Foreign key for selected character slots.

Content.Server.Database/Content.Server.Database.csproj

@@ -20,10 +20,4 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="3.1.0" />
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="3.1.4" />
   </ItemGroup>
-
-  <ItemGroup>
-    <Folder Include="Migrations\Postgres" />
-    <Folder Include="Migrations\Sqlite" />
-  </ItemGroup>
-
 </Project>

Content.Server.Database/Migrations/Postgres/20201006223000_SelectedCharacterSlotFk.cs

@@ -0,0 +1,19 @@
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+namespace Content.Server.Database.Migrations.Postgres
+{
+    [DbContext(typeof(PostgresServerDbContext))]
+    [Migration("20201006223000_SelectedCharacterSlotFk")]
+    public class SelectedCharacterSlotFk : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.Sql(@"ALTER TABLE preference
+ADD CONSTRAINT ""FK_preference_profile_selected_character_slot_preference_id""
+FOREIGN KEY (selected_character_slot, preference_id)
+REFERENCES profile (slot, preference_id)
+DEFERRABLE INITIALLY DEFERRED;");
+        }
+    }
+}

Content.Server.Database/Model.cs

@@ -55,6 +55,12 @@ namespace Content.Server.Database
     [Table("preference")]
     public class Preference
     {
+        // NOTE: on postgres there SHOULD be an FK ensuring that the selected character slot always exists.
+        // I had to use a migration to implement it and as a result its creation is a finicky mess.
+        // Because if I let EFCore know about it it would explode on a circular reference.
+        // Also it has to be DEFERRABLE INITIALLY DEFERRED so that insertion of new preferences works.
+        // Also I couldn't figure out how to create it on SQLite.
+
         [Column("preference_id")] public int Id { get; set; }
         [Column("user_id")] public Guid UserId { get; set; }
         [Column("selected_character_slot")] public int SelectedCharacterSlot { get; set; }