Hibernate高效查询,只查询部分/指定字段
2013-05-16 08:24
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Hibernate 使用查询部分/指定字段,有三种字现方式:
第一种是使用高级查询DetachedCriteria实现,代碼如下:
[java]
view plaincopyprint?
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:
[java]
view plaincopyprint?
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
[java]
view plaincopyprint?
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();
S
4000
ystem.out.println(id + " : " + name);
}
第三种方式是通过HQL语句实现,类似SQL,方法如下:
[java]
view plaincopyprint?
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);
}
第一种是使用高级查询DetachedCriteria实现,代碼如下:
[java]
view plaincopyprint?
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();
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:
[java]
view plaincopyprint?
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;
}
}
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
[java]
view plaincopyprint?
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();
S
4000
ystem.out.println(id + " : " + name);
}
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:
[java]
view plaincopyprint?
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);
}
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