Remove dependency on EF Core "Issue26779" AppContext switch

src/JsonApiDotNetCore/Configuration/JsonApiOptions.cs

@@ -102,12 +102,6 @@ public sealed class JsonApiOptions : IJsonApiOptions
         }
     };
 
-    static JsonApiOptions()
-    {
-        // Bug workaround for https://github.com/dotnet/efcore/issues/27436
-        AppContext.SetSwitch("Microsoft.EntityFrameworkCore.Issue26779", true);
-    }
-
     public JsonApiOptions()
     {
         _lazySerializerReadOptions = new Lazy<JsonSerializerOptions>(() => new JsonSerializerOptions(SerializerOptions), LazyThreadSafetyMode.PublicationOnly);

src/JsonApiDotNetCore/Repositories/EntityFrameworkCoreRepository.cs

@@ -547,6 +547,34 @@ private void MarkRelationshipAsLoaded(TResource leftResource, RelationshipAttrib
         EntityEntry<TResource> leftEntry = _dbContext.Entry(leftResource);
         CollectionEntry rightCollectionEntry = leftEntry.Collection(relationship.Property.Name);
         rightCollectionEntry.IsLoaded = true;
+
+        if (rightCollectionEntry.Metadata is ISkipNavigation skipNavigation)
+        {
+            MarkManyToManyRelationshipAsLoaded(leftEntry, skipNavigation);
+        }
+    }
+
+    private void MarkManyToManyRelationshipAsLoaded(EntityEntry<TResource> leftEntry, ISkipNavigation skipNavigation)
+    {
+        string[] primaryKeyNames = skipNavigation.ForeignKey.PrincipalKey.Properties.Select(property => property.Name).ToArray();
+        object?[] primaryKeyValues = GetCurrentKeyValues(leftEntry, primaryKeyNames);
+
+        string[] foreignKeyNames = skipNavigation.ForeignKey.Properties.Select(property => property.Name).ToArray();
+
+        foreach (EntityEntry joinEntry in _dbContext.ChangeTracker.Entries().Where(entry => entry.Metadata == skipNavigation.JoinEntityType).ToList())
+        {
+            object?[] foreignKeyValues = GetCurrentKeyValues(joinEntry, foreignKeyNames);
+
+            if (primaryKeyValues.SequenceEqual(foreignKeyValues))
+            {
+                joinEntry.State = EntityState.Unchanged;
+            }
+        }
+    }
+
+    private static object?[] GetCurrentKeyValues(EntityEntry entry, IEnumerable<string> keyNames)
+    {
+        return keyNames.Select(keyName => entry.Property(keyName).CurrentValue).ToArray();
     }
 
     protected async Task UpdateRelationshipAsync(RelationshipAttribute relationship, TResource leftResource, object? valueToAssign,

test/JsonApiDotNetCoreTests/IntegrationTests/CompositeKeys/Car.cs

@@ -47,4 +47,7 @@ public override string? Id
 
     [HasOne]
     public Dealership? Dealership { get; set; }
+
+    [HasMany]
+    public ISet<Dealership> PreviousDealerships { get; set; } = new HashSet<Dealership>();
 }

test/JsonApiDotNetCoreTests/IntegrationTests/CompositeKeys/CompositeDbContext.cs

@@ -34,5 +34,9 @@ protected override void OnModelCreating(ModelBuilder builder)
         builder.Entity<Dealership>()
             .HasMany(dealership => dealership.Inventory)
             .WithOne(car => car.Dealership!);
+
+        builder.Entity<Car>()
+            .HasMany(car => car.PreviousDealerships)
+            .WithMany(dealership => dealership.SoldCars);
     }
 }

test/JsonApiDotNetCoreTests/IntegrationTests/CompositeKeys/CompositeKeyTests.cs

@@ -508,4 +508,52 @@ await _testContext.RunOnDatabaseAsync(async dbContext =>
             carInDatabase.Should().BeNull();
         });
     }
+
+    [Fact]
+    public async Task Can_remove_from_ManyToMany_relationship()
+    {
+        // Arrange
+        Dealership existingDealership = _fakers.Dealership.Generate();
+        existingDealership.SoldCars = _fakers.Car.Generate(2).ToHashSet();
+
+        await _testContext.RunOnDatabaseAsync(async dbContext =>
+        {
+            await dbContext.ClearTableAsync<Car>();
+            dbContext.Dealerships.Add(existingDealership);
+            await dbContext.SaveChangesAsync();
+        });
+
+        var requestBody = new
+        {
+            data = new[]
+            {
+                new
+                {
+                    type = "cars",
+                    id = existingDealership.SoldCars.ElementAt(1).StringId
+                }
+            }
+        };
+
+        string route = $"/dealerships/{existingDealership.StringId}/relationships/soldCars";
+
+        // Act
+        (HttpResponseMessage httpResponse, string responseDocument) = await _testContext.ExecuteDeleteAsync<string>(route, requestBody);
+
+        // Assert
+        httpResponse.ShouldHaveStatusCode(HttpStatusCode.NoContent);
+
+        responseDocument.Should().BeEmpty();
+
+        await _testContext.RunOnDatabaseAsync(async dbContext =>
+        {
+            Dealership dealershipInDatabase = await dbContext.Dealerships.Include(dealership => dealership.SoldCars).FirstWithIdAsync(existingDealership.Id);
+
+            dealershipInDatabase.SoldCars.ShouldHaveCount(1);
+            dealershipInDatabase.SoldCars.Single().Id.Should().Be(existingDealership.SoldCars.ElementAt(0).Id);
+
+            List<Car> carsInDatabase = await dbContext.Cars.ToListAsync();
+            carsInDatabase.ShouldHaveCount(2);
+        });
+    }
 }

test/JsonApiDotNetCoreTests/IntegrationTests/CompositeKeys/Dealership.cs

@@ -13,4 +13,7 @@ public sealed class Dealership : Identifiable<int>
 
     [HasMany]
     public ISet<Car> Inventory { get; set; } = new HashSet<Car>();
+
+    [HasMany]
+    public ISet<Car> SoldCars { get; set; } = new HashSet<Car>();
 }