Domain Service in Silverlight+Entity Framework+Ria Services

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C#

service

RIA

Silverlight5

domain

, +

Hi,

When creating the domain ria services, we should make one service for each table or one service for all tables??

I'm asking this cause i created one service for each table, and worked fine with simple tables. But now i'm having problems with Parent/child tables...

private ParentMetadata()
            {
            }

            [Include]
            public Child Child{ get; set; }
            public string desc { get; set; }

}

Service Code for Parent

public IQueryable<Parent> GetParent()
        {
            return this.ObjectContext.Parents.Include("Child");
        }

And in the insert method i have:

private void OKButton_Click(object sender, RoutedEventArgs e)
        {
            Web.Services.ParentContext context;  
            context = new Web.Services.ParentContext();
            WMS.Web.Model.Parent obj = new WMS.Web.Model.Parent();

            Guid obj2 = Guid.NewGuid();
            obj.GUIDParent = obj2;
            obj.desc = descTextBox.Text;
            obj.Child.GUIDParent = obj2;
            obj.Child.desc = descTextBox.Text;
            context.Parents.Add(obj);

            try
            {
                context.SubmitChanges();
                MessageBox.Show("sucess");

                this.DialogResult = true;

            }
            catch (Exception ex)
            {
                MessageBox.Show("Error: " + ex.Message);
                this.DialogResult = false;
            }
        }

I'm always getting an error saying that obj.Child is null