Do not map annotation to database during migrations

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I’ve read the docs, searched StackOverflow and tried my best to dig into past issues. The best I could find was this but the method signatures seem to have changed since then.

I am trying to understand the “annotations” feature but it is undocumented.

When building a model I use this:

MyAnnotation value = GetSomeComplexObjectToUseAsAnnotation();
entityTypeBuilder
  .Property(x => x.Name)
  .HasAnnotation("SomeKey", value);

And later I can retrieve it using something like this:

context
  .Model
  .GetEntityTypes()
  .SelectMany(x => x.GetProperties())
  .Select(x => x.FindAnnotation("SomeKey")?.Value)
  .Where(x => x is MyAnnotation);

I use it as a way to pass around info concerning the model, which I can use for various purposes. That works!

But dotnet ef migrations add throws:

System.InvalidOperationException: Cannot scaffold C# literals of type ‘MyAnnotation’. The provider should implement CoreTypeMapping.GenerateCodeLiteral to support using it at design time. at Microsoft.EntityFrameworkCore.Design.Internal.CSharpHelper.UnknownLiteral(Object value) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateAnnotation(IAnnotation annotation, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateAnnotations(IEnumerable1 annotations, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GeneratePropertyAnnotations(IProperty property, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateProperty(String builderName, IProperty property, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateProperties(String builderName, IEnumerable1 properties, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityType(String builderName, IEntityType entityType, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityTypes(String builderName, IReadOnlyList1 entityTypes, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.Generate(String builderName, IModel model, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationsGenerator.GenerateMetadata(String migrationNamespace, Type contextType, String migrationName, String migrationId, IModel targetModel) at Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.ScaffoldMigration(String migrationName, String rootNamespace, String subNamespace, String language) at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType, String namespace) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType, String namespace) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_01.<Execute>b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

I assume the problem is the migration system is expecting a primitive type, but it gets an instance of MyAnnotation and doesn’t know how to map that to the database - but I don’t want it in the database.

In the post I linked above ajcvickers said:

since many annotations only affect runtime behavior, not the database schema.

So I assume (?) I can use the annotation system this way. How do I tell migrations to not map that annotation?

Include provider and version information

EF Core version: 5.0.11 Database provider: sqlite, postgres Target framework: dotnet5 Operating system: linux IDE: vscode 1.63.0

Thank you!

[bricelam]

Looks like you should be able to replace the IAnnotationCodeGenerator service and override AnnotationCodeGenerator.FilterIgnoredAnnotations to add exclusions.

[lonix1]

LOL you schooled me!

The docs say

This implementation returns false for all ‘IsHandledByConvention’ methods and null for all ‘GenerateFluentApi’ methods. Providers should override for the annotations that they understand.

So I fiddled with those and presumably that was the problem. I’ve since learned I don’t need to change anything other than the filter method, as you explained.

This very simple code works, for anyone who needs it:

public class MyDesignTimeServices : IDesignTimeServices
{
  public void ConfigureDesignTimeServices(IServiceCollection services)
    => services.AddSingleton<IAnnotationCodeGenerator, MyAnnotationCodeGenerator>();
}

public class MyAnnotationCodeGenerator : AnnotationCodeGenerator
{
  public MyAnnotationCodeGenerator(AnnotationCodeGeneratorDependencies dependencies) : base(dependencies) { }
  public override IEnumerable<IAnnotation> FilterIgnoredAnnotations(IEnumerable<IAnnotation> annotations) => 
    base.FilterIgnoredAnnotations(annotations).Where(a => a.Name != "SomeKey");
}

Thanks guys!