MyBatis基础（增、删、改、查以及动态SQL）

移动开发 2023-04-09 19:16:59 阅读次数: 0

中文官网：https://mybatis.org/mybatis-3/zh/index.html​​​​​​​

MyBatis是属于持久层（DAO层）的框架

封装了JDBC的很多操作细节，让开发者大大简化了DAO层的代码

在2010年从iBatis改名为Mybatis

一、创建核心配置文件（一般叫mybatis-config.xml），配置如下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <settings>
        <!--是否开启驼峰命名自动映射,默认false，created_time -> createdTime 如果不开启在mapper里面也可以设置 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
        <!--打印Sql日志log-->
<!--        <setting name="logImpl" value="STDOUT_LOGGING"/>-->
    </settings>

    <!--别名-->
    <typeAliases>
        <!--一旦设置了别名，不区分大小写-->
<!--        <typeAlias type="com.mj.bean.Skill" alias="skill"/>-->
<!--        <typeAlias type="com.mj.bean.Experience" alias="experience"/>-->
        <!--这个包下的所有类，都会有一个别名：短类名也就是全类名的最后一个单词-->
        <package name="com.mj.bean"/>
    </typeAliases>

    <environments default="dev">
        <environment id="dev">
            <!--采用JDBC的事物管理方法-->
            <transactionManager type="JDBC"/>
            <!--POOLED代表采用连接池的方式管理链接 更改成阿里巴巴的连接池-->
            <dataSource type="com.mj.common.DruidDataSourceFactory">
                <!--数据库驱动-->
                <!--阿里巴巴连接池这个名字是driverClassName-->
                <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/crm"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>

        <environment id="pro">
            <!--采用JDBC的事物管理方法-->
            <transactionManager type="JDBC"/>
            <!--POOLED代表采用连接池的方式管理链接-->
            <dataSource type="POOLED">
                <!--数据库驱动-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/crm"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <!--映射文件-->
        <mapper resource="mappers/skill.xml" />
        <mapper resource="mappers/experience.xml" />
    </mappers>

</configuration>

二、创建数据库映射mapper文件如下：

  • 单表查询如下：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="skill">
    <select id="list" resultType="com.mj.bean.Skill">
        SELECT * FROM skill
    </select>

    <select id="get" resultType="com.mj.bean.Skill">
        SELECT * FROM skill WHERE id = #{id}
    </select>

    <select id="list2" resultType="com.mj.bean.Skill">
        <!--不要用${id} 美元符代表的是直接替换，会有SQL注入的风险-->
        SELECT * FROM skill WHERE id > #{id} OR level > #{level} OR name LIKE #{name}
    </select>

    <!--  手动开启属性和数据库字段的映射  -->
<!--    <resultMap id="rm" type="com.mj.bean.Skill">-->
<!--        <id property="id" column="id"/>-->
<!--        <result property="createdTime" column="created_time"/>-->
<!--        <result property="name" column="name"/>-->
<!--        <result property="level" column="level"/>-->
<!--    </resultMap>-->
<!--    <select id="list" resultMap="rm">-->
<!--        SELECT * FROM skill-->
<!--    </select>-->

</mapper>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="skill">

    <!--  手动开启属性和数据库字段的映射  -->
    <resultMap id="rm" type="com.mj.bean.Skill">
         <!--  主键一般用id  -->
        <id property="id" column="id"/>
        <result property="createdTime" column="created_time"/>
        <result property="name" column="name"/>
        <result property="level" column="level"/>
    </resultMap>
    <select id="list" resultMap="rm">
        SELECT * FROM skill
    </select>

</mapper>
  •  联表查询如下：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="experience">

    <!--  第一种方式 -->
    <select id="list" resultType="com.mj.bean.Experience">
        SELECT
        t1.*,
        t2.id `company.id`,
        t2.name `company.name`,
        t2.intro `company.intro`
        FROM
        experience t1
        JOIN
        company t2
        ON t1.company_id = t2.id
    </select>

    <!--  第二种方式  -->
<!--    <resultMap id="rmExperience" type="com.mj.bean.Experience">-->
<!--        <result property="company.name" column="t2_name"/>-->
<!--        <result property="company.id" column="t2_id"/>-->
<!--        <result property="company.intro" column="t2_intro"/>-->
<!--    </resultMap>-->

<!--    <select id="list" resultMap="rmExperience">-->
<!--        SELECT-->
<!--        t1.*,-->
<!--        t2.id t2_id,-->
<!--        t2.name t2_name,-->
<!--        t2.intro t2_intro-->
<!--        FROM-->
<!--        experience t1-->
<!--        JOIN-->
<!--        company t2-->
<!--        ON t1.company_id = t2.id-->
<!--    </select>-->

</mapper>

三、test类中访问数据库

   @Test
    public void select() throws Exception{
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");

        // 创建一个工厂构建器
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();

        // 创建一个工厂
        SqlSessionFactory factory = builder.build(reader);

        // 创建一个session
        SqlSession session = factory.openSession();

        List<Skill> skills = session.selectList("skill.list");
        for (Skill skill : skills) {
            System.out.println(skill);
        }
    }

封装工具类：

public class MyBatises {
    private static SqlSessionFactory factory;
    static {
        try ( Reader reader = Resources.getResourceAsReader("mybatis-config.xml")) {
            // 创建一个工厂.factory 保留一份
            factory = new SqlSessionFactoryBuilder().build(reader);
            } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSession openSession() {
        return factory.openSession();
    }
}

访问数据库带参数如下：

 @Test
    public void select2() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){

           Skill skill = session.selectOne("skill.get",2);
           System.out.println(skill);
        }
    }

    @Test
    public void select3() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){
            // 以下两种方式都可以
//            HashMap map = new HashMap();
//            map.put("id",2);
//            map.put("level", 30);

            Skill skill = new Skill();
            skill.setId(2);
            skill.setLevel(30);
             skill.setName("%三%");
            List<Skill> skills = session.selectList("skill.list2",skill);
            for (Skill skill1 : skills) {
                System.out.println(skill1);
            }
        }
    }

更改阿里巴巴连接池：

     <!--阿里巴巴的连接池-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.2.11</version>
        </dependency>

mybatis配置文件：

        <environment id="dev">
            <!--采用JDBC的事物管理方法-->
            <transactionManager type="JDBC"/>
            <!--POOLED代表采用连接池的方式管理链接 更改成阿里巴巴的连接池-->
            <dataSource type="com.mj.common.DruidDataSourceFactory">
                <!--数据库驱动-->
                <!--阿里巴巴连接池这个名字是driverClassName-->
                <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/crm"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>

相关类的设置：

package com.mj.common;

import com.alibaba.druid.pool.DruidDataSource;
import org.apache.ibatis.datasource.pooled.PooledDataSourceFactory;

public class DruidDataSourceFactory extends PooledDataSourceFactory {
    public DruidDataSourceFactory() {
        this.dataSource = new DruidDataSource();
    }
}

 汇总增删改查如下：

测试类如下：

public class SkillTest {
    @Test
    public void select() throws Exception{
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");

        // 创建一个工厂构建器
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();

        // 创建一个工厂
        SqlSessionFactory factory = builder.build(reader);

        // 创建一个session
        SqlSession session = factory.openSession();

        List<Skill> skills = session.selectList("skill.list");
        for (Skill skill : skills) {
            System.out.println(skill);
        }
    }

    @Test
    public void select2() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){

           Skill skill = session.selectOne("skill.get",2);
           System.out.println(skill);
        }
    }

    @Test
    public void select3() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){
            // 以下两种方式都可以
//            HashMap map = new HashMap();
//            map.put("id",2);
//            map.put("level", 30);

            Skill skill = new Skill();
            skill.setId(2);
            skill.setLevel(30);
            skill.setName("%三%");

            List<Skill> skills = session.selectList("skill.list2",skill);
            for (Skill skill1 : skills) {
                System.out.println(skill1);
            }
        }
    }

    @Test
    public void select4() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){
            String string =  "%三%";
            List<Skill> skills = session.selectList("skill.list3",string);
            for (Skill skill1 : skills) {
                System.out.println(skill1);
            }
        }
    }

    @Test
    public void insert() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){

            Skill skill = new Skill("我是张三",1234);
            session.insert("skill.insert2",skill);
            System.out.println(skill.getId());
            // mybatis默认不会自动提交事物，需要手动管理
            session.commit();
        }
    }

    @Test
    public void update() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){

            Skill skill = new Skill("我是张三",1234);
            skill.setId(1);
            session.update("skill.update",skill);
            System.out.println(skill.getId());
            // mybatis默认不会自动提交事物，需要手动管理
            session.commit();
        }
    }

    @Test
    public void delete() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){

            Skill skill = new Skill();
            skill.setId(1);
            session.delete("skill.delete",skill);
            System.out.println(skill.getId());
            // mybatis默认不会自动提交事物，需要手动管理
            session.commit();
        }
    }

    @Test
    public void dynamicSQL() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){
            // id name level 三个条件
            Skill skill = new Skill();
            skill.setId(5);
            skill.setName("我是张三");
            skill.setLevel(12);
            List<Skill> skills = session.selectList("skill.dynamicSQL1",skill);
            for (Skill skill1 : skills) {
                System.out.println(skill1);
            }
        }
    }

    // 批量插入
    @Test
    public void batchInsert() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){
            List<Skill> skills = new ArrayList<>();
            skills.add(new Skill("天王1",34));
            skills.add(new Skill("天王2",35));
            skills.add(new Skill("天王3",36));
            session.insert("skill.batchInsert",skills);
            session.commit();
        }
    }

    // 批量删除
    @Test
    public void batchDelete() throws Exception{
        try ( SqlSession session = MyBatises.openSession()){
            List<Integer> ids = new ArrayList<>();
            ids.add(14);
            ids.add(16);
            ids.add(17);
            session.insert("skill.batchDelete",ids);
            session.commit();
        }
    }
}

mapper中skill.xml文件如下

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="skill">
    <!--查询所有数据-->
    <select id="list" resultType="skill">
        SELECT * FROM skill
    </select>

    <!--根据id查询数据-->
    <select id="get" parameterType="int" resultType="com.mj.bean.Skill">
        SELECT * FROM skill WHERE id = #{id}
    </select>

    <!--根据条件查找数据-->
    <select id="list2" parameterType="com.mj.bean.Skill" resultType="com.mj.bean.Skill">
        <!--不要用${id} 美元符代表的是直接替换，会有SQL注入的风险-->
        SELECT * FROM skill WHERE id > #{id} OR level > #{level} OR name LIKE #{name}
    </select>

    <!--根据条件查找数据-->
    <select id="list3" parameterType="String" resultType="com.mj.bean.Skill">
        <!--不要用${id} 美元符代表的是直接替换，会有SQL注入的风险-->
        SELECT * FROM skill WHERE name LIKE #{name}
    </select>

    <!-- 动态SQL -->
    <select id="dynamicSQL" parameterType="com.mj.bean.Skill" resultType="com.mj.bean.Skill">
        SELECT * FROM skill WHERE 1 = 1
        <if test="id != null">
            AND id > #{id}
        </if>
        <if test="name != null">
            AND name like #{name}
        </if>
        <if test="level != null">
            AND level &gt; #{level}
        </if>

    </select>

    <select id="dynamicSQL1" parameterType="com.mj.bean.Skill" resultType="com.mj.bean.Skill">
        SELECT * FROM skill
        <where>
            <if test="id != null">
                AND id > #{id}
            </if>
            <if test="name != null">
                AND name like #{name}
            </if>
            <if test="level != null">
                AND level &gt; #{level}
            </if>
        </where>

    </select>

    <!--  手动开启属性和数据库字段的映射  -->
<!--    <resultMap id="rm" type="com.mj.bean.Skill">-->
<!--        <id property="id" column="id"/>-->
<!--        <result property="createdTime" column="created_time"/>-->
<!--        <result property="name" column="name"/>-->
<!--        <result property="level" column="level"/>-->
<!--    </resultMap>-->
<!--    <select id="list" resultMap="rm">-->
<!--        SELECT * FROM skill-->
<!--    </select>-->

    <!--插入数据-->
    <insert id="insert" parameterType="com.mj.bean.Skill">
        INSERT INTO skill(name,level) VALUES (#{name},#{level})
    </insert>

    <!--插入数据后立刻返回ID-->
    <insert id="insert2" parameterType="com.mj.bean.Skill">
        INSERT INTO skill(name,level) VALUES (#{name},#{level})
        <!--插入之后就能拿到id-->
       <selectKey resultType="int" keyProperty="id" order="AFTER">
           SELECT LAST_INSERT_ID()
       </selectKey>
    </insert>

    <!--更新某条数据-->
    <update id="update"  parameterType="com.mj.bean.Skill">
        UPDATE skill SET name = #{name}, level = #{level} WHERE id = #{id}
    </update>

    <!--删除数据-->
    <delete id="delete" parameterType="int">
        DELETE  FROM skill WHERE id = #{id}
    </delete>

    <!--插入多条，批量添加, 能获取主键-->
    <insert id="batchInsert" 
         useGeneratedKeys="true"
            keyProperty="id"
    parameterType="List" >
        INSERT INTO skill(name, level) VALUES
        <foreach collection="list" item="skill" separator=",">
            (#{skill.name}, #{skill.level})
        </foreach>
    </insert>


    <!--删除多条，批量删除-->
    <delete id="batchDelete" parameterType="List" >
        DELETE FROM skill WHERE id IN
        <foreach collection="list"
                 item="id"
                 open="("
                 close=")"
                 separator=",">
            #{id}
        </foreach>

    </delete>


</mapper>

注：批量添加比单个多次添加效率高，批量操作生成的SQL语句可能会比较长，有可能会超过数据库的限制

mybatis配置文件写SQL语句的某些字符需要转义：

 &lt;        

 <  &gt;          >   &lt;&gt;     <> &amp;         &  &apos;       ' &quot;       "  

工程结构如下：

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