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:
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:Detachedcontext.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.Destinationswhere 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:Detachedcontext.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.Destinationswhere 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:Detachedcontext.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.Destinationswhere 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:Detachedcontext.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
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; |
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.
- ApplyPropertyChanges调用时,要求对应的[实体]在内存中,Attach不要求
- 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 - 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
myContext context = new myContext(); |
修改前 修改后 |
CreateEntityKey 创建EntityKey
myContext context = new myContext(); myTab nr = myTab.CreatemyTab(1); EntityKey ek= context.CreateEntityKey("myTab", nr); |
EntityKey
EntityContainerName 属性 |
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EntityKeyValues 集合 |
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EntitySetName 属性 |
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IsTemporary 属性 |
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GetEntitySet(System.Data.Metadata.Edm.MetadataWorkspace) 方法 |
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OnDeserialized(System.Runtime.Serialization.StreamingContext) 方法 |
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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); 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
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); 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 |
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Entity 属性 |
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EntityKey 属性 |
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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); 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); //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); context.AcceptAllChanges(); 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 */ |
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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); |
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。
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 |
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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(); |
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(); } |
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 { } } |
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