本主题说明如何通过导航属性来导航关系。有关更多信息，请参见导航属性 (EDM)。此示例获取其姓氏为“Zhou”的联系人的所有订单。Contact.SalesOrderHeader 导航属性用于获取每个联系人的 SalesOrderHeader 对象的集合。将使用以下每种 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
这是 LINQ to Entities 示例。
Using AWEntities As New AdventureWorksEntities
Dim contacts As ObjectQuery(Of Contact) = AWEntities.Contact
Dim ordersQuery = From contact In contacts _
Where contact.LastName = "Zhou" _
Select New With _
{.LastName = contact.LastName, _
.Orders = contact.SalesOrderHeader}
For Each order In ordersQuery
Console.WriteLine("Name: {0}", order.LastName)
For Each orderInfo In order.Orders
Console.WriteLine("Order ID: {0}, Order date: {1}, Total Due: {2}", _
orderInfo.SalesOrderID, orderInfo.OrderDate, orderInfo.TotalDue)
Next
Console.WriteLine("")
Next
End Using
using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
ObjectQuery<Contact> contacts = AWEntities.Contact;
var ordersQuery = from contact in contacts
where contact.LastName == "Zhou"
select new { LastName = contact.LastName, Orders = contact.SalesOrderHeader };
foreach (var order in ordersQuery)
{
Console.WriteLine("Name: {0}", order.LastName);
foreach (SalesOrderHeader orderInfo in order.Orders)
{
Console.WriteLine("Order ID: {0}, Order date: {1}, Total Due: {2}",
orderInfo.SalesOrderID, orderInfo.OrderDate, orderInfo.TotalDue);
}
Console.WriteLine("");
}
}
这是 Entity SQL 示例。
Using advWorksContext As New AdventureWorksEntities
Dim esqlQuery As String = "SELECT c.FirstName, c.SalesOrderHeader " & _
" FROM AdventureWorksEntities.Contact AS c where c.LastName = 'Zhou'"
Try
Dim objQuery As New ObjectQuery(Of DbDataRecord)(esqlQuery, advWorksContext)
For Each rec As DbDataRecord In objQuery
' Display contact's first name.
Console.WriteLine("First Name {0}: ", rec.Item(0))
Dim list As List(Of SalesOrderHeader) = DirectCast(rec.Item(1), List(Of SalesOrderHeader))
' Display SalesOrderHeader information
' associated with the contact.
For Each soh As SalesOrderHeader In list
Console.WriteLine(" Order ID: {0}, Order date: {1}, Total Due: {2}", _
soh.SalesOrderID, soh.OrderDate, soh.TotalDue)
Next
Next
Catch ex As EntityException
Console.WriteLine(ex.ToString())
Catch ex As InvalidOperationException
Console.WriteLine(ex.ToString())
End Try
End Using
using (AdventureWorksEntities advWorksContext =
new AdventureWorksEntities())
{
string esqlQuery = @"SELECT c.FirstName, c.SalesOrderHeader
FROM AdventureWorksEntities.Contact AS c where c.LastName = 'Zhou'";
try
{
foreach (DbDataRecord rec in
new ObjectQuery<DbDataRecord>(esqlQuery, advWorksContext))
{
// Display contact's first name.
Console.WriteLine("First Name {0}: ", rec[0]);
List<SalesOrderHeader> list = rec[1] as List<SalesOrderHeader>;
// Display SalesOrderHeader information
// associated with the contact.
foreach (SalesOrderHeader soh in list)
{
Console.WriteLine(" Order ID: {0}, Order date: {1}, Total Due: {2}",
soh.SalesOrderID, soh.OrderDate, soh.TotalDue);
}
}
}
catch (EntityException ex)
{
Console.WriteLine(ex.ToString());
}
catch (InvalidOperationException ex)
{
Console.WriteLine(ex.ToString());
}
}
这是查询生成器方法示例。
Using advWorksContext As New AdventureWorksEntities()
Try
' Define a query that returns a nested
' DbDataRecord for the projection.
Dim query As ObjectQuery(Of DbDataRecord) = _
advWorksContext.Contact.Select("it.FirstName, " _
+ "it.LastName, it.SalesOrderHeader") _
.Where("it.LastName = 'Zhou'")
For Each rec As DbDataRecord In query.Execute(MergeOption.AppendOnly)
' Display contact's first name.
Console.WriteLine("First Name {0}: ", rec(0))
' Display SalesOrderHeader information
' associated with the contact.
For Each soh As SalesOrderHeader In CType(rec(2), List(Of SalesOrderHeader))
Console.WriteLine(" Order ID: {0}, " + _
"Order date: {1}, Total Due: {2}", _
soh.SalesOrderID, soh.OrderDate, soh.TotalDue)
Next
Next
Catch ex As EntitySqlException
Console.WriteLine(ex.ToString())
End Try
End Using
using (AdventureWorksEntities advWorksContext =
new AdventureWorksEntities())
{
try
{
// Define a query that returns a nested
// DbDataRecord for the projection.
ObjectQuery<DbDataRecord> query =
advWorksContext.Contact.Select("it.FirstName, "
+ "it.LastName, it.SalesOrderHeader")
.Where("it.LastName = 'Zhou'");
foreach (DbDataRecord rec in
query.Execute(MergeOption.AppendOnly))
{
// Display contact's first name.
Console.WriteLine("First Name {0}: ", rec[0]);
List<SalesOrderHeader> list = rec[2]
as List<SalesOrderHeader>;
// Display SalesOrderHeader information
// associated with the contact.
foreach (SalesOrderHeader soh in list)
{
Console.WriteLine(" Order ID: {0}, " +
"Order date: {1}, Total Due: {2}",
soh.SalesOrderID, soh.OrderDate, soh.TotalDue);
}
}
}
catch (EntitySqlException ex)
{
Console.WriteLine(ex.ToString());
}
}