删除与EF6有多对多关系的实体记录

尝试删除相关记录时，我做错了。我有一个客户模型和一个客户组模型。一个客户可以属于多个客户组。

我希望能够从客户组中添加和删除客户。添加是容易的部分，当我尝试从客户组中删除客户时，整个记录将从客户组表中删除

为了使事情易于理解，这是我的代码。

 [Table("CustomerGroups")]
public class CustomerGroupModel
{
    [Key]
    [DataMember]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid CustomerGroupId { get; set; }

    [DataMember]
    public Guid BusinessId { get; set; }
    public virtual Business Business { get; set; }

    [DataMember]
    [Display(Name = "Group Name")]
    public string GroupName { get; set; }

     [ScriptIgnore]
    public virtual List<Customer> CustomersInGroup { get; set; }
}

我的客户模型

   [Table("Customers")]
[DataContract]
public class Customer
{

    [DataMember]
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public Guid Id { get; set; }

    [DataMember(IsRequired = true)]
    [Required(ErrorMessage = "First Name is required")]
    [Display(Name = "First Name")]
    public string FirstName { get; set; }

    [DataMember(IsRequired = true)]
    [Required(ErrorMessage = "Last Name is required")]
    [Display(Name = "Last Name")]
    public string LastName { get; set; }


    [DataMember]
    public string FullName
    {
        get { return string.Format("{0} {1}", FirstName, LastName); }
    }


    [DataMember]
    [Display(Name = "Groups")]
    //change this as ICollection failed with restsharp to bindICollection<CustomerGroupModel> SelectedGroups { get; set; }
    public virtual List<CustomerGroupModel> SelectedGroups { get; set; }


}

我的FluentApi

            modelBuilder.Entity<Customer>()
            .HasMany(x => x.SelectedGroups)
            .WithMany(x => x.CustomersInGroup).Map(
                m =>
                {
                    m.MapLeftKey("CustomerId");
                    m.MapRightKey("CustomerGroupId");
                    m.ToTable("CustomersInGroups");
                });

如您所见，我生成了一个名为CustomersInGroups的表。

当我尝试更新客户组时，我想删除所有现有记录，然后重新插入新选择的记录（除非有更好的方法可以这样做）

            using (var context = new MyContext())
            {
                var contextCustomer = context.Customers
                    .Include("SelectedGroups")
                    .SingleOrDefault(a => a.Id==customer.Customer.Id); 

                contextCustomer.SelectedGroups.ToList()
                        .ForEach(r => context.CustomerGroups.Remove(r));
                context.SaveChanges();

             }

当我执行此操作时，将删除表CustomerGroups中的所有记录。如何仅从customersingroups表中删除相关记录？

任何建议将不胜感激