实体框架一对多删除关系

Question

I have two entities Transaction and DiscountType

Transaction:

public class Transaction
{
    [Key]
    public int TransactionID { get; set; }
    public virtual DiscountType DiscountType { get; set; }
}

DiscountType:

public class DiscountType
{
    [Key]
    public int DiscountTypeID { get; set; }
    public virtual ICollection<Transaction> Transactions { get; set; }
    public float DiscountValue { get; set; }
    public bool Enabled {get; set;}
}

Relationship:

 modelBuilder.Entity<DiscountType>().HasMany(d => d.Transactions);

Aim:

I am trying to remove the relationship between the Transaction and the DiscountType, without actually removing either entity.

Problem:

Now I'm having no problem assigning a Discount to a transaction, but when I do the following:

 var transaction = context.Transactions.Where(t => t.TransactionID == 1).First();
 transaction.DiscountType = context.DiscountTypes.Where(d => d.DiscountTypeID == 1).First();
 context.SaveChanges();


 var _transaction = context.Transactions.Where(t => t.TransactionID == 1).First();
 _transaction.DiscountType = null;
 context.SaveChanges();

It's quite a peculiar problem I'm having. When this code is ran it does not remove the relationship between the two.

Actual Code:

As you can see, even after the = null; is executed, it still remains.

Answer 1

I think your select statement might need to be:

transaction.DiscountType = 
  context.DiscountTypes.Where(d => d.DiscountTypeID == 1).SingleOrDefault();

Answer 2

I think you better invert the relationship in the creation of the DbContext :

modelBuilder.Entity<Transaction>()
    .HasOptional(x => x.DiscountType)
    .WithOptionalPrincipal();

This creates a nullable foreign key to DiscountType in Transaction and I think it will allow you to set it to null .

(Personally I think it is a better way of putting it, because semantically it seems weird for a type to "have" Transactions, but a Transaction having a type is quite normal.)