entity framework - How do I implement DbContext inheritance for multiple databases in EF7 / .NET Core

Question

I am building web APIs in ASP.NET Core 1.1.

I have a number different databases (for different systems) which have common base schemas for configuration items such as Configuration, Users and groups (about 25 tables in all). I am trying to avoid duplicating the quite extensive EF configuration for the shared part of the model by inheriting from a base class as shown in the diagram.

However, this does not work because of the Entity Framework (EF) requirement to pass DbContextOptions<DerivedRepository> as a parameter to the constructor, where DerivedRepository must match the type of the repository the constructor is called on. The parameter must then be passed down to the base DbContext by calling :base(param).

So when (for example) InvestContext is initialised with DbContextOptions<InvestContext>, it calls base(DbContextOptions<InvestContext>) and EF throws an error because the call to the ConfigurationContext constructor is receiving a parameter of type DbContextOptions<InvestContext> instead of the required type DbContextOptions<ConfigurationContext>. Since the options field on DbContext is defined as

    private readonly DbContextOptions _options;

I can't see a way around this.

What is the best way to define the shared model once and use it multiple times? I guess I could create a helper function and call it from every derived context, but it's not nearly as clean or transparent as inheritance.

Answer 1

I would like to bring this post from the OP's GitHub issue to everyone's attention:

I was able to resolve this without a hack by providing a protected constructor that uses DbContextOptions without any type. Making the second constructor protected ensures that it will not get used by DI.

public class MainDbContext : DbContext {
    public MainDbContext(DbContextOptions<MainDbContext> options)
        : base(options) {
    }

    protected MainDbContext(DbContextOptions options)
        : base(options) {
    }
}

public class SubDbContext : MainDbContext {
    public SubDbContext (DbContextOptions<SubDbContext> options)
        : base(options) {
    }
}