精通Hibernate读书笔记

生成Java类

    使用hibernate tools(hbm2java)

自定义类型关联

    实现UserType接口或者CompositeUserType接口


扩充集合中的关联

    第五章比较复杂，中文版的89页。

Hibernate支持映射标注

    请参考http://annotations.hibernate.org

在XML建立查询语句

    在HBM文件加入查询语句，具体在</hibernate-mapping>那一行的前面。

    
  <query name="com.oreilly.hh.tracksNoLongerThan">
    <![CDATA[
        from Track as track
        where track.playTime <= :length
      ]]>
  </query>

    然后建立query时调用getNamedQuery("com.oreilly.hh.tracksNoLongerThan")

条件查询

    criteria.add

    模糊查询Restrictions.like("title", "%A%")
    不想写%的话可以使用Restrictions.like("title", "%A%", MatchMode.ANYWHERE)
    如果想进行区分大小写的批评，应该是使用ilike，而不是like

    如果你希望找出满足任意条件之一的对象，而非满足所有条件的对象，就得显式的使用Restrictions.disjunction()将这些条件分组。

    Criteria criteria  =  session.createCriteria(Track.class);
    Disjunction any = Restrictions.disjunction();
    any.add(Restrictions.le("playtime", length));
    any.add(Restrictions.le("title", "%A%");
    criteria.add(any);

   
    投影
   

      criteria.setProjection(Projections.property("title"));
      return  criteria.list();

    多个投影返回的是Array

    /**
     * Retrieve the titles and play times of any tracks that contain a
     * particular text string.
     * 
     * @param text the text to be matched, ignoring case, anywhere in the title.
     * @param session the Hibernate session that can retrieve data.
     * @return the matching titles and times wrapped in object arrays.
     */
    public static List titlesContainingTextWithPlayTimes(String text,
                                                         Session session) {
        Criteria criteria = session.createCriteria(Track.class);
        criteria.add(Restrictions.like("title", text, MatchMode.ANYWHERE)
                .ignoreCase());
        criteria.setProjection(Projections.projectionList().
                add(Projections.property("title")).
                add(Projections.property("playTime")));
        return criteria.list();
    }

    带聚合的投影

     /**
     * Print statistics about various media types.
     * 
     * @param session the Hibernate session that can retrieve data.
     */
    public static void printMediaStatistics(Session session) {
        Criteria criteria = session.createCriteria(Track.class);
        criteria.setProjection(Projections.projectionList().
                add(Projections.groupProperty("sourceMedia").as("media")).
                add(Projections.rowCount()).
                add(Projections.max("playTime")));
        criteria.addOrder(Order.asc("media"));

        for (Object o : criteria.list()) {
            Object[] array = (Object[])o;
            System.out.println(array[0] + " track count: " + array[1] +
                    "; max play time: " + array[2]);
        }
    }

示例查询

    /**
     * Retrieve any tracks that were obtained from a particular source media
     * type.
     * 
     * @param media the media type of interest.
     * @param session the Hibernate session that can retrieve data.
     * @return a list of {@link Track}s meeting the media restriction.
     */
    public static List tracksFromMedia(SourceMedia media, Session session) {
        Track track = new Track();
        track.setSourceMedia(media);
        Example example = Example.create(track);

        Criteria criteria = session.createCriteria(Track.class);
        criteria.add(example);
        criteria.addOrder(Order.asc("title"));
        return criteria.list();
    }

    默认的行为是，值为null的属性将被忽略，对字符串值按照区分大小写的、逐字的方式进行比较。如果想在比较时忽略值为0的属性。，可以调用example的excludeZeros()方法；或者，如果希望对值为null的属性进行匹配，可以调用excludeNone()。而excludeProperty()方法则可以让你明确忽略指定名称的特定属性，不过这像是在手工构建条件查询。为了调整字符串处理。还可以使用ignoreCase()和enableLike()方法，从他们的名字可以知道各自的用途。

    面向属性的criteria

    以前
    criteria.add(Restrictions.le("playTime", length));
    而是用
    criteria.add(Property,forName("playTime").le(length));

    criteria.addOrder(Order.asc("name").ignoreCase());
    而是用
    criteria.addOrder(Property.forName("name").asc().ignoreCase());
   
    投影
    criteria.setProjection(Projections.max("playTime"));
    等价的方法
    criteria.setProjection(Property.forName("playTime").max());

浅谈HQL

    比较代表性的例子

  <query name="com.oreilly.hh.tracksNoLongerThan">
    <![CDATA[
        select track.id, track.title from Track as track
        where track.playTime <= :length
        order by track.title desc
      ]]>
  </query>

  <query name="com.oreilly.hh.trackSummary">
    <![CDATA[
        select count(*), min(track.playTime), max(track.playTime)
        from Track as track
        where :artist in elements(track.artists)
      ]]>
  </query>

原生SQL查询

  <sql-query name="com.oreilly.hh.tracksEndingAt">
    <return alias="track" class="com.oreilly.hh.data.Track"/>
    <![CDATA[
         select {track.*}
        from TRACK as {track}
        where SECOND({track}.PLAYTIME) = :seconds
      ]]>
  </sql-query>

   
      return是告诉hibernate，我们准备再查询中使用track别名来引用Track对象，这样就能够在查询语句中使用简写的{track.*}来引用TRACK数据表中所需要的所有字段以创建Track实力（注意，在查询语句中这样使用别名时，必须用大括号将别名括起来。这能让我们“脱离”原生SQL语句环境，用hibernate映射类和属性来描述查询内容）

    注：此书看完后并不会精通hibernate...要想达到精通，还是看看《java persistence with hibernate》吧

PS：附件为《精通hibernate》中的源码。