如何：筛选数据（实体框架）
本主题介绍如何筛选查询结果。该示例返回表示大于 2,500 美元的所有联机订单的 SalesOrderHeader 对象的集合。下面使用以下 实体框架 查询技术演示同一示例：
LINQ to Entities
Entity SQL with ObjectQuery<T>
ObjectQuery <T> 的查询生成器方法
本主题中的示例基于 Adventure Works 销售模型。若要运行本示例中的代码，必须已将 AdventureWorks 销售模型添加到您的项目中，并将项目配置为使用 实体框架。为此，请完成如何：手动配置实体框架项目和如何：手动定义实体数据模型（实体框架） 中的过程。也可以使用实体数据模型向导定义 AdventureWorks 销售模型。有关更多信息，请参见如何：使用实体数据模型向导（实体框架）。
示例
以下是 LINQ to Entities 示例。
Using context As AdventureWorksEntities = _
New AdventureWorksEntities()
' Specify the order amount.
Dim orderCost As Integer = 2500
Try
' Define a LINQ query that returns only online orders
' more than the specified amount.
Dim onlineOrders = _
From order As SalesOrderHeader In context.SalesOrderHeader() _
Where order.OnlineOrderFlag = True And _
order.TotalDue > orderCost _
Select order
' Print order information.
For Each onlineOrder In onlineOrders
Console.WriteLine("Order ID:{0}Order date: " _
+ "{1}:d Order number: {2}", _
onlineOrder.SalesOrderID, _
onlineOrder.OrderDate, _
onlineOrder.SalesOrderNumber)
Next
Catch ex As EntitySqlException
Console.WriteLine(ex.ToString())
End Try
End Using
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
// Specify the order amount.
int orderCost = 2500;
try
{
// Define a LINQ query that returns only online orders
// more than the specified amount.
var onlineOrders =
from order in context.SalesOrderHeader
where order.OnlineOrderFlag == true &&
order.TotalDue > orderCost
select order;
// Print order information.
foreach (var onlineOrder in onlineOrders)
{
Console.WriteLine("Order ID: {0} Order date: "
+ "{1:d} Order number: {2}",
onlineOrder.SalesOrderID,
onlineOrder.OrderDate,
onlineOrder.SalesOrderNumber);
}
}
catch (EntitySqlException ex)
{
Console.WriteLine(ex.ToString());
}
}
以下是 Entity SQL 示例。
Using context As AdventureWorksEntities = _
New AdventureWorksEntities()
' Specify the order amount.
Dim orderCost As Integer = 2500
' Specify the Entity SQL query that returns only online orders
' more than the specified amount.
Dim queryString As String = "SELECT VALUE o FROM SalesOrderHeader AS o " _
+ "WHERE o.OnlineOrderFlag = TRUE AND o.TotalDue > @ordercost"
Try
' Define an ObjectQuery and pass the maxOrderCost parameter.
Dim onlineOrders As ObjectQuery(Of SalesOrderHeader) = _
New ObjectQuery(Of SalesOrderHeader)(queryString, context)
onlineOrders.Parameters.Add( _
New ObjectParameter("ordercost", orderCost))
' Print order information.
For Each onlineOrder In onlineOrders
Console.WriteLine("Order ID:{0}Order date: " _
+ "{1}:d Order number: {2}", _
onlineOrder.SalesOrderID, _
onlineOrder.OrderDate, _
onlineOrder.SalesOrderNumber)
Next
Catch ex As EntitySqlException
Console.WriteLine(ex.ToString())
End Try
End Using
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
// Specify the order amount.
decimal orderCost = 2500;
// Specify the Entity SQL query that returns only online orders
// more than the specified amount.
string queryString = @"SELECT VALUE o FROM SalesOrderHeader AS o
WHERE o.OnlineOrderFlag = TRUE AND o.TotalDue > @ordercost";
try
{
// Define an ObjectQuery and pass the maxOrderCost parameter.
ObjectQuery<SalesOrderHeader> onlineOrders =
new ObjectQuery<SalesOrderHeader>(queryString, context);
onlineOrders.Parameters.Add(
new ObjectParameter("ordercost", orderCost));
// Print order information.
foreach (var onlineOrder in onlineOrders)
{
Console.WriteLine("Order ID: {0} Order date: "
+ "{1:d} Order number: {2}",
onlineOrder.SalesOrderID,
onlineOrder.OrderDate,
onlineOrder.SalesOrderNumber);
}
}
catch (EntitySqlException ex)
{
Console.WriteLine(ex.ToString());
}
}
以下是查询生成器方法示例。
Using context As AdventureWorksEntities = _
New AdventureWorksEntities()
' Specify the order amount.
Dim orderCost As Integer = 2500
Try
' Define an ObjectQuery that returns only online orders
' more than the specified amount.
Dim onlineOrders As ObjectQuery(Of SalesOrderHeader) = _
context.SalesOrderHeader.Where("it.OnlineOrderFlag = TRUE") _
.Where("it.TotalDue > @ordercost", _
New ObjectParameter("ordercost", orderCost))
' Print order information.
For Each onlineOrder In onlineOrders
Console.WriteLine("Order ID:{0}Order date: " _
+ "{1}:d Order number: {2}", _
onlineOrder.SalesOrderID, _
onlineOrder.OrderDate, _
onlineOrder.SalesOrderNumber)
Next
Catch ex As EntitySqlException
Console.WriteLine(ex.ToString())
End Try
End Using
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
// Specify the order amount.
int orderCost = 2500;
try
{
// Define an ObjectQuery that returns only online orders
// more than the specified amount.
ObjectQuery<SalesOrderHeader> onlineOrders =
context.SalesOrderHeader
.Where("it.OnlineOrderFlag = TRUE AND it.TotalDue > @ordercost",
new ObjectParameter("ordercost", orderCost));
// Print order information.
foreach (var onlineOrder in onlineOrders)
{
var items = (from item in context.SalesOrderDetail
where item.SalesOrderHeader == onlineOrder
select item).Take(3);
Console.WriteLine("Order ID: {0} Order date: "
+ "{1:d} Order number: {2}",
onlineOrder.SalesOrderID,
onlineOrder.OrderDate,
onlineOrder.SalesOrderNumber);
}
}
catch (EntitySqlException ex)
{
Console.WriteLine(ex.ToString());
}
}