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Declaring interface members with generic return types: "The type parameter [generic type] cannot be used with type arguments"

I'm trying to write an interface to define the set of operations I expect my repositories' Unit of Work implementations to have, and I want this interface to be fulfilled by EF Core's `DbContext` class.

So far this is what I got: _(I know the name is awful, suggestions accepted)_:

```cs
public interface IDbContextable<TContext, TEntityEntry>
    where TContext : class, IDisposable
    where TEntityEntry : class
{
    public TEntityEntry Add([NotNullAttribute] object entity);

    public TEntityEntry<TEntity> Add<TEntity>([NotNullAttribute] TEntity entity)
        where TEntity : class;

    public int SaveChanges();
}
```

The first `Add` method's signature from EF Core is: `public virtual EntityEntry Add([NotNullAttribute] object entity);` - and it works fine.

I'm having trouble with the second. The compiler complains:


 > Error CS0307 The type parameter 'TEntityEntry' cannot be used with type arguments

For completeness, my context class looks like this:

```cs
public partial class EntityFrameworkContext : DbContext, IDbContextable<EntityFrameworkContext, EntityEntry>
{
    //... some extra methods here
}
```

How to properly declare the interface to get rid of the error, and so that the signature: `public virtual EntityEntry<TEntity> Add<TEntity>([NotNullAttribute] TEntity entity) where TEntity : class;` from EF Core becomes valid?

Thanks.