mybatis(四) 多表链接之一对多

本文主要是通过接口+映射文件的方式实现项目
一.创建一个java项目，新建javaProject
二.添加mybatis和mysql链接的jar包
三.创建数据库，特别注意创建外键
四.编写mybstis-cofig.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- mybatis-cofig配置文件 -->
<configuration>
<!--配置别名  -->
    <typeAliases>
        <typeAlias type="com.mybatis.one.to.many.pojo.User"
            alias="user" />
    </typeAliases>
    <!-- 创建数据层 运行环境 -->
    <environments default="development">
        <environment id="development">
        <!-- JDBC事务管理 -->
            <transactionManager type="JDBC"></transactionManager>
            <!-- 数据源 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/test" />
                <property name="username" value="root" />
                <property name="password" value="110119" />
            </dataSource>
        </environment>
    </environments>
    <!-- 映射文件群 -->
    <mappers>
    <!-- 实体类对应的映射文件 -->
        <mapper resource="com/mybatis/one/to/many/mapper/UserInterface.xml"/>
    </mappers>
</configuration>

五.创建实体类
1）User.java 一对多关系中的一

/**
 * @author wuchao
 * @time 下午3:18:42
 * @description TODO
 */
package com.mybatis.one.to.many.pojo;

import java.util.Date;
import java.util.List;

/**
 * @author wuchao
 * @time 下午3:18:42
 * 
 */
public class User {
    private int id;
    private String name;
    private String dept;
    private String phone;
    private String website;
    private Date createTimeDate;
    private List<Post> posts;

    /**
     * @author wuchao
     * @time 下午4:12:46
     */
    public User() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @author wuchao
     * @time 下午4:12:52
     */
    public User(int id, String name, String dept, String phone, String website,
            Date createTimeDate, List posts) {
        super();
        this.id = id;
        this.name = name;
        this.dept = dept;
        this.phone = phone;
        this.website = website;
        this.createTimeDate = createTimeDate;
        this.posts = posts;
    }

    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 String getDept() {
        return dept;
    }

    public void setDept(String dept) {
        this.dept = dept;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getWebsite() {
        return website;
    }

    public void setWebsite(String website) {
        this.website = website;
    }

    public Date getCreateTimeDate() {
        return createTimeDate;
    }

    public void setCreateTimeDate(Date createTimeDate) {
        this.createTimeDate = createTimeDate;
    }

    public List getPosts() {
        return posts;
    }

    public void setPosts(List posts) {
        this.posts = posts;
    }

}

2）Post.java 一对多的多的类

/**
 * @author wuchao
 * @time 下午3:23:27
 * @description TODO
 */
package com.mybatis.one.to.many.pojo;

/**
 * @author wuchao
 * @time 下午3:23:27
 * 
 */
public class Post {
    private int id;
    private String postName;
    private String title;
    private User user;

    /**
     * @author wuchao
     * @time 下午3:26:36
     */
    public Post() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @author wuchao
     * @time 下午3:26:43
     */
    public Post(int id, String postName, String title, User user) {
        super();
        this.id = id;
        this.postName = postName;
        this.title = title;
        this.user = user;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getPostName() {
        return postName;
    }

    public void setPostName(String postName) {
        this.postName = postName;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

}

六.配置User接口
UserInterface.java

/**
 * @author wuchao
 * @time 下午3:27:16
 * @description TODO
 */
package com.mybatis.one.to.many.dao;

import com.mybatis.one.to.many.pojo.User;

/**
 * @author wuchao
 * @time 下午3:27:16
 *
 */
public interface UserInterface {
    public User getUserById(int id);
}

七.实体类配置文件 在该配置文件中配置一对多的关系
UserInterface.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.one.to.many.dao.UserInterface">
    <resultMap type="user" id="resultUserMap">
        <id property="id" column="id" />
        <result property="name" column="name" />
        <result property="dept" column="dept" />
        <result property="phone" column="phone" />
        <result property="website" column="website" />
        <collection property="posts" ofType="com.mybatis.one.to.many.pojo.Post"
            column="userId">
            <id property="id" column="id"/>
            <result property="postName" column="postName"/>
            <result property="title" column="title"/>
        </collection>
    </resultMap>
    <select id="getUserById" parameterType="user" resultMap="resultUserMap">
        select u.* , p.*
        from user u, post p
        where u.id = p.userId and u.id = #{id}
    </select>
</mapper>

在配置文件中配置collection 表示一对多的关系，其中property的参数值与User实体类中属性 private List posts的值保持一直，否则会报错

org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'postList' in 'class com.mybatis.one.to.many.pojo.User'
### The error may exist in com/mybatis/one/to/many/mapper/UserInterface.xml
### The error may involve com.mybatis.one.to.many.dao.UserInterface.getUserById
### The error occurred while handling results
### SQL: select u.* , p.*   from user u, post p   where u.id = p.userId and u.id = ?
### Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'postList' in 'class com.mybatis.one.to.many.pojo.User'
    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
    at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:82)
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
    at com.sun.proxy.$Proxy2.getUserById(Unknown Source)
    at com.mybatis.ome.to.many.test.Test.main(Test.java:47)
Caused by: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'postList' in 'class com.mybatis.one.to.many.pojo.User'
    at org.apache.ibatis.reflection.Reflector.getGetInvoker(Reflector.java:419)
    at org.apache.ibatis.reflection.MetaClass.getGetInvoker(MetaClass.java:164)
    at org.apache.ibatis.reflection.wrapper.BeanWrapper.getBeanProperty(BeanWrapper.java:162)
    at org.apache.ibatis.reflection.wrapper.BeanWrapper.get(BeanWrapper.java:49)
    at org.apache.ibatis.reflection.MetaObject.getValue(MetaObject.java:122)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.instantiateCollectionPropertyIfAppropriate(DefaultResultSetHandler.java:1125)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.applyNestedResultMappings(DefaultResultSetHandler.java:957)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:914)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForNestedResultMap(DefaultResultSetHandler.java:877)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:324)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:299)
    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:192)
    at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
    at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
    at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
    ... 6 more

八.测试类 Test.java

“`
/**
* @author wuchao
* @time 下午3:50:07
* @description TODO
*/
package com.mybatis.ome.to.many.test;

import java.io.Reader;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.mybatis.one.to.many.dao.UserInterface;
import com.mybatis.one.to.many.pojo.Post;
import com.mybatis.one.to.many.pojo.User;

/**
* @author wuchao
* @time 下午3:50:07
*
*/
public class Test {
private static Reader reader;
private static SqlSessionFactory sqlSessionFactory;
static {
try {
reader = Resources.getResourceAsReader(“mybatis-config.xml”);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}

public static SqlSessionFactory getSession() {
    return sqlSessionFactory;
}

public static void main(String args[]) {
    SqlSession session = sqlSessionFactory.openSession();
    try {
        UserInterface userInterface = session
                .getMapper(UserInterface.class);
        User user = userInterface.getUserById(1);
        System.out.println("查询到的用户id是：" + user.getId());
        System.out.println("查询到的用户名字是：" + user.getName());
        System.out.println("查询到的用户网站：" + user.getWebsite());
        List<Post> posts = user.getPosts();
        for (Post post : posts) {
            System.out.println("查询出来的post名字是：" + post.getPostName());
            System.out.println("查询出来的post文本是："+post.getTitle());
        }
    } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
    }finally{
        session.close();
    }
}

}

“`