Hibernate 检索方式2

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紧接Hibernate 检索方式（一）

 

以下代码演示了 QBC 迫切左外连接 .

FetchMode.DEFAULT , 表示采用映射文件中配置得检索策略 .

FetchMode. JOIN

覆盖映射文件中配置的检索策略 , 在程序中显示指定

迫切左外连接检索策略 .

FetchMode.LAZY : 覆盖映射文件中配置的检索策略 , 中程序中

显示指定 延迟检索策略

List list = session.createCriteria(Person. class )

.setFetchMode( "adds" ,FetchMode. JOIN )

.add(Restrictions. eq ( "personName" , "jack" ))

.list();

 

以下代码演示了 QBC 内联接

List list = session.createCriteria(Adds.class)

.createAlias("person", "p")

.add(Restrictions.like("p.personName", "a", MatchMode.ANYWHERE))

.add(Restrictions.like("this.addName", "an", MatchMode.ANYWHERE))

.list();

 

 

 

投影查询是指查询结果仅包括部分实体或者实体的部分属性 . 投影是通过 select 关键字来实现的 .

 

以下代码通过投影查询返回记录数量 :

 

List list = session.createCriteria(Person. class )

.setProjection(Projections. rowCount ())

.add(

Restrictions. like ( "personName" , "a" , MatchMode. ANYWHERE ))

.list();

for ( int i=0;i<list.size();i++){

Integer count = (Integer)list.get(i);

System. out .println( "--- count =" +count);

}

 

 

 

 

 

以下代码通过 QBC 投影查询返回指定的列 :

Criteria criteria = session.createCriteria(Person. class );

criteria.setProjection(Projections. projectionList ().add(

Projections. property ( "personName" )).add(

Projections. property ( "email" )));

List list = criteria.list();

Iterator ite = list.iterator();

while (ite.hasNext()) {

Object[] object = (Object[])ite.next();

String personName = (String)object[0];

String email = (String)object[1];

}

 

 

 

在投影查询中使用 聚合函数 :

Criteria criteria = session.createCriteria(Person. class );

criteria.setProjection(

Projections. projectionList ()

.add(Projections. max ( "personid" ))

.add(Projections. min ( "personid" ))

.add(Projections. sum ( "personid" ))

.add(Projections. property ( "personName" ))

.add(Projections. avg ( "personid" ))

.add(Projections. count ( "personid" ))

.add(Projections. groupProperty ( "personName" )))

.addOrder(Order. asc ( "personName" ));

List list = criteria.list();

for ( int i = 0;i<list.size();i++){

Object[] object = (Object[])list.get(i);

Integer maxValue = (Integer)object[0];

Integer minValue = (Integer)object[1];

Integer sumValue= (Integer)object[2];

String personname = (String)object[3];

Double avgValue = (Double)object[4];

Integer countValue = (Integer)object[5];

}

 

 

以下代码演示了两个表关联后作投影查询 :

List list = session.createCriteria(Person.class)

.createAlias("adds","a")

.add(Restrictions.like

("personName", "a", MatchMode.ANYWHERE))

.add(Restrictions.like

("a.addName", "an", MatchMode.ANYWHERE))

.setProjection(Projections.projectionList()

.add(Projections.property("personid"))

.add(Projections.property("personName"))

.add(Projections.property("a.addsid"))

.add(Projections.property("a.addName")))

.list();