自动生成的备用密钥

Question

EF Core is generating an Alternate Key ( AK_UserRoles_UserId_RoleId ) for the following data model:

Data Model

 public class User : IdentityUser<Guid>
{
    [MaxLength(50)]
    public String FirstName { get; set; }

    [MaxLength(50)]
    public String LastName { get; set; }

    public virtual ICollection<UserRole> UserRoles { get; set; }
}

public class Role : IdentityRole<Guid>
{
    public string Description { get; set; }

    public virtual ICollection<UserGroupToRole> UserGroups { get; set; }
}


public class UserRole : IdentityUserRole<Guid>
{
    public Guid Id { get; set; }

    public virtual User User { get; set; }

    public virtual Role Role { get; set; }

    public int? EntityId { get; set; }

    public string EntityType { get; set; }
}

Model Builder

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.Entity<User>(i =>
        {
            i.ToTable("Users");
            i.HasKey(x => x.Id);
            i.Property(u => u.Id).HasDefaultValueSql("NEWID()");

            i.HasMany(u => u.UserRoles)
                .WithOne(ur => ur.User)
                .HasForeignKey(ur => ur.UserId)
                .IsRequired();
        });

        builder.Entity<Role>(i =>
        {
            i.ToTable("Roles");
            i.HasKey(x => x.Id);
            i.Property(u => u.Id).HasDefaultValueSql("NEWID()");
            i.HasMany(x => x.UserGroups);

            i.HasMany<UserRole>()
                .WithOne(ur => ur.Role)
                .HasForeignKey(ur => ur.RoleId)
                .IsRequired();
        });

        builder.Entity<UserRole>(i =>
        {
            i.ToTable("UserRoles");
            i.HasKey(x => x.Id);
            i.Property(x => x.Id).HasDefaultValueSql("NEWID()");
            i.HasIndex(x => new { x.UserId, x.RoleId, x.EntityId, x.EntityType }).IsUnique();
        });

    }

Resulting Migration

 migrationBuilder.CreateTable(
            name: "UserRoles",
            columns: table => new
            {
                Id = table.Column<Guid>(nullable: false, defaultValueSql: "NEWID()"),
                EntityId = table.Column<int>(nullable: true),
                EntityType = table.Column<string>(nullable: false),
                RoleId = table.Column<Guid>(nullable: false),
                UserId = table.Column<Guid>(nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_UserRoles", x => x.Id);
                table.UniqueConstraint("AK_UserRoles_UserId_RoleId", x => new { x.UserId, x.RoleId });
                table.ForeignKey(
                    name: "FK_UserRoles_Roles_RoleId",
                    column: x => x.RoleId,
                    principalTable: "Roles",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
                table.ForeignKey(
                    name: "FK_UserRoles_Users_UserId",
                    column: x => x.UserId,
                    principalTable: "Users",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            });

The AK_UserRoles_UserId_RoleId above is what is in question. I do not wish for this to be a constraint. How can I either adjust my model to allow the conventions to not apply the Unique Constraint or what can I do in the Model Builder to adjust this?

Answer 1

EF Core is not automatically generating alternate keys. In this particular case it's generated because the base IdentityDbContext implementation (inside base.OnModelCreating(builder); call) is defining { UserId, RoleId } as a primary key for the UserRole table. When your code sets the Id as a primary key, EF Core is not replacing the old one, but instead turns it into alternate key.

There is no fluent API for removing keys, so you have to use the mutable metadata model directly. The easiest is to remove the old primary key before defining the new one:

builder.Entity<UserRole>(i =>
{
    i.Metadata.RemoveKey(i.Metadata.FindPrimaryKey().Properties);
    // ...
});