ADO.NET Entity Framework(3)ObjectContext
1 说明 1
2 Context操作数据 1
2.1 AddObject 添加实体 1
2.2 DeleteObject 删除实体 1
2.3 Detach 分离实体 2
2.4 修改实体 2
2.5 ApplyPropertyChanges 修改实体 2
2.6 Attach / AttachTo 附加实体 2
2.7 CreateEntityKey 创建EntityKey 3
2.7.1 EntityKey 3
2.8 GetObjectByKey/TryGetObjectByKey 通过EntityKey得到实体 3
2.9 CreateQuery 创建查询 4
3 状态管理 4
3.1 EntityState 状态枚举 4
3.2 Context.ObjectStateManager 管理记录的状态 4
3.2.1 GetObjectStateEntry 得到状态实体 4
3.2.2 TryGetObjectStateEntry 得到状态实体 4
3.2.3 GetObjectStateEntries 得到状态实体集合 5
3.2.4 ObjectStateManagerChanged 事件 5
3.3 ObjectStateEntry 对象 5
3.3.1 基本属性 5
3.3.2 State 状态属性 6
3.3.3 CurrentValues 当前值 6
3.3.4 OriginalValues 原始值 6
3.3.5 GetModifiedProperties 得到被修改的属性 6
3.3.6 SetModified,SetModifiedProperty 标记为修改 7
3.3.7 Delete 标记为删除 7
3.3.8 AcceptChanges 方法 7
4 保存修改到数据库 8
4.1 Context.SaveChanges 方法 8
4.2 Context.SavingChanges 事件 9
4.3 Context.AcceptAllChanges 方法 9
5 连接属性 9
5.1 Context.DefaultContainerName 属性 9
5.2 Context.Connection 属性 9
5.3 Context.CommandTimeout 属性 10
6 Context.MetadataWorkspace 10
7 数据刷新与并发 10
7.1 缓存数据不会自动更新 10
7.2 [并发模式]值为[Fixed]的并发异常 11
7.3 ObjectContext.Refresh() 11
7.3.1 StoreWins 11
7.3.2 ClientWins 12
7.4 也可以先Refresh()再SaveChanges(),而不用异常捕获 13
8 事务处理 13
8.1 同一SubmitChanges 会做默认的事务处理 13
8.2 不同SubmitChanges 不会做事务处理 13
8.3 System.Data.Common.DbTransaction 13
8.4 死锁(两个Context使用DbTransaction) 14
8.5 TransactionScope 事务(两个Context) 14
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.
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
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
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SaveChanges(true) |
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SaveChanges(false) |
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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。
缓存数据不会自动更新
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[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
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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
{
}
}
