EntityFramework Core – Add an implementation of IDesignTimeDbContextFactory

Problem

Your DbContext in a separate project – class library project. You are trying to add new migration and update database, and you are running into this error:

Unable to create an object of type ‘CodingBlastDbContext’. Add an implementation of ‘IDesignTimeDbContextFactory’ to the project, or see https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns supported at design time.

 

Solution

So you need to implement this interface, and you are not sure how to do it.

You can add a class that implements IDesignTimeDbContextFactory inside of your Web project.

Here is the sample code:

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

        var builder = new DbContextOptionsBuilder<CodingBlastDbContext>();

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

        builder.UseSqlServer(connectionString);

        return new CodingBlastDbContext(builder.Options);
    }
}

 

Then, navigate to your Database project and run the following from command line:

dotnet ef migrations add InitialMigration -s ../Web/
dotnet ef database update -s ../Web/

-s stands for startup project and ../Web/ is the location of my web/startup project.

 

Code

The full example is available on GitHub.