The entity type 'MigrationOperation' requires a primary key to be defined

I am trying to build my first .NET app using Identity. It will be a basic Workout app, but I have been having trouble figuring out the Keys and ForeignKeys within Identity. Here is my ExerciseController:

 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 using WorkoutGenerator.Data.Migrations;

    namespace RandomWorkout.Models
    {
    public class Exercise
    {
        public string Name { get; set; }
        public string Description { get; set; }
        public MuscleGroup MuscleGroup { get; set; }
        public int MuscleGroupID { get; set; }
        [Key]
        public int ID { get; set; }

        [ForeignKey("ID")]
        public virtual ApplicationUser User { get; set; }

        public IList<ExerciseWorkout> ExerciseWorkouts { get; set; } = new List<ExerciseWorkout>();
    }

}`

When I run the migration however, I get the error

They entity type 'MigrationOperation' requires a primary key to be defined.

I have run into this issue with other entities, in which case I just had to make a new builder.Entity in my DbContext class. With the MigrationOperation however, this doesn't seem to be the case. Am I completely on the wrong track of how to JOIN my table with the auto generated User table? Thanks