hibernate配置文件set标签中的where orderby sort的使用
set集合中可以使用屬性：where來增加條件，使用order-by來排序.?
<set name="fileProduces"?
?????? inverse="true"?
?????? cascade="all-delete-orphan"?
?????? where="FILE_STATUS=1"?
?????? order-by="IS_PUBLISH desc,FILE_SUBMIT_TIME desc">?
????????? <key>?
??????????? <column name="EST_ID" precision="10" scale="0" not-null="true"/>?
????????? </key>?
?????? <one-to-many encoding="utf-8"?>????
<!DOCTYPE hibernate-mapping????
???? PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"????
??? "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">????
???
<hibernate-mapping>????
???
???? <class name="onlyfun.caterpillar.User" table="user">????
???????? ....????
???????? <set name="emails" table="email" sort="natural">????
???????????? <key column="id"/>????
???????????? <element type="java.lang.String"????
????????????????????? column="address"/>????
???????? </set>????
???? </class>????
???
</hibernate-mapping>sort="natural"表示使用物件的comparaTo()方法來進行排序，容器中的物件上必須有實作java.lang.Comparable 介面，例如String就有實作java.lang.Comparable介面，結果會使用字典順序來排列容器中的物件。????
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您可以實現自己的排序方式，只要定義一個類別來實作java.util.Comparator介面，例如：????
???
CustomComparator.java????
package onlyfun.caterpillar;????
???
import java.util.Comparator;????
???
public class CustomComparator implements Comparator {????
??? public int compare(Object o1, Object o2) {????
??????? if (((String) o1).equals(o2))????
??????????? return 0;????
??????? return ((Comparable) o1).compareTo(o2) * -1;????
???? }????
}????
在自訂的Comparator中，如果兩個物件的順序相同會傳回0，而為了方便比較物件，要求傳入的物件必須實作Comparable介面（例如 String物件就有實作Comparable介面），範例中只是簡單的將原來compareTo()傳回的值乘以負一，如此就可以簡單的讓排列順序相反，接著可以在映射文件中指定自訂的Comparator類別：????
???
User.hbm.xml????
<?xml version="1.0" encoding="utf-8"?>????
<!DOCTYPE hibernate-mapping????
???? PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"????
??? "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">????
???
<hibernate-mapping>????
???
???? <class name="onlyfun.caterpillar.User" table="user">????
???????? ....????
???????? <set name="emails" table="email"????
????????????? sort="onlyfun.caterpillar.CustomComparator">????
???????????? <key column="id"/>????
???????????? <element type="java.lang.String"????
????????????????????? column="address"/>????
???????? </set>????
???? </class>????
???
</hibernate-mapping>Bag與List並不適用於這種方式。????
???
另一個排序的方式則是在資料庫中進行，直接使用order by子句來排序，這可以在映射文件中使用order-by屬性來指定，例如：????
???
User.hbm.xml????
<?xml version="1.0" encoding="utf-8"?>????
<!DOCTYPE hibernate-mapping????
???? PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"????
??? "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">????
???
<hibernate-mapping>????
???
???? <class name="onlyfun.caterpillar.User" table="user">????
???????? ....????
???????? <set name="emails" table="email" order-by="address desc">????
???????????? <key column="id"/>????
???????????? <element type="java.lang.String"????
????????????????????? column="address"/>????
???????? </set>????
???? </class>????
???
</hibernate-mapping>觀察Hibernate所使用的SQL可以看到order by子句：????
???
Hibernate:????
select emails0_.id as id0_, emails0_.address as address0_????
from email emails0_ where emails0_.id=? order by emails0_.address desc??????
<PRE class=java name="code"></PRE>???
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hibernate 中对set对象的两种配置方法：
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（一）使用order-by对set排序，只需要修改set设置：
<set name="standards" ...?order-by="st_id desc"?>?
...
</set>
//注意：st_id必须是数据表里的字段名，不能使类里的属性名
//使用order-by，实质是hibernate自动在查询语句后面添加order by ...语句。
?
（二）使用sort对set排序
1.修改set设置：
<set name="standards" ...?sort="mypack.module.AsStandard"?>?
...
</set>
注意：
?????????? 属性standards要定义成：
?????????? private Set<AsStandard> standards = new?TreeSet<AsStandard>();
??????????? 不能定义成HashSet，否则 不能用sort进行排序。
?
2.修改实体类AsStandard：
public class AsStandard?implements Comparator?{?????????? // 1.实现接口Comparator
????? ...
????? public int?compare(Object o1, Object o2) {????????????????? // 2.实现方法compare
if(o1 instanceof AsStandard && o2 instanceof AsStandard){
AsStandard r1 = (AsStandard)o1;
AsStandard r2 = (AsStandard)o2;
if(r1.stId>r2.stId){????????? //stId是类里的属性名，不是数据表里的字段名
return 1;
}
}
return -1;
}
}
//如果支持泛型，可写成:
public class AsStandard?implements Comparator<AsStandard>?{?????????? // 1.实现接口Comparator
????? ...
????? public int compare(AsStandard o1, AsStandard o2) {???????????????? // 2.实现方法compare
if(o1.stId>o2.stId){
return -1;
}
return 1;
