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

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

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  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>