LINQ to Entities 常用查詢語句

要使用關聯實體返回區域性或完整的物件圖，需要在linq 標準查詢操作符之前執行include()操作符，如下列查詢所示，它將返回和前面「使用include()操作符進行預先載入」一節同樣的結果：

using (northwindentities ocnwind = new

northwindentities(
"name=northwindentities
"))  
}  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  
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 表示式語法和串聯方法呼叫區別較大。在4 個標準查詢操作符執行之後，要將objectquery改變為iqueryable型別，需要把include()操作符和linq 表示式相分隔，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)

可選地，可以使用下面這樣更為易讀的語法：

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);

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