entityMap|blocks|key|6os5l|text|我注意到不需要复制。显然，在向数据库添加模型的实例时(即使ID设置为数据库中已存在的实例)，实体框架会在数据库中插入新行并自动递增其主键。所以这个功能已经内置到EF中了。我不知道，抱歉。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|6sfmt|为了清楚起见，这里有一个例子：^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|F|9|@]|A|@]|B|$]]]]

I noticed that there is no need for copying. Apparently when adding an instance of a model to the database (even if the ID is set to one that already exists in the database), Entity Framework inserts a new row in the database and auto-increments it's primary key. So this functionality is already built-in into EF. I didn't know this, sorry. 
Just for clarity's sake here is an example: 

<pre><code>using(var database = new MyDbContext()) {
 MyModel myModel = database.FirstOrDefault(m =&gt; m.SomeProperty == someValue);
 myModel.SomeOtherProperty = someOtherValue; //user changed a value
 database.MyModels.Add(myModel); //even though the ID of myModel exists in the database, it gets added as a new row and the ID gets auto-incremented 
 database.SaveChanges();
}
</code></pre>

entityMap|blocks|key|8rsc4|text|使用ObjectContext时，QuantumHive提供的答案不起作用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1bgnh|在这种情况下返回的错误是：|8c1ev|要正确克隆实体框架对象(至少在EF6.0中)是：^0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|G|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|H|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|I|9|@]|A|@]|B|$]]]]

When using ObjectContext the answer provided by QuantumHive does not work.

The error returned in that situation is :

<pre><code>An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.
System.InvalidOperationException: An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.
 at System.Data.Objects.ObjectStateManager.AddEntry(IEntityWrapper wrappedObject, EntityKey passedKey, EntitySet entitySet, String argumentName, Boolean isAdded)
 at System.Data.Objects.ObjectContext.AddSingleObject(EntitySet entitySet, IEntityWrapper wrappedEntity, String argumentName)
 at System.Data.Objects.DataClasses.RelatedEnd.AddEntityToObjectStateManager(IEntityWrapper wrappedEntity, Boolean doAttach)
 at System.Data.Objects.DataClasses.RelatedEnd.AddGraphToObjectStateManager(IEntityWrapper wrappedEntity, Boolean relationshipAlreadyExists, Boolean addRelationshipAsUnchanged, Boolean doAttach)
 at System.Data.Objects.DataClasses.RelatedEnd.Add(IEntityWrapper wrappedTarget, Boolean applyConstraints, Boolean addRelationshipAsUnchanged, Boolean relationshipAlreadyExists, Boolean allowModifyingOtherEndOfRelationship, Boolean forceForeignKeyChanges)
 at System.Data.Objects.DataClasses.RelatedEnd.Add(IEntityWrapper wrappedEntity, Boolean applyConstraints)
 at System.Data.Objects.DataClasses.EntityReference`1.set_ReferenceValue(IEntityWrapper value)
 at System.Data.Objects.DataClasses.EntityReference`1.set_Value(TEntity value)
</code></pre>

To correctly clone an entity framework object (at least in EF6.0) is:

<pre><code>/// &lt;summary&gt;
/// Clone a replica of this item in the database
/// &lt;/summary&gt;
/// &lt;returns&gt;The cloned item&lt;/returns&gt;
public Item CloneDeep()
{
 using (var context = new EntityObjectContext())
 {
 var item = context.Items
 .Where(i =&gt; i.ItemID == this.ItemID)
 .Single();
 context.Detach(item);
 item.EntityKey = null;
 item.ItemID = 0;
 return item;
 }
}
</code></pre>

entityMap|blocks|key|dckkg|text|我发现这是为了看看是否有比我目前使用的更好的方法来克隆对象，并注意到，如果你试图做多个clones...at，至少如果你想避免多次创建上下文，那么公认的答案可能会有问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2d90u|我不知道这是不是最好的克隆方法，这就是为什么我在寻找另一种方法。但是，它是有效的。如果需要多次克隆一个实体，可以像这样使用JSON序列化到clone...something+(使用Newtonsoft+JSON)。^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|F|9|@]|A|@]|B|$]]]]

I found this looking to see if there was a better way to clone an object than I was currently using and noticed that there is a potential problem with the accepted answer if you are trying to do multiple clones...at least if you want to avoid creating your context many times...

I don't know if this is the best approach to cloning, which is why I was looking for another way. But, it works. If you need to clone an entity multiple times, you can use JSON serialization to clone...something like this (using Newtonsoft JSON).

<pre><code>using( var context = new Context() ) {
 Link link = context.Links.Where(x =&gt; x.Id == someId);
 bool isFirst = true;
 foreach( var id in userIds ) {
 if( isFirst ) {
 link.UserId = id;
 isFirst = false;
 }
 else {
 string cloneString = JsonConvert.SerializeObject(link);
 Link clone = JsonConvert.DeserializeObject&lt;Link&gt;(cloneString);
 clone.UserId = id;
 context.Links.Add(clone);
 }
 }
 context.SaveChanges();
}
</code></pre>

entityMap|blocks|key|1u7r3|text|Lori+Peterson建议在EF6中使用.AsNoTracking()执行克隆。我正在使用这个方法，并且可以确认它是有效的。您甚至可以包含子对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|moaj|从数据集中检索一个或多个实体时，可以告诉entity+Framework不要跟踪对该对象所做的任何更改，然后将该实体作为新实体添加到dataset中。使用.AsNoTracking时，上下文不知道有关现有实体的任何信息。^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|F|9|@]|A|@]|B|$]]]]

<a href="http://lorifpeterson.com/?p=75" rel="noreferrer">Lori Peterson</a> has suggested using .AsNoTracking() to perform cloning in EF6. I'm using this method and can confirm that it works. You can even include child objects.

<pre><code>var entity = context.Entities
 .AsNoTracking()
 .Include(x =&gt; x.ChildEntities)
 .FirstOrDefault(x =&gt; x.EntityId == entityId);

entity.SomeProperty = DateTime.Now;

context.Entities.Add(entity);
context.SaveChanges();
</code></pre>

<blockquote>
 When you are retrieving an entity or entities from a dataset, you can tell Entity Framework not to track any of the changes that you are making to that object and then add that entity as a new entity to the dataset. With using .AsNoTracking, the context doesn’t know anything about the existing entity.
</blockquote>

entityMap|blocks|key|ap42i|text|我使用postgres数据库：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|bkccp|上面提到的方法没有一个在我的例子中不起作用。我的第二个用法是：^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|F|9|@]|A|@]|B|$]]]]

I use postgres database: 

<pre><code>CREATE TABLE public."Table" ( 
 "Id" integer NOT NULL DEFAULT nextval('"Table_Id_seq"'::regclass),
 ...
</code></pre>

No one of mentioned methods do not work in my case. I use secondly: 

<pre><code>Table table = _context.Table.AsNoTracking().Select(s =&gt; new Table {
 // some properties, exept id
 }).FirstOrDefault();
_context.Table.Add(table);
await _context.SaveChangesAsync();
</code></pre>

In my MVVM program I have a Model class (say <code>MyModel</code>) from which I have an instance of reading from the database (using Entity Framework). When retrieving the object I'm presenting all the data to the user. Later on the user will be modifying some fields. 
What I want is to create the same object except for it's <code>ID</code> (since that <code>ID</code> is the primary key and auto incremented). 
So how could I approach this? I don't want to copy all fields one by one, this is not a robust approach. Because perhaps in the future the model may be modified, so this way I will have to take that into account in the cloning method. 

So is there any elegant way to copy the object and when saving in the database, it's ID gets auto incremented again? (Setting the ID to <code>null</code> gives me a compiler error, because it's of type <code>int</code>).

Entity Framework 6: Clone object except ID

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 在我的MVVM程序中，我有一个Model类(比如MyModel)，我有一个从数据库读取数据的实例(使用实体框架)。在检索对象时，我将所有数据呈现给用户。稍后，用户将修改一些字段。 我想要的是创建相同的对象，除了它的ID (因为该ID是主键并自动递增)。 那么，我该如何处理这个问题呢？我不想一个接一个地复制所有字段，这...

问实体框架6:除ID外的克隆对象
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