MyBatis系列目录--4. MyBatis别名、字段冲突、动态sql、日志、xml其他组件等若干优化

崬城衞

转载请注明出处哈:http://carlosfu.iyunv.com/blog/2238662




  一、mybatis执行日志

   加入log4j/logback能看到mybatis更详细的执行情况，以logback为例子

<logback.version>1.0.13</logback.version>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>${logback.version}</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>${logback.version}</version>
</dependency>
 
   配置(logback.xml)：默认debug，也可以分开logger去实现（org.apache.ibatis, java.sql）

<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="5 seconds">
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<root level="DEBUG">
<appender-ref ref="STDOUT"/>
</root>
</configuration>
 
 

二、实体别名

在xml配置中的resultType和parameterType都需要写全路径类名，这样不太方便，mybatis提供了别名机制解决这个问题。
 
1. 在mybatis-base.xml中添加如下（注意要添加到配置的最前头）

<typeAliases>
<typeAlias type="com.sohu.tv.bean.Player" alias="Player"/>
</typeAliases>
 
playerMapper.xml在使用resultType和parameterType直接写别名就可以了

<mapper namespace="com.sohu.tv.mapper.playerMapper">
<select id="getPlayer" parameterType="int" resultType="Player">
select id,name,age from players where id=#{id}
</select>
</mapper>
 
 
2. 如果想使得一个package下所有实体类都用简单类名作为别名，可以使用如下配置：

<typeAliases>
<!--
<typeAlias type="com.sohu.tv.bean.Player" alias="Player"/>
-->
<package name="com.sohu.tv.bean"/>
</typeAliases>
三、字段冲突：

1. 产生冲突

(1).  建表

CREATE TABLE club(
id INT PRIMARY KEY AUTO_INCREMENT,
name varchar(20) not null comment '俱乐部名称',
info varchar(255) not null comment '俱乐部简介',
create_date date comment '创建日期',
rank smallint comment '排名'
)ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COMMENT='俱乐部表';
INSERT INTO club(name, info, create_date, rank) VALUES('AC', 'AC米兰', '1899-12-26', 5);
INSERT INTO club(name, info, create_date, rank) VALUES('Real Madrid', '皇家马德里', '1902-03-06', 1);
INSERT INTO club(name, info, create_date, rank) VALUES('Inter', '国际米兰', '1908-03-09', 7);
 

(2). 实体类

package com.sohu.tv.bean;
import java.util.Date;
/**
* 俱乐部
*
* @author leifu
* @Date 2015年7月28日
* @Time 下午1:43:53
*/
public class Club {
/**
* 俱乐部id
*/
private int id;
/**
* 俱乐部名
*/
private String clubName;
/**
* 俱乐部描述
*/
private String clubInfo;
/**
* 创建日期
*/
private Date createDate;
/**
* 排名
*/
private int rank;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getClubName() {
return clubName;
}
public void setClubName(String clubName) {
this.clubName = clubName;
}
public String getClubInfo() {
return clubInfo;
}
public void setClubInfo(String clubInfo) {
this.clubInfo = clubInfo;
}
public Date getCreateDate() {
return createDate;
}
public void setCreateDate(Date createDate) {
this.createDate = createDate;
}
public int getRank() {
return rank;
}
public void setRank(int rank) {
this.rank = rank;
}
@Override
public String toString() {
return "Club [id=" + id + ", clubName=" + clubName + ", clubInfo=" + clubInfo + ", createDate=" + createDate
+ ", rank=" + rank + "]";
}
}
(3) Dao

package com.sohu.tv.mapper;
import java.util.List;
import com.sohu.tv.bean.Club;
/**
* 俱乐部Dao
* @author leifu
* @Date 2015年8月3日
* @Time 下午2:30:58
*/
public interface ClubDao {
/**
* 获取所有俱乐部信息
* @return
*/
public List<Club> getAllClubs();
}
 

(4). 添加clubMapper.xml配置

<?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.sohu.tv.mapper.ClubDao">
<select id="getAllClubs" resultType="Club">
select id,name,info,create_date,rank from club
</select>
</mapper>
(5). 添加clubMapper.xml到总配置文件中

<mappers>
<mapper resource="mapper/clubMapper.xml" />
</mappers>

(6). 单元测试：

package com.sohu.tv.test.mapper;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.sohu.tv.bean.Club;
import com.sohu.tv.mapper.ClubDao;
/**
* 俱乐部dao测试
*
* @author leifu
* @Date 2015年8月3日
* @Time 下午2:33:04
*/
public class ClubMapperXmlTest extends BaseTest {
private SqlSession sqlSession;
@Before
public void before() {
sqlSession = sessionFactory.openSession(true);
}
@After
public void after() {
sqlSession.close();
}
@Test
public void testGetAllClubs() {
ClubDao clubDao = sqlSession.getMapper(ClubDao.class);
List<Club> clubList = clubDao.getAllClubs();
if (clubList != null && !clubList.isEmpty()) {
System.out.println("clubList size: " + clubList.size());
for (Club club : clubList) {
System.out.println(club);
}
}
}
}
产生错误：

clubList size: 3
Club [id=1, clubName=null, clubInfo=null, createDate=null, rank=5]
Club [id=2, clubName=null, clubInfo=null, createDate=null, rank=1]
Club [id=3, clubName=null, clubInfo=null, createDate=null, rank=7]

 







2. 冲突解决的三种方法：

1.  mysql语句使用别名

<mapper namespace="com.sohu.tv.mapper.clubMapper">
<select id="selectAllClubs" resultType="com.sohu.tv.bean.Club">
select id,name as clubName,info as clubInfo,create_date as createDate,rank from club
</select>
</mapper>

2. 使用resultMap做转换

<select id="getAllClubs" resultType="Club" resultMap="clubResultMap">
select id,name,info,create_date,rank from club
</select>
<resultMap type="Club" id="clubResultMap">
<id property="id" column="id"/>
<result property="clubName" column="name"/>
<result property="clubInfo" column="info"/>
<result property="createDate" column="create_date"/>
<result property="rank" column="rank"/>
</resultMap>
 

3. 基于约定

以上两种在生产环境都不建议使用，应该按照一个约定实现（例如数据库字段用_隔开，实体类使用驼峰式）

<!--数据库的字段名到pojo类的属性名的自动映射-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
例如： create_date 对应 createDate

四、动态sql

1. sql标签:
    作用：省去每个sql语句都写一大串字段
 

<sql id="clubColumns">
id,name,info,create_date,rank
</sql>
<select id="getAllClubs" resultType="Club">
select <include refid="clubColumns"/> from club
</select>
 

2. where标签

作用: sql中的where语句

(1) ClubDao添加如下方法:

/**
* 根据名称查询
* @param name
* @return
*/
public Club getByName(String name);

(2) clubMapper.xml

<select id="getByName" parameterType="string" resultType="Club">
select <include refid="clubColumns"/> from club
<where>
name = #{name}
</where>
</select>

(3) 单元测试：

@Test
public void testGetByName() {
ClubDao clubDao = sqlSession.getMapper(ClubDao.class);
Club club = clubDao.getByName("AC");
System.out.println(club);
}

3. set(更新字段), choose(判断), where标签综合使用：

   (1)ClubDao添加如下接口

import org.apache.ibatis.annotations.Param;
/**
* 更新俱乐部排名
* @param id
* @param rank
*/
public void updateRank(@Param("id") int id, @Param("rank") int rank);
(2) clubMapper.xml添加对应的sql语句

<update id="updateRank" parameterType="Club">
update club
<set>
<choose>
<when test="rank > 0">rank=#{rank}</when>
<otherwise>rank=0</otherwise>
</choose>
</set>
<where>
id = #{id}
</where>
</update>
(3) 单元测试:

@Test
public void testUpdateRank() {
ClubDao clubDao = sqlSession.getMapper(ClubDao.class);
clubDao.updateRank(1, 1000);
}
4. foreach语句

示例：

(1) ClubDao添加如下接口

/**
* 根据id列表获取俱乐部信息
* @param ids
* @return
*/
public List<Club> getByIds(@Param("ids") List<Integer> ids);
(2) clubMapper.xml添加对应的sql语句

<select id="getByIds" parameterType="list" resultType="Club">
select <include refid="clubColumns"/> from club
<where>
<foreach collection="ids" item="id" open="AND (" close=")" separator="or">
id=#{id}
</foreach>
</where>
</select>

(3)单元测试

@Test
public void testGetByIds() {
ClubDao clubDao = sqlSession.getMapper(ClubDao.class);
List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(2);
printClubList(clubDao.getByIds(ids));
}
private void printClubList(List<Club> clubList) {
if (clubList != null && !clubList.isEmpty()) {
System.out.println("clubList size: " + clubList.size());
for (Club club : clubList) {
System.out.println(club);
}
}        
}
五、properties:

数据库配置可以单独写到一个配置文件中，例如db.properties

football.driver=com.mysql.jdbc.Driver
football.url=jdbc:mysql://localhost:3306/football
football.username=root
football.password=xxxx
 
mybatis全局配置文件中：

<?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">
<configuration>

<properties resource="db.properties" />
<settings>
<setting name="useColumnLabel" value="true" />
<setting name="mapUnderscoreToCamelCase" value="true" />
</settings>
<typeAliases>
<package name="com.sohu.tv.bean" />
</typeAliases>
<environments default="development">
<environment id="development">
<!-- 事务使用的是jdbc的方式 -->
<transactionManager type="JDBC" />
<!-- 连接池 -->
<dataSource type="POOLED">
<property name="driver" value="${football.driver}" />
<property name="url" value="${football.url}" />
<property name="username" value="${football.username}" />
<property name="password" value="${football.password}" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mapper/playerMapper.xml" />
<mapper class="com.sohu.tv.mapper.PlayerAnnotationDao" />
<mapper resource="mapper/clubMapper.xml" />
</mappers>
</configuration>