Most of explicit and lazy loading for no-tracking queries

Part of #10042

Current limitations are:

- The lazy-loading delegate injection doesn't support tracking of when an navigation is loaded or not; I have an idea for this
- There is no identity resolution when the entities are not tracked, even if the query behavior is NoTrackingWithIdentityResolution
- The model should validated for only a single service property for a given type

I will submit PRs and/or file issues for these things.

src/EFCore.Abstractions/Infrastructure/ILazyLoader.cs

@@ -34,6 +34,17 @@ void SetLoaded(
         [CallerMemberName] string navigationName = "",
         bool loaded = true);
 
+    /// <summary>
+    ///     Gets whether or not the given navigation as known to be completely loaded or known to be
+    ///     no longer completely loaded.
+    /// </summary>
+    /// <param name="entity">The entity on which the navigation property is located.</param>
+    /// <param name="navigationName">The navigation property name.</param>
+    /// <returns><see langword="true" />if the navigation is known to be loaded.</returns>
+    bool IsLoaded(
+        object entity,
+        [CallerMemberName] string navigationName = "");
+
     /// <summary>
     ///     Loads a navigation property if it has not already been loaded.
     /// </summary>

src/EFCore/ChangeTracking/Internal/InternalEntityEntry.cs

@@ -474,22 +474,23 @@ private void SetServiceProperties(EntityState oldState, EntityState newState)
         {
             foreach (var serviceProperty in EntityType.GetServiceProperties())
             {
-                this[serviceProperty]
-                    = serviceProperty
+                this[serviceProperty] = (this[serviceProperty] is IInjectableService injectableService
+                        ? injectableService.Attaching(Context, Entity, injectableService)
+                        : null)
+                    ?? serviceProperty
                         .ParameterBinding
-                        .ServiceDelegate(
-                            new MaterializationContext(
-                                ValueBuffer.Empty,
-                                Context),
-                            EntityType,
-                            Entity);
+                        .ServiceDelegate(new MaterializationContext(ValueBuffer.Empty, Context), EntityType, Entity);
             }
         }
         else if (newState == EntityState.Detached)
         {
             foreach (var serviceProperty in EntityType.GetServiceProperties())
             {
-                this[serviceProperty] = null;
+                if (!(this[serviceProperty] is IInjectableService detachable)
+                    || detachable.Detaching(Context, Entity))
+                {
+                    this[serviceProperty] = null;
+                }
             }
         }
     }
@@ -846,7 +847,8 @@ private T ReadShadowValue<T>(int shadowIndex)
     private static readonly MethodInfo ReadOriginalValueMethod
         = typeof(InternalEntityEntry).GetTypeInfo().GetDeclaredMethod(nameof(ReadOriginalValue))!;
 
-    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060",
+    [UnconditionalSuppressMessage(
+        "ReflectionAnalysis", "IL2060",
         Justification = "MakeGenericMethod wrapper, see https://github.com/dotnet/linker/issues/2482")]
     internal static MethodInfo MakeReadOriginalValueMethod(Type type)
         => ReadOriginalValueMethod.MakeGenericMethod(type);
@@ -858,7 +860,8 @@ private T ReadOriginalValue<T>(IProperty property, int originalValueIndex)
     private static readonly MethodInfo ReadRelationshipSnapshotValueMethod
         = typeof(InternalEntityEntry).GetTypeInfo().GetDeclaredMethod(nameof(ReadRelationshipSnapshotValue))!;
 
-    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060",
+    [UnconditionalSuppressMessage(
+        "ReflectionAnalysis", "IL2060",
         Justification = "MakeGenericMethod wrapper, see https://github.com/dotnet/linker/issues/2482")]
     internal static MethodInfo MakeReadRelationshipSnapshotValueMethod(Type type)
         => ReadRelationshipSnapshotValueMethod.MakeGenericMethod(type);
@@ -867,7 +870,8 @@ internal static MethodInfo MakeReadRelationshipSnapshotValueMethod(Type type)
     private T ReadRelationshipSnapshotValue<T>(IPropertyBase propertyBase, int relationshipSnapshotIndex)
         => _relationshipsSnapshot.GetValue<T>(this, propertyBase, relationshipSnapshotIndex);
 
-    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060",
+    [UnconditionalSuppressMessage(
+        "ReflectionAnalysis", "IL2060",
         Justification = "MakeGenericMethod wrapper, see https://github.com/dotnet/linker/issues/2482")]
     internal static MethodInfo MakeReadStoreGeneratedValueMethod(Type type)
         => ReadStoreGeneratedValueMethod.MakeGenericMethod(type);
@@ -882,7 +886,8 @@ private T ReadStoreGeneratedValue<T>(int storeGeneratedIndex)
     private static readonly MethodInfo ReadTemporaryValueMethod
         = typeof(InternalEntityEntry).GetTypeInfo().GetDeclaredMethod(nameof(ReadTemporaryValue))!;
 
-    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060",
+    [UnconditionalSuppressMessage(
+        "ReflectionAnalysis", "IL2060",
         Justification = "MakeGenericMethod wrapper, see https://github.com/dotnet/linker/issues/2482")]
     internal static MethodInfo MakeReadTemporaryValueMethod(Type type)
         => ReadTemporaryValueMethod.MakeGenericMethod(type);
@@ -895,7 +900,8 @@ private static readonly MethodInfo GetCurrentValueMethod
         = typeof(InternalEntityEntry).GetTypeInfo().GetDeclaredMethods(nameof(GetCurrentValue)).Single(
             m => m.IsGenericMethod);
 
-    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060",
+    [UnconditionalSuppressMessage(
+        "ReflectionAnalysis", "IL2060",
         Justification = "MakeGenericMethod wrapper, see https://github.com/dotnet/linker/issues/2482")]
     internal static MethodInfo MakeGetCurrentValueMethod(Type type)
         => GetCurrentValueMethod.MakeGenericMethod(type);
@@ -2001,11 +2007,14 @@ public void SetIsLoaded(INavigationBase navigation, bool loaded = true)
                 CoreStrings.ReferenceMustBeLoaded(navigation.Name, navigation.DeclaringEntityType.DisplayName()));
         }
 
-        _stateData.FlagProperty(navigation.GetIndex(), PropertyFlag.IsLoaded, isFlagged: loaded);
-
-        foreach (var lazyLoaderProperty in EntityType.GetServiceProperties().Where(p => p.ClrType == typeof(ILazyLoader)))
+        var lazyLoader = GetLazyLoader();
+        if (lazyLoader != null)
         {
-            ((ILazyLoader?)this[lazyLoaderProperty])?.SetLoaded(Entity, navigation.Name, loaded);
+            lazyLoader.SetLoaded(Entity, navigation.Name, loaded);
+        }
+        else
+        {
+            _stateData.FlagProperty(navigation.GetIndex(), PropertyFlag.IsLoaded, isFlagged: loaded);
         }
     }
 
@@ -2016,7 +2025,14 @@ public void SetIsLoaded(INavigationBase navigation, bool loaded = true)
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public bool IsLoaded(INavigationBase navigation)
-        => _stateData.IsPropertyFlagged(navigation.GetIndex(), PropertyFlag.IsLoaded);
+        => GetLazyLoader()?.IsLoaded(Entity, navigation.Name)
+            ?? _stateData.IsPropertyFlagged(navigation.GetIndex(), PropertyFlag.IsLoaded);
+
+    private ILazyLoader? GetLazyLoader()
+    {
+        var lazyLoaderProperty = EntityType.GetServiceProperties().FirstOrDefault(p => p.ClrType == typeof(ILazyLoader));
+        return lazyLoaderProperty != null ? (ILazyLoader?)this[lazyLoaderProperty] : null;
+    }
 
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

src/EFCore/Diagnostics/CoreLoggerExtensions.cs

@@ -1108,7 +1108,7 @@ private static string ExecutionStrategyRetrying(EventDefinitionBase definition,
     /// <param name="navigationName">The name of the navigation property.</param>
     public static void LazyLoadOnDisposedContextWarning(
         this IDiagnosticsLogger<DbLoggerCategory.Infrastructure> diagnostics,
-        DbContext context,
+        DbContext? context,
         object entityType,
         string navigationName)
     {
@@ -1188,7 +1188,7 @@ private static string NavigationLazyLoading(EventDefinitionBase definition, Even
     /// <param name="navigationName">The name of the navigation property.</param>
     public static void DetachedLazyLoadingWarning(
         this IDiagnosticsLogger<DbLoggerCategory.Infrastructure> diagnostics,
-        DbContext context,
+        DbContext? context,
         object entityType,
         string navigationName)
     {

src/EFCore/Diagnostics/LazyLoadingEventData.cs

@@ -16,13 +16,13 @@ public class LazyLoadingEventData : DbContextEventData
     /// </summary>
     /// <param name="eventDefinition">The event definition.</param>
     /// <param name="messageGenerator">A delegate that generates a log message for this event.</param>
-    /// <param name="context">The current <see cref="DbContext" />.</param>
+    /// <param name="context">The current <see cref="DbContext" />, or <see langword="null" /> if it is no longer available.</param>
     /// <param name="entity">The entity instance on which lazy loading was initiated.</param>
     /// <param name="navigationPropertyName">The navigation property name of the relationship to be loaded.</param>
     public LazyLoadingEventData(
         EventDefinitionBase eventDefinition,
         Func<EventDefinitionBase, EventData, string> messageGenerator,
-        DbContext context,
+        DbContext? context,
         object entity,
         string navigationPropertyName)
         : base(eventDefinition, messageGenerator, context)

src/EFCore/Infrastructure/Internal/LazyLoader.cs

@@ -3,6 +3,7 @@
 
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
+using Microsoft.EntityFrameworkCore.Internal;
 
 namespace Microsoft.EntityFrameworkCore.Infrastructure.Internal;
 
@@ -12,10 +13,12 @@ namespace Microsoft.EntityFrameworkCore.Infrastructure.Internal;
 ///     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 class LazyLoader : ILazyLoader
+public class LazyLoader : ILazyLoader, IInjectableService
 {
     private bool _disposed;
+    private bool _detached;
     private IDictionary<string, bool>? _loadedStates;
+    private List<(object Entity, string NavigationName)>? _isLoading;
 
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -47,6 +50,17 @@ public virtual void SetLoaded(
         _loadedStates[navigationName] = loaded;
     }
 
+    /// <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 IsLoaded(object entity, string navigationName = "")
+        => _loadedStates != null
+            && _loadedStates.TryGetValue(navigationName, out var loaded)
+            && loaded;
+
     /// <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
@@ -61,7 +75,7 @@ public virtual void SetLoaded(
     ///     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>
-    protected virtual DbContext Context { get; }
+    protected virtual DbContext? Context { get; set; }
 
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -75,16 +89,28 @@ public virtual void Load(object entity, [CallerMemberName] string navigationName
         Check.NotNull(entity, nameof(entity));
         Check.NotEmpty(navigationName, nameof(navigationName));
 
-        if (ShouldLoad(entity, navigationName, out var entry))
+        var navEntry = (entity, navigationName);
+        if (!(_isLoading ??= new List<(object Entity, string NavigationName)>()).Contains(navEntry))
         {
             try
             {
-                entry.Load();
+                _isLoading.Add(navEntry);
+                if (ShouldLoad(entity, navigationName, out var entry))
+                {
+                    try
+                    {
+                        entry.Load();
+                    }
+                    catch
+                    {
+                        entry.IsLoaded = false;
+                        throw;
+                    }
+                }
             }
-            catch
+            finally
             {
-                SetLoaded(entity, navigationName, false);
-                throw;
+                _isLoading.Remove(navEntry);
             }
         }
     }
@@ -103,53 +129,49 @@ public virtual async Task LoadAsync(
         Check.NotNull(entity, nameof(entity));
         Check.NotEmpty(navigationName, nameof(navigationName));
 
-        if (ShouldLoad(entity, navigationName, out var entry))
+        var navEntry = (entity, navigationName);
+        if (!(_isLoading ??= new List<(object Entity, string NavigationName)>()).Contains(navEntry))
         {
             try
             {
-                await entry.LoadAsync(cancellationToken).ConfigureAwait(false);
+                _isLoading.Add(navEntry);
+                if (ShouldLoad(entity, navigationName, out var entry))
+                {
+                    try
+                    {
+                        await entry.LoadAsync(cancellationToken).ConfigureAwait(false);
+                    }
+                    catch
+                    {
+                        entry.IsLoaded = false;
+                        throw;
+                    }
+                }
             }
-            catch
+            finally
             {
-                SetLoaded(entity, navigationName, false);
-                throw;
+                _isLoading.Remove(navEntry);
             }
         }
     }
 
     private bool ShouldLoad(object entity, string navigationName, [NotNullWhen(true)] out NavigationEntry? navigationEntry)
     {
-        if (_loadedStates != null
-            && _loadedStates.TryGetValue(navigationName, out var loaded)
-            && loaded)
+        if (!_detached && !IsLoaded(entity, navigationName))
         {
-            navigationEntry = null;
-            return false;
-        }
-
-        if (_disposed)
-        {
-            Logger.LazyLoadOnDisposedContextWarning(Context, entity, navigationName);
-        }
-        else if (Context.ChangeTracker.LazyLoadingEnabled)
-        {
-            // Set early to avoid recursive loading overflow
-            SetLoaded(entity, navigationName, loaded: true);
-
-            var entityEntry = Context.Entry(entity); // Will use local-DetectChanges, if enabled.
-            var tempNavigationEntry = entityEntry.Navigation(navigationName);
-
-            if (entityEntry.State == EntityState.Detached)
+            if (_disposed)
             {
-                Logger.DetachedLazyLoadingWarning(Context, entity, navigationName);
+                Logger.LazyLoadOnDisposedContextWarning(Context, entity, navigationName);
             }
-            else if (!tempNavigationEntry.IsLoaded)
+            else if (Context!.ChangeTracker.LazyLoadingEnabled) // Check again because the nav may be loaded without the loader knowing
             {
-                Logger.NavigationLazyLoading(Context, entity, navigationName);
-
-                navigationEntry = tempNavigationEntry;
+                navigationEntry = Context.Entry(entity).Navigation(navigationName); // Will use local-DetectChanges, if enabled.
+                if (!navigationEntry.IsLoaded)
+                {
+                    Logger.NavigationLazyLoading(Context, entity, navigationName);
 
-                return true;
+                    return true;
+                }
             }
         }
 
@@ -164,5 +186,35 @@ private bool ShouldLoad(object entity, string navigationName, [NotNullWhen(true)
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public virtual void Dispose()
-        => _disposed = true;
+    {
+        Context = null;
+        _disposed = true;
+    }
+
+    /// <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 Detaching(DbContext context, object entity)
+    {
+        _detached = true;
+        Dispose();
+        return false;
+    }
+
+    /// <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 IInjectableService? Attaching(DbContext context, object entity, IInjectableService? existingService)
+    {
+        _disposed = false;
+        _detached = false;
+        Context = context;
+        return this;
+    }
 }