I am working with a large external data model, that I have no authority over, ie. I can’t change modify the data structure. I need to store this data structure as a field in another record and store this record using EF Core.

My data structure looks something like the following:

public sealed record GameAnalysis
{
    public Guid AnalysisID { get; } = Guid.NewGuid();
    public string SomeField { get; init; }
    public Game Game { get; init; }
}

Where Game is the external data model that I spoke about. This data model has lists and nested objects:

public class Game
{
    public Guid GameID { get; } = Guid.NewGuid();
    public string SomeField { get; init; }
    public SomeClassWithoutID Stadium { get; init; }
    public List<Player> Players { get; init; }
    // more fields...
}

I initially tried to make EF Core just set up everything for me, however I got errors that some classes of the nested objects within the Game class do not contain any ID’s.

I looked into alternative ways of storing this model and even though it is generally not advisable to store data objects as JSON, I do believe that it is the way to go in this case (correct me if I am wrong). I can write a converter using .HasConversion(), but ideally, I would like to able to index into this data model using LINQ.

In EF Core 7, JSON columns were added, which seem to solve my problem exactly. However, I can’t get it to work. My OnModelCreating looks like this:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<GameAnalysis>().OwnsOne(
        analysis => analysis.Game, ownedNavigationBuilder =>
        {
            ownedNavigationBuilder.ToJson();
        });
}

When using this, I get the same errors as when I just tried to let EF Core take the reins:

Unable to create a ‘DbContext’ of type ”. The exception ‘The entity of type SomeClassWithoutID’ requires a primary key to be defined.’ was thrown while attempting to create an instance.

I can remove the errors one-by-one by adding calls to OwnsOne and OwnsMany, but it is quite the hassle to add this to added nested objects within the model. Why is this still needed when using ToJson() or am I missing something?