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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