EF中的EntityState几个状态的说明

时间：2023-03-09 16:14:36
EF中的EntityState几个状态的说明

之前使用EF，我们都是通过调用SaveChanges方法把增加/修改/删除的数据提交到数据库，但是上下文是如何知道实体对象是增加、修改还是删除呢？答案是通过EntityState枚举来判断的，我们看一个方法：

/// <summary>

        /// 查看实体状态

        /// </summary>

        private static void GetOneEntityToSeeEntityState()

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                var destination = context.Destinations.Find(4);

                EntityState stateBefore = context.Entry(destination).State;

                Console.WriteLine(stateBefore);

            }

        }

注：使用EntityState需添加引用system.data    
跑下程序，输出结果为：Unchanged。从英文意思我们已经猜到一二：取出来的数据是Unchanged，那么添加、修改、删除自然也就是Added、Modified、Deleted了。我们在EntityState上按F12定位到其定义看看：

EF中的EntityState几个状态的说明

的确，当调用SaveChanges方法的时候，EF会根据EntityState这个枚举检测到实体的状态，然后执行相应的增/删/改操作。它们的具体意思分别为：

  • Detached：对象存在，但未由对象服务跟踪。在创建实体之后、但将其添加到对象上下文之前，该实体处于此状态；
  • Unchanged：自对象加载到上下文中后，或自上次调用 System.Data.Objects.ObjectContext.SaveChanges() 方法后，此对象尚未经过修改；
  • Added：对象已添加到对象上下文，但尚未调用 System.Data.Objects.ObjectContext.SaveChanges() 方法；
  • Deleted：使用 System.Data.Objects.ObjectContext.DeleteObject(System.Object) 方法从对象上下文中删除了对象；
  • Modified：对象已更改，但尚未调用 System.Data.Objects.ObjectContext.SaveChanges() 方法。

ok，已经知道了这个，我们利用EntityState这个枚举修改下之前单个实体的增删改方法：

增加：

/// <summary>

        /// 添加：DbSet.Add = > EntityState.Added

        /// </summary>

        private static void TestAddDestination()

        {

            var jacksonHole = new DbContexts.Model.Destination

            {

                Name = "Jackson Hole,Wyoming",

                Description = "Get your skis on."

            };

            //AddDestinationByDbSetAdd(jacksonHole);

            AddDestinationByEntityStateAdded(jacksonHole);

        }

        private static void AddDestinationByDbSetAdd(DbContexts.Model.Destination destination)

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                context.Destinations.Add(destination);

                context.SaveChanges();

            }

        }

        private static void AddDestinationByEntityStateAdded(DbContexts.Model.Destination destination)

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                Console.WriteLine(context.Entry(destination).State);    //添加前：Detached

                context.Entry(destination).State = EntityState.Added;

                Console.WriteLine(context.Entry(destination).State);    //添加后：Added

                context.SaveChanges();

            }

        }
exec sp_executesql N'insert [baga].[Locations]([LocationName], [Country], [Description], [Photo], [TravelWarnings], [ClimateInfo])

values (@0, null, @1, null, null, null)

select [LocationID]

from [baga].[Locations]

where @@ROWCOUNT > 0 and [LocationID] = scope_identity()',N'@0 nvarchar(200),@1 nvarchar(500)',@0=N'Jackson Hole,Wyoming',@1=N'Get your skis on.'

监控到的sql也跟之前调用DbSet.Add方法添加实体的没什么区别。

我们看一个标记实体为未改变实体：

/// <summary>

        /// 标记一个未改变的实体

        /// </summary>

        private static void TestAttachDestination()

        {

            DbContexts.Model.Destination canyon;

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                canyon = (from d in context.Destinations

                          where d.Name == "Grand Canyon"

                          select d).Single();

            }

            AttachDestination(canyon);

        }

        private static void AttachDestination(DbContexts.Model.Destination destination)

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                Console.WriteLine(context.Entry(destination).State);    //标记前：Detached

                context.Destinations.Attach(destination);  //修改使用Attach方法

                //context.Entry(destination).State = EntityState.Unchanged;   //跟Attach方法一样效果

                Console.WriteLine(context.Entry(destination).State);    //标记后：Unchanged

                context.SaveChanges();

            }

        }

可以看出，实体从数据库取出是Detached状态，调用Attach方法变成了Unchanged状态。Unchanged状态会被SaveChanges方法忽略掉，不会有任何sql发送到数据库。

修改：

/// <summary>

        /// 修改：EntityState.Modified

        /// </summary>

        private static void TestUpdateDestination()

        {

            DbContexts.Model.Destination canyon;

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                canyon = (from d in context.Destinations

                          where d.Name == "Grand Canyon"

                          select d).Single();

            }

            canyon.TravelWarnings = "Don't Fall in!";

            UpdateDestination(canyon);

        }

        private static void UpdateDestination(DbContexts.Model.Destination destination)

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                Console.WriteLine(context.Entry(destination).State);    //修改前：Detached

                context.Entry(destination).State = EntityState.Modified;

                Console.WriteLine(context.Entry(destination).State);    //修改后：Modified

                context.SaveChanges();

            }

        }
exec sp_executesql N'update [baga].[Locations]

set [LocationName] = @0, [Country] = @1, [Description] = @2, [Photo] = null, [TravelWarnings] = @3, [ClimateInfo] = null

where ([LocationID] = @4)

',N'@0 nvarchar(200),@1 nvarchar(max) ,@2 nvarchar(500),@3 nvarchar(max) ,@4 int',@0=N'Grand Canyon',@1=N'USA',@2=N'One huge canyon.',@3=N'Don''t Fall in!',@4=1

我们标记实体为Modified后调用SaveChanges方法后，EF知道要更新实体了，但是它并不知道具体更新的是哪一列，所以每一列都更新了。见上面的sql

删除：

/// <summary>

        /// 删除：DbSet.Remove = > EntityState.Deleted

        /// </summary>

        private static void TestDeleteDestination()

        {

            DbContexts.Model.Destination canyon;

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                canyon = (from d in context.Destinations

                          where d.Name == "Grand Canyon"

                          select d).Single();

            }

            //DeleteDestination(canyon);

            DeleteDestinationByEntityStateDeletion(canyon);

        }

        private static void DeleteDestination(DbContexts.Model.Destination destination)

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                context.Destinations.Attach(destination);  //先告诉EF这个实体

                context.Destinations.Remove(destination);  //执行删除

                context.SaveChanges();

            }

        }

        private static void DeleteDestinationByEntityStateDeletion(DbContexts.Model.Destination destination)

        {

            using (var context = new DbContexts.DataAccess.BreakAwayContext())

            {

                Console.WriteLine(context.Entry(destination).State);    //删除前：Detached

                context.Entry(destination).State = EntityState.Deleted;

                Console.WriteLine(context.Entry(destination).State);    //删除后：Deleted

                context.SaveChanges();

            }

        }
exec sp_executesql N'delete [baga].[Locations]

where ([LocationID] = @0)',N'@0 int',@0=1
 
 
 
 
 
 
 
 
 
ADO.NET Entity Framework学习笔记(3)ObjectContext对象[转] 
说明


ObjectContext提供了管理数据的功能

EF中的EntityState几个状态的说明
Context操作数据


AddObject 添加实体









将实体添加到集合中,

创建实体时,状态为EntityState.Detached

当调用AddObject将实体添加到Context时,状态为EntityState.Added







myContext context = new myContext();

myTab r = new myTab();

r.ID = 10;

r.a = "wxwinter";

Console.WriteLine(r.EntityState); //print:Detached

context.AddTomyTab(r);

Console.WriteLine(r.EntityState); //print:Added

context.SaveChanges();







myContext context = new myContext();

myTab newrow = new myTab() { a = "wxd", b = "lzm", c = "wxwinter" };

context.AddObject("myTab",newrow);

context.SaveChanges();








DeleteObject 删除实体









将集合中的实体添标记为删除

当调用Context.DeleteObject时,并不是将实体移除集合,而是将实体添标记为EntityState.Deleted ,在下次调用SaveChanges()方法时跟新数据库







myContext context = new myContext();

myTab r = context.myTab.First(p=>p.ID==1);

Console.WriteLine(r.EntityState); //print:Unchanged

context.DeleteObject(r);

Console.WriteLine(r.EntityState); //print:Deleted

context.SaveChanges();








Detach 分离实体









将实体从Context中分离,将状态标记为EntityState.Detached 。







myContext context = new myContext();

myTab r = myTab.CreatemyTab(22);

Console.WriteLine(r.EntityState); //print:Detached

context.AddTomyTab(r);

Console.WriteLine(r.EntityState); //print:Added

context.Detach(r);

Console.WriteLine(r.EntityState); //print: Detached








修改实体









可以直接修在实体对象上修改

当修改在Context中的实体时,会将实体的状态标记为EntityState.Modified







myContext context = new myContext();

myTab r = context.myTab.First(p=>p.ID==1);

Console.WriteLine(r.EntityState); //print:Unchanged

r.a = "wxwinter";

Console.WriteLine(r.EntityState); //print:Modified

context.SaveChanges();








ApplyPropertyChanges 修改实体









使用ApplyPropertyChanges,可以使用不在集合中的实体覆盖到集合中主键对应用实体上,如果内存中没有主键对应的记录,会报错:“ObjectStateManager 不包含具有对“XXX”类型的对象的引用的 ObjectStateEntry。”该方法还有一个特点就是，会拿内存中的对象（新对象）和context中的对象（旧对象）对比，自动生成对应字段修改的Update语句，如果内存中的对象与context中的对象完全相等(每个字段的值都相等),将不生成响应的Update







myContext context = new myContext();

myTab r1 = context.myTab.First(p => p.ID == 1);

myTab nr = myTab.CreatemyTab(1);

nr.a = "wxwinter";

Console.WriteLine(nr.EntityState); //print:Detached

Console.WriteLine(r1.EntityState); //print:Unchanged

context.ApplyPropertyChanges("myTab", nr);

myTab r2 = context.myTab.First(p => p.ID == 1);

Console.WriteLine(nr.EntityState); //print:Detached

Console.WriteLine(r2.EntityState); //print:Modified

context.SaveChanges();







Orders order;
using (NorthwindEntities ne = new NorthwindEntities())
{
    //利用EntityObject.Execute(MergeOption.NoTracking)，等效于使用ObjectContext.Dettach(EntityObject)
    //查询并分离对象
    order = ne.Orders.Execute(MergeOption.NoTracking).Where(v => v.OrderID == 10248).FirstOrDefault();
}
//修改分离的值
order.ShipName = "1111111111111111";
//使用分离的对象 order 更新 
using (NorthwindEntities context = new NorthwindEntities())
{
    //将数据载入到context中以便更新
    context.GetObjectByKey(order.EntityKey);
    //使用order 更新 context中的对应对象
    context.ApplyPropertyChanges(order.EntityKey.EntitySetName, order);
    context.SaveChanges();
}









Attach / AttachTo 附加实体


使用Attach方法可将[外部实体]附加到Context集合中

在使用 服务器/客户端模式,或要将[实体]从Context集合中分离,修改后要用Context更新回数据库时,可用这种方式

Attach与ApplyPropertyChanges有类似之处,都是将Context集合外的[实体]与Context集合内的[实体]同步.

    

  1. ApplyPropertyChanges调用时,要求对应的[实体]在内存中,Attach不要求
    2. 

  2. ApplyPropertyChanges调用后,集合内的实体状态会标记为EntityState.Modified
    Attach调用后不会修改合内的实体状态,如要SaveChanges(),要手动标记EntityState.Modified
    3. 

  3. ApplyPropertyChanges是用[外部实体]全覆盖Context集合中的[实体],
    Attach方式,通过SetModifiedProperty()方法,可在调用SaveChanges()时,只修改只定有字段值
    4. 








myContext context = new myContext(); 
myTab v = myTab.CreatemyTab(1);  
v.EntityKey = context.CreateEntityKey("myTab", v); 
v.a = "wxwinter";
context.Attach(v);
//context.AttachTo("myTab", v);
ObjectStateEntry ose = context.ObjectStateManager.GetObjectStateEntry(v);
//设置修改
ose.SetModified();
//指定修改的字段名
ose.SetModifiedProperty("a");
context.SaveChanges();







修改前

EF中的EntityState几个状态的说明

修改后

EF中的EntityState几个状态的说明








CreateEntityKey 创建EntityKey







myContext context = new myContext();

myTab nr = myTab.CreatemyTab(1);

EntityKey ek= context.CreateEntityKey("myTab", nr);






EntityKey









EntityContainerName 属性

 






EntityKeyValues 集合

 






EntitySetName 属性

 






IsTemporary 属性

 






GetEntitySet(System.Data.Metadata.Edm.MetadataWorkspace) 方法

 






OnDeserialized(System.Runtime.Serialization.StreamingContext) 方法

 






OnDeserializing(System.Runtime.Serialization.StreamingContext) 方法

 







GetObjectByKey/TryGetObjectByKey 通过EntityKey得到实体









myContext context = new myContext();

myTab nr = myTab.CreatemyTab(1);

EntityKey ek= context.CreateEntityKey("myTab", nr);

myTab r = context.GetObjectByKey(ek) as myTab ;

Console.WriteLine("{0},{1},{2},{3}", r.ID, r.a, r.b, r.c);







myContext context = new myContext();

myTab nr = myTab.CreatemyTab(1);

EntityKey ek= context.CreateEntityKey("myTab", nr);
object obj;

if (context.TryGetObjectByKey(ek,out obj))

{

myTab r = obj as myTab;

Console.WriteLine("{0},{1},{2},{3}", r.ID, r.a, r.b, r.c);

}








CreateQuery 创建查询









更多见esql







myContext context = new myContext();

string esql = "SELECT VALUE DBItemList FROM myContext.DBItemList";

// ObjectQuery<DBItemList> query = new ObjectQuery<DBItemList>(esql, context);

ObjectQuery<DBItemList> query = context.CreateQuery<DBItemList>(esql);

foreach (DBItemList r in query)

{

Console.WriteLine(r.NameID);

}








状态管理


EntityState 状态枚举







EntityState.Added 已通过AddObject方法加到集合中，AcceptChanges 尚未调用。

EntityState.Deleted 已通过 DeleteObject 方法被删除。

EntityState.Detached 已被创建，但不属于任何集合。在以下情况下立即处于此状态：创建之后添加到集合中之前；或从集合中移除之后。

EntityState.Modified 已被修改，AcceptChanges 尚未调用。

EntityState.Unchanged 自上次调用 AcceptChanges 以来尚未更改






Context.ObjectStateManager 管理记录的状态


GetObjectStateEntry 根据实体对象或实体主键得到状态实体


实体必须在当前连接对象context中否则无法获取实体状态会引发：
ObjectStateManager 不包含具有对“context ”类型的对象的引用的 ObjectStateEntry
也就是该方法无法获取已分离的实体对象状态









ObjectStateEntry = GetObjectStateEntry(实体对像/EntityKey)

得到所指定的[实体对像]或EntityKey的 ObjectStateEntry







myContext context = new myContext();

myTab r = myTab.CreatemyTab(22);

context.AddTomyTab(r);

// ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

ObjectStateEntry ose = context.ObjectStateManager.GetObjectStateEntry(r.EntityKey);

Console.WriteLine(ose.State); //print:Added








TryGetObjectStateEntry 根据实体对象或实体主键得到状态实体









bool = TryGetObjectStateEntry(实体对像/EntityKey,out ObjectStateEntry)

得到所指定的[实体对像]或EntityKey的 ObjectStateEntry







myContext context = new myContext();

myTab r = myTab.CreatemyTab(22);

context.AddTomyTab(r);

ObjectStateEntry ose;

if( context.ObjectStateManager.TryGetObjectStateEntry(r,out ose))

{

Console.WriteLine(ose.State); //print:Added

}








GetObjectStateEntries 根据状态类型得到状态实体集合









IEnumerable<ObjectStateEntry> = GetObjectStateEntries(EntityState枚举)

返回IEnumerable<ObjectStateEntry>,得到EntityState枚举所指定的某种状态的列表







myContext context = new myContext();

myTab r = myTab.CreatemyTab(22);

context.AddTomyTab(r);

IEnumerable<ObjectStateEntry> oseList = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added);

foreach (ObjectStateEntry v in oseList)

{

Console.WriteLine("{0},{1},{2}", v.State, v.CurrentValues["ID"], v.EntitySet.Name);

}

//print:Added,22,myTab








ObjectStateManagerChanged 事件









CollectionChangeEventHandler(object sender, CollectionChangeEventArgs e)

e.Action : 集合操作行为

System.ComponentModel.CollectionChangeAction.Add

System.ComponentModel.CollectionChangeAction.Refresh

System.ComponentModel.CollectionChangeAction.Remove

e.Element : 操作的实体对象







void ObjectStateManager_ObjectStateManagerChanged(object sender, CollectionChangeEventArgs e)

{

Console.WriteLine(e.Action);
    myTab v = e.Element as myTab;

Console.WriteLine("{0}",v.ID);

}

//===================================

myContext context = new myContext();

context.ObjectStateManager.ObjectStateManagerChanged+=new CollectionChangeEventHandler(ObjectStateManager_ObjectStateManagerChanged);

myTab r = myTab.CreatemyTab(22);

context.AddTomyTab(r);

/*

*print:

Add

22

*/








ObjectStateEntry 对象


基本属性









IsRelationship 属性

 






Entity 属性

 






EntityKey 属性

 






EntitySet 属性

 







State 状态属性









EntityState 枚举







myContext context = new myContext();

myTab r = myTab.CreatemyTab(22);

context.AddTomyTab(r);

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

Console.WriteLine(ose.State); //print:Added








CurrentValues 当前值









处于 deleted 或 detached 状态的对象没有当前值。







myContext context = new myContext();

myTab r = new myTab() { ID = 22, a = "wxwinter" };

context.AddTomyTab(r);

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

Console.WriteLine("{0},{1}",ose.CurrentValues["ID"],ose.CurrentValues["a"]);

//print: 22,wxwinter








OriginalValues 原始值









处于 added 或 detached 状态的对象没有原始值







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

r.a = "wxwinter";

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Modified

CurrentValues :1,wxwinter

OriginalValues:1,aa

*/








GetModifiedProperties 得到被修改的属性









返回IEnumerable<string>

得到被修改的属性集合







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

r.a = "wxwinter";

r.b = "wxd";

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

IEnumerable<string> list = ose.GetModifiedProperties();

foreach (string pr in list)

{

Console.WriteLine(pr);

}

/*

* print:

a

b

*/








SetModified,SetModifiedProperty 标记为修改









SetModified() 方法将记录标记为 EntityState.Modified

只是这样,调用Context.SaveChanges方法是无法保存修改到数据库中的,Context.SaveChanges方法要查找被修改过的属性,

可用SetModifiedProperty方法标记被修改过的属性







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

r.a = "wxwinter";

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);
ose.AcceptChanges();

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Unchanged

CurrentValues :1,wxwinter

OriginalValues:1,wxwinter

*/

ose.SetModified();

ose.SetModifiedProperty("a");

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Modified

CurrentValues :1,wxwinter

OriginalValues:1,wxwinter

*/

context.SaveChanges();








Delete 标记为删除









标记为EntityState.Deleted







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

ose.Delete();

Console.WriteLine(ose.State); //print: Detached

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

//print:OriginalValues:1,wxwinter







用 context.DeleteObject方法的效果与上例一样

myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);
ObjectStateEntry ose = context.ObjectStateManager.GetObjectStateEntry(r);
context.DeleteObject(r);
Console.WriteLine(ose.State); //print: Detached
Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

//print:OriginalValues:1,wxwinter








AcceptChanges 方法









将记录的状态置为EntityState.Unchanged

用[CurrentValues 当前值]替换[OriginalValues 原始值],

使用[ Context.AcceptAllChanges 方法]也有同样效果

注意:状态为[EntityState.Deleted ]的记录,会被[Detach]







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);
r.a = "wxwinter";

context.AcceptAllChanges(); 
ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

ose.AcceptChanges();

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Unchanged

CurrentValues :1,wxwinter

OriginalValues:1,wxwinter

*/







当调用AcceptChanges时,如果对像处于[EntityState.Deleted ],会将对象移除集合,这时对像的状态为[EntityState.Detached ]

myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

ose.Delete();

ose.AcceptChanges();

Console.WriteLine(ose.State); //print: Detached








保存修改到数据库


Context.SaveChanges 方法


如果集合中有状态为EntityState.Added的记录,用[CurrentValues 当前值]添加到数据库中

如果集合中有状态为EntityState.Deleted的记录,从数据库是删除与之对应的数据库记录

如果集合中有状态为EntityState.Modified的记录,用[OriginalValues 原始值]与对应的数据库记录比效,查看并发, 用[CurrentValues 当前值]更新与之对应的数据库记录








SaveChanges(true)



将数据保存到数据库后

将所有记录状态标记为EntityState.Unchanged ,(调用Context.AcceptAllChanges )







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

r.a = "wxwinter";

ObjectStateEntry ose = context.ObjectStateManager.GetObjectStateEntry(r);

context.SaveChanges(true);

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Unchanged

CurrentValues :1,wxwinter

OriginalValues:1,wxwinter

*/







SaveChanges()



与SaveChanges(true)相同







SaveChanges(false)



将数据保存到数据库,

但并不改变记录状态







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

r.a = "wxwinter";

ObjectStateEntry ose = context.ObjectStateManager.GetObjectStateEntry(r);

context.SaveChanges(false);

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Modified

CurrentValues :1,wxwinter

OriginalValues:1,aa

*/








Context.SavingChanges 事件









myContext context = new myContext();

context.SavingChanges+=new EventHandler(context_SavingChanges);

myTab r = context.myTab.First(p => p.ID == 1);
r.a = "wxwinter"; 
context.SaveChanges();







void context_SavingChanges(object sender, EventArgs e)

{

myContext context = sender as myContext;

Console.WriteLine(context.DefaultContainerName);

}








Context.AcceptAllChanges 方法









将所有记录的状态置为EntityState.Unchanged

用[CurrentValues 当前值]替换[OriginalValues 原始值]

效果与对所在记录的ObjectStateEntry上调用AcceptAllChanges一样

注意:状态为[EntityState.Deleted ]的记录,会被[Detach]







myContext context = new myContext();

myTab r = context.myTab.First(p => p.ID == 1);

r.a = "wxwinter";

context.AcceptAllChanges();

ObjectStateEntry ose= context.ObjectStateManager.GetObjectStateEntry(r);

Console.WriteLine(ose.State);

Console.WriteLine("CurrentValues :{0},{1}", ose.CurrentValues["ID"], ose.CurrentValues["a"]);

Console.WriteLine("OriginalValues:{0},{1}", ose.OriginalValues["ID"], ose.OriginalValues["a"]);

/*

* print:

Unchanged

CurrentValues :1,wxwinter

OriginalValues:1,wxwinter

*/








连接属性


Context.DefaultContainerName 属性


Context.Connection 属性


Context.CommandTimeout 属性


Context.MetadataWorkspace


数据刷新与并发


EF提供了两种并发冲突处理方式：放任不管方式和开放式并发。默认采用放任不管的方式处理。

如果要使用开放式并发，必须设置相应属性上的[并发模式]值[Fixed]

后修改数据的ObjectContext缓存了旧版本的数据时,当提交修改后系统就会抛出"OptimisticConcurrencyException"（开放式并发异常）。

当程序捕获到异常以后，可以使用ObjectContext的Refresh方法对异常采取处理。

EF中的EntityState几个状态的说明EF中的EntityState几个状态的说明
缓存数据不会自动更新









公共



myContext context1 = new myContext();

myContext context2 = new myContext();







查询



foreach (var r in context1.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}

Console.WriteLine("---------------------");

foreach (var r in context2.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}







a,this is a

b,this is b

c,this is c

---------------------

a,this is a

b,this is b

c,this is c







修改



DBItem dbitem1 = context1.DBItem.First(p => p.ItemID == "a");

dbitem1.ItemMatter = "hello";

context1.SaveChanges();







再查询



foreach (var r in context1.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}

Console.WriteLine("---------------------");

foreach (var r in context2.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}







a,hello

b,this is b

c,this is c

---------------------

a,this is a

b,this is b

c,this is c








[并发模式]值为[Fixed]的并发异常


注意,只有后修改数据的ObjectContext缓存了旧版本的数据时,长会产生异常








DBItem dbitem1 = context1.DBItem.First(p => p.ItemID == "a");

dbitem1.ItemMatter = "hello";

context1.SaveChanges();

DBItem dbitem2 = context2.DBItem.First(p => p.ItemID == "a");

dbitem2.ItemMatter = "wxwinter";

context2.SaveChanges();







EF中的EntityState几个状态的说明








ObjectContext.Refresh()


Refresh的第一个参数RefreshMode枚举,RefreshMode.StoreWins,RefreshMode.ClientWins

StoreWins


StoreWins : Refresh以后，用数据库的值回写,当前的修改值被放弃








公共



myContext context1 = new myContext();

myContext context2 = new myContext();







查询



foreach (var r in context1.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}

Console.WriteLine("---------------------");

foreach (var r in context2.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}







a,this is a

b,this is b

c,this is c

---------------------

a,this is a

b,this is b

c,this is c







修改



DBItem dbitem1 = context1.DBItem.First(p => p.ItemID == "a");

dbitem1.ItemMatter = "hello";

context1.SaveChanges();

DBItem dbitem2 = context2.DBItem.First(p => p.ItemID == "a");

dbitem2.ItemMatter = "wxwinter";

try

{

context2.SaveChanges();

}

catch

{

context2.Refresh( RefreshMode.StoreWins , dbitem2);

}







在System.Data.OptimisticConcurrencyException 中第一次偶然出现的"System.Data.Entity.dll"类型的异常







再查询



foreach (var r in context1.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}

Console.WriteLine("---------------------");

foreach (var r in context2.DBItem)

{

Console.WriteLine("{0},{1}", r.ItemID, r.ItemMatter);

}







a,hello

b,this is b

c,this is c

---------------------

a,hello

b,this is b

c,this is c








ClientWins


StoreWins: Refresh以后，当前的修改值仍存在,只是告诉ObjectContext知到的并发问题了,这时再调用 ObjectContext.SaveChanges()时,ObjectContext就不会报[开放式并发异常]








DBItem dbitem1 = context1.DBItem.First(p => p.ItemID == "a");

dbitem1.ItemMatter = "hello";

context1.SaveChanges();

DBItem dbitem2 = context2.DBItem.First(p => p.ItemID == "a");

dbitem2.ItemMatter = "wxwinter";

try

{

context2.SaveChanges();

}

catch

{

context2.Refresh(RefreshMode.ClientWins, dbitem2);

context2.SaveChanges();

}







EF中的EntityState几个状态的说明








也可以先Refresh()再SaveChanges(),而不用异常捕获







DBItem dbitem1 = context1.DBItem.First(p => p.ItemID == "a");

dbitem1.ItemMatter = "hello";

context1.SaveChanges();

DBItem dbitem2 = context2.DBItem.First(p => p.ItemID == "a");

dbitem2.ItemMatter = "wxwinter";

context2.Refresh(RefreshMode.ClientWins, dbitem2);

context2.SaveChanges();






事务处理


同一SubmitChanges 会做默认的事务处理


下例由于ItemID主键冲突,两条数据都不会被插入






myContext context1 = new myContext();

DBItem item1 = new DBItem();

item1.ItemID = "w";

item1.ItemMatter = "wxwinter";

context1.AddObject("DBItem", item1);

DBItem item2 = new DBItem();

item2.ItemID = "w";

item2.ItemMatter = "wxd";

context1.AddObject("DBItem", item2);

context1.SaveChanges();






不同SubmitChanges 不会做事务处理


下例由于ItemID主键冲突,后一条数据都不会被插入






myContext context1 = new myContext();

DBItem item1 = new DBItem();

item1.ItemID = "w";

item1.ItemMatter = "wxwinter";

context1.AddObject("DBItem", item1);

context1.SaveChanges();

myContext context2 = new myContext();

DBItem item2 = new DBItem();

item2.ItemID = "w";

item2.ItemMatter = "wxd";

context2.AddObject("DBItem", item2);

context2.SaveChanges();






System.Data.Common.DbTransaction


下例由于ItemID主键冲突,两条数据都不会被插入






myContext context1 = new myContext();

DBItem item1 = new DBItem();

item1.ItemID = "w";

item1.ItemMatter = "wxwinter";

context1.AddObject("DBItem", item1);

if (context1.Connection.State != ConnectionState.Open)

{

context1.Connection.Open();

}

System.Data.Common.DbTransaction tran = context1.Connection.BeginTransaction();

context1.SaveChanges();

try

{

DBItem item2 = new DBItem();

item2.ItemID = "w";

item2.ItemMatter = "wxd";

context1.AddObject("DBItem", item2);

context1.SaveChanges();

tran.Commit();

}

catch

{

tran.Rollback();

}






死锁(两个Context使用DbTransaction)







myContext context1 = new myContext();

DBItem item1 = new DBItem();

item1.ItemID = "w";

item1.ItemMatter = "wxwinter";

context1.AddObject("DBItem", item1);

if (context1.Connection.State != ConnectionState.Open)

{

context1.Connection.Open();

}

System.Data.Common.DbTransaction tran = context1.Connection.BeginTransaction();

context1.SaveChanges();

try

{

myContext context2 = new myContext();

DBItem item2 = new DBItem();

item2.ItemID = "w";

item2.ItemMatter = "wxd";

context2.AddObject("DBItem", item2);

context2.SaveChanges();

tran.Commit();

}

catch

{

tran.Rollback();

}






TransactionScope 事务(两个Context)


System.Transactions.TransactionScope

可解决[死锁(两个Context使用DbTransaction)]

下例由于ItemID主键冲突,两条数据都不会被插入






using (System.Transactions.TransactionScope tc = new TransactionScope())

{

try

{

myContext context1 = new myContext();

DBItem item1 = new DBItem();

item1.ItemID = "w";

item1.ItemMatter = "wxwinter";

context1.AddObject("DBItem", item1);

context1.SaveChanges();

myContext context2 = new myContext();

DBItem item2 = new DBItem();

item2.ItemID = "w";

item2.ItemMatter = "wxd";

context2.AddObject("DBItem", item2);

context2.SaveChanges();

tc.Complete();

}

catch

{

}

}

相关文章