EF Core: Argument type is not assignable to parameter

Question

EF Core: Argument type is not assignable to parameter

.net c# entity-framework entity-framework-core

Question

I have some inheritance chain which start from interface and endsup with actual implmenetation going a couple of steps.

However, this code is 100% correct

IBaseModel model = new ErrorModel();

But when I'm trying something like that:

class MyContext: DbContext{
    public DbSet<ErrorModel> Errors {get; set}
}

and later

DbSet<IBaseModel> set = new MyContext().Errors

this not working (not compiled) and say that Argument Type DbSet<ErrorModel> is not assignable to parameter DbSet<IBaseModel>

What is the problem there and how to resolve it?

UPD1: It's also not working if I'm using base class instead of interface. And code like this

IQueryable<IBaseModel> tests = new MyContext().Errors

also compiled without any issues.

silent_coder

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Ph0en1x · Accepted Answer · 7/5/2016 3:30:51 PM

This is not working, because DbSet<Item> not inherited from DbSet<BaseItem> and it's logically quite difference things, because DbSet<> is a mutable structure. You could add BaseItem into DbSet<BaseItem> but ofcourse you can't add it to DbSet<Item> so this will not work. With the same reason you can't convert lists or other mutable structures.

However, for immutable structures like IEnumerable or IReadOnlyCollection this conversion will work just fine.

EF Core: Argument type is not assignable to parameter

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