Add the ability to run migrations on DbContexts in referenced assemblies

As far as I know, this is not currently possible. The use case is to create a modular system, where modules (in separate assemblies) each contribute one or more DbContexts to the main application. When you run migration add on the main project (possibly with the --all flag), it will include DbContexts in referenced assemblies.

I don’t know if this would scan assemblies or use the DI container (in ASP, at least). Perhaps both. The latter would provide access to connection strings configured in that way.

Related questions:

1. Is this an appropriate way to supply the main application with additional entities, while still having a DbContext local to the module to use in services/repositories specific to that module? It will mean that there will be quite a few DbContexts (zero or more per module), but I don’t think that this could affect performance in any way, since they should be lazy-loaded via DI.
2. I haven’t yet looked into this, but there will be times when I would need something like an IdentityUser in the module’s DbContext. For example, if it’s a forum module, it might have a Topic entity with a relationship to an ApplicationUser/IdentityUser. Is it possible to add a DbSet to a DbContext using an interface maybe, where the concrete type is later discovered? Like public DbSet<IIdentityUser> User { get; set; } (that interface doesn’t actually exist, it’s just an example). The same question would apply to adding the relationship to the entity itself.

[glen-84]

@rowanmiller, Thanks, I will reply there.

@bricelam,

One may not have control of the project containing the DbContext. Imagine a “forum” module that you install with NuGet. You can’t run migrations there, because you don’t have the source, and regardless, it won’t produce the desired result, which is a combined migration in the application that included the module.

The second option that you mentioned will not work either.

What is required is the following:

1. I create a web application.
2. I install a “module” (forum/blog/etc.) as a NuGet/DNX dependency.
3. I add the DbContext from the module with services.AddEntityFramework().AddDbContext<TheModule.ForumDbContext)>() or by passing the services container to the module during Startup and letting it add its own context (this is the way that I had planned to do it).
4. I run dnx . ef migration add MyMigration --all from the web application, and it creates a migration that includes all DbContexts (either by looking at contexts added via the services container, or by doing “assembly scanning”)

This (along with #757) would be very powerful, and would help in enabling the creation of modular applications. Please keep it in mind when working on related issues.

[bricelam]

I have no idea what work needs to be done for this issue anymore. 😃 I suspect most of it will be covered by #2294. Moving to a discussion and closing. Please create new issues for anything that you think is not already tracked elsewhere.