Criteria中的setResultTransformer [英] setResultTransformer in Criteria

问题描述

标准API中setResultTransformer方法的用法是什么？有人可以用一个简单的例子来解释吗？

问候，

解决方案

不使用setProjections（）的Criteria查询的默认ResultTransformer将为 ROOT_ENTITY 。

如果我们将Student与Many关系为ManyToMany关系，则查询可能如下所示...

<$ p $会话会话=（会话）getEntityManager（）。getDelegate（）;
Criteria crit = session.createCriteria（Student.class）
.createAlias（'departments'，'department'）;

该查询将返回重复项。但将 ResultTransformer 设置为...

  crit.setResultTransformer（CriteriaSpecification .DISTINCT_ROOT_ENTITY）; 
  

现在，当Hibernate收集结果时，结果将不同。 （或者我的意思是unmarshalls？）

如果你不希望Hibernate以 List< Student> List< Object []> 然后

  crit.setResultTransformer（CriteriaSpecification.PROJECTION）
  

What is the use of setResultTransformer method in criteria API? Can someone explain this with a simple example? I read the javadocs but i am not able to understand them clearly.

Regards,

解决方案

The default ResultTransformer for a Criteria query which does not use setProjections() will be ROOT_ENTITY.

If we have Student in a ManyToMany relationship to Department a query might look like this ...

    Session session = (Session) getEntityManager().getDelegate();
    Criteria crit = session.createCriteria(Student.class)
        .createAlias('departments', 'department');

This query will return duplicates. But set the ResultTransformer as ...

    crit.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);

Now the results will be distinct when Hibernate marshalls the results. (Or do I mean unmarshalls?)

If you do not want Hibernate to return the query as a List<Student> but prefer to handle the results as a List<Object[]> then

    crit.setResultTransformer(CriteriaSpecification.PROJECTION)

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