There are multiple approaches to take. The cleanest approach is to use the Except
extension method if you have overriden Equals
and GetHashCode
. If you have not, there are other options.
// have you overriden Equals/GetHashCode?
IEnumerable<Customer> resultsA = listA.Except(listB);
// no override of Equals/GetHashCode? Can you provide an IEqualityComparer<Customer>?
IEnumerable<Customer> resultsB = listA.Except(listB, new CustomerComparer()); // Comparer shown below
// no override of Equals/GetHashCode + no IEqualityComparer<Customer> implementation?
IEnumerable<Customer> resultsC = listA.Where(a => !listB.Any(b => b.Id == a.Id));
// are the lists particularly large? perhaps try a hashset approach
HashSet<int> customerIds = new HashSet<int>(listB.Select(b => b.Id).Distinct());
IEnumerable<Customer> resultsD = listA.Where(a => !customerIds.Contains(a.Id));
...
class CustomerComparer : IEqualityComparer<Customer>
{
public bool Equals(Customer x, Customer y)
{
return x.Id.Equals(y.Id);
}
public int GetHashCode(Customer obj)
{
return obj.Id.GetHashCode();
}
}
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…