Many to many relation between Identity and custom table. EF7 - Code first - asp.net

Question

How can I make many to many relation between AspNetRoles from Identity 3.0 and my custom table? I want simple 3 table, with both PermissionId and RoleId, something like AspNetUsersRole. I have something like this:
public class Permission
{
public int PermissionId { get; set; }
public string Name { get; set; }
public virtual ICollection<ApplicationRole> Roles { get; set; }
}
public class ApplicationRole : IdentityRole
{
public virtual ICollection<Permission> Permissions { get; set; }
}
But when I want to add migration, I got error:
Unable to determine the relationship represented by navigation property 'ApplicationRole.Permissions' of type 'ICollection<Permission>'. Either manually configure the relationship, or ignore this property from the model.

Answer 1

EF Core (EF7) does not currently support many to many relationship without a join entity. (Reference)
So, what you should do is to create an entity class for the join table and mapping two separate one-to-many relationships. Like;
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<PostTag>()
.HasKey(t => new { t.PostId, t.TagId });
modelBuilder.Entity<PostTag>()
.HasOne(pt => pt.Post)
.WithMany(p => p.PostTags)
.HasForeignKey(pt => pt.PostId);
modelBuilder.Entity<PostTag>()
.HasOne(pt => pt.Tag)
.WithMany(t => t.PostTags)
.HasForeignKey(pt => pt.TagId);
}
public class PostTag
{
public int PostId { get; set; }
public Post Post { get; set; }
public string TagId { get; set; }
public Tag Tag { get; set; }
}

Answer 2

Regarding to this question answer, it can be done more easily like this-
class Photo
{
public int Id { get; set; }
public ICollection<PersonPhoto> PersonPhotos{ get; set; }
}
class PersonPhoto
{
public int PhotoId { get; set; }
public Photo Photo { get; set; }
public int PersonId { get; set; }
public Person Person { get; set; }
}
class Person
{
public int Id { get; set; }
public ICollection<PersonPhoto> PersonPhotos{ get; set; }
}
Be sure to configure PersonPhoto with a composite key:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<PersonPhoto>().HasKey(x => new { x.PhotoId, x.PersonId });
}
To navigate, use a Select:
// person.Photos
var photos = person.PersonPhotos.Select(c => c.Photo);

Answer 3

Add This namespace-
using Microsoft.AspNetCore.Identity;
public class Permission
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int PermissionId { get; set; }
public string Name { get; set; }
public string UserIdFK { get; set; } //Foreign Key of Identity tbl
[ForeignKey("UserIdFK")]
public IdentityUser UserDetail { get; set; }
}
That's it, Happy coding :)