hibernate 条件查询(Criteria Queries)

第 16 章  条件查询(Criteria Queries)

具有一个直观的、可扩展的条件查询API是Hibernate的特色。

16.1. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> Criteria crit  =  sess.createCriteria(Cat. class );
crit.setMaxResults( 50 );
List cats  =  crit.list();

16.2. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> List cats  =  sess.createCriteria(Cat. class )
    .add( Restrictions.like( " name " ,  " Fritz% " ) )
    .add( Restrictions.or(
        Restrictions.eq(  " age " ,  new  Integer( 0 ) ),
        Restrictions.isNull( " age " )
    ) )
    .list();

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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();

16.3. 结果集排序

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

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> List cats  =  sess.createCriteria(Cat. class )
    .add( Restrictions.like( " name " ,  " F% " )
    .addOrder( Order.asc( " name " ) )
    .addOrder( Order.desc( " age " ) )
    .setMaxResults( 50 )
    .list();

 

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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();

16.4. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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()。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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 " );
}

16.5. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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 20.1 节 “ 抓取策略(Fetching strategies) ”可以获得更多信息。
16.6. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> List results  =  session.createCriteria(Cat. class )
    .add( Example.create(cat) )
    .createCriteria( " mate " )
        .add( Example.create( cat.getMate() ) )
    .list();

16.7. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> List results  =  session.createCriteria(Cat. class )
    .setProjection( Projections.rowCount() )
    .add( Restrictions.eq( " color " , Color.BLACK) )
    .list();

List results  =  session.createCriteria(Cat. class )
    .setProjection( Projections.projectionList()
        .add( Projections.rowCount() )
        .add( Projections.avg( " weight " ) )
        .add( Projections.max( " weight " ) )
        .add( Projections.groupProperty( " color " ) )
    )
    .list();

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：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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();

16.8. 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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。

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> 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();