Add migration with different assembly

Solution 1:

All EF commands have this check:

if (targetAssembly != migrationsAssembly) 
       throw MigrationsAssemblyMismatchError;

targetAssembly = the target project you are operating on. On the command line, it is the project in the current working directory. In Package Manager Console, it is whatever project is selected in the drop down box on the top right of that window pane.

migrationsAssembly = assembly containing code for migrations. This is configurable. By default, this will be the assembly containing the DbContext, in your case, Project.Data.dll. As the error message suggests, you have have a two options to resolve this

1 - Change target assembly.

cd Project.Data/
dotnet ef --startup-project ../Project.Api/ migrations add Initial

// code doesn't use .MigrationsAssembly...just rely on the default
options.UseSqlServer(connection)

2 - Change the migrations assembly.

cd Project.Api/
dotnet ef migrations add Initial

// change the default migrations assembly
options.UseSqlServer(connection, b => b.MigrationsAssembly("Project.Api"))

Solution 2:

I had the same problem until I noticed that on the package manager console top bar => "Default Projects" was supposed to be "Project.Data" and not "Project.API".

Once you target the "Project.Data" from the dropdown list and run the migration you should be fine.

default project selection

Solution 3:

Using EF Core 2, you can easily separate your Web project from your Data (DbContext) project. In fact, you just need to implement the IDesignTimeDbContextFactory interface. According to Microsoft docs, IDesignTimeDbContextFactory is:

A factory for creating derived DbContext instances. Implement this interface to enable design-time services for context types that do not have a public default constructor. At design-time, derived DbContext instances can be created in order to enable specific design-time experiences such as Migrations. Design-time services will automatically discover implementations of this interface that are in the startup assembly or the same assembly as the derived context.

In the bottom code snippet you can see my implementation of DbContextFactory which is defined inside my Data project:

public class DbContextFactory : IDesignTimeDbContextFactory<KuchidDbContext>
{
    public KuchidDbContext CreateDbContext(string[] args)
    {
        var configuration = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json")
            .Build();

        var dbContextBuilder = new DbContextOptionsBuilder<KuchidDbContext>();

        var connectionString = configuration.GetConnectionString("Kuchid");

        dbContextBuilder.UseSqlServer(connectionString);

        return new KuchidDbContext(dbContextBuilder.Options);
    }
}

Now, I can initialize EF migration by setting my Web project as the StartUp project and selecting my Data project inside the Package Manager Console.

Add-Migration initial

You can find more details here. However, this blog post uses an obsoleted class instead of IDesignTimeDbContextFactory.

Solution 4:

Add Migration With CLI Command:

dotnet ef migrations add NewMigration --project YourAssemblyName

Add Migration With PMC Command:

Add-Migration NewMigration -Project YourAssemblyName

Link About CLI Commands

Link About PMC Commands

Solution 5:

I ran on the same problem and found this

We’re you trying to run your migrations on a class library? So was I. Turns out this isn’t supported yet, so we’ll need to work around it.

EDIT: I found solution on this git repo