如何：使用导航属性导航关系（实体框架）
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。 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 以及 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。若要运行本主题中的代码，则必须已经将 Adventure Works 销售模型添加到了您的项目中，并且已经将项目配置为使用实体框架。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）或如何：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）。
示例
这是 LINQ to Entities 示例。
Dim lastName = "Zhou"
Using context As New AdventureWorksEntities
Dim contacts As ObjectSet(Of Contact) = context.Contacts
Dim ordersQuery = From contact In contacts _
Where contact.LastName = lastName _
Select New With _
{.LastName = contact.LastName, _
.Orders = contact.SalesOrderHeaders}
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
string lastName = "Zhou";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
var ordersQuery = from contact in contacts
where contact.LastName == lastName
select new { LastName = contact.LastName, Orders = contact.SalesOrderHeaders };
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 context As New AdventureWorksEntities()
Dim esqlQuery As String = "SELECT c.FirstName, c.SalesOrderHeaders " & _
" FROM AdventureWorksEntities.Contacts AS c where c.LastName = @ln"
Dim query As New ObjectQuery(Of DbDataRecord)(esqlQuery, context)
' Add parameters to the collection.
query.Parameters.Add(New ObjectParameter("ln", "Zhou"))
For Each rec As DbDataRecord In query
' Display contact's first name.
Console.WriteLine("First Name {0}: ", rec(0))
Dim list As List(Of SalesOrderHeader) = TryCast(rec(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
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
string esqlQuery = @"SELECT c.FirstName, c.SalesOrderHeaders
FROM AdventureWorksEntities.Contacts AS c where c.LastName = @ln";
ObjectQuery<DbDataRecord> query = new ObjectQuery<DbDataRecord>(esqlQuery, context);
query.Parameters.Add(new ObjectParameter("ln", "Zhou"));
foreach (DbDataRecord rec in query)
{
// 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);
}
}
}
这是查询生成器方法示例。
Dim lastName = "Zhou"
Using context As New AdventureWorksEntities()
' Define a query that returns a nested
' DbDataRecord for the projection.
Dim query As ObjectQuery(Of DbDataRecord) = context.Contacts.Select("it.FirstName, it.LastName, it.SalesOrderHeaders") _
.Where("it.LastName = @ln", New ObjectParameter("ln", lastName))
For Each rec As DbDataRecord In query.Execute(MergeOption.AppendOnly)
' Display contact's first name.
Console.WriteLine("First Name {0}: ", rec(0))
Dim list As List(Of SalesOrderHeader) = TryCast(rec(2), 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
End Using
string lastName = "Zhou";
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Define a query that returns a nested
// DbDataRecord for the projection.
ObjectQuery<DbDataRecord> query =
context.Contacts.Select("it.FirstName, "
+ "it.LastName, it.SalesOrderHeaders")
.Where("it.LastName = @ln", new ObjectParameter("ln", lastName));
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);
}
}
}