ibatis实战之中的一个对多关联
在实际开发中,我们经常遇到关联数据的情况,如User对象拥有若干Book对象
每一个Book对象描写叙述了归属于一个User信息,这样的情况下,我们应该怎样处理？
通过单独的Statement操作固然能够实现(通过Statement用于读取用户数据,再手工调用另外一个Statement
依据用户ID返回相应的book信息).只是这样未免失之繁琐.以下我们就看看在ibatis中,怎样对关联数据进行操。
ibatis中,提供了Statement嵌套支持,通过Statement嵌套,我们就可以实现关联数据的操作。
例如以下步骤演示一对多关联
1、创建user(id,name,age)表和book(id,name,uid)表2、POJO类
public class User implements Serializable {
private static final long serialVersionUID = 1L;
private int id;
private String name;
private int age;
/**
* ibatis一对多关联
*/
private Set<Book> books = new HashSet<Book>();
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Set<Book> getBooks() {
return books;
}
public void setBooks(Set<Book> books) {
this.books = books;
}
}public class Book {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}3、创建User.xml文件
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE sqlMap PUBLIC "-//iBATIS.com//DTD SQL Map 2.0//EN" "http://www.ibatis.com/dtd/sql-map-2.dtd"> <sqlMap namespace="User"> <typeAlias alias="user" type="com.itmyhome.User" /> <typeAlias alias="book" type="com.itmyhome.Book"/> <!-- 一对多查询,一个User相应多个Book --> <resultMap id="get_user_result" class="user"> <result property="id" column="id"/> <result property="name" column="name"/> <result property="age" column="age"/> <result property="books" column="id" select="User.getBookByUserId"/> </resultMap> <!-- 查询主表 --> <select id="getUser" parameterClass="java.lang.String" resultMap="get_user_result"> <![CDATA[ select * from user where id = #id# ]]> </select> <!-- 查询子表 --> <select id="getBookByUserId" parameterClass="int" resultClass="book"> <![CDATA[ select * from book where uid = #uid# ]]> </select> </sqlMap>
4、SqlMapConfig.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE sqlMapConfig PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN" "http://www.ibatis.com/dtd/sql-map-config-2.dtd"> <sqlMapConfig> <settings cacheModelsEnabled="true" enhancementEnabled="true" lazyLoadingEnabled="true" errorTracingEnabled="true" maxRequests="32" maxSessions="10" maxTransactions="5" useStatementNamespaces="true" /> <transactionManager type="JDBC"> <dataSource type="SIMPLE"> <property name="JDBC.Driver" value="com.mysql.jdbc.Driver" /> <property name="JDBC.ConnectionURL" value="jdbc:mysql://localhost:3306/ibatis" /> <property name="JDBC.Username" value="root" /> <property name="JDBC.Password" value="root" /> <property name="Pool.MaximumActiveConnections" value="10" /> <property name="Pool.MaximumIdleConnections" value="5" /> <property name="Pool.MaximumCheckoutTime" value="120000" /> <property name="Pool.TimeToWait" value="500" /> <property name="Pool.PingQuery" value="select 1 from ACCOUNT" /> <property name="Pool.PingEnabled" value="false" /> <property name="Pool.PingConnectionsOlderThan" value="1" /> <property name="Pool.PingConnectionsNotUsedFor" value="1" /> </dataSource> </transactionManager> <sqlMap resource="com/itmyhome/User.xml" /> </sqlMapConfig>以上可能须要改动ConnectionURL,Username,Password
5、MyAppSqlConfig.java
import java.io.Reader;
import com.ibatis.common.resources.Resources;
import com.ibatis.sqlmap.client.SqlMapClient;
import com.ibatis.sqlmap.client.SqlMapClientBuilder;
public class MyAppSqlConfig {
private static final SqlMapClient sqlMap;
static {
try {
String resource = "SqlMapConfig.xml";
Reader reader = Resources.getResourceAsReader(resource); //读取配置文件
sqlMap = SqlMapClientBuilder.buildSqlMapClient(reader);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException("Error initializing MyAppSqlConfig class. Cause: " + e);
}
}
public static SqlMapClient getSqlMapInstance() {
return sqlMap;
}
}6、測试类
public class UserTest {
public static void main(String[] args) {
SqlMapClient sqlMap = MyAppSqlConfig.getSqlMapInstance();
try {
/**
* 查询ID为5的用户,以下查询如果有数据存在
*/
List list = sqlMap.queryForList("User.getUser","5");
for(int i=0;i<list.size();i++){
User user = (User)list.get(i);
/**
* 得到User所拥有的Book
*/
Set<Book> books = (Set<Book>)user.getBooks();
Iterator ite = books.iterator();
while(ite.hasNext()){
Book book = (Book)ite.next();
System.out.println("用户:"+user.getName()+",书籍: "+book.getName());
}
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}这里通过在resultMap中定义嵌套查询getBookByUserId,我们实现了关联数据的读取。
项目结构图:
项目源代码下载：http://download.csdn.net/detail/itmyhome/7495501
