Hibernate 检索方式2

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紧接Hibernate 检索方式（一）

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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

Listlist = session.createCriteria(Person.class)

.setFetchMode("adds",FetchMode.JOIN)

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

.list();

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以下代码演示了QBC 内联接

Listlist = session.createCriteria(Adds.class)

.createAlias("person","p")

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

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

.list();

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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.

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以下代码通过投影查询返回记录数量:

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Listlist = session.createCriteria(Person.class)

.setProjection(Projections.rowCount())

.add(

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

.list();

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

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

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

}

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以下代码通过QBC投影查询返回指定的列:

Criteriacriteria = session.createCriteria(Person.class);

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

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

Projections.property("email")));

Listlist = criteria.list();

Iteratorite = list.iterator();

while(ite.hasNext()) {

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

String personName = (String)object[0];

String email = (String)object[1];

}

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在投影查询中使用聚合函数:

Criteriacriteria = 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"));

Listlist = criteria.list();

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

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

IntegermaxValue = (Integer)object[0];

IntegerminValue = (Integer)object[1];

IntegersumValue= (Integer)object[2];

Stringpersonname = (String)object[3];

DoubleavgValue = (Double)object[4];

IntegercountValue= (Integer)object[5];

}

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以下代码演示了两个表关联后作投影查询:

Listlist = 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();