EF Core - How to self reference a model with one to many relationship?

Question

I am trying to develop a basic Referral System with ASP.NET Core Identity, where a user can be referred by another user and can also refer to users.

MemberUser entity:

public class MemberUser : IdentityUser
{
    [Required]
    [MaxLength(100)]
    public string FirstName { get; set; } = string.Empty;

    [Required]
    [MaxLength(100)]
    public string LastName { get; set; } = string.Empty;

    public string? ReferrerId { get; set; }
    public virtual MemberUser Referrer { get; set; }
    public virtual List<MemberUser> Referrals { get; set; }

}

DBContext:

protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);
    builder.Entity<MemberUser>()
        .HasOne(mu => mu.Referrer)
        .WithMany(mu => mu.Referrals)
        .HasForeignKey(mu => mu.ReferrerId)
        .OnDelete(DeleteBehavior.NoAction);

}

When I ran dotnet ef database update it produces an error:

Introducing FOREIGN KEY constraint 'FK_AspNetUsers_AspNetUsers_ReferrerId' on table 'AspNetUsers' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint or index. See previous errors.

protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.CreateTable(
            name: "AspNetRoles",
            columns: table => new
            {
                Id = table.Column<string>(type: "nvarchar(450)", nullable: false),
                Name = table.Column<string>(type: "nvarchar(256)", maxLength: 256, nullable: true),
                NormalizedName = table.Column<string>(type: "nvarchar(256)", maxLength: 256, nullable: true),
                ConcurrencyStamp = table.Column<string>(type: "nvarchar(max)", nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetRoles", x => x.Id);
            });

        migrationBuilder.CreateTable(
            name: "AspNetUsers",
            columns: table => new
            {
                Id = table.Column<string>(type: "nvarchar(450)", nullable: false),
                FirstName = table.Column<string>(type: "nvarchar(100)", maxLength: 100, nullable: false),
                LastName = table.Column<string>(type: "nvarchar(100)", maxLength: 100, nullable: false),
                ReferrerId = table.Column<string>(type: "nvarchar(450)", nullable: false),
                UserName = table.Column<string>(type: "nvarchar(256)", maxLength: 256, nullable: true),
                NormalizedUserName = table.Column<string>(type: "nvarchar(256)", maxLength: 256, nullable: true),
                Email = table.Column<string>(type: "nvarchar(256)", maxLength: 256, nullable: true),
                NormalizedEmail = table.Column<string>(type: "nvarchar(256)", maxLength: 256, nullable: true),
                EmailConfirmed = table.Column<bool>(type: "bit", nullable: false),
                PasswordHash = table.Column<string>(type: "nvarchar(max)", nullable: true),
                SecurityStamp = table.Column<string>(type: "nvarchar(max)", nullable: true),
                ConcurrencyStamp = table.Column<string>(type: "nvarchar(max)", nullable: true),
                PhoneNumber = table.Column<string>(type: "nvarchar(max)", nullable: true),
                PhoneNumberConfirmed = table.Column<bool>(type: "bit", nullable: false),
                TwoFactorEnabled = table.Column<bool>(type: "bit", nullable: false),
                LockoutEnd = table.Column<DateTimeOffset>(type: "datetimeoffset", nullable: true),
                LockoutEnabled = table.Column<bool>(type: "bit", nullable: false),
                AccessFailedCount = table.Column<int>(type: "int", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetUsers", x => x.Id);
                table.ForeignKey(
                    name: "FK_AspNetUsers_AspNetUsers_ReferrerId",
                    column: x => x.ReferrerId,
                    principalTable: "AspNetUsers",
                    principalColumn: "Id");
            });

        migrationBuilder.CreateTable(
            name: "AspNetRoleClaims",
            columns: table => new
            {
                Id = table.Column<int>(type: "int", nullable: false)
                    .Annotation("SqlServer:Identity", "1, 1"),
                RoleId = table.Column<string>(type: "nvarchar(450)", nullable: false),
                ClaimType = table.Column<string>(type: "nvarchar(max)", nullable: true),
                ClaimValue = table.Column<string>(type: "nvarchar(max)", nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetRoleClaims", x => x.Id);
                table.ForeignKey(
                    name: "FK_AspNetRoleClaims_AspNetRoles_RoleId",
                    column: x => x.RoleId,
                    principalTable: "AspNetRoles",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateTable(
            name: "AspNetUserClaims",
            columns: table => new
            {
                Id = table.Column<int>(type: "int", nullable: false)
                    .Annotation("SqlServer:Identity", "1, 1"),
                UserId = table.Column<string>(type: "nvarchar(450)", nullable: false),
                ClaimType = table.Column<string>(type: "nvarchar(max)", nullable: true),
                ClaimValue = table.Column<string>(type: "nvarchar(max)", nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetUserClaims", x => x.Id);
                table.ForeignKey(
                    name: "FK_AspNetUserClaims_AspNetUsers_UserId",
                    column: x => x.UserId,
                    principalTable: "AspNetUsers",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateTable(
            name: "AspNetUserLogins",
            columns: table => new
            {
                LoginProvider = table.Column<string>(type: "nvarchar(128)", maxLength: 128, nullable: false),
                ProviderKey = table.Column<string>(type: "nvarchar(128)", maxLength: 128, nullable: false),
                ProviderDisplayName = table.Column<string>(type: "nvarchar(max)", nullable: true),
                UserId = table.Column<string>(type: "nvarchar(450)", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetUserLogins", x => new { x.LoginProvider, x.ProviderKey });
                table.ForeignKey(
                    name: "FK_AspNetUserLogins_AspNetUsers_UserId",
                    column: x => x.UserId,
                    principalTable: "AspNetUsers",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateTable(
            name: "AspNetUserRoles",
            columns: table => new
            {
                UserId = table.Column<string>(type: "nvarchar(450)", nullable: false),
                RoleId = table.Column<string>(type: "nvarchar(450)", nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetUserRoles", x => new { x.UserId, x.RoleId });
                table.ForeignKey(
                    name: "FK_AspNetUserRoles_AspNetRoles_RoleId",
                    column: x => x.RoleId,
                    principalTable: "AspNetRoles",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
                table.ForeignKey(
                    name: "FK_AspNetUserRoles_AspNetUsers_UserId",
                    column: x => x.UserId,
                    principalTable: "AspNetUsers",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateTable(
            name: "AspNetUserTokens",
            columns: table => new
            {
                UserId = table.Column<string>(type: "nvarchar(450)", nullable: false),
                LoginProvider = table.Column<string>(type: "nvarchar(128)", maxLength: 128, nullable: false),
                Name = table.Column<string>(type: "nvarchar(128)", maxLength: 128, nullable: false),
                Value = table.Column<string>(type: "nvarchar(max)", nullable: true)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_AspNetUserTokens", x => new { x.UserId, x.LoginProvider, x.Name });
                table.ForeignKey(
                    name: "FK_AspNetUserTokens_AspNetUsers_UserId",
                    column: x => x.UserId,
                    principalTable: "AspNetUsers",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

        migrationBuilder.CreateIndex(
            name: "IX_AspNetRoleClaims_RoleId",
            table: "AspNetRoleClaims",
            column: "RoleId");

        migrationBuilder.CreateIndex(
            name: "RoleNameIndex",
            table: "AspNetRoles",
            column: "NormalizedName",
            unique: true,
            filter: "[NormalizedName] IS NOT NULL");

        migrationBuilder.CreateIndex(
            name: "IX_AspNetUserClaims_UserId",
            table: "AspNetUserClaims",
            column: "UserId");

        migrationBuilder.CreateIndex(
            name: "IX_AspNetUserLogins_UserId",
            table: "AspNetUserLogins",
            column: "UserId");

        migrationBuilder.CreateIndex(
            name: "IX_AspNetUserRoles_RoleId",
            table: "AspNetUserRoles",
            column: "RoleId");

        migrationBuilder.CreateIndex(
            name: "EmailIndex",
            table: "AspNetUsers",
            column: "NormalizedEmail");

        migrationBuilder.CreateIndex(
            name: "IX_AspNetUsers_ReferrerId",
            table: "AspNetUsers",
            column: "ReferrerId");

        migrationBuilder.CreateIndex(
            name: "UserNameIndex",
            table: "AspNetUsers",
            column: "NormalizedUserName",
            unique: true,
            filter: "[NormalizedUserName] IS NOT NULL");
    }

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

        migrationBuilder.DropTable(
            name: "AspNetUserClaims");

        migrationBuilder.DropTable(
            name: "AspNetUserLogins");

        migrationBuilder.DropTable(
            name: "AspNetUserRoles");

        migrationBuilder.DropTable(
            name: "AspNetUserTokens");

        migrationBuilder.DropTable(
            name: "AspNetRoles");

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

Answer 1

You can manually fix your migration file by modifying the relationship like below:

 constraints: table =>
            {
                table.PrimaryKey("PK_AspNetUsers", x => x.Id);
                table.ForeignKey(
                    name: "FK_AspNetUsers_AspNetUsers_ReferrerId",
                    column: x => x.ReferrerId,
                    principalTable: "AspNetUsers",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.NoAction);
            });

Or you can remove this migration and add another that includes the correct onDelete action as I mentioned in the comments.