树形结构之五 数据提取-递归查询
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也是关于树型结构的内容 ，就是数据库递归查询，我在项目中用的是oralce数据库 ，它提供了递归查询的功能，
像普通的查询一样，在网上了解了一下，发现很多数据库都提供了递归查询的实现，如mysql,db2,oralce等。
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下面贴出来一个角色信息的hibernate配置文件来，里面用到了这种查询。
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<?xml version="1.0" encoding="GBK"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping><class name="com.ylsoft.power.domain.entity.Catalog" table="PLATFORM_POWER_CATALOG"><cache usage="read-write" region="power_catalog"/><id name="catalogId" type="java.lang.Integer"><column name="catalogId" not-null="true" length="20" /><generator type="java.lang.String" column="label"length="20" /><property name="url" type="java.lang.String" column="url"length="500" /><property name="enable" type="java.lang.Boolean" update="true"insert="true" column="enable" /><property name="corder" type="java.lang.Integer" update="true"insert="true" column="corder" /><many-to-one name="parent" column="parentId"cascade="all"><key column="catalogId" /><one-to-many entity-name="com.ylsoft.power.domain.entity.Action" /></set><!-- departs --><set name="fields" cascade="all" ><key column="catalogId" /><one-to-many entity-name="com.ylsoft.power.domain.entity.Field" /></set></class><sql-query name="com.ylsoft.power.domain.entity.Catalog.Descendants"><return alias="catalog"class="com.ylsoft.power.domain.entity.Catalog"> <return-property name="parent"> <return-column name="parentCatalogId"/> </return-property></return>select c.catalogId as {catalog.catalogId},c.label as {catalog.label},c.enable as {catalog.enable},c.url as {catalog.url},c.parentId as parentCatalogId,c.corder as {catalog.corder}from platform_power_catalog cstart with catalogId=:catalogId connect by prior catalogId=parentIdorder by c.catalogid</sql-query><!-- 得到指定部门的所有上级部门 --><sql-query name="com.ylsoft.power.domain.entity.Catalog.Ancestors"><return alias="catalog"class="com.ylsoft.power.domain.entity.Catalog"> <return-property name="parent"> <return-column name="parentCatalogId"/> </return-property></return>select c.catalogId as {catalog.catalogId},c.label as {catalog.label},c.enable as {catalog.enable},c.url as {catalog.url},c.parentId as parentCatalogId,c.corder as {catalog.corder}from platform_power_catalog cstart with catalogId=:catalogId connect by prior parentId=catalogIdorder by c.catalogid</sql-query></hibernate-mapping>?
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这里用了hibernate，其实就是一个普通的查询语句。