使用Projection获取集合(休眠) [英] Getting Collections using Projection(hibernate)

问题描述

Employee.java

Employee.java

public class Employee
{
String id;
String name;
List<String> designations;
List<String> qualifications;
}

Employee.hbm.xml

Employee.hbm.xml

<hibernate-mapping>
  <class name="com.novelty.Employee" table="Employee">
    <id column="ID" name="id" type="long">
      <generator class="increment"/>
    </id>
    <property column="name" name="name"/>

    <list lazy="false" name="designations" table="designations">
      <key column="ID"/>
      <list-index column="idx"/>
      <element column="designation" type="string"/>
    </list>

   <list lazy="false" name="qualifications" table="qualifications">
      <key column="ID"/>
      <list-index column="idx"/>
      <element column="qualification" type="string"/>
    </list>
</hibernate-mapping>

我需要获取特定雇员的指定列表(我具有姓名或ID).我不想整体获取Employee对象并获取列表.我尝试了投影，但徒劳无功.

I need to get the list of designation for a particular employee(I have name or id).I don't want to get the Employee object as a whole and get the list. I tried with projections but futile.

Criteria criteria = session.createCriteria(c);
ProjectionList proList = Projections.projectionList();
proList.add(Projections.property("designations"));
criteria.setProjection(proList);
List list = criteria.list();

我得到了以下异常堆栈跟踪.

I got the following exception stack trace.

Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
    at org.hibernate.loader.criteria.CriteriaLoader.getResultColumnOrRow(CriteriaLoader.java:148)
    at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:639)
    at org.hibernate.loader.Loader.doQuery(Loader.java:829)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
    at org.hibernate.loader.Loader.doList(Loader.java:2533)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
    at org.hibernate.loader.Loader.list(Loader.java:2271)
    at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
    at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
    at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)

推荐答案

由于designations是列表，因此您应该join它

Since designations is a list you should join it

    try {
            Criteria criteria = session.createCriteria(Employee.class);
            criteria.setFetchMode("designations", FetchMode.JOIN);
             List list = criteria.list();

        } catch (Exception e) {
             //print e 
        }

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