ObjectStateManager.TryGetObjectStateEntry 方法
定义
尝试返回特定对象或关系项的 ObjectStateEntry 对象。Tries to return an ObjectStateEntry object for a specific object or relationship entry.
重载
| TryGetObjectStateEntry(EntityKey, ObjectStateEntry) |
尝试检索具有指定 ObjectStateEntry 的对象或关系的对应 EntityKey。Tries to retrieve the corresponding ObjectStateEntry for the object or relationship with the specified EntityKey. |
| TryGetObjectStateEntry(Object, ObjectStateEntry) |
尝试检索指定的 ObjectStateEntry 的对应 Object。Tries to retrieve the corresponding ObjectStateEntry for the specified Object. |
TryGetObjectStateEntry(EntityKey, ObjectStateEntry)
尝试检索具有指定 ObjectStateEntry 的对象或关系的对应 EntityKey。Tries to retrieve the corresponding ObjectStateEntry for the object or relationship with the specified EntityKey.
public:
bool TryGetObjectStateEntry(System::Data::EntityKey ^ key, [Runtime::InteropServices::Out] System::Data::Objects::ObjectStateEntry ^ % entry);
public bool TryGetObjectStateEntry (System.Data.EntityKey key, out System.Data.Objects.ObjectStateEntry entry);
member this.TryGetObjectStateEntry : System.Data.EntityKey * ObjectStateEntry -> bool
Public Function TryGetObjectStateEntry (key As EntityKey, ByRef entry As ObjectStateEntry) As Boolean
参数
- entry
- ObjectStateEntry
此方法返回时,包含给定 ObjectStateEntry 的 EntityKey。此参数传递时未经初始化。When this method returns, contains an ObjectStateEntry for the given EntityKey This parameter is passed uninitialized.
返回
一个布尔值,如果对给定的 true 具有对应的 ObjectStateEntry,则为 EntityKey;否则为 false。A Boolean value that is true if there is a corresponding ObjectStateEntry for the given EntityKey; otherwise, false.
例外
为 key 提供了一个 null(在 Visual Basic 中为 Nothing)值。A null (Nothing in Visual Basic) value is provided for key.
示例
本主题中的示例基于 " Microsoft SQL Server 产品示例:数据库"。The examples in this topic are based on the Microsoft SQL Server Product Samples: Database.
该示例尝试检索给定的 ObjectStateEntry 的对应 EntityKey。The example attempts to retrieve the corresponding ObjectStateEntry for the given EntityKey.
int orderId = 43680;
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
ObjectStateManager objectStateManager = context.ObjectStateManager;
ObjectStateEntry stateEntry = null;
var order = (from o in context.SalesOrderHeaders
where o.SalesOrderID == orderId
select o).First();
// Attempts to retrieve ObjectStateEntry for the given EntityKey.
bool isPresent = objectStateManager.TryGetObjectStateEntry(((IEntityWithKey)order).EntityKey, out stateEntry);
if (isPresent)
{
Console.WriteLine("The entity was found");
}
}
Dim orderId As Integer = 43680
Using context As New AdventureWorksEntities()
Dim objectStateManager As ObjectStateManager = context.ObjectStateManager
Dim stateEntry As ObjectStateEntry = Nothing
Dim order = (From o In context.SalesOrderHeaders
Where o.SalesOrderID = orderId
Select o).First()
' Attempts to retrieve ObjectStateEntry for the given EntityKey.
Dim isPresent As Boolean = objectStateManager.TryGetObjectStateEntry(DirectCast(order, IEntityWithKey).EntityKey, stateEntry)
If isPresent Then
Console.WriteLine("The entity was found")
End If
End Using
下面的示例使用返回的 TryGetObjectStateEntry(EntityKey, ObjectStateEntry) 的 ObjectStateManager 方法,根据对象的实体键获取对象。The following example uses the TryGetObjectStateEntry(EntityKey, ObjectStateEntry) method on the returned ObjectStateManager to get an object based on its entity key.
private static void ApplyItemUpdates(SalesOrderDetail originalItem,
SalesOrderDetail updatedItem)
{
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
context.SalesOrderDetails.Attach(updatedItem);
// Check if the ID is 0, if it is the item is new.
// In this case we need to chage the state to Added.
if (updatedItem.SalesOrderDetailID == 0)
{
// Because the ID is generated by the database we do not need to
// set updatedItem.SalesOrderDetailID.
context.ObjectStateManager.ChangeObjectState(updatedItem, System.Data.EntityState.Added);
}
else
{
// If the SalesOrderDetailID is not 0, then the item is not new
// and needs to be updated. Because we already added the
// updated object to the context we need to apply the original values.
// If we attached originalItem to the context
// we would need to apply the current values:
// context.ApplyCurrentValues("SalesOrderDetails", updatedItem);
// Applying current or original values, changes the state
// of the attached object to Modified.
context.ApplyOriginalValues("SalesOrderDetails", originalItem);
}
context.SaveChanges();
}
}
Private Shared Sub ApplyItemUpdates(ByVal originalItem As SalesOrderDetail, ByVal updatedItem As SalesOrderDetail)
Using context As New AdventureWorksEntities()
context.SalesOrderDetails.Attach(updatedItem)
' Check if the ID is 0, if it is the item is new.
' In this case we need to chage the state to Added.
If updatedItem.SalesOrderDetailID = 0 Then
' Because the ID is generated by the database we do not need to
' set updatedItem.SalesOrderDetailID.
context.ObjectStateManager.ChangeObjectState(updatedItem, System.Data.EntityState.Added)
Else
' If the SalesOrderDetailID is not 0, then the item is not new
' and needs to be updated. Because we already added the
' updated object to the context we need to apply the original values.
' If we attached originalItem to the context
' we would need to apply the current values:
' context.ApplyCurrentValues("SalesOrderDetails", updatedItem);
' Applying current or original values, changes the state
' of the attached object to Modified.
context.ApplyOriginalValues("SalesOrderDetails", originalItem)
End If
context.SaveChanges()
End Using
End Sub
注解
使用 TryGetObjectStateEntry(EntityKey, ObjectStateEntry) 方法可返回 ObjectStateEntry,而不必处理 InvalidOperationException 方法引发的 GetObjectStateEntry(EntityKey)。Use TryGetObjectStateEntry(EntityKey, ObjectStateEntry) to return an ObjectStateEntry without having to handle the InvalidOperationException raised by the GetObjectStateEntry(EntityKey) method.
适用于
TryGetObjectStateEntry(Object, ObjectStateEntry)
尝试检索指定的 ObjectStateEntry 的对应 Object。Tries to retrieve the corresponding ObjectStateEntry for the specified Object.
public:
bool TryGetObjectStateEntry(System::Object ^ entity, [Runtime::InteropServices::Out] System::Data::Objects::ObjectStateEntry ^ % entry);
public bool TryGetObjectStateEntry (object entity, out System.Data.Objects.ObjectStateEntry entry);
member this.TryGetObjectStateEntry : obj * ObjectStateEntry -> bool
Public Function TryGetObjectStateEntry (entity As Object, ByRef entry As ObjectStateEntry) As Boolean
参数
- entity
- Object
检索到的 Object 所属的 ObjectStateEntry。The Object to which the retrieved ObjectStateEntry belongs.
- entry
- ObjectStateEntry
此方法返回时,包含给定 ObjectStateEntry 的 EntityKey。此参数传递时未经初始化。When this method returns, contains the ObjectStateEntry for the given EntityKey This parameter is passed uninitialized.
返回
一个布尔值,如果对给定的对象具有对应的 true,则该值为 ObjectStateEntry;否则为 false。A Boolean value that is true if there is a corresponding ObjectStateEntry for the given object; otherwise, false.
注解
使用 TryGetObjectStateEntry(Object, ObjectStateEntry) 方法可返回 ObjectStateEntry,而不必处理 InvalidOperationException 方法引发的 GetObjectStateEntry(Object)。Use the TryGetObjectStateEntry(Object, ObjectStateEntry) method to return an ObjectStateEntry without having to handle the InvalidOperationException raised by the GetObjectStateEntry(Object) method.