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MyBatis(5)之映射文件中的常用标签

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准备

# jdbc.properties
jdbc.url=jdbc:mysql://192.168.208.192:3306/test?characterEncoding=utf-8
jdbc.driver=com.mysql.jdbc.Driver
jdbc.username=root
jdbc.password=root
# log4j.properties
log4j.rootLogger = debug,stdout,E

### 输出信息到控制抬 ###
log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n

### 输出DEBUG 级别以上的日志到=E://logs/error.log ###
log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
log4j.appender.D.File = E://logs/log.log
log4j.appender.D.Append = true
log4j.appender.D.Threshold = DEBUG
log4j.appender.D.layout = org.apache.log4j.PatternLayout
log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

### 输出ERROR 级别以上的日志到=E://logs/error.log ###
log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
log4j.appender.E.File =E://logs/error.log 
log4j.appender.E.Append = true
log4j.appender.E.Threshold = ERROR 
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n
<!-- mybatis/SqlMapConfig.xml -->
<?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>
    <!--
    加载属性文件
        先加载内部标签,再加载外部文件,名称一致时,会覆盖内部标签内容
     -->
    <properties resource="jdbc.properties"/>

    <!--别名扫描-->
    <typeAliases>
        <package name="com.zze.mybatis.pojo" />
    </typeAliases>

    <!-- 和 spring 整合后 environments配置将废除-->
    <environments default="development">
        <environment id="development">
            <!-- 使用jdbc事务管理-->
            <transactionManager type="JDBC"/>
            <!-- 数据库连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <!-- 加载映射文件 -->
    <mappers>
        <package name="com.zze.mybatis.mapper"/>
    </mappers>
</configuration>
// com.zze.mybatis.pojo.User
import java.util.Date;

public class User {
    private Integer id;
    private String name;
    private Date birthday;

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}
// com.zze.mybatis.util.SqlSessionFactoryUtil
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 java.io.IOException;
import java.io.InputStream;

public class SqlSessionFactoryUtil {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        // 创建 SqlSessionFactoryBuilder 对象
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        // 创建核心配置文件的输入流
        InputStream resourceAsStream = null;
        try {
            resourceAsStream = Resources.getResourceAsStream("mybatis/SqlMapConfig.xml");
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 创建 Session 工厂
        sqlSessionFactory = sqlSessionFactoryBuilder.build(resourceAsStream);
    }

    /**
     * 打开一个 Session
     *
     * @return SqlSession 实例
     */
    public static SqlSession openSession() {
        return sqlSessionFactory.openSession();
    }

    /**
     * 打开一个 Session
     *
     * @param autoCommit 是否自动提交事务
     * @return SqlSession 实例
     */
    public static SqlSession openSession(Boolean autoCommit) {
        return sqlSessionFactory.openSession(autoCommit);
    }
}
<!-- pom.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zze.mybatis</groupId>
    <artifactId>mybatis_test2</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.25</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.2.8</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.0-rc1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.0-rc1</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>javassist</groupId>
            <artifactId>javassist</artifactId>
            <version>3.11.0.GA</version>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.1.1</version>
        </dependency>
        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>2.2.2</version>
        </dependency>
        <dependency>
            <groupId>asm</groupId>
            <artifactId>asm</artifactId>
            <version>3.3.1</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.37</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

示例

字段映射-resultMap

如果表字段名与 POJO 属性名不一致,则可通过 resultMap 标签配置表字段与 POJO 属性的映射关系:

<!-- com/zze/mybatis/mapper/UserMapper.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.zze.mybatis.mapper.UserMapper">
    <resultMap id="userMap" type="user">
        <!--
        id 配置对应主键字段
            property:属性名
            column:字段名
        -->
        <id property="id" column="uid"/>
        <!--
        result 配置普通属性字段
            property:属性名
            column:字段名
        -->
        <result property="name" column="username"/>
        <!--
        非关联查询时
        属性名与字段名相同的 result 映射可以省略不写
        -->
        <!--<result property="birthday" column="birthday"/>-->
    </resultMap>

    <select id="getAll" resultMap="userMap">
        select id uid,name username,birthday from user;
    </select>
</mapper>
// com.zze.mybatis.mapper.UserMapper
import com.zze.mybatis.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getAll();
}
import com.zze.mybatis.mapper.UserMapper;
import com.zze.mybatis.pojo.User;
import com.zze.mybatis.util.SqlSessionFactoryUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

public class MyBatisTest {
    private UserMapper userMapper;

    @Before
    public void init() {
        SqlSession sqlSession = SqlSessionFactoryUtil.openSession();
        userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @Test
    public void test() {
        List<User> all = userMapper.getAll();
        for (User user : all) {
            System.out.println(user);
        }
        /*
        ==>  Preparing: select id uid,name username,birthday from user;
         */
    }
}

动态sql-where&if

当 sql 条件需要动态拼接时,可以使用 whereif 标签:

<!-- com/zze/mybatis/mapper/UserMapper.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.zze.mybatis.mapper.UserMapper">
    <select id="getByUser" resultType="user" parameterType="user">
        select id,name,birthday from user
        <where>
            <if test="name!=null and name!=''">
                name like '%${name}%'
            </if>
        </where>
    </select>
</mapper>
// com.zze.mybatis.mapper.UserMapper
import com.zze.mybatis.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getByUser(User user);
}
package com.zze.mybatis.test;

import com.zze.mybatis.mapper.UserMapper;
import com.zze.mybatis.pojo.User;
import com.zze.mybatis.util.SqlSessionFactoryUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

public class MyBatisTest {
    private UserMapper userMapper;

    @Before
    public void init() {
        SqlSession sqlSession = SqlSessionFactoryUtil.openSession();
        userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @Test
    public void test() {
        User user = new User();
        user.setName("张");
        List<User> userList1 = userMapper.getByUser(user);
        userList1.forEach(u-> System.out.println(u));
        /*
        ==>  Preparing: select id,name,birthday from user WHERE name like '%张%'
         */
        user.setName(null);
        List<User> userList2 = userMapper.getByUser(user);
        userList2.forEach(u-> System.out.println(u));
        /*
        ==>  Preparing: select id,name,birthday from user
         */
    }
}

sql片段-sql&include

当一段 sql 要被频繁在多处使用时,可以将这段 sql 单独抽取出来:

<!-- com/zze/mybatis/mapper/UserMapper.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.zze.mybatis.mapper.UserMapper">
    <sql id="userAllField">
      id,name,birthday
    </sql>
    <select id="getAll" resultType="user">
        select
        <include refid="userAllField"/>
        from user
    </select>
</mapper>

// com.zze.mybatis.mapper.UserMapper
import com.zze.mybatis.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getAll();
}
package com.zze.mybatis.test;

import com.zze.mybatis.mapper.UserMapper;
import com.zze.mybatis.pojo.User;
import com.zze.mybatis.util.SqlSessionFactoryUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

public class MyBatisTest {
    private UserMapper userMapper;

    @Before
    public void init() {
        SqlSession sqlSession = SqlSessionFactoryUtil.openSession();
        userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @Test
    public void test() {
        List<User> userList = userMapper.getAll();
        userList.forEach(u-> System.out.println(u));
        /*
        ==>  Preparing: select id,name,birthday from user
         */
    }
}

循环-foreach

编写 sql 时也可以通过传入集合来动态拼装条件:

// com.zze.mybatis.pojo.QueryVO
package com.zze.mybatis.pojo;

import java.util.List;

public class QueryVO {
    private List<Integer> idList;

    public List<Integer> getIdList() {
        return idList;
    }

    public void setIdList(List<Integer> idList) {
        this.idList = idList;
    }
}
<!-- com/zze/mybatis/mapper/UserMapper.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.zze.mybatis.mapper.UserMapper">
    <select id="getByIdList" resultType="user" parameterType="queryvo">
        select * from user
        <where>
            <foreach collection="idList" open="id in (" close=")" separator="," item="id">
              #{id}
            </foreach>
        </where>
    </select>
</mapper>
// com.zze.mybatis.mapper.UserMapper
import com.zze.mybatis.pojo.QueryVO;
import com.zze.mybatis.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getByIdList(QueryVO queryVO);
}
package com.zze.mybatis.test;

import com.zze.mybatis.mapper.UserMapper;
import com.zze.mybatis.pojo.QueryVO;
import com.zze.mybatis.pojo.User;
import com.zze.mybatis.util.SqlSessionFactoryUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

import java.util.Arrays;
import java.util.List;

public class MyBatisTest {
    private UserMapper userMapper;

    @Before
    public void init() {
        SqlSession sqlSession = SqlSessionFactoryUtil.openSession();
        userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @Test
    public void test() {
        QueryVO queryVO = new QueryVO();
        queryVO.setIdList(Arrays.asList(1, 2, 3));
        List<User> userList = userMapper.getByIdList(queryVO);
        userList.forEach(u-> System.out.println(u));
        /*
        ==>  Preparing: select * from user WHERE id in ( ? , ? , ? )
        ==> Parameters: 1(Integer), 2(Integer), 3(Integer)
         */
    }
}

要注意的是 mybatis 的 Mapper 参数不支持直接传入集合,但我们可以如上示例将它放在包装类中传入。

# MyBatis  

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