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How to refer to the same class twice from one Entity Framework entity?
I have two classes, Contestant and Picture, with the following setup:
public class Contestant
{
...
public int AvatarID { get; set; }
[ForeignKey(nameof(AvatarID))]
public virtual Picture? Avatar { get; set; }
public virtual ICollection<Picture>? Pictures { get; set; }
...
}
public class Picture
{
...
public int ContestantID { get; set; }
[ForeignKey(nameof(ContestantID))]
public virtual Contestant? Contestant { get; set; }
...
}
Each contestant instance has a set of pictures and a single picture from the set that serves as their avatar.
The original setup (without AvatarID or Avatar relationship) worked fine. After adding the Avatar field and relationship, I get a run-time error message when I try to load either the Contestant set or Picture set. It reads:
System.InvalidOperationException: 'Unable to determine the relationship represented by navigation 'Contestant.Avatar' of type 'Picture.' Either manually configure the relationship, or ignore this property using the '[NotMapper]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.'
From my research, this happens when a class refers to another class twice. The answers I saw all involved the same class having both keys of the relationship. For example, a Project class might have multiple employees assigned, one as ProjectEngineer the other as AssignedDeveloper. For those, defining the [ForeignKey()] in the same file worked. I do not know what I need to do, here or possibly in the DbContext's OnModelCreating method.
1 answer
The following users marked this post as Works for me:
| User | Comment | Date |
|---|---|---|
| FrankLuke | (no comment) | Oct 13, 2022 at 03:17 |
I tried to replicate your case and the only workable solution I could find is to use OnModelCreating configuration (fluent style) instead of attributes:
public class Contestant
{
public int Id { get; set; }
public int AvatarID { get; set; }
public virtual Picture? Avatar { get; set; }
public virtual ICollection<Picture>? Pictures { get; set; }
}
public class Picture
{
public int Id { get; set; }
public int ContestantID { get; set; }
public virtual Contestant? Contestant { get; set; }
public virtual Contestant? ContestantInverse { get; set; }
}
modelBuilder.Entity<Contestant>()
.HasOne(u => u.Avatar)
.WithOne(r => r.Contestant)
.HasForeignKey<Contestant>(u => u.AvatarID)
.HasConstraintName("FK_Contestant_Avatar")
.OnDelete(DeleteBehavior.Restrict);
modelBuilder.Entity<Picture>()
.HasOne(d => d.ContestantInverse)
.WithMany(p => p.Pictures)
.HasConstraintName("FK_Picture_Contestant")
.OnDelete(DeleteBehavior.Restrict);
The Picture needs two navigation properties related to Contestant since it has two relations with it (1:1 and n:1).
As a side note, while liking the attributes more, I decided to use the fluent syntax only because some configurations are not supported by the attributes (e.g. index on 2+ properties), and having the configuration split in two can lead to confusion.
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