c# - Where should I put Database.EnsureCreated?

Question

I have an Entity Framework Core + ASP.NET Core application and when my application starts up I want to ensure that the database is created, and eventually (once I have migrations) I want to ensure that those are also run.

Initially I put Database.EnsureCreated() into the constructor of my DbContext but that appears to run every time someone hits my application since a new instance of the DbContext is created each time.

I tried to put it into my startup code, but I need an instance of my DbContext to do that and it is unclear how exactly to get one. I am configuring EF as so:

serviceCollection.AddEntityFramework()
    .AddSqlServer()
    .AddDbContext<Models.MyContext>(options => options.UseSqlServer(...));

I don't see a way to get an instance of the DbContext from the service collection, and I don't see any appropriate singleton to inject a DbContext into so I can do some one-time initialization.

So what is the best place to ensure some code related to my DbContext is called once per application run?

Answer 1

At the time of this writing, there is not a "correct" place to run code on application startup such that it executes within the request scope (see https://github.com/aspnet/Hosting/issues/373).

For now, the workaround is to do the following, but it won't work in more complex multi-application scenarios (see https://github.com/aspnet/EntityFramework/issues/3070#issuecomment-142752126)

public class Startup
{
    ...

    public void Configure(IApplicationBuilder applicationBuilder, ...)
    {
        ...
        // NOTE: this must go at the end of Configure
        var serviceScopeFactory = applicationBuilder.ApplicationServices.GetRequiredService<IServiceScopeFactory>()
        using (var serviceScope = serviceScopeFactory.CreateScope())
        {
            var dbContext = serviceScope.ServiceProvider.GetService<MyDbContext>();
            dbContext.Database.EnsureCreated();
        }
    }
}