了解Grails中的新会话 [英] understanding withNewSession in Grails

问题描述

首先，Grails的文档用NewSession解释如下：

  https://grails.github.io/grails -doc / latest / ref / Domain％20Classes / withNewSession.html 
  

Defn：提供一种执行方式代码在新的Hibernate会话的上下文中，该会话与当前绑定的会话共享相同的事务（JDBC连接）资源。

我是中级grails用户，所以我不是虽然我理解Grails是如何使用会话的，但对上述定义感到满意。你能提供一个例子解释使用

  Domain.withNewSession {session  - > 
 // do work 
} 
  

我会很感激！我很快就回到我自己的问题，我发布了答案，我得到了任何人可能会发现这个问题的解决方案。有用。

以下是一个简单的例子，可以用来理解NewSession。

  def c = null 
 
 Event.withNewSession {
 
c = Event .first（）
 
} 
 
 c.name =Test
 println c.save（）
  

上面的代码会导致异常。 c是一个域对象，但是因为它是在一个newsession块中查询的，所以它只与这个新会话相关联。

抛出的异常是：

  org.hibernate.LazyInitializationException：could不初始化代理 - 没有会话
  

这是为什么.save（）调用。

  def c = null 
 
 Event.withNewSession {
 
c = Event .first（）
 
} 
 
 println c.isAttached（）
  

得到的结果是

  false 
  

因此，您可以看到该域与旧会话分离。这是一种新的用法。 Withnewsession将创建一个新会话，以便在withnewsession块中查询的任何域将仅附加到此新会话，并在退出newsession块后分离。

First of all the documentation of grails explains withNewSession as follows:

https://grails.github.io/grails-doc/latest/ref/Domain%20Classes/withNewSession.html

Defn: Provides a way to execute code within the context of a new Hibernate session which shares the same transactional (JDBC Connection) resource as the currently bound session.

I am an intermediate grails user so i am not comfortable with the above definition although i understand how grails make use of sessions. Can you provide an example that explains the use of

Domain.withNewSession { session ->
    // do work
}

I will appreciate a lot!

解决方案

Ok i am coming back to my own question after a long time and i am posting the answer i got for anyone who might find this useful.

Here is a simple example to understand withNewSession.

def c = null

Event.withNewSession{

  c = Event.first()

}

c.name = "Test"
println c.save()

The above code will cause an exception. c is a domain object but since it was queried inside a newsession block it is only associated with this new session.

The thrown exception is

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

Here is the reason why the exception was thrown when .save() was called.

def c = null

Event.withNewSession{

  c = Event.first()

}

println c.isAttached()

The output got is

false

So, you can see the domain was detached from old session. This is one usage of withnewsession. Withnewsession will create a new session so any domains that were queried inside the withnewsession block will be only attached to this new session and will be detached after exiting the newsession block.

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