Linq Attach Child entity to PArent based on common field - linq

Question

I have a parent and child as separate objects. Now I have to combine both based on the join condition.
My entities are
public class Customer
{
private int customerId;
private string customerName;
private List<Order> orders;
}
public class Order
{
private int customerId;
private int orderId;
private string OrderName;
}
Here, customerId is the join field.
I have list of customers, but it has only CustomerId and CustomerName data. It doesn't have Orders ( order object is empty for each customer)
I have _orders as separate object like below.
List<Customer> _customers;
List<Order> _orders;
Now I have to join both and finally, I need _customers object which should have _orders as well.
I have used foreach statement to attach the orders to each customer like below.
_customers.ForEach(c =>
{
c.orders = _orders.Where(o => o.customerId == c.customerId).ToList();
});
But, I want to exclude foreach loop and trying to get through join condition.
Could someone help with this?
Thanks in advance.

Answer 1

You could use GroupJoin to achieve this :
List<Customer> result = _customers.GroupJoin(_orders,
c => c.customerId,
o => o.customerId,
(c, o) => new Customer
{
customerId = c.customerId,
customerName = c.customerName,
orders = o.ToList()
}).ToList();
Test in dotnetfiddle : https://dotnetfiddle.net/OJN480
I hope you find this helpful.