Regression issue where command line migrations with -o updates the snapshot in the project

[theo-albers]

File a bug

Up to EF Core 3.x the behavior was like this:

• in your C# project folder where you have EF Core migrations
• dotnet ef migrations add SecondVersion -o c:\temp
• in the folder c:\temp we now have:
  • SecondVersion.cs
  • SecondVersion.designer.cs
  • MyDbContextModelSnapshot.cs
• in the project folder nothing is changed

With EF Core 3.x I can rerun "dotnet ef migrations add SecondVersion" without the -o option and it will add the exact same migration to my project.

In EF Core 5.x the behavior is like this:

• in your C# project folder where you have EF Core migrations
• dotnet ef migrations add SecondVersion -o c:\temp
• in the folder c:\temp we now have:
  • SecondVersion.cs
  • SecondVersion.designer.cs
• in the project folder the model snapshot is changed
  • MyDbContextModelSnapshot.cs

With EF Core 5.x I can rerun "dotnet ef migrations add SecondVersion" without the -o option and it will add an empty migration to my project, because the model snapshot is already changed.

I expect the -o option to respect the output path and not to touch my local model snapshot file. This allows me to easily check my migration, change the code, redo, etc. until I'm satisfied with the outcome.

Run run-testcase.cmd in the sample project to see the behavior.
EfCoreSample.zip

[AndriySvyryd]

@bricelam

[bricelam]

This is the result of fixing #13342. The migration generated by dotnet ef migrations add must be added to the project.

Here are some options for previewing a migration:

1. Use dotnet ef migrations remove to remove it and generate a new, corrected one
2. Use version control to revert the changes and generate a new one
3. Use the underlying APIs to build your own tool:

    var db = new MyDbContext();
   
    var serviceCollection = new ServiceCollection();
    serviceCollection.AddEntityFrameworkDesignTimeServices();
    serviceCollection.AddDbContextDesignTimeServices(db);
    var serviceProvider = serviceCollection.BuildServiceProvider();
   
    // Scaffold a migration
    var migrationsScaffolder = serviceProvider.GetService<IMigrationsScaffolder>();
    var migration = migrationsScaffolder.ScaffoldMigration(migrationName, rootNamespace);
   
    File.WriteAllText(migrationFile, migration.MigrationCode, Encoding.UTF8);
    File.WriteAllText(migrationMetadataFile, migration.MetadataCode, Encoding.UTF8);
    File.WriteAllText(modelSnapshotFile, migration.SnapshotCode, Encoding.UTF8);

[theo-albers]

Thanks for listing the alternatives. I guess I have to learn a new habit and undo the snapshot file when using the -o option. I can see the need for the #13342 fix in case you really want to use the -o option to place the migrations in a specific folder in your project.