One to Many Relationship with Join Table using EF Code First

问题

I have a question about how to configure the one to many relationship with a join table using Code First fluent API. I have a Company, Contact Object both share a common Address Object like below

Class Address {
       public int AddressId
       .....
    }

Class Company {
   public int CompanyId
   ......
   public virtual ICollection<Address> Address
}

Class Contact {
   public int ContactID
   .......
   public virtual ICollection<Address> Address
}

My expected DB structure would be

Company Table
   CompanyId PK NOT NULL
   .....

Contact Table
    ContactId PK NOT NULL
    .....

Address Table
    AddressId PK NOT NULL
    .....

CompanyAddress Table
    CompanyId NOT NULL
    AddressId NOT NULL

ContactAddress Table
    ContactId NOT NULL
    AddressId NOT NULL

I was able to achieve this by using the below fluent API

modelBuilder.Entity<Company>()
  .HasMany(c => c.Address)
  .WithMany()
  .Map(m =>
    {
      m => m.MapLeftKey("CompanyId")
            .MapRightKey("AddressId")
            .ToTable("CompanyAddress")});

modelBuilder.Entity<Contact>()
  .HasMany(c => c.Address)
  .WithMany()
  .Map(m =>
    {
      m => m.MapLeftKey("ContactId")
            .MapRightKey("AddressId")
            .ToTable("ContactAddress")});

but EF start to treat Company and Address as Many to Many relationship and when I try to delete Company or Contacts it does not delete the corresponding Address record(since EF treats them as many to many), how can I define this type of relationship using EF with cascading delete option. I searched for more than 3 days and was suprised no one has talked or raised this type of scenarios, so wondering whether my approach is wrong or the answer is very trivial.

回答1:

You cannot have that with the many-to-many (it's what you're creating - and what you described).

When you delete company / contact - the 'join' table records get deleted.

You can simplify that and just do this in your config (remove all you have):

modelBuilder.Entity<Company>()
    .HasMany(c => c.Address)
    .WithOptional()
    .WillCascadeOnDelete(true);

modelBuilder.Entity<Contact>()
    .HasMany(c => c.Address)
    .WithOptional()
    .WillCascadeOnDelete(true);

来源：https://stackoverflow.com/questions/15824135/one-to-many-relationship-with-join-table-using-ef-code-first