如何：显式加载 POCO 实体（实体框架）
本主题中的示例演示如何使用 ObjectContext 的 LoadProperty 方法显式加载相关对象。 有关使用延迟加载访问相关对象的示例，请参见如何：使用延迟加载来加载相关对象（实体框架）。 LoadProperty 方法可用于 POCO 实体和从 EntityObject 派生的实体。
本主题中的示例使用在如何：定义 POCO 实体（实体框架）中定义的 POCO 数据类、在如何：定义自定义对象上下文（实体框架）中创建的 AdventureWorksEntities 类（派生自 ObjectContext）以及在如何：自定义建模和映射文件以使用自定义对象（实体框架）中定义的基于 AdventureWorks 的数据模型。
示例
此示例返回前五个 Order 对象并调用 LoadProperty 方法以显式加载每个 Order 的相关 LineItem 对象。
Using context As New POCOAdventureWorksEntities()
Try
' Disable lazy loading.
context.ContextOptions.LazyLoadingEnabled = False
' Get the first five orders.
For Each order As Order In context.Orders.Take(5)
' Because LazyLoadingEnabled is set to false,
' we need to explicitly load the related line items for the order.
context.LoadProperty(order, "LineItems")
Console.WriteLine(String.Format("PO Number: {0}", order.ExtendedInfo.PurchaseOrderNumber))
Console.WriteLine(String.Format("Order Date: {0}", order.OrderDate.ToString()))
Console.WriteLine("Order items:")
For Each item As LineItem In order.LineItems
Console.WriteLine(String.Format("Product: {0} " & "Quantity: {1}", item.ProductID, item.OrderQty))
Next
Next
Catch ex As InvalidOperationException
Console.WriteLine(ex.Message)
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Using
using (POCOAdventureWorksEntities context =
new POCOAdventureWorksEntities())
{
try
{
// Disable lazy loading.
context.ContextOptions.LazyLoadingEnabled = false;
// Get the first five orders.
foreach (Order order in context.Orders.Take(5))
{
// Because LazyLoadingEnabled is set to false,
// we need to explicitly load the related line items for the order.
context.LoadProperty(order, "LineItems");
Console.WriteLine(String.Format("PO Number: {0}",
order.ExtendedInfo.PurchaseOrderNumber));
Console.WriteLine(String.Format("Order Date: {0}",
order.OrderDate.ToString()));
Console.WriteLine("Order items:");
foreach (LineItem item in order.LineItems)
{
Console.WriteLine(String.Format("Product: {0} "
+ "Quantity: {1}", item.ProductID,
item.OrderQty));
}
}
}
catch (InvalidOperationException ex)
{
Console.WriteLine(ex.Message);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}