Hibernate：包含一对多关系的示例查询 [英] Hibernate: Query By Example involving one-to-many relationship

问题描述

我最近开始使用Criteria API的示例组件查询，并遇到了一个奇怪的问题 - 尝试执行搜索时抛出org.hibernate.QueryException。

我的场景如下所示：

我有一个类A，它的一个属性有一组类B的实例（Set< ; B> listOfBs）。这被映射为A中的一对多关系。

我希望在B的示例实例上设置标准查询，例如指定所有B一个属性值为somevalue，然后应用该标准来查找所有在其集合中具有这样的B的A。这是我正在使用（或希望）的代码：

 条件aCrit = session.createCriteria（A.class）; 
 
 a aExampleInstance = new A（）; 
示例aExampleCriteria = Example.create（aExampleInstance）; 
 
标准bCrit = atCrit.createCriteria（listOfBs）; 
 B bExampleInstance = new B（）; 
 bExampleInstance .setProperty（somevalue）; 
 bCrit.add（Example.create（bExampleInstance））; 
 
列表< A> results = aCrit.add（aExampleCriteria）.list（）; 
  

我正在使用XML映射，而A映射它与B的关系如下（A.hbm。 xml）：

 < set name =listOfBstable =Binverse =falsecascade =all懒惰= 真 > 
< key column =A_IDnot-null =true/> 
<一对多课程=B/> 
< / set> 
  

我意识到这可能不是正确的方法 - 任何更好的建议都是值得欢迎的。无论如何，麻烦的是我得到一个异常：

org.hibernate.QueryException：无法解析属性：_com of：B

我已经搜索并意识到异常告诉我的是什么。然而，在我的任何一个类中都没有声明这样的属性名 - 在我看来，这可能是Hibernate在引导下使用的任何工具的一部分，以使持久性看起来透明。

我很好奇，如果这是一个已知问题，是否有人们使用的解决方法，或者可能是更新版本的解决方案？我使用Hibernate 3.6.6。

任何建议/经验将不胜感激。

谢谢！ p>

解决方案

  org.hibernate.QueryException：无法解析属性：_com：B 
  

异常说明它找不到b中的属性_com b
$ b <这意味着在你的以下代码中是错误的。

  B bExampleInstance = new B（）; 
 bExampleInstance .setProperty（somevalue）; 
  

是A和B中相同的属性名称，与您设置的相同。

I've recently started playing with the query by example component of the Criteria API and have run into a strange issue - an org.hibernate.QueryException is thrown when trying to perform a search.

My scenarios is as follows:

I have a class A, which as one of its properties has a set of instances of class B (Set< B> listOfBs). This is mapped as a one-to-many relationship in A.

I was hoping to set a criteria query on an example instance of B, for example specifying all B's with a property value of "somevalue", and then apply that criteria to find all A's that have such a B in their set. This is the code I am using (or hoping to):

    Criteria aCrit = session.createCriteria(A.class);

    A aExampleInstance = new A();
    Example aExampleCriteria = Example.create(aExampleInstance );

    Criteria bCrit = atCrit.createCriteria("listOfBs");
    B bExampleInstance = new B();
    bExampleInstance .setProperty("somevalue");
    bCrit.add(Example.create(bExampleInstance ));

    List<A> results = aCrit.add(aExampleCriteria).list();

I am using XML mapping, and A is mapping it's relation to B as follows (A.hbm.xml):

   <set name="listOfBs" table="B" inverse="false" cascade="all" lazy="true">
       <key column="A_ID" not-null="true"/>
       <one-to-many class="B"/>
   </set>

I realize that this might not be the right approach - any better suggestions are welcome. In any case, the trouble is that I get an exception:

org.hibernate.QueryException: could not resolve property: _com of: B

I have searched and realize what the exception is telling me. However there is no such property name declared in any of my classes - it would seem to me that this might be part of whatever instrumentation Hibernate uses under the hood to make persistence seem transparent.

I'm curious if this is a known issue, whether there is a workaround people have used, or perhaps a resolution in a newer version? I am using Hibernate 3.6.6.

Any advice/experiences would be appreciated.

Thanks!

解决方案

 org.hibernate.QueryException: could not resolve property: _com of: B

exception tells that it couldnt find the property _com in b

it means that in following code of yours is erroneous.

  B bExampleInstance = new B();
  bExampleInstance .setProperty("somevalue"); 

is the name of property is same in A and B and same which you have set.

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