blocks|key|1353335|text|对于实体框架，大多数情况下SaveChanges()就足够了。这将创建一个事务，或在任何环境事务中登记，并在该事务中执行所有必要的工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1353336|不过，有时SaveChanges(false)+%2B+AcceptAllChanges()配对也很有用。|1353337|最有用的地方是在您想要跨两个不同上下文执行分布式事务的情况下。|1353338|例如，像这样(不好的)：|1353339|using+(TransactionScope+scope+=+new+TransactionScope())
{
++++//Do+something+with+context1
++++//Do+something+with+context2

++++//Save+and+discard+changes
++++context1.SaveChanges();

++++//Save+and+discard+changes
++++context2.SaveChanges();

++++//if+we+get+here+things+are+looking+good.
++++scope.Complete();
}|code-block|syntax|javascript|1353340|如果context1.SaveChanges()成功，但context2.SaveChanges()失败，则整个分布式事务将中止。但不幸的是，实体框架已经丢弃了context1上的更改，因此您不能重放或有效地记录失败。|1353341|但如果您将代码更改为如下所示：|1353342|using+(TransactionScope+scope+=+new+TransactionScope())
{
++++//Do+something+with+context1
++++//Do+something+with+context2

++++//Save+Changes+but+don't+discard+yet
++++context1.SaveChanges(false);

++++//Save+Changes+but+don't+discard+yet
++++context2.SaveChanges(false);

++++//if+we+get+here+things+are+looking+good.
++++scope.Complete();
++++context1.AcceptAllChanges();
++++context2.AcceptAllChanges();

}|1353343|当对SaveChanges(false)的调用将必要的命令发送到数据库时，上下文本身不会改变，因此您可以在必要时再次执行此操作，或者您可以根据需要询问ObjectStateManager。|1353344|这意味着如果事务实际上抛出了异常，您可以通过重试或在某个地方记录每个上下文ObjectStateManager的状态来进行补偿。|1353345|有关更多信息，请参阅my+blog+post。|1353346|entityMap|0|LINK|mutability|MUTABLE|url|https://twitter.com/adjames|1|https://docs.microsoft.com/en-gb/archive/blogs/alexj/savechangesfalse^0|D|D|0|5|13|0|0|0|0|2|M|S|M|28|8|0|0|0|2|I|23|I|0|11|I|0|A|2|0|D|9|1|0^^$0|@$1|2|3|4|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1I|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|1J|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1K|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|1S|8|@]|D|@]|E|$]]|$1|U|3|V|5|N|7|1T|8|@]|D|@]|E|$O|P]]|$1|W|3|X|5|6|7|1U|8|@$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]]|D|@]|E|$]]|$1|Y|3|Z|5|6|7|1Z|8|@$9|20|A|21|B|C]]|D|@]|E|$]]|$1|10|3|11|5|6|7|22|8|@]|D|@$9|23|A|24|1|25]|$9|26|A|27|1|28]]|E|$]]|$1|12|3|-4|5|6|7|29|8|@]|D|@]|E|$]]]|13|$14|$5|15|16|17|E|$18|19]]|1A|$5|15|16|17|E|$18|1B]]]]

With the Entity Framework most of the time <code>SaveChanges()</code> is sufficient. This creates a transaction, or enlists in any ambient transaction, and does all the necessary work in that transaction.

Sometimes though the <code>SaveChanges(false) + AcceptAllChanges()</code> pairing is useful.

The most useful place for this is in situations where you want to do a distributed transaction across two different Contexts.

I.e. something like this (bad):

<pre><code>using (TransactionScope scope = new TransactionScope())
{
 //Do something with context1
 //Do something with context2

 //Save and discard changes
 context1.SaveChanges();

 //Save and discard changes
 context2.SaveChanges();

 //if we get here things are looking good.
 scope.Complete();
}
</code></pre>

If <code>context1.SaveChanges()</code> succeeds but <code>context2.SaveChanges()</code> fails the whole distributed transaction is aborted. But unfortunately the Entity Framework has already discarded the changes on <code>context1</code>, so you can't replay or effectively log the failure.

But if you change your code to look like this:

<pre><code>using (TransactionScope scope = new TransactionScope())
{
 //Do something with context1
 //Do something with context2

 //Save Changes but don't discard yet
 context1.SaveChanges(false);

 //Save Changes but don't discard yet
 context2.SaveChanges(false);

 //if we get here things are looking good.
 scope.Complete();
 context1.AcceptAllChanges();
 context2.AcceptAllChanges();

}
</code></pre>

While the call to <code>SaveChanges(false)</code> sends the necessary commands to the database, the context itself is not changed, so you can do it again if necessary, or you can interrogate the <code>ObjectStateManager</code> if you want.

This means if the transaction actually throws an exception you can compensate, by either re-trying or logging state of each contexts <code>ObjectStateManager</code> somewhere.

See <a href="https://twitter.com/adjames" rel="noreferrer">my</a> <a href="https://docs.microsoft.com/en-gb/archive/blogs/alexj/savechangesfalse" rel="noreferrer">blog post</a> for more.

blocks|key|1353430|text|因为某些数据库可能会在dbContextTransaction.Commit()抛出异常，所以最好这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1353431|using+(var+context+=+new+BloggingContext())+
{+
++using+(var+dbContextTransaction+=+context.Database.BeginTransaction())+
++{+
++++try+
++++{+
++++++context.Database.ExecuteSqlCommand(+
++++++++++@"UPDATE+Blogs+SET+Rating+=+5"+%2B+
++++++++++++++"+WHERE+Name+LIKE+'%25Entity+Framework%25'"+
++++++++++);+

++++++var+query+=+context.Posts.Where(p+=>+p.Blog.Rating+>=+5);+
++++++foreach+(var+post+in+query)+
++++++{+
++++++++++post.Title+%2B=+"[Cool+Blog]";+
++++++}+

++++++context.SaveChanges(false);+

++++++dbContextTransaction.Commit();+

++++++context.AcceptAllChanges();
++++}+
++++catch+(Exception)+
++++{+
++++++dbContextTransaction.Rollback();+
++++}+
++}+
}+|code-block|syntax|javascript|1353432|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|$]]

Because some database can throw an exception at dbContextTransaction.Commit() so better this:

<pre><code>using (var context = new BloggingContext()) 
{ 
 using (var dbContextTransaction = context.Database.BeginTransaction()) 
 { 
 try 
 { 
 context.Database.ExecuteSqlCommand( 
 @"UPDATE Blogs SET Rating = 5" + 
 " WHERE Name LIKE '%Entity Framework%'" 
 ); 

 var query = context.Posts.Where(p =&gt; p.Blog.Rating &gt;= 5); 
 foreach (var post in query) 
 { 
 post.Title += "[Cool Blog]"; 
 } 

 context.SaveChanges(false); 

 dbContextTransaction.Commit(); 

 context.AcceptAllChanges();
 } 
 catch (Exception) 
 { 
 dbContextTransaction.Rollback(); 
 } 
 } 
} 
</code></pre>

I have been investigating transactions and it appears that they take care of themselves in EF as long as I pass <code>false</code> to <code>SaveChanges()</code> and then call <code>AcceptAllChanges()</code> if there are no errors:

<pre><code>SaveChanges(false);
// ...
AcceptAllChanges();
</code></pre>

What if something goes bad? don't I have to rollback or, as soon as my method goes out of scope, is the transaction ended?

What happens to any indentiy columns that were assigned half way through the transaction? I presume if somebody else added a record after mine before mine went bad then this means there will be a missing Identity value.

Is there any reason to use the standard <code>TransactionScope</code> class in my code?

Using Transactions or SaveChanges(false) and AcceptAllChanges()?

数据库

我一直在调查事务，似乎只要我将false传递给SaveChanges()，然后在没有错误的情况下调用AcceptAllChanges()，它们就会在EF中自行处理：SaveChanges(false);// ...AcceptAllChanges();如果事情变坏了怎么办？我不需要回滚吗?或者，一旦我的方法超出作用域，...

问使用事务还是使用SaveChanges(false)和AcceptAllChanges()？
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