MyBatis

MyBatis 是一个半自动 ORM 框架，支持自定义 SQL、存储过程以及高级映射。

快速开始

pom.xml

<dependencies>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.13</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis.spring.boot</groupId>
        <artifactId>mybatis-spring-boot-starter</artifactId>
        <version>3.0.3</version>
    </dependency>
</dependencies>

配置

mybatis:
  mapper-locations: classpath:mapper/*.xml
  type-aliases-package: com.example.entity
  configuration:
    map-underscore-to-camel-case: true
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

接口方式

@Mapper
public interface UserMapper {
    @Select("SELECT * FROM user WHERE id = #{id}")
    User findById(Long id);

    @Insert("INSERT INTO user(name, age) VALUES(#{name}, #{age})")
    @Options(useGeneratedKeys = true, keyProperty = "id")
    int insert(User user);

    @Update("UPDATE user SET name = #{name}, age = #{age} WHERE id = #{id}")
    int update(User user);

    @Delete("DELETE FROM user WHERE id = #{id}")
    int deleteById(Long id);
}

XML 映射

<?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.example.mapper.UserMapper">

    <resultMap id="UserResultMap" type="com.example.entity.User">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <result property="createTime" column="create_time"/>
    </resultMap>

    <select id="findById" resultMap="UserResultMap">
        SELECT * FROM user WHERE id = #{id}
    </select>

    <select id="findAll" resultMap="UserResultMap">
        SELECT * FROM user ORDER BY id DESC
    </select>

    <insert id="insert" useGeneratedKeys="true" keyProperty="id">
        INSERT INTO user(name, age, create_time)
        VALUES(#{name}, #{age}, #{createTime})
    </insert>

    <update id="update">
        UPDATE user
        SET name = #{name}, age = #{age}
        WHERE id = #{id}
    </update>

    <delete id="deleteById">
        DELETE FROM user WHERE id = #{id}
    </delete>

</mapper>

动态 SQL

<select id="search" resultMap="UserResultMap">
    SELECT * FROM user
    <where>
        <if test="name != null and name != ''">
            AND name LIKE CONCAT('%', #{name}, '%')
        </if>
        <if test="age != null">
            AND age = #{age}
        </if>
    </where>
    ORDER BY id DESC
</select>

<update id="updateSelective">
    UPDATE user
    <set>
        <if test="name != null">name = #{name},</if>
        <if test="age != null">age = #{age},</if>
    </set>
    WHERE id = #{id}
</update>

<select id="findByIds" resultMap="UserResultMap">
    SELECT * FROM user
    WHERE id IN
    <foreach collection="ids" item="id" open="(" separator="," close=")">
        #{id}
    </foreach>
</select>

<insert id="batchInsert">
    INSERT INTO user(name, age) VALUES
    <foreach collection="users" item="user" separator=",">
        (#{user.name}, #{user.age})
    </foreach>
</insert>

一对一、一对多映射

<resultMap id="OrderDetailMap" type="com.example.entity.Order">
    <id property="id" column="id"/>
    <result property="orderNo" column="order_no"/>
    <result property="userId" column="user_id"/>

    <!-- 一对一：association -->
    <association property="user" javaType="com.example.entity.User">
        <id property="id" column="user_id"/>
        <result property="name" column="user_name"/>
    </association>

    <!-- 一对多：collection -->
    <collection property="items" ofType="com.example.entity.OrderItem">
        <id property="id" column="item_id"/>
        <result property="productName" column="product_name"/>
        <result property="quantity" column="quantity"/>
    </collection>
</resultMap>

总结

1. 配置：mybatis-config.xml、mapper.xml
2. CRUD：注解方式、XML 方式
3. 动态 SQL：if、where、set、foreach
4. 映射：resultMap、association、collection