C#•this hour

Data seeding with anonymous objects in .NET 9

I recently began migrating some projects from .NET 8 to .NET 9. One of the things I now run into is the Seeding part with Entity Framework Core. My seeding in my projects is done in the OnModelCreating and I add an extra environment variable to ensure that this part does not happen all the time. I then use something like:

    modelBuilder.Entity<MyDtoClass>().HasData(
      new
      {
          ...
      });

    modelBuilder.Entity<MyDtoClass>().HasData(
      new
      {
          ...
      });

The reason I am using anonymous objects is that I make use of shadow properties for several objects and I fill these properties in my override of SaveChangesAsync. This way I just just add a couple of marker classes to some of my DTO objects like ICreateable, IUpdateable or ISoftDeletable and then these shadow properties are automatically filled when required. For Seeding my data I generate certain information dynamically (e.g. GUIDs and dates/times) which has not been a problem in .NET 8 but I do turn off the warning I get:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.ConfigureWarnings(warnings => warnings.Ignore(RelationalEventId.PendingModelChangesWarning));
}

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.ConfigureWarnings(warnings => warnings.Ignore(RelationalEventId.PendingModelChangesWarning));
}

Now with .NET 9 there is a new way of seeding data. So, the data seeding happens somewhere else. The example Microsoft gives is at: https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-9.0/whatsnew#improved-data-seeding

context.Set<Blog>().Add(new Blog { Url = "http://test.com/" });
context.SaveChanges();

context.Set<Blog>().Add(new Blog { Url = "http://test.com/" });
context.SaveChanges();

Unfortunately by using this context.Set<T>().Add method I am no longer able to add an anonymous object so it now becomes impossible for me to use with the shadow properties as they are not defined for my DTOs. How can I handle this scenario without going back to the old way?

What's New in EF Core 9

Overview of new features in EF Core 9

1 Reply

Jimmacle•18h ago

what do you need access to the shadow properties for? anonymous objects sounds cursed, if you need access to the properties in your code then just make them regular properties that is also not a new way of seeding data, that's just using EF Core to access your database - the article is pointing out the UseSeeding method specifically as a new convenience but you could always just write your own seeding code (also, that article suggests it only works with EnsureCreated which you probably shouldn't be using)

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Data seeding with anonymous objects in .NET 9

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