Compare two lists of object linq

Question

I have one online database on wcf and one offline database. I want to synchronize those so I started with mapping the online data into an object of offline data.

List<com.somee.wobservice.Customer> onlineCus = myservice.QueryCustomer();
List<Customer> offlineCus = dbc.Customers.ToList();
List<Customer> onlineCusMap = new List<Customer>();

foreach (com.somee.wobservice.Customer c in onlineCus)
{
     Customer cus = new Customer();
     cus.customer_id = c.customer_id;
     cus.customer_name = c.customer_name;
     cus.customer_email = c.customer_email;
     cus.password = c.password;
     cus.balance = c.balance;

     onlineCusMap.Add(cus);
 }

Now, I have 2 objects of the class Customer (a table in my database). But when I compared to get the except from them, it returned all data of the offline database (suppose to be no data because the data in those objects are same)

List<Customer> toInsert = offlineCus.Except(onlineCusMap).ToList();

Any suggestion to compare those 2 objects?

Does your Customer class override Equals and GetHashCode? If not, that's why it's not finding any duplicates. — Jon Skeet
– Jon Skeet, Commented Jun 7, 2014 at 8:20
Try implementing IEquatable<customer> suggested by the msdn docs. Which overrides the above methods. Not sure if this is required though. — brumScouse
– brumScouse, Commented Jun 7, 2014 at 8:24

James · Accepted Answer · 2014-06-07 08:24:48Z

1

As Jon pointed out in the comment in order to use Except you would need to override Equals/GetHashCode in order to determine what distinguishes a customer; By default your comparator will be by reference which in most cases will not suffice.

An alternative to that would be to just query for any customers which do not exist in the onlineCusMap list. I think it's probably safe to assume that customer_id is going to be unique enough to distinguish a customer

List<Customer> toInsert = 
    offlineCus.Where(x => !onlineCusMap.Any(y => y.customer_id == x.customer_id))
              .ToList();

If you do decide to override Equals I suggest you read the guidelines on how to do so correctly because it's not quite as simple as it may seem.

answered Jun 7, 2014 at 8:24

James

82.4k19 gold badges172 silver badges245 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jackie Ngo Anh Khoi Over a year ago

You're right, your linq statement looks more lovely than Equals example. Thanks a lot!!

Collectives™ on Stack Overflow

Compare two lists of object linq

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related