Hibernate三大类查询总结1

Hibernate三大类查询总结

文章分类:Java编程

  Hibernate目前总共分为三大类查询：cretiria,hql,本地sql 【以下篇章搜集于网络，感谢作者】

第一：关于cretiria的查询

   具有一个直观的、可扩展的条件查询API是Hibernate的特色。

15.1. 创建一个Criteria 实例
org.hibernate.Criteria接口表示特定持久类的一个查询。Session是 Criteria实例的工厂。

<SPAN style="FONT-SIZE: medium">Criteria crit = sess.createCriteria(Cat.class);
 crit.setMaxResults(50);
List cats = crit.list();</SPAN>

Criteria crit = sess.createCriteria(Cat.class);
crit.setMaxResults(50);
List cats = crit.list();

 
15.2. 限制结果集内容
一个单独的查询条件是org.hibernate.criterion.Criterion 接口的一个实例。org.hibernate.criterion.Restrictions类 定义了获得某些内置Criterion类型的工厂方法。

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.like("name", "Fritz%") )
      .add( Restrictions.between("weight", minWeight, maxWeight) )
     .list();
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.like("name", "Fritz%") )
     .add( Restrictions.between("weight", minWeight, maxWeight) )
     .list();

 
约束可以按逻辑分组。

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.like("name", "Fritz%") )
     .add( Restrictions.or(
          Restrictions.eq( "age", new Integer(0) ),
          Restrictions.isNull("age")
     ) )
     .list();
 List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.in( "name", new String[] { "Fritz", "Izi", "Pk" } ) )
     .add( Restrictions.disjunction()
          .add( Restrictions.isNull("age") )
       .add( Restrictions.eq("age", new Integer(0) ) )
       .add( Restrictions.eq("age", new Integer(1) ) )
       .add( Restrictions.eq("age", new Integer(2) ) )
     ) )
     .list();</SPAN>

List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.like("name", "Fritz%") )
     .add( Restrictions.or(
         Restrictions.eq( "age", new Integer(0) ),
         Restrictions.isNull("age")
     ) )
     .list();
List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.in( "name", new String[] { "Fritz", "Izi", "Pk" } ) )
     .add( Restrictions.disjunction()
         .add( Restrictions.isNull("age") )
      .add( Restrictions.eq("age", new Integer(0) ) )
      .add( Restrictions.eq("age", new Integer(1) ) )
      .add( Restrictions.eq("age", new Integer(2) ) )
     ) )
     .list();

 
Hibernate提供了相当多的内置criterion类型(Restrictions 子类), 但是尤其有用的是可以允许你直接使用SQL。

 

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.sql("lower({alias}.name) like lower(?)", "Fritz%", Hibernate.STRING) )
     .list();
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.sql("lower({alias}.name) like lower(?)", "Fritz%", Hibernate.STRING) )
     .list();

 

{alias}占位符应当被替换为被查询实体的列别名。

Property实例是获得一个条件的另外一种途径。你可以通过调用Property.forName() 创建一个Property。

<SPAN style="FONT-SIZE: medium">Property age = Property.forName("age");
 List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.disjunction()
         .add( age.isNull() )
       .add( age.eq( new Integer(0) ) )
       .add( age.eq( new Integer(1) ) )
       .add( age.eq( new Integer(2) ) )
     ) )
      .add( Property.forName("name").in( new String[] { "Fritz", "Izi", "Pk" } ) )
     .list();</SPAN>

Property age = Property.forName("age");
List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.disjunction()
         .add( age.isNull() )
      .add( age.eq( new Integer(0) ) )
      .add( age.eq( new Integer(1) ) )
      .add( age.eq( new Integer(2) ) )
     ) )
     .add( Property.forName("name").in( new String[] { "Fritz", "Izi", "Pk" } ) )
     .list();

 
15.3. 结果集排序
你可以使用org.hibernate.criterion.Order来为查询结果排序。

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.like("name", "F%")
      .addOrder( Order.asc("name") )
      .addOrder( Order.desc("age") )
      .setMaxResults(50)
     .list();
 List cats = sess.createCriteria(Cat.class)
      .add( Property.forName("name").like("F%") )
      .addOrder( Property.forName("name").asc() )
      .addOrder( Property.forName("age").desc() )
      .setMaxResults(50)
     .list();
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.like("name", "F%")
     .addOrder( Order.asc("name") )
     .addOrder( Order.desc("age") )
     .setMaxResults(50)
     .list();
List cats = sess.createCriteria(Cat.class)
     .add( Property.forName("name").like("F%") )
     .addOrder( Property.forName("name").asc() )
     .addOrder( Property.forName("age").desc() )
     .setMaxResults(50)
     .list();

 

15.4. 关联
你可以使用createCriteria()非常容易的在互相关联的实体间建立 约束。 
 

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.like("name", "F%")
      .createCriteria("kittens")
          .add( Restrictions.like("name", "F%")
     .list();
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.like("name", "F%")
     .createCriteria("kittens")
         .add( Restrictions.like("name", "F%")
     .list();

 

注意第二个 createCriteria()返回一个新的 Criteria实例，该实例引用kittens 集合中的元素。

接下来，替换形态在某些情况下也是很有用的。

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .createAlias("kittens", "kt")
      .createAlias("mate", "mt")
      .add( Restrictions.eqProperty("kt.name", "mt.name") )
     .list();
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .createAlias("kittens", "kt")
     .createAlias("mate", "mt")
     .add( Restrictions.eqProperty("kt.name", "mt.name") )
     .list();

 

(createAlias()并不创建一个新的 Criteria实例。)

Cat实例所保存的之前两次查询所返回的kittens集合是 没有被条件预过滤的。如果你希望只获得符合条件的kittens， 你必须使用returnMaps()。

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .createCriteria("kittens", "kt")
          .add( Restrictions.eq("name", "F%") )
     .returnMaps()
     .list();
Iterator iter = cats.iterator();
 while ( iter.hasNext() ) {
     Map map = (Map) iter.next();
     Cat cat = (Cat) map.get(Criteria.ROOT_ALIAS);
      Cat kitten = (Cat) map.get("kt");
}
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .createCriteria("kittens", "kt")
         .add( Restrictions.eq("name", "F%") )
     .returnMaps()
     .list();
Iterator iter = cats.iterator();
while ( iter.hasNext() ) {
     Map map = (Map) iter.next();
     Cat cat = (Cat) map.get(Criteria.ROOT_ALIAS);
     Cat kitten = (Cat) map.get("kt");
}

 

15.5. 动态关联抓取
你可以使用setFetchMode()在运行时定义动态关联抓取的语义。

<SPAN style="FONT-SIZE: medium">List cats = sess.createCriteria(Cat.class)
      .add( Restrictions.like("name", "Fritz%") )
      .setFetchMode("mate", FetchMode.EAGER)
      .setFetchMode("kittens", FetchMode.EAGER)
     .list();
</SPAN>

List cats = sess.createCriteria(Cat.class)
     .add( Restrictions.like("name", "Fritz%") )
     .setFetchMode("mate", FetchMode.EAGER)
     .setFetchMode("kittens", FetchMode.EAGER)
     .list();

 

这个查询可以通过外连接抓取mate和kittens。 查看第 19.1 节 “ 抓取策略(Fetching strategies) ”可以获得更多信息。

15.6. 查询示例
org.hibernate.criterion.Example类允许你通过一个给定实例 构建一个条件查询。

<SPAN style="FONT-SIZE: medium">Cat cat = new Cat();
 cat.setSex('F');
cat.setColor(Color.BLACK);
 List results = session.createCriteria(Cat.class)
     .add( Example.create(cat) )
     .list();</SPAN>

Cat cat = new Cat();
cat.setSex('F');
cat.setColor(Color.BLACK);
List results = session.createCriteria(Cat.class)
     .add( Example.create(cat) )
     .list();

 
版本属性、标识符和关联被忽略。默认情况下值为null的属性将被排除。

你可以自行调整Example使之更实用。

<SPAN style="FONT-SIZE: medium">Example example = Example.create(cat)
      .excludeZeroes()            //exclude zero valued properties
      .excludeProperty("color")   //exclude the property named "color"
      .ignoreCase()               //perform case insensitive string comparisons
      .enableLike();              //use like for string comparisons
 List results = session.createCriteria(Cat.class)
     .add(example)
     .list();</SPAN>

Example example = Example.create(cat)
     .excludeZeroes()            //exclude zero valued properties
     .excludeProperty("color")   //exclude the property named "color"
     .ignoreCase()               //perform case insensitive string comparisons
     .enableLike();              //use like for string comparisons
List results = session.createCriteria(Cat.class)
     .add(example)
     .list();

 
你甚至可以使用examples在关联对象上放置条件。

<SPAN style="FONT-SIZE: medium">List results = session.createCriteria(Cat.class)
     .add( Example.create(cat) )
      .createCriteria("mate")
         .add( Example.create( cat.getMate() ) )
     .list();
</SPAN>

List results = session.createCriteria(Cat.class)
     .add( Example.create(cat) )
     .createCriteria("mate")
         .add( Example.create( cat.getMate() ) )
     .list();

 

15.7. 投影(Projections)、聚合（aggregation）和分组（grouping）
org.hibernate.criterion.Projections是 Projection 的实例工厂。我们通过调用 setProjection()应用投影到一个查询。

在一个条件查询中没有必要显式的使用 "group by" 。某些投影类型就是被定义为 分组投影，他们也出现在SQL的group by子句中。

你可以选择把一个别名指派给一个投影，这样可以使投影值被约束或排序所引用。下面是两种不同的实现方式：

<SPAN style="FONT-SIZE: medium">List results = session.createCriteria(Cat.class)
      .setProjection( Projections.alias( Projections.groupProperty("color"), "colr" ) )
      .addOrder( Order.asc("colr") )
     .list();
 List results = session.createCriteria(Cat.class)
      .setProjection( Projections.groupProperty("color").as("colr") )
      .addOrder( Order.asc("colr") )
     .list();
</SPAN>

List results = session.createCriteria(Cat.class)
     .setProjection( Projections.alias( Projections.groupProperty("color"), "colr" ) )
     .addOrder( Order.asc("colr") )
     .list();
List results = session.createCriteria(Cat.class)
     .setProjection( Projections.groupProperty("color").as("colr") )
     .addOrder( Order.asc("colr") )
     .list();

 

alias()和as()方法简便的将一个投影实例包装到另外一个 别名的Projection实例中。简而言之，当你添加一个投影到一个投影列表中时 你可以为它指定一个别名：

<SPAN style="FONT-SIZE: medium">List results = session.createCriteria(Cat.class)
     .setProjection( Projections.projectionList()
          .add( Projections.rowCount(), "catCountByColor" )
          .add( Projections.avg("weight"), "avgWeight" )
          .add( Projections.max("weight"), "maxWeight" )
          .add( Projections.groupProperty("color"), "color" )
     )
      .addOrder( Order.desc("catCountByColor") )
      .addOrder( Order.desc("avgWeight") )
     .list();
 List results = session.createCriteria(Domestic.class, "cat")
      .createAlias("kittens", "kit")
     .setProjection( Projections.projectionList()
          .add( Projections.property("cat.name"), "catName" )
          .add( Projections.property("kit.name"), "kitName" )
     )
      .addOrder( Order.asc("catName") )
      .addOrder( Order.asc("kitName") )
     .list();</SPAN>

List results = session.createCriteria(Cat.class)
     .setProjection( Projections.projectionList()
         .add( Projections.rowCount(), "catCountByColor" )
         .add( Projections.avg("weight"), "avgWeight" )
         .add( Projections.max("weight"), "maxWeight" )
         .add( Projections.groupProperty("color"), "color" )
     )
     .addOrder( Order.desc("catCountByColor") )
     .addOrder( Order.desc("avgWeight") )
     .list();
List results = session.createCriteria(Domestic.class, "cat")
     .createAlias("kittens", "kit")
     .setProjection( Projections.projectionList()
         .add( Projections.property("cat.name"), "catName" )
         .add( Projections.property("kit.name"), "kitName" )
     )
     .addOrder( Order.asc("catName") )
     .addOrder( Order.asc("kitName") )
     .list();

 
你也可以使用Property.forName()来表示投影：

<SPAN style="FONT-SIZE: medium">List results = session.createCriteria(Cat.class)
      .setProjection( Property.forName("name") )
      .add( Property.forName("color").eq(Color.BLACK) )
     .list();
 List results = session.createCriteria(Cat.class)
     .setProjection( Projections.projectionList()
          .add( Projections.rowCount().as("catCountByColor") )
          .add( Property.forName("weight").avg().as("avgWeight") )
          .add( Property.forName("weight").max().as("maxWeight") )
          .add( Property.forName("color").group().as("color" )
     )
      .addOrder( Order.desc("catCountByColor") )
      .addOrder( Order.desc("avgWeight") )
     .list();</SPAN>

List results = session.createCriteria(Cat.class)
     .setProjection( Property.forName("name") )
     .add( Property.forName("color").eq(Color.BLACK) )
     .list();
List results = session.createCriteria(Cat.class)
     .setProjection( Projections.projectionList()
         .add( Projections.rowCount().as("catCountByColor") )
         .add( Property.forName("weight").avg().as("avgWeight") )
         .add( Property.forName("weight").max().as("maxWeight") )
         .add( Property.forName("color").group().as("color" )
     )
     .addOrder( Order.desc("catCountByColor") )
     .addOrder( Order.desc("avgWeight") )
     .list();

 
15.8. 离线(detached)查询和子查询
DetachedCriteria类使你在一个session范围之外创建一个查询，并且可以使用任意的 Session来执行它。

<SPAN style="FONT-SIZE: medium">DetachedCriteria query = DetachedCriteria.forClass(Cat.class)
      .add( Property.forName("sex").eq('F') );

Session session = ....;
Transaction txn = session.beginTransaction();
 List results = query.getExecutableCriteria(session).setMaxResults(100).list();
txn.commit();
session.close();
DetachedCriteria也可以用以表示子查询。条件实例包含子查询可以通过 Subqueries或者Property获得。

 DetachedCriteria avgWeight = DetachedCriteria.forClass(Cat.class)
 .setProjection( Property.forName("weight").avg() );
 session.createCriteria(Cat.class)
.add( Property.forName("weight).gt(avgWeight) )
.list();
 DetachedCriteria weights = DetachedCriteria.forClass(Cat.class)
 .setProjection( Property.forName("weight") );
 session.createCriteria(Cat.class)
 .add( Subqueries.geAll("weight", weights) )
.list();</SPAN>

DetachedCriteria query = DetachedCriteria.forClass(Cat.class)
     .add( Property.forName("sex").eq('F') );
    
Session session = ....;
Transaction txn = session.beginTransaction();
List results = query.getExecutableCriteria(session).setMaxResults(100).list();
txn.commit();
session.close();
DetachedCriteria也可以用以表示子查询。条件实例包含子查询可以通过 Subqueries或者Property获得。 

DetachedCriteria avgWeight = DetachedCriteria.forClass(Cat.class)
.setProjection( Property.forName("weight").avg() );
session.createCriteria(Cat.class)
.add( Property.forName("weight).gt(avgWeight) )
.list();
DetachedCriteria weights = DetachedCriteria.forClass(Cat.class)
.setProjection( Property.forName("weight") );
session.createCriteria(Cat.class)
.add( Subqueries.geAll("weight", weights) )
.list();

 
甚至相互关联的子查询也是有可能的：

<SPAN style="FONT-SIZE: medium">DetachedCriteria avgWeightForSex = DetachedCriteria.forClass(Cat.class, "cat2")
 .setProjection( Property.forName("weight").avg() )
 .add( Property.forName("cat2.sex").eqProperty("cat.sex") );
 session.createCriteria(Cat.class, "cat")
.add( Property.forName("weight).gt(avgWeightForSex) )
.list();</SPAN>

DetachedCriteria avgWeightForSex = DetachedCriteria.forClass(Cat.class, "cat2")
.setProjection( Property.forName("weight").avg() )
.add( Property.forName("cat2.sex").eqProperty("cat.sex") );
session.createCriteria(Cat.class, "cat")
.add( Property.forName("weight).gt(avgWeightForSex) )
.list();