OJB中的多表查询和更新-中间件-zhiding-软件频道-至顶网

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OJB的文章实在是少的可怜，自己总结了一下一些重点的内容。想到哪里写到哪里吧比如有课程(event)和类别(catalog)两张表，二者是多对多的关系，关系表叫做catalogEventBridge。

来源：中国IT实验室 2007年09月26日

OJB的文章实在是少的可怜，自己总结了一下一些重点的内容。想到哪里写到哪里吧

比如有课程(event)和类别(catalog)两张表，二者是多对多的关系，关系表叫做catalogEventBridge，字段为[catalogID,eventID]，现在要做的是一旦查询出一个catalog，就要把相关的event也全部搜索出来。

1.repository_user.xml中作如下定义：

<class-descriptor class="org.pie.vls.Catalog.Catalog" table="catalog">
<field-descriptor name="catalogID" column="catalogID" jdbc-type="INTEGER"
primarykey="true" /> <field-descriptor name="catalogName" column="catalogName"
jdbc-type="VARCHAR" /> <collection-descriptor name="catalogEventList" element-
class-ref="org.pie.vls.Catalog.CatalogEventBridge" auto-retrieve="true" auto-
update="true" auto-delete="true"> <inverse-foreignkey field-ref="catalogID"/>
</collection-descriptor> </class-descriptor> <class-descriptor
class="org.pie.vls.Catalog.CatalogEventBridge" table="catalogEventBridge">
<field-descriptor name="catalogID" column="catalogID" jdbc-type="INTEGER"
primarykey="true" /> <field-descriptor name="eventTypeID" column="eventTypeID"
jdbc-type="INTEGER" primarykey="true" /> </class-descriptor> <class-descriptor
class="org.pie.vls.EventType.EventType" table="eventType" > <field-descriptor
name="eventTypeID" column="eventTypeID" jdbc-type="INTEGER" primarykey="true"
autoincrement="true" />
<field-descriptor
name="eventTypeTitle"
column="eventTypeTitle"
jdbc-type="VARCHAR"
/>
... ...
</class-descriptor>

2. bean文件的定义

EventType.java

public class EventType implements Cloneable, Comparable {
private String eventTypeTitle;
private String eventTypeCode;
private String eventTypeDesc;
private int eventTypeID;
public int getEventTypeID() {
return this.eventTypeID;
}
public void setEventTypeID(int value) {
this.eventTypeID = value;
}
... ...
}

catalog.java

public class Catalog implements Comparable {
private int catalogID;
private String catalogName = "";
private List catalogEventList = new Vector();
/**
* @return Returns the catalogID.
*/
public int getCatalogID() {
return catalogID;
}
/**
* @param catalogID The catalogID to set.
*/
public void setCatalogID(int catalogID) {
this.catalogID = catalogID;
}
/**
* @return Returns the catalogName.
*/
public String getCatalogName() {
return catalogName;
}
/**
* @param catalogName The catalogName to set.
*/
public void setCatalogName(String catalogName) {
this.catalogName = catalogName;
}
/**
* @return Returns the catalogEventList.
*/
public List getCatalogEventList() {
return catalogEventList;
}
/**
* @param catalogEventList The catalogEventList to set.
*/
public void setCatalogEventList(List catalogEventList) {
this.catalogEventList = catalogEventList;
}
}

查看本文来源

CatalogEventBridge.java

public class CatalogEventBridge {
private int catalogID = 0;
private int eventTypeID = 0;
/**
* @return Returns the catalogID.
*/
public int getCatalogID() {
return catalogID;
}
/**
* @param catalogID The catalogID to set.
*/
public void setCatalogID(int catalogID) {
this.catalogID = catalogID;
}
/**
* @return Returns the eventTypeID.
*/
public int getEventTypeID() {
return eventTypeID;
}
/**
* @param eventTypeID The eventTypeID to set.
*/
public void setEventTypeID(int eventTypeID) {
this.eventTypeID = eventTypeID;
}
}

3. 定义DAO

import java.util.Collection;
import java.util.Iterator;
import org.apache.log4j.Logger;
import org.apache.ojb.broker.PersistenceBroker;
import org.apache.ojb.broker.PersistenceBrokerFactory;
import org.apache.ojb.broker.query.Criteria;
import org.apache.ojb.broker.query.QueryByCriteria;
import org.apache.ojb.broker.query.QueryFactory;
import org.odmg.Implementation;
import org.pie.vls.Application.AbstractVLSBase;
public class CatalogDAO extends AbstractVLSBase {
private Collection catalogList;
private PersistenceBroker broker;
private static final Logger logger = Logger.getLogger(Catalog.class);
private int catalogID = 0;
public CatalogDAO(Implementation impl) {
super(impl);
init();
}
public CatalogDAO(Implementation impl, int catalogID) {
super(impl);
this.catalogID = catalogID;
init();
}
/* (non-Javadoc)
* @see org.pie.vls.Application.VLSBase#init()
*/
public void init() {
// TODO Auto-generated method stub
try {
broker = PersistenceBrokerFactory.defaultPersistenceBroker();
broker.clearCache();
Criteria crit = new Criteria();
if (this.catalogID > 0) {
crit.addEqualTo("catalogID", new Integer(this.catalogID));
}
QueryByCriteria tquery = QueryFactory.newQuery(Catalog.class, crit);
this.catalogList = broker.getCollectionByQuery(tquery);
broker.clearCache();
broker.close();
} catch (Throwable t) {
logger.error(t.getMessage(), t);
}
}
public boolean isEmpty(){
return this.catalogList.isEmpty();
}
public Collection getCatalogList() {
return this.catalogList;
}
public Catalog getCatalog() {
Iterator iter = this.catalogList.iterator();
Catalog catalog = (Catalog) iter.next();
return catalog;
}
public void create(Catalog catalog) {
update(catalog);
}
public void update(Catalog catalog) {
try {
broker = PersistenceBrokerFactory.defaultPersistenceBroker();
broker.clearCache();
broker.beginTransaction();
broker.store(catalog);
broker.commitTransaction();
broker.close();
} catch (Throwable t) {
logger.error(t.getMessage(), t);
}
}
public void delete(Catalog catalog) {
try {
broker = PersistenceBrokerFactory.defaultPersistenceBroker();
broker.clearCache();
broker.beginTransaction();
broker.delete(catalog);
broker.commitTransaction();
broker.close();
} catch (Throwable t) {
logger.error(t.getMessage(), t);
}
}
}

catalogEventBridgeDAO.java和eventTypeDAO.java跟上面的这个DAO类似，就不再重复。

使用方法就很简单了，只要通过CatalogDAO得到了一个catalog的实例，那么就可以通过catalog.getCatalogEventList()来获得bridge表中相关的数据，同样，调用catalogDAO中的create,update和delete方法，不仅对catalog表作操作，同样也对catalogEventBridge表中的数据作操作。

查看本文来源

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