亲宝软件园·资讯

展开

MyBatis 多表联合查询

紫竹风 人气:0

这篇文章我打算来简单的谈谈 mybatis 的多表联合查询。起初是觉得挺简单的,没必要拿出来写,毕竟 mybatis 这东西现在是个开发的都会用,而且网上的文章也是一搜罗一大堆,根本就用不着我来重复。但是吧,就我前几天在做一个多表联合查询的时候,竟然出了很多意想不到的问题,而且这些问题的出现,并不是对 mybatis 不了解,而是在用的过程中会或多或少的忽略一些东西,导致提示各种错误。

背景

老规矩,开始之前,还是要先说说这件事的背景。也就是最近几天,公司要做一个后台的管理平台,由于之前的一些限制,这次要做成单独的项目进行部署,因此就要重新考虑很多东西。索性这几天有时间,就做了一个小 Demo ,实现 mybatis 的多表联合查询的,由于之前用的是 Hibernate 做的联合查询,众所周知,Hibernate 是全自动的数据库持久层框架,它可以通过实体来映射数据库,通过设置一对多、多对一、一对一、多对多的关联来实现联合查询。

正文

下面就来说一下 mybatis 是通过什么来实现多表联合查询的。首先看一下表关系,如图:

这里,我已经搭好了开发的环境,用到的是 SpringMVC + Spring + MyBatis,当然,为了简单期间,你可以不用搭前端的框架,只使用 Spring + MyBatis 就可以,外加 junit 测试即可。环境我就不带大家搭了,这里只说涉及到联合查询的操作。
设计好表之后,我用到了 mybatis 的自动生成工具 mybatis generator 生成的实体类、mapper 接口、以及 mapper xml 文件。由于是测试多表联合查询,因此需要自己稍加改动。
下面是 User 和 Role 的实体类代码:

User

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.domain;
import java.io.Serializable;
import java.util.List;
public class User implements Serializable {
    private String id;
    private String username;
    private String password;
    private List<Role> roles;
    private static final long serialVersionUID = 1L;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id == null ? null : id.trim();
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username == null ? null : username.trim();
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password == null ? null : password.trim();
    }
    public List<Role> getRoles() {
        return roles;
    }
    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }
    @Override
    public boolean equals(Object that) {
        if (this == that) {
            return true;
        }
        if (that == null) {
            return false;
        }
        if (getClass() != that.getClass()) {
            return false;
        }
        User other = (User) that;
        return (this.getId() == null ? other.getId() == null : this.getId().equals(other.getId()))
            && (this.getUsername() == null ? other.getUsername() == null : this.getUsername().equals(other.getUsername()))
            && (this.getPassword() == null ? other.getPassword() == null : this.getPassword().equals(other.getPassword()));
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((getId() == null) ? 0 : getId().hashCode());
        result = prime * result + ((getUsername() == null) ? 0 : getUsername().hashCode());
        result = prime * result + ((getPassword() == null) ? 0 : getPassword().hashCode());
        return result;
    }
}</span>

Role

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.domain;
import java.io.Serializable;
public class Role implements Serializable {
    private String id;
    private String name;
    private String jsms;
    private String bz;
    private Integer jlzt;
    private String glbm;
    private String userid;
    private static final long serialVersionUID = 1L;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id == null ? null : id.trim();
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name == null ? null : name.trim();
    }
    public String getJsms() {
        return jsms;
    }
    public void setJsms(String jsms) {
        this.jsms = jsms == null ? null : jsms.trim();
    }
    public String getBz() {
        return bz;
    }
    public void setBz(String bz) {
        this.bz = bz == null ? null : bz.trim();
    }
    public Integer getJlzt() {
        return jlzt;
    }
    public void setJlzt(Integer jlzt) {
        this.jlzt = jlzt;
    }
    public String getGlbm() {
        return glbm;
    }
    public void setGlbm(String glbm) {
        this.glbm = glbm == null ? null : glbm.trim();
    }
    public String getUserid() {
        return userid;
    }
    public void setUserid(String userid) {
        this.userid = userid == null ? null : userid.trim();
    }
    @Override
    public boolean equals(Object that) {
        if (this == that) {
            return true;
        }
        if (that == null) {
            return false;
        }
        if (getClass() != that.getClass()) {
            return false;
        }
        Role other = (Role) that;
        return (this.getId() == null ? other.getId() == null : this.getId().equals(other.getId()))
            && (this.getName() == null ? other.getName() == null : this.getName().equals(other.getName()))
            && (this.getJsms() == null ? other.getJsms() == null : this.getJsms().equals(other.getJsms()))
            && (this.getBz() == null ? other.getBz() == null : this.getBz().equals(other.getBz()))
            && (this.getJlzt() == null ? other.getJlzt() == null : this.getJlzt().equals(other.getJlzt()))
            && (this.getGlbm() == null ? other.getGlbm() == null : this.getGlbm().equals(other.getGlbm()))
            && (this.getUserid() == null ? other.getUserid() == null : this.getUserid().equals(other.getUserid()));
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((getId() == null) ? 0 : getId().hashCode());
        result = prime * result + ((getName() == null) ? 0 : getName().hashCode());
        result = prime * result + ((getJsms() == null) ? 0 : getJsms().hashCode());
        result = prime * result + ((getBz() == null) ? 0 : getBz().hashCode());
        result = prime * result + ((getJlzt() == null) ? 0 : getJlzt().hashCode());
        result = prime * result + ((getGlbm() == null) ? 0 : getGlbm().hashCode());
        result = prime * result + ((getUserid() == null) ? 0 : getUserid().hashCode());
        return result;
    }
}</span>

首先讲一下业务,这里用到的 User 、Role 的对应关系是,一个用户有多个角色,也就是 User : Role 是 1 : n 的关系。因此,在 User 的实体中加入一个 Role 的属性,对应一对多的关系。
然后就是 mapper 接口和 xml 文件了:
mapper接口
UserMapper

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.mapper;
import com.sica.domain.User;
import java.util.List;
public interface UserMapper {
    int deleteByPrimaryKey(String id);
    int insert(User record);
    int insertSelective(User record);
    User selectByPrimaryKey(String id);
    int updateByPrimaryKeySelective(User record);
    int updateByPrimaryKey(User record);
    List<User> queryForList();
}</span>

mapper xml文件
UserMapper

<span style="font-family:Comic Sans MS;font-size:12px;"><?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.sica.mapper.UserMapper">
    <resultMap id="BaseResultMap" type="com.sica.domain.User">
        <id column="id" property="id" jdbcType="VARCHAR"/>
        <result column="username" property="username" jdbcType="VARCHAR"/>
        <result column="password" property="password" jdbcType="VARCHAR"/>
    </resultMap>
 
    <resultMap id="queryForListMap" type="com.sica.domain.User">
        <id column="id" property="id" jdbcType="VARCHAR"/>
        <result column="username" property="username" jdbcType="VARCHAR"/>
        <result column="password" property="password" jdbcType="VARCHAR"/>
        <collection property="roles" javaType="java.util.List" ofType="com.sica.domain.Role">
            <id column="r_id" property="id" jdbcType="VARCHAR" />
            <result column="r_name" property="name" jdbcType="VARCHAR" />
            <result column="r_jsms" property="jsms" jdbcType="VARCHAR" />
            <result column="r_bz" property="bz" jdbcType="VARCHAR" />
            <result column="r_jlzt" property="jlzt" jdbcType="INTEGER" />
            <result column="r_glbm" property="glbm" jdbcType="VARCHAR" />
        </collection>
    </resultMap>
    <select id="queryForList" resultMap="queryForListMap">
        SELECT
          u.id,
          u.username,
          u.password,
          r.id r_id,
          r.name r_name,
          r.jsms r_jsms,
          r.bz r_bz,
          r.jlzt r_jlzt,
          r.glbm r_glbm
        FROM
          user u
        LEFT JOIN
          role r
        ON
          u.id = r.userid
    </select>
    <sql id="Base_Column_List">
      id, username, password
    </sql>
    <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.String">
        select
        <include refid="Base_Column_List"/>
        from user
        where id = #{id,jdbcType=VARCHAR}
    </select>
    <delete id="deleteByPrimaryKey" parameterType="java.lang.String">
    delete from user
    where id = #{id,jdbcType=VARCHAR}
    </delete>
    <insert id="insert" parameterType="com.sica.domain.User">
    insert into user (id, username, password
      )
    values (#{id,jdbcType=VARCHAR}, #{username,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}
      )
    </insert>
    <insert id="insertSelective" parameterType="com.sica.domain.User">
        insert into user
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="id != null">
                id,
            </if>
            <if test="username != null">
                username,
            </if>
            <if test="password != null">
                password,
            </if>
        </trim>
        <trim prefix="values (" suffix=")" suffixOverrides=",">
            <if test="id != null">
                #{id,jdbcType=VARCHAR},
            </if>
            <if test="username != null">
                #{username,jdbcType=VARCHAR},
            </if>
            <if test="password != null">
                #{password,jdbcType=VARCHAR},
            </if>
        </trim>
    </insert>
    <update id="updateByPrimaryKeySelective" parameterType="com.sica.domain.User">
        update user
        <set>
            <if test="username != null">
                username = #{username,jdbcType=VARCHAR},
            </if>
            <if test="password != null">
                password = #{password,jdbcType=VARCHAR},
            </if>
        </set>
        where id = #{id,jdbcType=VARCHAR}
    </update>
    <update id="updateByPrimaryKey" parameterType="com.sica.domain.User">
    update user
    set username = #{username,jdbcType=VARCHAR},
      password = #{password,jdbcType=VARCHAR}
    where id = #{id,jdbcType=VARCHAR}
  </update>
</mapper></span>

之后,我扩展了一个 Dao 接口,当然,你也可以直接使用 mapper 接口,都是一样的。
Dao 接口
IUserDao

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.dao;
 
import com.sica.mapper.UserMapper;
 
/**
 * Created by IntelliJ IDEA.
 * Package: com.sica.dao
 * Name: IUserDao
 * User: xiang.li
 * Date: 2015/5/22
 * Time: 15:25
 * Desc: To change this template use File | Settings | File Templates.
 */
public interface IUserDao extends UserMapper {
 
}</span>

下面就是 service 和实现层的代码了。
IUserService

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.service;
import com.sica.domain.User;
import java.util.List;
/**
 * Created by xiang.li on 2015/1/31.
 */
public interface IUserService {
    /**
     * 根据Id查询用户对象
     * @param id 编号
     * @return 用户对象
     */
    User getUserById(String id);
    /**
     * 根据用户名查询用户对象
     * @return  List
     */
    List<User> queryUserList();
}</span>

UserServiceImpl

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.service.impl;
import com.sica.dao.IUserDao;
import com.sica.domain.User;
import com.sica.service.IUserService;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
import java.util.List;
/**
 * Created by xiang.li on 2015/1/31.
 */
@Service("userService")
public class UserServiceImpl implements IUserService {
    @Resource
    public IUserDao userDao;
    @Override
    public User getUserById(String id) {
        return this.userDao.selectByPrimaryKey(id);
    }
    @Override
    public List<User> queryUserList() {
        return userDao.queryForList();
    }
}</span>

当然,还有所谓的 applicationContext.xml 配置,不过,我这里叫 spring-mybatis.xml。

<span style="font-family:Comic Sans MS;font-size:12px;"><?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
 
    <!-- 自动扫描 -->
    <context:component-scan base-package="com.sica"/>
    <!-- 引入配置文件 -->
    <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
          p:location="classpath:jdbc.properties"
          />
 
    <!-- 配置数据库连接池 -->
    <!-- 初始化连接大小 -->
    <!-- 连接池最大数量 -->
    <!-- 连接池最大空闲 -->
    <!-- 连接池最小空闲 -->
    <!-- 获取连接最大等待时间 -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"
          p:driverClassName="${jdbc.driver}"
          p:url="${jdbc.url}"
          p:username="${jdbc.username}"
          p:password="${jdbc.password}"
          p:initialSize="${jdbc.initialSize}"
          p:maxActive="${jdbc.maxActive}"
          p:maxIdle="${jdbc.maxIdle}"
          p:minIdle="${jdbc.minIdle}"
          p:maxWait="${jdbc.maxWait}"
          />
 
    <!-- spring和MyBatis完美整合,不需要mybatis的配置映射文件 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean" lazy-init="default"
          p:dataSource-ref="dataSource"
          p:mapperLocations="classpath:com/sica/mapping/*.xml"
          />
 
    <!-- DAO接口所在包名,Spring会自动查找其下的类 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"
          p:basePackage="com.sica.dao"
          p:sqlSessionFactoryBeanName="sqlSessionFactory"
          />
 
    <!-- (事务管理)transaction manager, use JtaTransactionManager for global tx -->
    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"
          p:dataSource-ref="dataSource"
          />
</beans></span>

最后,我用到的是 junit 进行的测试,测试代码如下。
GetUserTest

<span style="font-family:Comic Sans MS;font-size:12px;">package com.sica.user;
 
import com.alibaba.fastjson.JSON;
import com.sica.domain.User;
import com.sica.service.IUserService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
import javax.annotation.Resource;
import java.util.List;
 
/**
 * Created by xiang.li on 2015/2/1.
 */
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:spring-mybatis.xml")
public class GetUserTest {
 
    private static String UUID = "3";
    @Resource
    private IUserService userService;
    private static Logger logger = LoggerFactory.getLogger(GetUserTest.class);
 
    @Test
    public void test() {
        User user = userService.getUserById(UUID);
        logger.info(JSON.toJSONString(user));
    }
 
    /**
     * 测试联合查询
     */
    @Test
    public void test2() {
        List<User> users = userService.queryUserList();
        logger.info(JSON.toJSONString(users));
    }
}</span>

测试结果

可以看到,所有的用户和用户对应的角色都全部查出来了,这说明,这次的测试很成功。

关于优化

对于优化嘛,我这里简单的提几点,大家可以考虑一下。首先,就是对表的设计,在设计表初期,不仅仅要考虑到数据库的规范性,还好考虑到所谓的业务,以及对性能的影响,比如,如果从规范性角度考虑的话,可能就会分多个表,但是如果从性能角度来考虑的话,庞大的数据量在多表联合查询的时候,相对于单表来说,就会慢很多,这时,如果字段不是很多的话,可以考虑冗余几个字段采用单表的设计。
其次嘛,就是在 sql 上下功夫了,对于联合查询,sql 的优化是很有必要的,到底是采用 INNER JOIN,还是采用 LEFT JOIN 亦或是 RIGHT JOIN 、OUTTER JOIN 等,都是要在满足业务需求之后,通过测试性能得出的结论。
再次嘛,就是在程序中调用的时候了,是采用懒加载,还是采用非懒加载的方式,这也算是一个因素吧,具体的还是要考虑业务的需要。
最后嘛,就要用到数据库的缓存了,或者在数据库与程序的中间再加一层缓存。不过,还是建议用好数据库本身自带的缓存功能。

加载全部内容

相关教程
猜你喜欢
用户评论