ADO.NET Entity Framework学习笔记(3)ObjectContext对象

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

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中移除,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

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.

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

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();

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
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 得到状态实体

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 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 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