Hibernate - 查询部分字段

使用Hibernate 只查詢部分字段，有三种字现方式：

第一种是使用高级查询DetachedCriteria实现，代碼如下：

String alias = "user_"; //查詢時的table別名

DetachedCriteria dc = DetachedCriteria.forClass(User.class,alias);

ProjectionList pList = Projections.projectionList();

pList.add(Projections.property(alias + "." + "id").as("id"));

pList.add(Projections.property(alias + "." + "name").as("name"));

pList.add(Projections.property(alias + "." + "age").as("age"));

pList.add(Projections.property(alias + "." + "sex").as("sex"));

dc.setProjection(pList);

dc.setResultTransformer(Transformers.aliasToBean(User.class));

resultList = memberService.findByDetached(dc).size();

第二种方式是通过HQL语句new POJO()实现，方法如下：

package com.domain;

public class Link {

private String id;

private String name;

private String url;

private Integer index;

public Link(){}

//因为：String hql = "select new Link(id,name) from Link";

//所以必须要有接受2个参数的构造函数

public Link(String id,String name){

this.id = id;

this.name = name;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getUrl() {

return url;

}

public void setUrl(String url) {

this.url = url;

}

}

通過HQL语句查询

String hql = "select new Link(id,name) from Link";

Query query = session.createQuery(hql);

//默认查询出来的list里存放的是一个Object对象，但是在这里list里存放的不再是默认的Object对象了，而是Link对象了

List<Link> links = query.list();

for(Link link : links){

String id = link.getId();

String name = link.getName();

System.out.println(id + " : " + name);

}

第三种方式是通过HQL语句实现，类似SQL，方法如下：

String hql = "select id,name from Link";

Query query = session.createQuery(hql);

//默认查询出来的list里存放的是一个Object数组，还需要转换成对应的javaBean。

List<Object[]> links = query.list();

for(Object[] link : links){

String id = link[0];

String name = link[1];

System.out.println(id + " : " + name);

}