Entity Framework Code First Many to Many Setup For Existing Tables

I have the following tables Essence, EssenseSet, and Essense2EssenceSet

Essense2EssenceSet is the linking table that creates the M:M relationship.

I've been unable to get the M:M relationship working though in EF code first though.

Here's my code:

[Table("Essence", Schema = "Com")]
    public class Essence
    {
        public int EssenceID { get; set; }
        public string Name { get; set; }
        public int EssenceTypeID { get; set; }
        public string DescLong { get; set; }
        public string DescShort { get; set; }
        public virtual ICollection<EssenceSet> EssenceSets { get; set; }
        public virtual EssenceType EssenceType { get; set; }
    }

    [Table("EssenceSet", Schema = "Com")]
    public class EssenceSet
    {
        public int EssenceSetID { get; set; }
        public int EssenceMakerID { get; set; }
        public string Name { get; set; }
        public string DescLong { get; set; }
        public string DescShort { get; set; }

        public virtual ICollection<Essence> Essences { get; set; }
    }

[Table("Essence2EssenceSet", Schema = "Com")]
    public class Essence2EssenceSet
    {
        //(PK / FK)
        [Key] [Column(Order = 0)] [ForeignKey("Essence")] public int EssenceID { get; set; }
        [Key] [Column(Order = 1)] [ForeignKey("EssenceSet")] public int EssenceSetID { get; set; }

        //Navigation
        public virtual Essence Essence { get; set; }
        public virtual EssenceSet EssenceSet { get; set; }
    }
            public class EssenceContext : DbContext
            {
                public DbSet<Essence> Essences { get; set; }
                public DbSet<EssenceSet> EssenceSets { get; set; }
                public DbSet<Essence2EssenceSet> Essence2EssenceSets { get; set; }

                protected override void OnModelCreating(DbModelBuilder mb)
                {
                    mb.Entity<Essence>()
                        .HasMany(e => e.EssenceSets)
                        .WithMany(set => set.Essences)
                        .Map(mc =>
                            {
                                mc.ToTable("Essence2EssenceSet");
                                mc.MapLeftKey("EssenceID");
                                mc.MapRightKey("EssenceSetID");
                            });
                }
        }

This is the code I'm trying to run:

    Essence e = new Essence();
                            e.EssenceTypeID = (int)(double)dr[1];
                            e.Name          = dr[2].ToString();
                            e.DescLong      = dr[3].ToString();

                            //Get Essence Set
                            int setID = (int)(double)dr[0];
                            var set = ctx.EssenceSets.Find(setID);
                            e.EssenceSets = new HashSet<EssenceSet>();
                            e.EssenceSets.Add(se开发者_JS百科t);
                            ctx.Essences.Add(e);
ctx.SaveChanges();

And here's the error:

An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception.

I'm not able to find the problem. I'd greatly appreciate help setting this up right. Thanks!

Remove your Essence2EssenceSet model class. If junction table contains only keys of related entities participating in many-to-many relations it is not needed to map it as entity. Also make sure that your fluent mapping of many-to-many relations specifies schema for table:

mb.Entity<Essence>()
  .HasMany(e => e.EssenceSets)
  .WithMany(set => set.Essences)
  .Map(mc =>
      {
          mc.ToTable("Essence2EssenceSet", "Com");
          mc.MapLeftKey("EssenceID");
          mc.MapRightKey("EssenceSetID");
      });