Enum lookup table creating redundant foreign key reference to itself

[TAGC]

In certain cases, configuring enum lookups on an owned type (via the new ConfigureOwnedEnumLookup extension method) causes EF Core to generate an enum lookup table with a redundant foreign key reference to itself. This results in a warning appearing within the Package Manager Console when creating migrations (given an enum called Month):

Microsoft.EntityFrameworkCore.Model.Validation[10614]
 The foreign key {'Id'} on entity type 'EnumWithNumberLookup<Month> targets itself, it should be removed since it serves no purpose.

This is a minor issue and it's really just to bring it to your attention in case you have any idea what might be causing it. I don't believe it will affect behaviour in any way.

Steps To Reproduce

It's difficult to reproduce this issue. I've set up both a dummy .NET Core console app project and my real ASP.NET Core-based project to create the exact same minimal set of entities that exposes the issue. The relevant classes are listed below.

Domain

A "product consultant" (not modelled) can optionally have an "annual target". An "annual target" owns zero or many "monthly targets", each of which correspond to a month of the year.

public class AnnualTarget
{
 protected AnnualTarget()
 {
 // Required by EF
 }

 public int YearStartPeriod { get; private set; }
 public int Target => MonthlyTargets.Sum(x => x.Target);
 protected virtual IReadOnlyCollection<MonthlyTarget> MonthlyTargets { get; private set; } = null!;
 private int ProductConsultantId { get; set; }
}

public class MonthlyTarget
{
 protected MonthlyTarget()
 {
 // Required by EF
 }

 public MonthlyTarget(int yearStartPeriod, Month month, int target)
 {
 YearStartPeriod = yearStartPeriod;
 Month = month;
 Target = target;
 }

 public Month Month { get; private set; }
 public int YearStartPeriod { get; private set; }
 public int Target { get; private set; }
 public int Adjustment { get; private set; }
 private int ProductConsultantId { get; set; }
}

public enum Month
{
 January = 1,
 February = 2,
 March = 3,
 April = 4,
 May = 5,
 June = 6,
 July = 7,
 August = 8,
 September = 9,
 October = 10,
 November = 11,
 December = 12
}

Context

public class AnnualTargetConfiguration : IEntityTypeConfiguration<AnnualTarget>
{
 private readonly ModelBuilder _modelBuilder;
 private readonly EnumLookupOptions _enumLookupOptions;

 public AnnualTargetConfiguration(ModelBuilder modelBuilder, EnumLookupOptions enumLookupOptions)
 {
 _modelBuilder = modelBuilder;
 _enumLookupOptions = enumLookupOptions;
 }

 public void Configure(EntityTypeBuilder<AnnualTarget> builder)
 {
 builder.ToTable(nameof(AnnualTarget));

 builder.HasKey(
 "ProductConsultantId",
 nameof(AnnualTarget.YearStartPeriod));

 builder.OwnsMany<MonthlyTarget>("MonthlyTargets", b =>
 {
 b.ToTable(nameof(MonthlyTarget));
 b.WithOwner();
 b.HasKey(
 "ProductConsultantId",
 nameof(MonthlyTarget.YearStartPeriod),
 nameof(MonthlyTarget.Month));

 b.ConfigureOwnedEnumLookup(_enumLookupOptions, _modelBuilder); 
 });
 }
}

public class CommissionsContext : DbContext
{
 protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
 {
 base.OnConfiguring(optionsBuilder);

 if (!optionsBuilder.IsConfigured)
 {
 optionsBuilder.UseSqlServer("Data Source=tcp:dev.db.sales.mycompany.co.uk;Trusted_Connection=Yes;database=Commissions");
 optionsBuilder.UseLazyLoadingProxies();
 }
 }

 protected override void OnModelCreating(ModelBuilder modelBuilder)
 {
 var enumLookupOptions = EnumLookupOptions.Default.SetNamingScheme(x => x.Pascalize());
 modelBuilder.ApplyConfiguration(new AnnualTargetConfiguration(modelBuilder, enumLookupOptions));
 modelBuilder.ConfigureEnumLookup(enumLookupOptions);
 }
}

Outputs

The generated migration file (..._InitialCreate.cs) is identical between the dummy project and the real project:

public partial class InitialCreate : Migration
{
 protected override void Up(MigrationBuilder migrationBuilder)
 {
 migrationBuilder.CreateTable(
 name: "AnnualTarget",
 columns: table => new
 {
 YearStartPeriod = table.Column<int>(nullable: false),
 ProductConsultantId = table.Column<int>(nullable: false)
 },
 constraints: table =>
 {
 table.PrimaryKey("PK_AnnualTarget", x => new { x.ProductConsultantId, x.YearStartPeriod });
 });

 migrationBuilder.CreateTable(
 name: "Month",
 columns: table => new
 {
 Id = table.Column<int>(nullable: false),
 Name = table.Column<string>(nullable: true)
 },
 constraints: table =>
 {
 table.PrimaryKey("PK_Month", x => x.Id);
 });

 migrationBuilder.CreateTable(
 name: "MonthlyTarget",
 columns: table => new
 {
 Month = table.Column<int>(nullable: false),
 YearStartPeriod = table.Column<int>(nullable: false),
 ProductConsultantId = table.Column<int>(nullable: false),
 Target = table.Column<int>(nullable: false),
 Adjustment = table.Column<int>(nullable: false)
 },
 constraints: table =>
 {
 table.PrimaryKey("PK_MonthlyTarget", x => new { x.ProductConsultantId, x.YearStartPeriod, x.Month });
 table.ForeignKey(
 name: "FK_MonthlyTarget_Month_Month",
 column: x => x.Month,
 principalTable: "Month",
 principalColumn: "Id",
 onDelete: ReferentialAction.Cascade);
 table.ForeignKey(
 name: "FK_MonthlyTarget_AnnualTarget_ProductConsultantId_YearStartPeriod",
 columns: x => new { x.ProductConsultantId, x.YearStartPeriod },
 principalTable: "AnnualTarget",
 principalColumns: new[] { "ProductConsultantId", "YearStartPeriod" },
 onDelete: ReferentialAction.Cascade);
 });

 migrationBuilder.InsertData(
 table: "Month",
 columns: new[] { "Id", "Name" },
 values: new object[,]
 {
 { 1, "January" },
 { 2, "February" },
 { 3, "March" },
 { 4, "April" },
 { 5, "May" },
 { 6, "June" },
 { 7, "July" },
 { 8, "August" },
 { 9, "September" },
 { 10, "October" },
 { 11, "November" },
 { 12, "December" }
 });

 migrationBuilder.CreateIndex(
 name: "IX_Month_Name",
 table: "Month",
 column: "Name",
 unique: true,
 filter: "[Name] IS NOT NULL");

 migrationBuilder.CreateIndex(
 name: "IX_MonthlyTarget_Month",
 table: "MonthlyTarget",
 column: "Month");
 }

 protected override void Down(MigrationBuilder migrationBuilder)
 {
 migrationBuilder.DropTable(
 name: "MonthlyTarget");

 migrationBuilder.DropTable(
 name: "Month");

 migrationBuilder.DropTable(
 name: "AnnualTarget");
 }
}

However, the generated designer scripts differ between the two projects.

Dummy .NET Console Project (working as intended)

// <auto-generated />
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Metadata;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
using experiment.Data;

namespace experiment.Migrations
{
 [DbContext(typeof(CommissionsContext))]
 [Migration("20200917121204_InitialCreate")]
 partial class InitialCreate
 {
 protected override void BuildTargetModel(ModelBuilder modelBuilder)
 {
#pragma warning disable 612, 618
 modelBuilder
 .HasAnnotation("ProductVersion", "3.1.8")
 .HasAnnotation("Relational:MaxIdentifierLength", 128)
 .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);

 modelBuilder.Entity("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<experiment.Models.Month>", b =>
 {
 b.Property<int>("Id")
 .HasColumnType("int");

 b.Property<string>("Name")
 .HasColumnType("nvarchar(450)");

 b.HasKey("Id");

 b.HasIndex("Name")
 .IsUnique()
 .HasFilter("[Name] IS NOT NULL");

 b.ToTable("Month");

 b.HasData(
 new
 {
 Id = 1,
 Name = "January"
 },
 new
 {
 Id = 2,
 Name = "February"
 },
 new
 {
 Id = 3,
 Name = "March"
 },
 new
 {
 Id = 4,
 Name = "April"
 },
 new
 {
 Id = 5,
 Name = "May"
 },
 new
 {
 Id = 6,
 Name = "June"
 },
 new
 {
 Id = 7,
 Name = "July"
 },
 new
 {
 Id = 8,
 Name = "August"
 },
 new
 {
 Id = 9,
 Name = "September"
 },
 new
 {
 Id = 10,
 Name = "October"
 },
 new
 {
 Id = 11,
 Name = "November"
 },
 new
 {
 Id = 12,
 Name = "December"
 });
 });

 modelBuilder.Entity("experiment.Models.Targets.AnnualTarget", b =>
 {
 b.Property<int>("ProductConsultantId")
 .HasColumnType("int");

 b.Property<int>("YearStartPeriod")
 .HasColumnType("int");

 b.HasKey("ProductConsultantId", "YearStartPeriod");

 b.ToTable("AnnualTarget");
 });

 modelBuilder.Entity("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<experiment.Models.Month>", b =>
 {
 b.HasOne("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<experiment.Models.Month>", null)
 .WithMany()
 .HasForeignKey("Id")
 .OnDelete(DeleteBehavior.Cascade)
 .IsRequired();
 });

 modelBuilder.Entity("experiment.Models.Targets.AnnualTarget", b =>
 {
 b.OwnsMany("experiment.Models.Targets.MonthlyTarget", "MonthlyTargets", b1 =>
 {
 b1.Property<int>("ProductConsultantId")
 .HasColumnType("int");

 b1.Property<int>("YearStartPeriod")
 .HasColumnType("int");

 b1.Property<int>("Month")
 .HasColumnType("int");

 b1.Property<int>("Adjustment")
 .HasColumnType("int");

 b1.Property<int>("Target")
 .HasColumnType("int");

 b1.HasKey("ProductConsultantId", "YearStartPeriod", "Month");

 b1.HasIndex("Month");

 b1.ToTable("MonthlyTarget");

 b1.HasOne("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<experiment.Models.Month>", null)
 .WithMany()
 .HasForeignKey("Month")
 .OnDelete(DeleteBehavior.Cascade)
 .IsRequired();

 b1.WithOwner()
 .HasForeignKey("ProductConsultantId", "YearStartPeriod");
 });
 });
#pragma warning restore 612, 618
 }
 }
}

Real ASP.NET Core Project (has issue)

// <auto-generated />
using MyCompany.Commissions.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Metadata;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.EntityFrameworkCore.Storage.ValueConversion;

namespace MyCompany.Commissions.Infrastructure.Migrations
{
 [DbContext(typeof(CommissionsContext))]
 [Migration("20200917115338_InitialCreate")]
 partial class InitialCreate
 {
 protected override void BuildTargetModel(ModelBuilder modelBuilder)
 {
#pragma warning disable 612, 618
 modelBuilder
 .HasAnnotation("ProductVersion", "3.1.8")
 .HasAnnotation("Relational:MaxIdentifierLength", 128)
 .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);

 modelBuilder.Entity("MyCompany.Commissions.Domain.ProductConsultants.Targets.AnnualTarget", b =>
 {
 b.Property<int>("ProductConsultantId")
 .HasColumnType("int");

 b.Property<int>("YearStartPeriod")
 .HasColumnType("int");

 b.HasKey("ProductConsultantId", "YearStartPeriod");

 b.ToTable("AnnualTarget");
 });

 modelBuilder.Entity("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<MyCompany.Commissions.Domain.ProductConsultants.Month>", b =>
 {
 b.Property<int>("Id")
 .HasColumnType("int");

 b.Property<string>("Name")
 .HasColumnType("nvarchar(450)");

 b.HasKey("Id");

 b.HasIndex("Name")
 .IsUnique()
 .HasFilter("[Name] IS NOT NULL");

 b.ToTable("Month");

 b.HasData(
 new
 {
 Id = 1,
 Name = "January"
 },
 new
 {
 Id = 2,
 Name = "February"
 },
 new
 {
 Id = 3,
 Name = "March"
 },
 new
 {
 Id = 4,
 Name = "April"
 },
 new
 {
 Id = 5,
 Name = "May"
 },
 new
 {
 Id = 6,
 Name = "June"
 },
 new
 {
 Id = 7,
 Name = "July"
 },
 new
 {
 Id = 8,
 Name = "August"
 },
 new
 {
 Id = 9,
 Name = "September"
 },
 new
 {
 Id = 10,
 Name = "October"
 },
 new
 {
 Id = 11,
 Name = "November"
 },
 new
 {
 Id = 12,
 Name = "December"
 });
 });

 modelBuilder.Entity("MyCompany.Commissions.Domain.ProductConsultants.Targets.AnnualTarget", b =>
 {
 b.OwnsMany("MyCompany.Commissions.Domain.ProductConsultants.Targets.MonthlyTarget", "MonthlyTargets", b1 =>
 {
 b1.Property<int>("ProductConsultantId")
 .HasColumnType("int");

 b1.Property<int>("YearStartPeriod")
 .HasColumnType("int");

 b1.Property<int>("Month")
 .HasColumnType("int");

 b1.Property<int>("Adjustment")
 .HasColumnType("int");

 b1.Property<int>("Target")
 .HasColumnType("int");

 b1.HasKey("ProductConsultantId", "YearStartPeriod", "Month");

 b1.HasIndex("Month");

 b1.ToTable("MonthlyTarget");

 b1.HasOne("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<MyCompany.Commissions.Domain.ProductConsultants.Month>", null)
 .WithMany()
 .HasForeignKey("Month")
 .OnDelete(DeleteBehavior.Cascade)
 .IsRequired();

 b1.WithOwner()
 .HasForeignKey("ProductConsultantId", "YearStartPeriod");
 });
 });

 modelBuilder.Entity("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<MyCompany.Commissions.Domain.ProductConsultants.Month>", b =>
 {
 b.HasOne("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<MyCompany.Commissions.Domain.ProductConsultants.Month>", null)
 .WithMany()
 .HasForeignKey("Id")
 .OnDelete(DeleteBehavior.Cascade)
 .IsRequired();
 });
#pragma warning restore 612, 618
 }
 }
}

The problem lies at the end of the designer file for the ASP.NET Core project:

modelBuilder.Entity("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<MyCompany.Commissions.Domain.ProductConsultants.Month>", b =>
 {
 b.HasOne("SpatialFocus.EntityFrameworkCore.Extensions.EnumWithNumberLookup<MyCompany.Commissions.Domain.ProductConsultants.Month>", null)
 .WithMany()
 .HasForeignKey("Id")
 .OnDelete(DeleteBehavior.Cascade)
 .IsRequired();
 });