Tukukkk

I have a class hierarchy that I want to store in a database using EF Core migrations, but there are various complicating factors that make me unsure of what to do.

Here's the class hierarchy:

public sealed class Character

{

    private List<Relationship> relationships = new List<Relationship>();



    public string Name { get; set; }

    public ReadOnlyCollection<Relationship> Relationships { get; } 



    public Character()

    {

        Relationships = new ReadOnlyCollection<Relationship>(this.relationships);

    }

}





public class Relationship

{

    public Character FirstCharacter { get; set; }

    public Character SecondCharacter { get; set; }

    public string Name { get; set; }

}

So a character can have various relationships, which have a reference to two characters. Internal logic in the class makes sure that all Relationships in foo.Relationships always have a reference to foo in either Relationship.FirstCharacter or Relationship.SecondCharacter.

One complication is that I can't modify the class hierarchy, so I need to use the fluent API only. Because Character has no Id property, those are created via Shadow Properties as follows:

modelBuilder.Entity<Character>.Property<Guid>("Id")

                              .ValueGeneratedOnAdd()

                              .HasConversion<string>()

                              .HasAnnotation("Key", 0);

Now, I need to somehow express that Character has many Relationships, and that Relationship has one FirstCharacter pointing to Character, and one SecondCharacter pointing to Character as well. I cannot figure out how to do this. I currently have the following:

modelBuilder.Entity<Character>()

    .HasMany(c => c.Relationships)

    .WithOne(r => r.FirstCharacter);

EF complains that Relationship has no primary key, so I define one as follows:

modelBuilder.Entity<Relationship>()

            .HasKey("FirstCharacterId", "SecondCharacterId");

("FirstCharacterId" and "SecondCharacterId" are not properties that exist, but those get generated in the Migration as foreign keys, so they do exist at that point.)

Oddly, when I create a migration using this, EF generates a foreign key for both FirstCharacter AND SecondCharacter, despite WithOne() only pointing to FirstCharacter:

migrationBuilder.CreateTable(

    name: "Relationship",

    columns: table => new

    {

        FirstCharacterId = table.Column<string>(nullable: false),

        SecondCharacterId = table.Column<string>(nullable: false),

        Name = table.Column<string>(nullable: true)

    },

    constraints: table =>

    {

        table.PrimaryKey("PK_Relationship", x => new { x.FirstCharacterId, x.SecondCharacterId });

        table.ForeignKey(

            name: "FK_Relationship_Characters_FirstCharacterId",

            column: x => x.FirstCharacterId,

            principalTable: "Characters",

            principalColumn: "Id",

            onDelete: ReferentialAction.Cascade);

        table.ForeignKey(

            name: "FK_Relationship_Characters_SecondCharacterId",

            column: x => x.SecondCharacterId,

            principalTable: "Characters",

            principalColumn: "Id",

            onDelete: ReferentialAction.Cascade);

        });

I don't understand why it also created the SecondCharacter foreign key when I only define one for FirstCharacter. Also. I'm not sure if this is the proper way to do what I want, because I apparently don't really understand what is going on in the .HasMany().WithOne calls. Any ideas?