IdentityUserLogin<string>' requires a primary key to be defined error while adding migration [duplicate]

I am using 2 different Dbcontexts. i want to use 2 different databases users and mycontext. While doing that i am getting a error The entity type 'Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserLogin' requires a primary key to be defined. I think there is something wrong with IdentityUser please suggest me where can i change my code so that i can add migration.

My Dbcontext class:

 class MyContext : DbContext
{
    public DbSet<Post> Posts { get; set; }
    public DbSet<Tag> Tags { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(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 Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public AppUser User {get; set;}
    public string Content { get; set; }

    public List<PostTag> PostTags { get; set; }
}

public class Tag
{
    public string TagId { get; set; }

    public List<PostTag> PostTags { get; set; }
}

public class PostTag
{
    public int PostId { get; set; }
    public Post Post { get; set; }

    public string TagId { get; set; }
    public Tag Tag { get; set; }
}

and AppUser class:

public class AppUser : IdentityUser
{
  //some other propeties
}

when I try to Add migration the following error occurs.

The entity type 'Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserLogin<string>' requires a primary key to be defined.

give me solution to resolve the issue..

To reduce the link to a nutshell, try this:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    ...

See Above link for more.

This issue will start coming as soon as you wrote the following lines in DBContext without adding 'base.OnModelCreating(modelBuilder);'

protected override void OnModelCreating(ModelBuilder modelBuilder)
{

}

Two solutions:

1) Don't override OnModelCreating in DbContext Until it becomes necessary

2) Override but call base.OnModelCreating(modelBuilder)

The problem is AppUser is inherited from IdentityUser and their primary keys are not mapped in the method OnModelCreating of dbcontext.

There is already a post available with resolution. Visit the below link

EntityType 'IdentityUserLogin' has no key defined. Define the key for this EntityType

Hope this helps.