blocks|key|2890807|text|因为这两条线。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2890808|EmployeeService+es+=+new+EmployeeService();
CityService+cs+=+new+CityService();|code-block|syntax|javascript|2890809|..。不要在构造函数中带参数，我猜你在类中创建了一个上下文。当您加载city1时...|offset|length|style|CODE|2890810|Payroll.Entities.City+city1+=+cs.SelectCity(...);|2890811|...you将city1附加到CityService中的上下文。稍后，您将添加一个city1作为对新Employee+e1的引用，并将包含此对city1的引用的e1添加到EmployeeService的上下文中。因此，您将city1附加到两个不同的上下文，这就是异常所抱怨的。|2890812|您可以通过在服务类之外创建上下文并在两个服务中注入和使用它来修复此问题：|2890813|EmployeeService+es+=+new+EmployeeService(context);
CityService+cs+=+new+CityService(context);+//+same+context+instance|2890814|您的服务类看起来有点像存储库，它只负责单一的实体类型。在这种情况下，当您为服务使用单独的上下文时，一旦涉及到实体之间的关系，您总是会遇到麻烦。|2890815|您还可以创建一个服务，该服务负责一组密切相关的实体，如EmployeeCityService+(只有一个上下文)，并将Button1_Click方法中的整个操作委托给此服务的一个方法。|2890816|entityMap^0|0|0|Y|5|0|0|7|5|F|B|15|5|1E|8|1N|2|1Z|5|28|2|2D|F|33|5|0|0|0|0|R|J|1N|D|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@$I|13|J|14|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|16|8|@$I|17|J|18|K|L]|$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]|$I|1F|J|1G|K|L]|$I|1H|J|1I|K|L]|$I|1J|J|1K|K|L]|$I|1L|J|1M|K|L]|$I|1N|J|1O|K|L]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1P|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1Q|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|1R|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1S|8|@$I|1T|J|1U|K|L]|$I|1V|J|1W|K|L]]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1X|8|@]|9|@]|A|$]]]|Z|$]]

Because these two lines ...

<pre><code>EmployeeService es = new EmployeeService();
CityService cs = new CityService();
</code></pre>

... don't take a parameter in the constructor, I guess that you create a context within the classes. When you load the <code>city1</code>...

<pre><code>Payroll.Entities.City city1 = cs.SelectCity(...);
</code></pre>

...you attach the <code>city1</code> to the context in <code>CityService</code>. Later you add a <code>city1</code> as a reference to the new <code>Employee</code> <code>e1</code> and add <code>e1</code> including this reference to <code>city1</code> to the context in <code>EmployeeService</code>. As a result you have <code>city1</code> attached to two different context which is what the exception complains about.

You can fix this by creating a context outside of the service classes and injecting and using it in both services:

<pre><code>EmployeeService es = new EmployeeService(context);
CityService cs = new CityService(context); // same context instance
</code></pre>

Your service classes look a bit like repositories which are responsible for only a single entity type. In such a case you will always have trouble as soon as relationships between entities are involved when you use separate contexts for the services.

You can also create a single service which is responsible for a set of closely related entities, like an <code>EmployeeCityService</code> (which has a single context) and delegate the whole operation in your <code>Button1_Click</code> method to a method of this service.

blocks|key|233741|text|我也有同样的问题，但我对@Slauma的解决方案(尽管在某些情况下很好)的问题是，它建议我将上下文传递给服务，这意味着上下文可以从我的控制器中获得。它还强制我的控制器和服务层之间的紧密耦合。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|233742|我使用依赖注入将服务/存储库层注入控制器，因此无法从控制器访问上下文。|233743|我的解决方案是让服务/存储库层使用相同的上下文实例--+Singleton。|233744|上下文单例类：|offset|length|style|BOLD|233745|参考：http://msdn.microsoft.com/en-us/library/ff650316.aspx|233746|和http://csharpindepth.com/Articles/General/Singleton.aspx|233747|public+sealed+class+MyModelDbContextSingleton
{
++private+static+readonly+MyModelDbContext+instance+=+new+MyModelDbContext();

++static+MyModelDbContextSingleton()+{+}

++private+MyModelDbContextSingleton()+{+}

++public+static+MyModelDbContext+Instance
++{
++++get
++++{
++++++return+instance;
++++}
++}
}++|code-block|syntax|javascript|233748|存储库类：|233749|public+class+ProjectRepository+:+IProjectRepository
{
++MyModelDbContext+context+=+MyModelDbContextSingleton.Instance;
++[...]|233750|确实存在其他解决方案，比如实例化一次上下文并将其传递到服务/存储库层的构造函数中，或者我读到的实现工作单元模式的其他解决方案中。我相信还有更多的..。|233751|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/ff650316.aspx|1|http://csharpindepth.com/Articles/General/Singleton.aspx^0|0|0|0|0|7|0|3|1H|0|0|1|1K|1|0|0|0|5|0|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1B|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1C|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|1D|8|@$H|1E|I|1F|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|1G|8|@]|9|@$H|1H|I|1I|1|1J]]|A|$]]|$1|N|3|O|5|6|7|1K|8|@]|9|@$H|1L|I|1M|1|1N]]|A|$]]|$1|P|3|Q|5|R|7|1O|8|@]|9|@]|A|$S|T]]|$1|U|3|V|5|6|7|1P|8|@$H|1Q|I|1R|J|K]]|9|@]|A|$]]|$1|W|3|X|5|R|7|1S|8|@]|9|@]|A|$S|T]]|$1|Y|3|Z|5|6|7|1T|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]]|11|$12|$5|13|14|15|A|$16|17]]|18|$5|13|14|15|A|$16|19]]]]

I had the same problem but my issue with the @Slauma's solution (although great in certain instances) is that it recommends that I pass the context into the service which implies that the context is available from my controller. It also forces tight coupling between my controller and service layers. 

I'm using Dependency Injection to inject the service/repository layers into the controller and as such do not have access to the context from the controller. 

My solution was to have the service/repository layers use the same instance of the context - Singleton. 

Context Singleton Class: 

Reference: <a href="http://msdn.microsoft.com/en-us/library/ff650316.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/ff650316.aspx</a> 
and <a href="http://csharpindepth.com/Articles/General/Singleton.aspx" rel="nofollow noreferrer">http://csharpindepth.com/Articles/General/Singleton.aspx</a>

<pre class="lang-cs prettyprint-override"><code>public sealed class MyModelDbContextSingleton
{
 private static readonly MyModelDbContext instance = new MyModelDbContext();

 static MyModelDbContextSingleton() { }

 private MyModelDbContextSingleton() { }

 public static MyModelDbContext Instance
 {
 get
 {
 return instance;
 }
 }
} 
</code></pre>

Repository Class:

<pre class="lang-cs prettyprint-override"><code>public class ProjectRepository : IProjectRepository
{
 MyModelDbContext context = MyModelDbContextSingleton.Instance;
 [...]
</code></pre>

Other solutions do exist such as instantiating the context once and passing it into the constructors of your service/repository layers or another I read about which is implementing the Unit of Work pattern. I'm sure there are more...

blocks|key|228458|text|我也有同样的问题，我可以解决创建一个我正在尝试更新的对象的新实例。然后，我将该对象传递给我的存储库。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|228459|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I had the same problem and I could solve making a new instance of the object that I was trying to Update. Then I passed that object to my reposotory.

blocks|key|3104908|text|这是一个旧线程，但是另一个解决方案，我更喜欢的是，只是更新cityId，而不是将孔模型City分配给Employee……要做到这一点，员工应该如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3104909|public+class+Employee{
++++...
++++public+int?+CityId;+//The+?+is+for+allow+City+nullable
++++public+virtual+City+City;
}|code-block|syntax|javascript|3104910|那么分配就足够了：|3104911|e1.CityId=city1.ID;|3104912|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

This is an old thread, but another solution, which I prefer, is just update the cityId and not assign the hole model City to Employee... to do that Employee should look like:

<pre class="lang-cs prettyprint-override"><code>public class Employee{
 ...
 public int? CityId; //The ? is for allow City nullable
 public virtual City City;
}
</code></pre>

Then it's enough assigning:

<pre class="lang-cs prettyprint-override"><code>e1.CityId=city1.ID;
</code></pre>

blocks|key|232331|text|重现的步骤可以简化为：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|232332|var+contextOne+=+new+EntityContext();
var+contextTwo+=+new+EntityContext();

var+user+=+contextOne.Users.FirstOrDefault();

var+group+=+new+Group();
group.User+=+user;

contextTwo.Groups.Add(group);
contextTwo.SaveChanges();|code-block|syntax|javascript|232333|没有错误的代码：|232334|var+context+=+new+EntityContext();

var+user+=+context.Users.FirstOrDefault();

var+group+=+new+Group();
group.User+=+user;+//+Be+careful+when+you+set+entity+properties.+
//+Be+sure+that+all+objects+came+from+the+same+context

context.Groups.Add(group);
context.SaveChanges();|232335|只使用一个EntityContext就可以解决这个问题。有关其他解决方案，请参阅其他答案。|offset|length|style|CODE|232336|entityMap^0|0|0|0|0|5|D|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Steps to reproduce can be simplified to this:

<pre class="lang-cs prettyprint-override"><code>var contextOne = new EntityContext();
var contextTwo = new EntityContext();

var user = contextOne.Users.FirstOrDefault();

var group = new Group();
group.User = user;

contextTwo.Groups.Add(group);
contextTwo.SaveChanges();
</code></pre>

Code without error:

<pre class="lang-cs prettyprint-override"><code>var context = new EntityContext();

var user = context.Users.FirstOrDefault();

var group = new Group();
group.User = user; // Be careful when you set entity properties. 
// Be sure that all objects came from the same context

context.Groups.Add(group);
context.SaveChanges();
</code></pre>

Using only one <code>EntityContext</code> can solve this. Refer to other answers for other solutions.

blocks|key|2890957|text|对于注入和更糟糕的单例，你可以在添加之前调用分离方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2890958|EntityFramework+6：((IObjectContextAdapter)cs).ObjectContext.Detach(city1);|CODE|2890959|EntityFramework+4：cs.Detach(city1);|2890960|如果你不需要第一个DBContext对象，还有另一种方法。只需使用关键字将其封装在中：|2890961|Payroll.Entities.City+city1;
using+(CityService+cs+=+new+CityService())
{
++city1+=+cs.SelectCity(Convert.ToInt64(cmbCity.SelectedItem.Value));
}|code-block|syntax|javascript|2890962|entityMap^0|M|2|0|I|1K|0|I|H|0|15|2|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@$9|X|A|Y|B|H]]|D|@]|E|$]]|$1|I|3|J|5|6|7|Z|8|@$9|10|A|11|B|H]]|D|@]|E|$]]|$1|K|3|L|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@]|E|$]]|$1|M|3|N|5|O|7|15|8|@]|D|@]|E|$P|Q]]|$1|R|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|S|$]]

Alternatively to injection and even worse Singleton, you can call Detach method before Add.

EntityFramework 6: <code>((IObjectContextAdapter)cs).ObjectContext.Detach(city1);</code>

EntityFramework 4: <code>cs.Detach(city1);</code>

There is yet another way, in case you don't need first DBContext object. Just wrap it with using keyword:

<pre><code>Payroll.Entities.City city1;
using (CityService cs = new CityService())
{
 city1 = cs.SelectCity(Convert.ToInt64(cmbCity.SelectedItem.Value));
}
</code></pre>

blocks|key|3104983|text|在我的例子中，我使用的是ASP.NET身份框架。我使用了内置的UserManager.FindByNameAsync方法来检索ApplicationUser实体。然后，我尝试在不同DbContext上新创建的实体上引用此实体。这导致了您最初看到的异常。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3104984|我只用来自UserManager方法的Id创建了一个新的ApplicationUser实体，并引用了这个新实体，从而解决了这个问题。|3104985|entityMap^0|V|R|1R|F|2I|9|0|5|B|J|2|S|F|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|I|$]]

In my case, I was using the ASP.NET Identity Framework. I had used the built in <code>UserManager.FindByNameAsync</code> method to retrieve an <code>ApplicationUser</code> entity. I then tried to reference this entity on a newly created entity on a different <code>DbContext</code>. This resulted in the exception you originally saw.

I solved this by creating a new <code>ApplicationUser</code> entity with only the <code>Id</code> from the <code>UserManager</code> method and referencing that new entity.

blocks|key|228533|text|错误来源：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|228534|ApplicationUser+user+=+await+UserManager.FindByIdAsync(User.Identity.Name);
ApplicationDbContext+db+=+new+ApplicationDbContent();
db.Users.Uploads.Add(new+MyUpload{FileName="newfile.png"});
await+db.SavechangesAsync();/ZZZZZZZ|code-block|syntax|javascript|228535|希望有人能节省一些宝贵的时间|228536|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Error source:

<pre><code>ApplicationUser user = await UserManager.FindByIdAsync(User.Identity.Name);
ApplicationDbContext db = new ApplicationDbContent();
db.Users.Uploads.Add(new MyUpload{FileName="newfile.png"});
await db.SavechangesAsync();/ZZZZZZZ
</code></pre>

Hope someone saves some precious time

blocks|key|3105006|text|在整个事务中使用相同的DBContext对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3105007|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Use the same DBContext object throughout the transaction.

blocks|key|3105031|text|在这种情况下，错误非常明显:实体框架不能使用IEntityChangeTracker的多个实例或者通常是DbContext的多个实例来跟踪实体。解决方案是:使用DbContext的一个实例；通过单个存储库访问所有需要的实体(取决于DbContext的一个实例)；或者关闭对通过引发此特定异常的存储库以外的存储库访问的所有实体的跟踪。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3105032|在遵循.Net+Core+Web+API中的控制反转模式时，我经常发现我的控制器具有如下依赖关系：|3105033|private+readonly+IMyEntityRepository+myEntityRepo;+//+depends+on+MyDbContext
private+readonly+IFooRepository+fooRepo;+//+depends+on+MyDbContext
private+readonly+IBarRepository+barRepo;+//+depends+on+MyDbContext
public+MyController(
++++IMyEntityRepository+myEntityRepo,+
++++IFooRepository+fooRepo,+
++++IBarRepository+barRepo)
{
++++this.fooRepo+=+fooRepo;
++++this.barRepo+=+barRepo;
++++this.myEntityRepo+=+myEntityRepo;
}|code-block|syntax|javascript|3105034|和用法，如|3105035|...
myEntity.Foo+=+await+this.fooRepository.GetFoos().SingleOrDefaultAsync(f+=>+f.Id+==+model.FooId);
if+(model.BarId.HasValue)
{
++++myEntity.Foo.Bar+=+await+this.barRepository.GetBars().SingleOrDefaultAsync(b+=>+b.Id+==+model.BarId.Value);
}

...
await+this.myEntityRepo.UpdateAsync(myEntity);+//+this+throws+an+error!|3105036|因为所有三个存储库都依赖于每个请求的不同DbContext实例，所以我有两个选择来避免这个问题并维护单独的存储库:更改DbContext的注入，以便每次调用只创建一次新实例：|3105037|//+services.AddTransient<DbContext,+MyDbContext>();+<-+one+instance+per+ctor.+bad
services.AddScoped<DbContext,+MyDbContext>();+//+<-+one+instance+per+call.+good!|3105038|或者，如果子实体正以只读方式使用，请关闭对该实例的跟踪：|3105039|myEntity.Foo.Bar+=+await+this.barRepo.GetBars().AsNoTracking().SingleOrDefault(b+=>+b.Id+==+model.BarId);|3105040|entityMap^0|M|K|1G|9|28|9|37|9|0|0|0|0|0|K|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1B|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|S|3|T|5|J|7|1G|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1H|8|@]|D|@]|E|$]]|$1|W|3|X|5|J|7|1I|8|@]|D|@]|E|$K|L]]|$1|Y|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|Z|$]]

In this case, it turns out the error is very clear: Entity Framework cannot track an entity using multiple instances of <code>IEntityChangeTracker</code> or typically, multiple instances of <code>DbContext</code>. The solutions are: use one instance of <code>DbContext</code>; access all needed entities through a single repository (depending on one instance of <code>DbContext</code>); or turning off tracking for all entities accessed via a repository other than the one throwing this particular exception.

When following an inversion of control pattern in .Net Core Web API, I frequently find that I have controllers with dependencies such as:

<pre><code>private readonly IMyEntityRepository myEntityRepo; // depends on MyDbContext
private readonly IFooRepository fooRepo; // depends on MyDbContext
private readonly IBarRepository barRepo; // depends on MyDbContext
public MyController(
 IMyEntityRepository myEntityRepo, 
 IFooRepository fooRepo, 
 IBarRepository barRepo)
{
 this.fooRepo = fooRepo;
 this.barRepo = barRepo;
 this.myEntityRepo = myEntityRepo;
}
</code></pre>

and usage like

<pre><code>...
myEntity.Foo = await this.fooRepository.GetFoos().SingleOrDefaultAsync(f =&gt; f.Id == model.FooId);
if (model.BarId.HasValue)
{
 myEntity.Foo.Bar = await this.barRepository.GetBars().SingleOrDefaultAsync(b =&gt; b.Id == model.BarId.Value);
}

...
await this.myEntityRepo.UpdateAsync(myEntity); // this throws an error!
</code></pre>

Since all three repositories depend on different <code>DbContext</code> instances per request, I have two options to avoid the problem and maintain separate repositories: change the injection of the DbContext to create a new instance only once per call:

<pre><code>// services.AddTransient&lt;DbContext, MyDbContext&gt;(); &lt;- one instance per ctor. bad
services.AddScoped&lt;DbContext, MyDbContext&gt;(); // &lt;- one instance per call. good!
</code></pre>

or, if the child entity is being used in a read-only manner, turning off tracking on that instance:

<pre><code>myEntity.Foo.Bar = await this.barRepo.GetBars().AsNoTracking().SingleOrDefault(b =&gt; b.Id == model.BarId);
</code></pre>

blocks|key|232439|text|在为一个项目(ASP.Net+MVC+EF6.2)实现IoC之后，我遇到了同样的问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|232440|通常，我会在控制器的构造函数中初始化数据上下文，并使用相同的上下文来初始化所有存储库。|232441|但是，使用IoC实例化存储库会导致它们都有单独的上下文，我开始收到这个错误。|232442|现在，我又回到了用一个共同的上下文更新存储库，同时我想出了一个更好的方法。|232443|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I hit this same problem after implementing IoC for a project (ASP.Net MVC EF6.2).

Usually I would initialise a data context in the constructor of a controller and use the same context to initialise all my repositories.

However using IoC to instantiate the repositories caused them all to have separate contexts and I started getting this error.

For now I've gone back to just newing up the repositories with a common context while I think of a better way.

blocks|key|3105100|text|这就是我遇到这个问题的原因。首先，我需要保存我的Order，它需要一个对ApplicationUser表的引用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3105101|++ApplicationUser+user+=+new+ApplicationUser();
++user+=+UserManager.FindById(User.Identity.GetUserId());

++Order+entOrder+=+new+Order();
++entOrder.ApplicationUser+=+user;+//I+need+this+user+before+saving+to+my+database+using+EF|code-block|syntax|javascript|3105102|问题是我正在初始化一个新的ApplicationDbContext来保存我的新Order实体：|3105103|+ApplicationDbContext+db+=+new+ApplicationDbContext();
+db.Entry(entOrder).State+=+EntityState.Added;
+db.SaveChanges();|3105104|因此，为了解决这个问题，我使用了相同的ApplicationDbContext，而不是使用ASP.NET+MVC的内置UserManager。|3105105|而不是这样：|3105106|user+=+UserManager.FindById(User.Identity.GetUserId());|3105107|我使用了现有的ApplicationDbContext实例：|3105108|//db+instance+here+is+the+same+instance+as+my+db+on+my+code+above.
user+=+db.Users.Find(User.Identity.GetUserId());+|3105109|entityMap^0|O|5|10|F|0|0|13|5|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1A|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1B|8|@]|D|@]|E|$]]|$1|S|3|T|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|U|3|V|5|6|7|1D|8|@]|D|@]|E|$]]|$1|W|3|X|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|Y|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|Z|$]]

This is how I encountered this issue. First I need to save my <code>Order</code> which needs a reference to my <code>ApplicationUser</code> table:

<pre><code> ApplicationUser user = new ApplicationUser();
 user = UserManager.FindById(User.Identity.GetUserId());

 Order entOrder = new Order();
 entOrder.ApplicationUser = user; //I need this user before saving to my database using EF
</code></pre>

The problem is that I am initializing a new ApplicationDbContext to save my new <code>Order</code> entity:

<pre><code> ApplicationDbContext db = new ApplicationDbContext();
 db.Entry(entOrder).State = EntityState.Added;
 db.SaveChanges();
</code></pre>

So in order to solve the problem, I used the same ApplicationDbContext instead of using the built-in UserManager of ASP.NET MVC.

Instead of this:

<pre><code>user = UserManager.FindById(User.Identity.GetUserId());
</code></pre>

I used my existing ApplicationDbContext instance:

<pre><code>//db instance here is the same instance as my db on my code above.
user = db.Users.Find(User.Identity.GetUserId()); 
</code></pre>

blocks|key|2891137|text|对于我的场景，我们有一个解决方案，其中几个应用程序引用相同的上下文。我必须更新unity.config文件，将生存期类型添加到上下文中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2891138|<lifetime+type="PerResolveLifetimeManager"+/>|code-block|syntax|javascript|2891139|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For my scenario we have a solution with several applications referencing the same context. I had to update the unity.config file adding lifetime type to the context.
<pre><code>&lt;lifetime type=&quot;PerResolveLifetimeManager&quot; /&gt;
</code></pre>

I am trying to save Employee details, which has references with City. But everytime I try to save my contact, which is validated I get the exception "ADO.Net Entity Framework An entity object cannot be referenced by multiple instances of IEntityChangeTracker"

I had read so many post but still not getting the exact idea of what to do...
my Save button click code is given below

<pre><code>protected void Button1_Click(object sender, EventArgs e)
 {
 EmployeeService es = new EmployeeService();
 CityService cs = new CityService();

 DateTime dt = new DateTime(2008, 12, 12);
 Payroll.Entities.Employee e1 = new Payroll.Entities.Employee();

 Payroll.Entities.City city1 = cs.SelectCity(Convert.ToInt64(cmbCity.SelectedItem.Value));

 e1.Name = "Archana";
 e1.Title = "aaaa";
 e1.BirthDate = dt;
 e1.Gender = "F";
 e1.HireDate = dt;
 e1.MaritalStatus = "M";
 e1.City = city1; 

 es.AddEmpoyee(e1,city1);
 }
</code></pre>

and Employeeservice Code

<pre><code>public string AddEmpoyee(Payroll.Entities.Employee e1, Payroll.Entities.City c1)
 {
 Payroll_DAO1 payrollDAO = new Payroll_DAO1();
 payrollDAO.AddToEmployee(e1); //Here I am getting Error..
 payrollDAO.SaveChanges();
 return "SUCCESS";
 }
</code></pre>

entity object cannot be referenced by multiple instances of IEntityChangeTracker. while adding related objects to entity in Entity Framework 4.1

我正在尝试保存员工详细信息，其中引用了City。但是每次我尝试保存我的联系人时，我得到了异常"ADO.Net实体框架一个实体对象不能被IEntityChangeTracker的多个实例引用“我读了这么多帖子，但还是不知道该怎么做……我的保存按钮点击代码如下所示protected void Button1_Click(o...

问entity对象不能被多个IEntityChangeTracker实例引用。向entity Framework 4.1中的Entity添加相关对象时
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