ObjectStateManager 类

定义

public ref class ObjectStateManager

public class ObjectStateManager

type ObjectStateManager = class

Public Class ObjectStateManager

继承

Object

ObjectStateManager

示例

以下示例从ObjectContext上下文中获取ObjectStateManager并使用状态管理器访问对象。

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");
    }
}

下面的示例使用 TryGetObjectStateEntry(EntityKey, ObjectStateEntry) 返回 ObjectStateManager 的方法根据其实体键获取对象。

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();
    }
}

注解

ObjectStateManager 跟踪查询结果，并提供用于合并多个重叠查询结果的逻辑。 当用户插入、删除或修改对象时，它还会执行内存中更改跟踪，并提供更新的更改集。 更改处理器使用此更改集来保留修改。

此类通常用于应用程序中，而不是直接在应用程序中使用 ObjectContext 。