InMemory - bad key management for derived entity types

[saliksaly]

Using in-memory database, ef core 3.1. (or 3.0)
Having abstract class Animal and two derived classes: Cat and Dog.
All are registered as entities in DbContext.
Seeding 2 Cat entities in DbContext.OnModelCreating.

1st problem:
When inserting a new Cat entity to DbSet, receiving error: "ArgumentException: An item with the same key has already been added. Key: 1".
The Id for the new entity shuld be 3 because there are already two.

2nd problem:
When inserting a new Dog entity to DbSet, it behaves inappropriately: replaces Cat entity with id 1 with the new Dog entity and adds new Dog entity with id 1!

Steps to reproduce

Here is asp net core demo app to demonstarte the problem described:
https://github.com/saliksaly/aspnetcoreapp-efcore-inherited-entity-id-problem

Further technical details

EF Core version: 3.1.0
Database provider: Microsoft.EntityFrameworkCore.InMemory
Target framework: .NET Core 3.1
Operating system: Win10 v. 1809
IDE: Visual Studio Community 2019 16.4.4

[ajcvickers]

@saliksaly I was able to reproduce this and it does look like a bug.

Note for team: it looks like the code that peeks into the in-memory database to decide what key value to use is not working correctly when there is inheritance mapping.

[saliksaly]

Hi, would not be there any workaround until 5.0.0 version?
Maybe something similar to DbContextExtensions.ResetValueGenerators in #6872?

[ajcvickers]

@saliksaly Just wanted to let you know that I have started investigating a workaround, but it may take me a while.

[ajcvickers]

@saliksaly I have a PR out to fix this for EF Core 5.0. Here's a workaround for 3.1:

private static void BumpGenerator(
    DbContext context, Type entityClrType, string propertyName, int newLowBound)
{
    var entityType = context.Model.FindEntityType(entityClrType);
    var property = entityType.FindProperty(propertyName);
    var options = context.GetService<IDbContextOptions>().FindExtension<InMemoryOptionsExtension>();
    var inMemoryStore = context.GetService<IInMemoryStoreCache>().GetStore(options.StoreName);
    var generator = inMemoryStore.GetIntegerValueGenerator<int>(property);
    
    var values = new object[entityType.GetDeclaredProperties().Count()];
    values[property.GetIndex()] = newLowBound;
    generator.Bump(values);
}

Use it like this:

BumpGenerator(context, typeof(AnimalBase), nameof(AnimalBase.Id), 2);

context.Add(
    new Cat
    {
        Name = "Tom",
    });

Passing 2 here means that the next value generated will be 3.

Note: this workaround uses EF internal code. This code will change in new releases of EF Core and the workaround will likely break. Use only with EF Core 3.1.

[ShoSashko]

@ajcvickers
I just wanted to clarify. I have the same issue but with string as a key.
EF Core version: 3.1.0
Database provider: Microsoft.EntityFrameworkCore.InMemory
Target framework: .NET Core 3.1

{"An item with the same key has already been added. Key: [email protected]"}

Please let me know if there is any workaround?

[ajcvickers]

@ShoSashko There is a workaround posted above.

[ShoSashko]

@ajcvickers Thanks for the quick response.

Not sure how I can apply this workaround for my specific case, having a string as a PK.
I've tried to change the workaround posted above from int to string

private static void BumpGenerator(
    DbContext context, Type entityClrType, string propertyName, string newLowBound)
        {
            var entityType = context.Model.FindEntityType(entityClrType);
            var property = entityType.FindProperty(propertyName);
            var options = context.GetService<IDbContextOptions>().FindExtension<InMemoryOptionsExtension>();
            var inMemoryStore = context.GetService<IInMemoryStoreCache>().GetStore(options.StoreName);
            var generator = inMemoryStore.GetIntegerValueGenerator<string>(property);

            var values = new object[entityType.GetDeclaredProperties().Count()];
            values[property.GetIndex()] = newLowBound;
            generator.Bump(values);
        }

But it throwing exception of the generator.Bump.

I have doubts that it will work anyway, there is no equal method for GetIntegerValueGenerator for the string.

Please let me know if I am even on the right track.

[ajcvickers]

@ShoSashko No, this code doesn't make sense for strings, but then usually automatically generating string key values also doesn't make sense. You may be running into this breaking change.

[saliksaly]

I have applied the fix to the demo app:
https://github.com/saliksaly/aspnetcoreapp-efcore-inherited-entity-id-problem

I works now, no problems.