I designed three entities with navigation properties (code first approach, unnecessary properties are omitted):

Image (represents image info in database):

public class Image
{
    public long Id { get; init; }

    public long? PlayerId { get; set; }
    public Player Player { get; set; }

    public long? PublicationId { get; set; }
    public Publication Publication { get; set; }
}

Publication (some domain entity):

public class Publication
{
    public long Id { get; init; }

    public long? ImageTitleId { get; set; }
    public Image ImageTitle { get; set; }

    public long? ImageBackgroundId { get; set; }
    public Image ImageBackground { get; set; }
}

Player (some domain entity):

public class Player
{
    public long Id { get; init; }

    public long? ImageProfileId { get; set; }
    public Image ImageProfile { get; set; }

    public long? ImageLogoId { get; set; }
    public Image ImageLogo { get; set; }
}

Business rules are:

1. Image is dependent entity in all cases
2. Publication/Player is principal entity in these relationships
3. Publication/Player can have related image or not (one-to-one-or-zero)

The difficulty for me here is multiple relationships between two entities (therefore tables in database) (Title Image, Background Image, etc).

EF can not automatically detect principal/dependent entity and i can not figure out how to config Fluent API in such case.

CodePudding user response：

I think you missed some properties in Image Entity. I changed Image model as below:

public class Image
{
    public long Id { get; init; }

    public long? ImageProfilePlayerId { get; set; }
    public Player ImageProfilePlayer { get; set; }

    public long? ImageLogoPlayerId { get; set; }
    public Player ImageLogoPlayer { get; set; }


    public long? ImageTitlePublicationId { get; set; }
    public Publication ImageTitlePublication { get; set; }

    public long? ImageBackgroundId { get; set; }
    public Publication ImageBackground { get; set; }
}

and Paley and Publication as below (they are same as yours):

 public class Publication
{
    public long Id { get; init; }

    public long? ImageTitleId { get; set; }
    public Image ImageTitle { get; set; }

    public long? ImageBackgroundId { get; set; }
    public Image ImageBackground { get; set; }
}

public class Player
{
    public long Id { get; init; }

    public long? ImageProfileId { get; set; }
    public Image ImageProfile { get; set; }

    public long? ImageLogoId { get; set; }
    public Image ImageLogo { get; set; }
}

and used below config for models in OnModelCreating in DbContext:

   protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Image>(e => {
            e.HasOne(x => x.ImageProfilePlayer).WithOne(x => x.ImageProfile).HasForeignKey<Player>(x => x.ImageProfileId).IsRequired(false);
            e.HasOne(x => x.ImageLogoPlayer).WithOne(x => x.ImageLogo).HasForeignKey<Player>(x => x.ImageLogoId).IsRequired(false);
            e.HasOne(x => x.ImageTitlePublication).WithOne(x => x.ImageTitle).HasForeignKey<Publication>(x => x.ImageTitleId).IsRequired(false);
            e.HasOne(x => x.ImageBackground).WithOne(x => x.ImageBackground).HasForeignKey<Publication>(x => x.ImageBackgroundId).IsRequired(false);
        });

     
    }

the result is :