LINQ to Entities 常用查询语句

要使用关联实体返回局部或完整的对象图，需要在LINQ 标准查询操作符之前执行Include()操作符，如下列查询所示，它将返回和前面“使用Include()操作符进行预先加载”一节同样的结果：

using (NorthwindEntities ocNwind = new 
NorthwindEntities("name=NorthwindEntities"))  
{  
List<Order> orderList = null;  
ObjectQuery<Order> orders = ocNwind.Orders;  
orders.MergeOption = MergeOptions.AppendOnly;  
var orderQuery = orders.Include("Order_Details")  
.Include("Customer")  
.Include("Employee")  
.Include("Shipper")  
.Where(o => o.Customer.Country == "Brazil")  
.OrderByDescending(o => o.OrderID)  
.Select(o => o)  
.Take(5);  
foreach (Order order in orderQuery)  
{  
// Materialize the object  
orderList.Add(order);  
}  
}  
VB 9.0  
Using ocNwind As New NorthwindEntities("name=NorthwindEntities")  
Dim orderList As List(Of Order) = Nothing  
Dim oqOrders As ObjectQuery(Of Order) = ocNwind.Orders  
orders.MergeOption = MergeOptions.AppendOnly  
Dim orderQuery = oqOrders.Include("Order_Details") _  
.Include("Customer") _  
.Include("Employee") _  
.Include("Shipper") _  
.Where(Function(o) o.Customer.Country = "Brazil") _  
.OrderByDescending(Function(o) o.OrderID) _  
.Select(Function(o) o) _  
.Take(5)  
For Each oqOrder As Order In orderQuery  
' Materialize the object  
orderList.Add(oqOrder)  
Next oqOrder  
End Using 

LINQ 表达式语法和串联方法调用区别较大。在4 个标准查询操作符执行之后，要将ObjectQuery<Order>改变为IQueryable<Order>类型，需要把Include()操作符和LINQ 表达式相分隔，如下所示：

ordersorders = orders.Include("Order_Details")  
.Include("Customer")  
.Include("Employee")  
.Include("Shipper");  
orderQuery = (from o in orders  
where o.Customer.Country == "Brazil"  
orderby o.OrderID descending  
select o).Take(5);  
VB 9.0  
oqOrdersoqOrders = oqOrders.Include("Order_Details")  
.Include("Customer")  
.Include("Employee")  
.Include("Shipper")  
orderQuery = (From o In oqOrders _  
Where o.Customer.Country = "Brazil" _  
Order By o.OrderID Descending _  
Select o).Take(5) 

可选地，可以使用下面这样更为易读的语法：

orderQuery = (from o in orders.Include("Order_Details")  
.Include("Customer")  
.Include("Employee")  
.Include("Shipper")  
where o.Customer.Country == "Brazil"  
orderby o.OrderID descending  
select o).Take(5);  
VB 9.0  
orderQuery = (From o In oqOrders.Include("Order_Details" _  
.Include("Customer") _  
.Include("Employee") _  
.Include("Shipper") _  
Where o.Customer.Country = "Brazil" _  
Order By o.OrderID Descending _  
select o).Take(5);