从存储过程中获取地址对象列表的不同项目

Question

So I am trying to get unique addresses only from my list but for some reason the .Distinct is not working

I tried :

 List<Address> addresses = _db.Database.SqlQuery<Address>(
 "GetSampleAddresses @workflow_id, @records ", param1, param2).Distinct().ToList();

And

 var json = new JavaScriptSerializer().Serialize(addresses.Distinct());

But neither removes the duplicates, any idea why ?

Answer 1

The thing is that when you're using .Disctinct() overload without parameters it will compare objects on reference base (by using by using the default equality comparer). Other words same object added twice to your collection will be treated as duplication, but two different objects with same fields/properties won't be equal.
To compare by specific fields you'll have to provide IEqualityComparer which will do a comparison:

var json = new JavaScriptSerializer().Serialize(addresses.Distinct(new AddressComparer()));

And AddressComparer itself:

class AddressComparer: IEqualityComparer<Address>
{
    public bool Equals(Address x, Address y)
    {         
        //Check whether the compared objects reference the same data. 
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether any of the compared objects is null. 
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
             return false;

        // Compare properties here. 
        // Assuming that two Addresses are equal when Street and Code are equal.
        return x.Street == y.Street && x.Code == y.Code;
    }    

    // If two objects are equal GetHashCode for both should return same value.
    public int GetHashCode(Address address)
    {
        if (Object.ReferenceEquals(address, null)) 
            return 0;

        int hashAddress = address.Street == null ? 0 : address.Street.GetHashCode();
        int hashCode = address.Code.GetHashCode();

        // Calculate new hash code from unique values combinaiton.
        return hashAddress ^ hashCode;
    }

}