog;

    public LazyPost()
    {
    }

    private LazyPost(ILazyLoader loader)
    {
        _loader = loader;
    }

    public int Id { get; set; }

    public LazyBlog LazyBlog
    {
        get => _loader.Load(this, ref _lazyBlog);
        set => _lazyBlog = value;
    }
}
```

This example is the same as the last example, except EF is matching the delegate type and parameter name and injecting a delegate for the ILazyLoader.Load method so that the entity class does not need to reference the EF assembly. A small extension method can be included in the entity assembly to make it a bit easier to use the delegate.

```C#
public class LazyPocoBlog
{
    private readonly Action<object, string> _loader;
    private ICollection<LazyPocoPost> _lazyPocoPosts = new List<LazyPocoPost>();

    public LazyPocoBlog()
    {
    }

    private LazyPocoBlog(Action<object, string> lazyLoader)
    {
        _loader = lazyLoader;
    }

    public int Id { get; set; }

    public ICollection<LazyPocoPost> LazyPocoPosts
        => _loader.Load(this, ref _lazyPocoPosts);
}

public class LazyPocoPost
{
    private readonly Action<object, string> _loader;
    private LazyPocoBlog _lazyPocoBlog;

    public LazyPocoPost()
    {
    }

    private LazyPocoPost(Action<object, string> lazyLoader)
    {
        _loader = lazyLoader;
    }

    public int Id { get; set; }

    public LazyPocoBlog LazyPocoBlog
    {
        get => _loader.Load(this, ref _lazyPocoBlog);
        set => _lazyPocoBlog = value;
    }
}

public static class TestPocoLoadingExtensions
{
    public static TRelated Load<TRelated>(
        this Action<object, string> loader,
        object entity,
        ref TRelated navigationField,
        [CallerMemberName] string navigationName = null)
        where TRelated : class
    {
        loader?.Invoke(entity, navigationName);

        return navigationField;
    }
}
```

samples/OracleProvider/src/OracleProvider/Metadata/Conventions/OracleConventionSetBuilder.cs

@@ -3,6 +3,7 @@
 
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal;
+using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.EntityFrameworkCore.Storage.Converters;
 using Microsoft.EntityFrameworkCore.Storage.Internal;
@@ -54,7 +55,9 @@ public static ConventionSet Build()
                 new RelationalConventionSetBuilderDependencies(oracleTypeMapper, currentContext: null, setFinder: null))
                 .AddConventions(
                     new CoreConventionSetBuilder(
-                        new CoreConventionSetBuilderDependencies(oracleTypeMapper))
+                        new CoreConventionSetBuilderDependencies(
+                            oracleTypeMapper,
+                            new ConstructorBindingFactory()))
                         .CreateConventionSet());
         }
     }

samples/OracleProvider/test/OracleProvider.FunctionalTests/WithConstructorsOracleTest.cs

@@ -0,0 +1,40 @@
+// 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 Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Storage;
+using Microsoft.EntityFrameworkCore.TestUtilities;
+
+namespace Microsoft.EntityFrameworkCore
+{
+    public class WithConstructorsOracleTest : WithConstructorsTestBase<WithConstructorsOracleTest.WithConstructorsOracleFixture>
+    {
+        public WithConstructorsOracleTest(WithConstructorsOracleFixture fixture)
+            : base(fixture)
+        {
+        }
+
+        protected override void UseTransaction(DatabaseFacade facade, IDbContextTransaction transaction)
+            => facade.UseTransaction(transaction.GetDbTransaction());
+
+        public class WithConstructorsOracleFixture : WithConstructorsFixtureBase
+        {
+            protected override ITestStoreFactory TestStoreFactory => OracleTestStoreFactory.Instance;
+
+            protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext context)
+            {
+                base.OnModelCreating(modelBuilder, context);
+
+                modelBuilder.Entity<HasContext<DbContext>>().ToTable("HasContext_DbContext");
+                modelBuilder.Entity<HasContext<WithConstructorsContext>>().ToTable("HasContext_WithConstructorsContext");
+                modelBuilder.Entity<HasContext<OtherContext>>().ToTable("HasContext_OtherContext");
+
+                modelBuilder.Entity<Blog>(
+                    b => { b.Property("_blogId").HasColumnName("BlogId"); });
+
+                modelBuilder.Entity<Post>(
+                    b => { b.Property("_id").HasColumnName("Id"); });
+            }
+        }
+    }
+}

src/EFCore.Design/Migrations/Design/CSharpSnapshotGenerator.cs

@@ -668,7 +668,8 @@ protected virtual void GenerateEntityTypeAnnotations(
                 annotations,
                 RelationshipDiscoveryConvention.NavigationCandidatesAnnotationName,
                 RelationshipDiscoveryConvention.AmbiguousNavigationsAnnotationName,
-                InversePropertyAttributeConvention.InverseNavigationsAnnotationName);
+                InversePropertyAttributeConvention.InverseNavigationsAnnotationName,
+                CoreAnnotationNames.ConstructorBinding);
 
             if (annotations.Any())
             {

src/EFCore.InMemory/Query/Internal/IMaterializerFactory.cs

@@ -19,6 +19,6 @@ public interface IMaterializerFactory
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
-        Expression<Func<IEntityType, ValueBuffer, object>> CreateMaterializer([NotNull] IEntityType entityType);
+        Expression<Func<IEntityType, ValueBuffer, DbContext, object>> CreateMaterializer([NotNull] IEntityType entityType);
     }
 }

src/EFCore.InMemory/Query/Internal/InMemoryQueryModelVisitor.cs

@@ -49,7 +49,7 @@ private static IEnumerable<TEntity> EntityQuery<TEntity>(
             QueryContext queryContext,
             IEntityType entityType,
             IKey key,
-            Func<IEntityType, ValueBuffer, object> materializer,
+            Func<IEntityType, ValueBuffer, DbContext, object> materializer,
             bool queryStateManager)
             where TEntity : class
             => ((InMemoryQueryContext)queryContext).Store
@@ -67,7 +67,8 @@ private static IEnumerable<TEntity> EntityQuery<TEntity>(
                                             key,
                                             new EntityLoadInfo(
                                                 valueBuffer,
-                                                vr => materializer(t.EntityType, vr)),
+                                                queryContext.Context,
+                                                (vr, c) => materializer(t.EntityType, vr, c)),
                                             queryStateManager,
                                             throwOnNullKey: false);
                                 }));

src/EFCore.InMemory/Query/Internal/MaterializerFactory.cs

@@ -35,7 +35,7 @@ public MaterializerFactory([NotNull] IEntityMaterializerSource entityMaterialize
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
-        public virtual Expression<Func<IEntityType, ValueBuffer, object>> CreateMaterializer(IEntityType entityType)
+        public virtual Expression<Func<IEntityType, ValueBuffer, DbContext, object>> CreateMaterializer(IEntityType entityType)
         {
             Check.NotNull(entityType, nameof(entityType));
 
@@ -45,17 +45,21 @@ var entityTypeParameter
             var valueBufferParameter
                 = Expression.Parameter(typeof(ValueBuffer), "valueBuffer");
 
+            var contextParameter
+                = Expression.Parameter(typeof(DbContext), "context");
+
             var concreteEntityTypes
                 = entityType.GetConcreteTypesInHierarchy().ToList();
 
             if (concreteEntityTypes.Count == 1)
             {
-                return Expression.Lambda<Func<IEntityType, ValueBuffer, object>>(
+                return Expression.Lambda<Func<IEntityType, ValueBuffer, DbContext, object>>(
                     _entityMaterializerSource
                         .CreateMaterializeExpression(
-                            concreteEntityTypes[0], valueBufferParameter),
+                            concreteEntityTypes[0], valueBufferParameter, contextParameter),
                     entityTypeParameter,
-                    valueBufferParameter);
+                    valueBufferParameter,
+                    contextParameter);
             }
 
             var returnLabelTarget = Expression.Label(typeof(object));
@@ -71,7 +75,7 @@ var blockExpressions
                             returnLabelTarget,
                             _entityMaterializerSource
                                 .CreateMaterializeExpression(
-                                    concreteEntityTypes[0], valueBufferParameter))),
+                                    concreteEntityTypes[0], valueBufferParameter, contextParameter))),
                     Expression.Label(
                         returnLabelTarget,
                         Expression.Default(returnLabelTarget.Type))
@@ -87,14 +91,15 @@ var blockExpressions
                         Expression.Return(
                             returnLabelTarget,
                             _entityMaterializerSource
-                                .CreateMaterializeExpression(concreteEntityType, valueBufferParameter)),
+                                .CreateMaterializeExpression(concreteEntityType, valueBufferParameter, contextParameter)),
                         blockExpressions[0]);
             }
 
-            return Expression.Lambda<Func<IEntityType, ValueBuffer, object>>(
+            return Expression.Lambda<Func<IEntityType, ValueBuffer, DbContext, object>>(
                 Expression.Block(blockExpressions),
                 entityTypeParameter,
-                valueBufferParameter);
+                valueBufferParameter,
+                contextParameter);
         }
     }
 }

src/EFCore.Relational/Query/ExpressionVisitors/Internal/BufferedEntityShaper`.cs

@@ -28,7 +28,7 @@ public BufferedEntityShaper(
             [NotNull] IQuerySource querySource,
             bool trackingQuery,
             [NotNull] IKey key,
-            [NotNull] Func<ValueBuffer, object> materializer,
+            [NotNull] Func<ValueBuffer, DbContext, object> materializer,
             [CanBeNull] Dictionary<Type, int[]> typeIndexMap)
             : base(querySource, trackingQuery, key, materializer)
         {
@@ -53,7 +53,7 @@ var entity
                 = (TEntity)queryContext.QueryBuffer
                     .GetEntity(
                         Key,
-                        new EntityLoadInfo(valueBuffer, Materializer, _typeIndexMap),
+                        new EntityLoadInfo(valueBuffer, queryContext.Context, Materializer, _typeIndexMap),
                         queryStateManager: IsTrackingQuery,
                         throwOnNullKey: !AllowNullResult);
 

src/EFCore.Relational/Query/ExpressionVisitors/Internal/BufferedOffsetEntityShaper.cs

@@ -25,7 +25,7 @@ public BufferedOffsetEntityShaper(
             [NotNull] IQuerySource querySource,
             bool trackingQuery,
             [NotNull] IKey key,
-            [NotNull] Func<ValueBuffer, object> materializer,
+            [NotNull] Func<ValueBuffer, DbContext, object> materializer,
             [CanBeNull] Dictionary<Type, int[]> typeIndexMap)
             : base(querySource, trackingQuery, key, materializer, typeIndexMap)
         {

src/EFCore.Relational/Query/ExpressionVisitors/Internal/EntityShaper.cs

@@ -23,7 +23,7 @@ protected EntityShaper(
             [NotNull] IQuerySource querySource,
             bool trackingQuery,
             [NotNull] IKey key,
-            [NotNull] Func<ValueBuffer, object> materializer)
+            [NotNull] Func<ValueBuffer, DbContext, object> materializer)
             : base(querySource)
         {
             IsTrackingQuery = trackingQuery;
@@ -47,7 +47,7 @@ protected EntityShaper(
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
-        protected virtual Func<ValueBuffer, object> Materializer { get; }
+        protected virtual Func<ValueBuffer, DbContext, object> Materializer { get; }
 
         /// <summary>
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used

src/EFCore.Relational/Query/ExpressionVisitors/Internal/IMaterializerFactory.cs

@@ -22,7 +22,7 @@ public interface IMaterializerFactory
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
-        Expression<Func<ValueBuffer, object>> CreateMaterializer(
+        Expression<Func<ValueBuffer, DbContext, object>> CreateMaterializer(
             [NotNull] IEntityType entityType,
             [NotNull] SelectExpression selectExpression,
             [NotNull] Func<IProperty, SelectExpression, int> projectionAdder,

src/EFCore.Relational/Query/ExpressionVisitors/Internal/MaterializerFactory.cs

@@ -41,7 +41,7 @@ public MaterializerFactory(
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
         ///     directly from your code. This API may change or be removed in future releases.
         /// </summary>
-        public virtual Expression<Func<ValueBuffer, object>> CreateMaterializer(
+        public virtual Expression<Func<ValueBuffer, DbContext, object>> CreateMaterializer(
             IEntityType entityType,
             SelectExpression selectExpression,
             Func<IProperty, SelectExpression, int> projectionAdder,
@@ -57,6 +57,9 @@ public virtual Expression<Func<ValueBuffer, object>> CreateMaterializer(
             var valueBufferParameter
                 = Expression.Parameter(typeof(ValueBuffer), "valueBuffer");
 
+            var contextParameter
+                = Expression.Parameter(typeof(DbContext), "context");
+
             var concreteEntityTypes
                 = entityType.GetConcreteTypesInHierarchy().ToList();
 
@@ -72,12 +75,13 @@ var concreteEntityTypes
             var materializer
                 = _entityMaterializerSource
                     .CreateMaterializeExpression(
-                        concreteEntityTypes[0], valueBufferParameter, indexMap);
+                        concreteEntityTypes[0], valueBufferParameter, contextParameter, indexMap);
 
             if (concreteEntityTypes.Count == 1
                 && concreteEntityTypes[0].RootType() == concreteEntityTypes[0])
             {
-                return Expression.Lambda<Func<ValueBuffer, object>>(materializer, valueBufferParameter);
+                return Expression.Lambda<Func<ValueBuffer, DbContext, object>>(
+                    materializer, valueBufferParameter, contextParameter);
             }
 
             var discriminatorProperty = concreteEntityTypes[0].Relational().DiscriminatorProperty;
@@ -98,7 +102,8 @@ var discriminatorPredicate
                 selectExpression.Predicate
                     = new DiscriminatorPredicateExpression(discriminatorPredicate, querySource);
 
-                return Expression.Lambda<Func<ValueBuffer, object>>(materializer, valueBufferParameter);
+                return Expression.Lambda<Func<ValueBuffer, DbContext, object>>(
+                    materializer, valueBufferParameter, contextParameter);
             }
 
             var discriminatorValueVariable
@@ -160,7 +165,8 @@ var discriminatorValue
 
                 materializer
                     = _entityMaterializerSource
-                        .CreateMaterializeExpression(concreteEntityType, valueBufferParameter, indexMap);
+                        .CreateMaterializeExpression(
+                            concreteEntityType, valueBufferParameter, contextParameter, indexMap);
 
                 blockExpressions[1]
                     = Expression.IfThenElse(
@@ -177,9 +183,10 @@ var discriminatorValue
             selectExpression.Predicate
                 = new DiscriminatorPredicateExpression(discriminatorPredicate, querySource);
 
-            return Expression.Lambda<Func<ValueBuffer, object>>(
+            return Expression.Lambda<Func<ValueBuffer, DbContext, object>>(
                 Expression.Block(new[] { discriminatorValueVariable }, blockExpressions),
-                valueBufferParameter);
+                valueBufferParameter,
+                contextParameter);
         }
 
         private static readonly MethodInfo _createUnableToDiscriminateException

src/EFCore.Relational/Query/ExpressionVisitors/Internal/UnbufferedEntityShaper.cs

@@ -24,7 +24,7 @@ public UnbufferedEntityShaper(
             [NotNull] IQuerySource querySource,
             bool trackingQuery,
             [NotNull] IKey key,
-            [NotNull] Func<ValueBuffer, object> materializer)
+            [NotNull] Func<ValueBuffer, DbContext, object> materializer)
             : base(querySource, trackingQuery, key, materializer)
         {
         }
@@ -51,7 +51,7 @@ public virtual TEntity Shape(QueryContext queryContext, ValueBuffer valueBuffer)
                 }
             }
 
-            return (TEntity)Materializer(valueBuffer);
+            return (TEntity)Materializer(valueBuffer, queryContext.Context);
         }
 
         /// <summary>

src/EFCore.Relational/Query/ExpressionVisitors/Internal/UnbufferedOffsetEntityShaper.cs

@@ -24,7 +24,7 @@ public UnbufferedOffsetEntityShaper(
             [NotNull] IQuerySource querySource,
             bool trackingQuery,
             [NotNull] IKey key,
-            [NotNull] Func<ValueBuffer, object> materializer)
+            [NotNull] Func<ValueBuffer, DbContext, object> materializer)
             : base(querySource, trackingQuery, key, materializer)
         {
         }

src/EFCore.Relational/Query/ExpressionVisitors/RelationalEntityQueryableExpressionVisitor.cs

@@ -340,7 +340,7 @@ private static IShaper<TEntity> CreateEntityShaper<TEntity>(
             IQuerySource querySource,
             bool trackingQuery,
             IKey key,
-            Func<ValueBuffer, object> materializer,
+            Func<ValueBuffer, DbContext, object> materializer,
             Dictionary<Type, int[]> typeIndexMap,
             bool useQueryBuffer)
             where TEntity : class

src/EFCore.Specification.Tests/DatabindingTestBase.cs

@@ -862,7 +862,7 @@ public virtual void Entity_added_to_context_is_added_to_navigation_property_bind
         {
             using (var context = CreateF1Context())
             {
-                var ferrari = context.Teams.Include(t => t.Drivers).Single(t => t.Id == Team.Ferrari);
+                var ferrari = context.Teams.Single(t => t.Id == Team.Ferrari);
                 var navBindingList = ((IListSource)ferrari.Drivers).GetList();
 
                 var larry = new Driver
@@ -882,7 +882,7 @@ public virtual void Entity_added_to_navigation_property_binding_list_is_added_to
         {
             using (var context = CreateF1Context())
             {
-                var ferrari = context.Teams.Include(t => t.Drivers).Single(t => t.Id == Team.Ferrari);
+                var ferrari = context.Teams.Single(t => t.Id == Team.Ferrari);
                 var navBindingList = ((IListSource)ferrari.Drivers).GetList();
                 var localDrivers = context.Drivers.Local;
 
@@ -909,7 +909,7 @@ public virtual void Entity_removed_from_navigation_property_binding_list_is_remo
         {
             using (var context = CreateF1Context())
             {
-                var ferrari = context.Teams.Include(t => t.Drivers).Single(t => t.Id == Team.Ferrari);
+                var ferrari = context.Teams.Single(t => t.Id == Team.Ferrari);
                 var navBindingList = ((IListSource)ferrari.Drivers).GetList();
                 var localDrivers = context.Drivers.Local;