EF Core - Create a migration without connection string

Question

I have been ranging across multiple questions, tutorials and examples for something that fits this problem.

What if I don't know my connection string at the time I want to create my first initial migration? Given I am given the opportunity to set the connection string at the time of instantiating context eg:

var connection = @"Server=(localdb)\mssqllocaldb;Database=JobsLedgerDB;Trusted_Connection=True;ConnectRetryCount=0";
var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
optionsBuilder.UseSqlServer(connection);

using (var context = new BloggingContext(optionsBuilder.Options))
{
  // do stuff
}

As described in the docs..

If you need to have a connection string to run migrations then for those situations where you don't have one (Tenant database where you get a connection string from a user account) how do you run an initial migration??

Do you create a dummy connection string to create the migration.. seems dodgy to me. I would love some input on this.

I'm not sure if I understood your question correctly. But you do need to test out your app and so at some point of time you would need to have a working database, right? For development I'd normally use my local DB (SQL Server 2017), and the connection string would be pointing to the local server. — VT Chiew
– VT Chiew, Commented May 5, 2019 at 4:52
Possible duplicate of EF core - Creating a migration for a database without a connection string and in another class library — Peter Bons
– Peter Bons, Commented May 6, 2019 at 9:28
I suugest you edit the previous question instead of asking basically the same again. — Peter Bons
– Peter Bons, Commented May 6, 2019 at 9:29
Did you find something about this? I was also adding migrations with a dummy connection string, but when it comes to Remove-Migration, I guess it does not accept a dummy string, it fails. — ibubi
– ibubi, Commented Jan 24, 2020 at 21:39

Vočko · Accepted Answer · 2021-06-08 07:10:29Z

1

You can implement IDesignTimeDbContextFactory that will be used instead your host builder in the design time. UseSqlServer now has a parameterless overload.

It will look like this and has to be in the same assembly as the db context or in the startup project:

public class MyAppDbContextFactory: IDesignTimeDbContextFactory<MyAppDbContext>
{
    public MyAppDbContext CreateDbContext(string[] args)
    {
        var optionsBuilder = new DbContextOptionsBuilder<MyAppDbContext>();
        optionsBuilder.UseSqlServer();
            
        return new MyAppDbContext(optionsBuilder.Options);
    }
}

More details can be found here: https://learn.microsoft.com/en-us/ef/core/cli/dbcontext-creation?tabs=dotnet-core-cli#from-a-design-time-factory

edited Jun 8, 2021 at 7:10

answered Jun 8, 2021 at 3:48

Vočko

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2 Comments

Mykhailo K. Over a year ago

In my case, EF generates only one statement in a SQL script - creating "__EFMigrationsHistory" table.

TheClockTwister Jun 7 at 21:09

What about poor peasants like me who don't use Microsoft SQL Server, but MariaDB or similar with the "Pomelo.EntityFrameworkCore.MySql" package?

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