如何告诉 EF Core 相同类型的两个属性？

Question

I have a set of models representing legal cases. One of the actions a user can do on a case is generate a document. This action is saved as a History entity, with an associated HistoryFile entity that contains the data about the file. Other actions may result in a History entity, with zero or multiple associated HistoryFile entities.

Cut-down versions of these two classes looks like this...

  public class History {
    public int Id { get; set; }
    public ObservableCollection<HistoryFile> HistoryFiles { get; set; }
  }

  public class HistoryFile {
    public int Id { get; set; }
    public int HistoryId { get; set; }
    public History History { get; set; }
  }

The next requirement is that a user can pick up on a document that was previously generated and continue working on it. The bit where I'm getting stuck is that the HistoryFile entity needs a reference back to the History entity that held the previous version. This means that I need to add two lines of code to the HistoryFile entity...

  public class HistoryFile {
    public int Id { get; set; }
    public int HistoryId { get; set; }
    public History History { get; set; }
    public int? PreviousHistoryId { get; set; }
    public virtual History PreviousHistory { get; set; }
  }

This means that there are two links from a HistoryFile to a History , one required one which is the parent History entity (via the History property) and an optional one via the PreviousHistory property.

I can't work out how to set this up for EF Core. As the code stands now, when I try to add a migration, I get the following error...

Cannot create a relationship between 'History.HistoryFiles' and 'HistoryFile.PreviousHistory' because a relationship already exists between 'History.HistoryFiles' and 'HistoryFile.History'. Navigation properties can only participate in a single relationship. If you want to override an existing relationship call 'Ignore' on the navigation 'HistoryFile.PreviousHistory' first in 'OnModelCreating'.

I tried adding the following to my DbContext ...

builder.Entity<HistoryFile>(entity => {
  entity.HasOne(hf => hf.History)
    .WithMany(h => h.HistoryFiles)
    .HasForeignKey(hf => hf.HistoryId)
    .OnDelete(DeleteBehavior.Restrict);
  entity.HasOne(hf => hf.PreviousHistory)
    .WithMany(h => h.HistoryFiles)
    .HasForeignKey(hf => hf.PreviousHistoryId)
    .OnDelete(DeleteBehavior.Restrict);
});

...but it didn't make any difference.

Anyone able to tell me how I configure this so that EF Core knows that there are two distinct links between the two entities?

I'm using EF Core 5.0.7 in a .NET5 project in case it makes a difference.

Thanks

Answer 1

Got it.

I needed to add the following two lines to the History class...

public virtual ICollection<HistoryFile> HistoryFilesParentHistory { get; set; }
public virtual ICollection<HistoryFile> HistoryFilesPreviousHistory { get; set; }

...and then change the code I added to the DbContext to look like this...

builder.Entity<HistoryFile>(entity => {
  entity.HasOne(hf => hf.History)
    .WithMany(h => h.HistoryFilesParentHistory)
    .HasForeignKey(hf => hf.HistoryId)
    .OnDelete(DeleteBehavior.Restrict);
  entity.HasOne(hf => hf.PreviousHistory)
    .WithMany(h => h.HistoryFilesPreviousHistory)
    .HasForeignKey(hf => hf.PreviousHistoryId)
    .OnDelete(DeleteBehavior.Restrict);
});

This worked fine.