title: Design-time DbContext Creation - EF Core author: bricelam ms.author: bricelam ms.date: 10/27/2017 ms.technology: entity-framework-core

Design-time DbContext Creation¶

Some of the EF Tools commands require a DbContext instance to be created at design time (for example, when running Migrations commands). There are various ways the tools will try and do this.

From application services¶

If your startup project is an ASP.NET Core app, the tools will try to obtain the DbContext object from the application’s service provider. This is done by invoking Program.BuildWebHost() and accessing the IWebHost.Services property. Any DbContext registered using IServiceCollection.AddDbContext<TContext>() can be found and created this way. This pattern was introduced in ASP.NET Core 2.0

Using the default constructor¶

If the DbContext can’t be obtained from the application service provider, the tools will find the DbContext type inside the project and try to create it using its default constructor.

From a design-time factory¶

You can also tell the tools how to create your DbContext by implementing IDesignTimeDbContextFactory. If a class implementing this interface is found inside your project, the tools will bypass the other ways of creating the DbContext and always use the factory at design time. This is especially useful if you need to configure the DbContext differently for design time than at runtime.

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;

namespace MyProject
{
    public class BloggingContextFactory : IDesignTimeDbContextFactory<BloggingContext>
    {
        public BloggingContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
            optionsBuilder.UseSqlite("Data Source=blog.db");

            return new BloggingContext(optionsBuilder.Options);
        }
    }
}

[!NOTE] The args parameter is currently unused. There is an issue tracking the ability to specify design-time arguments from the tools.