ADO.NET Entity Framework学习札记(3)ObjectContext对象
日期：2014-05-20 浏览次数：21085 次
说明
ObjectContext提供了管理数据的功能
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Context操作数据
AddObject 添加实体
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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 |
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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(); |
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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
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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 |
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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
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将实体从Context中移除,将状态标记为EntityState.Detached |
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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
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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 |
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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
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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 |
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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(); |
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
- pplyPropertyChanges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
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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); ose.SetModified(); ose.SetModifiedProperty("a"); context.SaveChanges(); |
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修改前
修改后
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CreateEntityKey 创建EntityKey
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myContext context = new myContext(); myTab nr = myTab.CreatemyTab(1); EntityKey ek= context.CreateEntityKey("myTab", nr); |
EntityKey
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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 |
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GetObjectByKey/TryGetObjectByKey 通过EntityKey得到实体
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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); |
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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
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更多见esql |
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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); } |
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状态管理
EntityState 状态枚举
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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 得到状态实体
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ObjectStateEntry = GetObjectStateEntry(实体对像/EntityKey) 得到所指定的[实体对像]或EntityKey的 ObjectStateEntry |
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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 得到状态实体
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bool = TryGetObjectStateEntry(实体对像/EntityKey,out ObjectStateEntry) 得到所指定的[实体对像]或EntityKey的 ObjectStateEntry |
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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 得到状态实体集合
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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 |
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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
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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 |
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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
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IsRelationship 属性 |
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Entity 属性 |
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EntityKey 属性 |
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EntitySet 属性 |
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State 状态属性
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EntityState 枚举 |
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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
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处于 deleted 或 detached 状态的对象没有当前值。 |
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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
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处于 added 或 detached 状态的对象没有原始值 |
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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
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返回IEnumerable<string> 得到被修改的属性集合 |
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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
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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 |
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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
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标记为EntityState.Deleted |
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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 |
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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
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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] |
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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 */ |
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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 |
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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
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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 ) |
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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 |
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SaveChanges(false) |
将数据保存到数据库, 但并不改变记录状态 |
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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
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myContext context = new myContext(); context.SavingChanges+=new EventHandler(context_SavingChanges); myTab r = context.myTab.First(p => p.ID == 1); r.a = "wxwinter"; context.SaveChanges(); |
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void context_SavingChanges(object sender, EventArgs e) { myContext context = sender as myContext; Console.WriteLine(context.DefaultContainerName); } |
Context.AcceptAllChanges 方法
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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] |
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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 */ |
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连接属性
Context.DefaultContainerName 属性
Context.Connection 属性
Context.CommandTimeout 属性
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Context.MetadataWorkspace
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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
