Entity framework 6 : generic method AddOrUpdate
<p>I spend so much time trying implement a generic method to add or update a entity with a related entity (relation one to many) but I am stuck...</p>

<p>The method must receives 2 parameters, the first is the parent, second is the child. The goal is to save child entity into parent (adding if does not exist or update)</p>

<p>There is the generic method signature:</p>

<pre><code>    public static bool AddOrUpdate&lt;T,U&gt;(T ItemToSave,U ItemRelated, int ID) where T : class where U : class
    {
        using (var context = new dbContext())
        {                
            var parent = context.Set&lt;T&gt;().Find(ID);
            if (parent == null) return;
            // how to retrieve now the child (ItemRelated) from the parent (ItemToSave) in order to add into it or update ?

            return context.SaveChanges() &gt; 0;
        }
    }
</code></pre>

<p>This method is located in a static class 'Service'
and I want to be able to call Service.AddOrUpdate(Order _order, OrderLine _orderline, _order.OrderId) from any class.</p>

<p>I am stuck at retrieving the child from parent and to add or update into it.</p>

<p>Can anyone please help me to achieve that ?</p>