How to manually define DBContext code snippet for table without primary keys?

Hello,

I followed these instructions ( https://docs.microsoft.com/en-us/ef/core/get-started/aspnetcore/existing-db ) to automatically create database models/entity classes and the DBContext class, however one of the tables does not have any primary keys defined so the Scaffold-DbContext command did not generate the entity class for it. 

This table is basically a small 2 column table for defining a many-to-many relationship between 2 other tables.

Creating the Entity class was straight forward, but what should the proper code snippet be for the DBContext class for this?  

The manually created Entity class:

public class UserLocationManyToMany
{


    public int UserId { get; set; }

    public int? LocationId { get; set; }


}

The following is the DBContext code snippet (pls correct if incorrect):

modelBuilder.Entity<UserLocationManyToManyTable>(entity =>
{

entity.ToTable("UserLocation");
entity.HasIndex(e => e.UserId).HasName("userId_idx");

entity.Property(e => e.UserId).HasColumnName("userId");
entity.Property(e => e.LocationId).HasColumnName("locationId");

}

In addition to the statements above, does anyone know how to define the following?:

1. the many-to-many relationship (between "User" table to "Location" table)
2. the primary key (my understanding is that this is necessary)

Thanks!

victor