var q =
        from c in db.Customers
        join o in db.Orders on c.CustomerID equals o.CustomerID into ords
        join e in db.Employees on c.City equals e.City into emps
        select new {c.ContactName, ords=ords.Count(), emps=emps.Count()};

bindinsource.DataSource = q;

            db = new Northwind(Program.connString);
            db.ObjectTrackingEnabled = false;// Если эту строку убрать деталь считывается!
            MasterbindingSource.DataSource = db.Orders;
            DetailbindingSource.DataSource = MasterbindingSource;
            DetailbindingSource.DataMember =  Order_Details

            db = new Northwind(Program.connString);
            db.ObjectTrackingEnabled = false;// Если эту строку убрать деталь считывается!
            MasterbindingSource.DataSource = db.Orders;
            DetailbindingSource.DataSource = MasterbindingSource;
            DetailbindingSource.DataMember =  Order_Details

this.MasterbindingSource = new System.Windows.Forms.BindingSource(this.components);
this.DetailbindingSource = new System.Windows.Forms.BindingSource(this.components);
this.dataGridView1.DataSource = this.MasterbindingSource;
this.dataGridView2.DataSource = this.DetailbindingSource;
// MasterbindingSource
// 
this.MasterbindingSource.DataSource = typeof(NorthwindMapping.Order);

// DetailbindingSource
// 
this.DetailbindingSource.DataMember = "Order_Details";
this.DetailbindingSource.DataSource = this.MasterbindingSource;

        Northwind db;
        public Form1()
        {
            InitializeComponent();
            db = new Northwind(Program.connString);
            db.ObjectTrackingEnabled = false;
            MasterbindingSource.DataSource = db.Orders;//
            bindingSource1.DataSource = db.Products;// master

        }

 var customers = testDS.Tables["Customers"].AsEnumerable();

    var orderCounts = from c in customers
        where c.Field<string>("CustomerID") != "AAAAA"
        select new {CustomerID = c.Field<string>("CustomerID"), 
            OrderCount = c.GetChildRows("CustomersOrders").Count()};
datagridview.Datasource = orderCounts; 

var customers = testDS.Tables["Customers"].AsEnumerable();
    var orders = testDS.Tables["Orders"].AsEnumerable();

    var smallOrders =
        from c in customers
        from o in orders
        where c.Field<string>("CustomerID") == o.Field<string>("CustomerID") &&
            o.Field<decimal>("Total") <  500 .00M
        select new {CustomerID = (string) c["CustomerID"], OrderID = (int) o["OrderID"], Total = (decimal) o["Total"]};

    DataTable myOrders = new DataTable();
    myOrders.Columns.Add("CustomerID", typeof(string));
    myOrders.Columns.Add("OrderID", typeof(int));
    myOrders.Columns.Add("Total", typeof(decimal));

    foreach (var result in smallOrders.Take( 10 ))
    {
        myOrders.Rows.Add(new object[] { result.CustomerID, result.OrderID, result.Total });
    }

using (NorthwindEntities db = new NorthwindEntities()) {

    var customers = db.CreateQuery<Customer>(
        "SELECT VALUE c FROM NorthwindEntities.Customers AS c");

    foreach (var c in customers) {
        Console.WriteLine(c.Display());
    }
}