初识Mybatis

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Mybatis

基本信息

Mybatis是基于java的持久层框架，避免了繁琐的JDBC代码、手动设置参数和获取返回的结果集。mybatis可以使用xml配置文件或者注解的方式进行配置。

功能架构

  1. api接口层：提供给外部使用的接口API，开发人员通过这些本地API来操纵数据库。接口层一接收到调用请求就会调用数据处理层来完成具体的数据处理。
  2. 数据处理层：负责具体的SQL查找、SQL解析、SQL执行和执行结果映射处理等。它主要的目的是根据调用的请求完成一次数据库操作。
  3. 基础支撑层：负责最基础的功能支撑，包括连接管理、事务管理、配置加载和缓存处理，这些都是共用的东西，将他们抽取出来作为最基础的组件。为上层的数据处理层提供最基础的支撑。

执行过程

graph TD
创建SqlSessionFactory --> 创建sqlSession --> 执行sql --> 关闭session
创建sqlSession --> 获取mapper
获取mapper --> 执行sql
执行sql --> 提交事务
提交事务 --> 关闭session

也可以集成到springboot当中，直接注入到bean中：

@Configuration
@MapperScan(basePackages = "com.example.mybatis.dao", sqlSessionFactoryRef = "exampleSqlSessionFactory")
public class ExampleDataSourceConfig {

    @Bean(name = "exampleDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.example")
    public DataSource exampleDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "exampleSqlSessionFactory")
    public SqlSessionFactory exampleSqlSessionFactory(@Qualifier("examplelDataSource") DataSource datasource)
            throws Exception {
        SqlSessionFactoryBean bean = new SqlSessionFactoryBean();
        bean.setDataSource(datasource);
        bean.setConfiguration(configuration());
        bean.setMapperLocations(
                new PathMatchingResourcePatternResolver().getResources("classpath*:mappers/*.xml"));
        return bean.getObject();
    }

    @Bean("exampleSqlSessionTemplate")
    public SqlSessionTemplate exampleSqlSessionTemplate(
            @Qualifier("exampleSqlSessionFactory") SqlSessionFactory sessionfactory) {
        return new SqlSessionTemplate(sessionfactory);
    }

    @Bean
    @ConfigurationProperties(prefix = "mybatis.configuration")
    public org.apache.ibatis.session.Configuration configuration(){
        return new org.apache.ibatis.session.Configuration();
    }

整合包 mybatis-spring-boot-starter

  1. 导入依赖包
  2. 配置文件
  3. 编写mybatis配置
  4. 编写sql
  5. service层调用dao层
  6. controller调用service层

mybatis所对应的mapper.xml文件，实体类,接口文件等，都可以使用mybatis-generator文件去自动生成。

动态SQL

Mybatis最强大的功能就是可支持动态sql语句的编写。 使用mybatis-generator文件后，会自动生成mapper.xml，包含基本的增删改查的语句。

也可以再自定义一些sql语句。

<?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.sensetime.med.bd.project.biz.dao.UserMapper">
  <resultMap id="BaseResultMap" type="com.sensetime.med.bd.project.biz.entity.User">
    <id column="id" jdbcType="BIGINT" property="id" />
    <result column="name" jdbcType="VARCHAR" property="name" />
    <result column="age" jdbcType="INTEGER" property="age" />
    <result column="sex" jdbcType="INTEGER" property="sex" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    id, name, age, sex
  </sql>
  <select id="selectByExample" parameterType="com.sensetime.med.bd.project.biz.entity.UserExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    'false' as QUERYID,
    <include refid="Base_Column_List" />
    from user
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <select id="selectByPrimaryKey" parameterType="java.lang.Long" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from user
    where id = #{id,jdbcType=BIGINT}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Long">
    delete from user
    where id = #{id,jdbcType=BIGINT}
  </delete>
  <delete id="deleteByExample" parameterType="com.sensetime.med.bd.project.biz.entity.UserExample">
    delete from user
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" keyColumn="id" keyProperty="id" parameterType="com.sensetime.med.bd.project.biz.entity.User" useGeneratedKeys="true">
    insert into user (name, age, sex
      )
    values (#{name,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER}, #{sex,jdbcType=INTEGER}
      )
  </insert>
  <insert id="insertSelective" keyColumn="id" keyProperty="id" parameterType="com.sensetime.med.bd.project.biz.entity.User" useGeneratedKeys="true">
    insert into user
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="name != null">
        name,
      </if>
      <if test="age != null">
        age,
      </if>
      <if test="sex != null">
        sex,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="name != null">
        #{name,jdbcType=VARCHAR},
      </if>
      <if test="age != null">
        #{age,jdbcType=INTEGER},
      </if>
      <if test="sex != null">
        #{sex,jdbcType=INTEGER},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.sensetime.med.bd.project.biz.entity.UserExample" resultType="java.lang.Long">
    select count(*) from user
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update user
    <set>
      <if test="record.id != null">
        id = #{record.id,jdbcType=BIGINT},
      </if>
      <if test="record.name != null">
        name = #{record.name,jdbcType=VARCHAR},
      </if>
      <if test="record.age != null">
        age = #{record.age,jdbcType=INTEGER},
      </if>
      <if test="record.sex != null">
        sex = #{record.sex,jdbcType=INTEGER},
      </if>
    </set>
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update user
    set id = #{record.id,jdbcType=BIGINT},
      name = #{record.name,jdbcType=VARCHAR},
      age = #{record.age,jdbcType=INTEGER},
      sex = #{record.sex,jdbcType=INTEGER}
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByPrimaryKeySelective" parameterType="com.sensetime.med.bd.project.biz.entity.User">
    update user
    <set>
      <if test="name != null">
        name = #{name,jdbcType=VARCHAR},
      </if>
      <if test="age != null">
        age = #{age,jdbcType=INTEGER},
      </if>
      <if test="sex != null">
        sex = #{sex,jdbcType=INTEGER},
      </if>
    </set>
    where id = #{id,jdbcType=BIGINT}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.sensetime.med.bd.project.biz.entity.User">
    update user
    set name = #{name,jdbcType=VARCHAR},
      age = #{age,jdbcType=INTEGER},
      sex = #{sex,jdbcType=INTEGER}
    where id = #{id,jdbcType=BIGINT}
  </update>
</mapper>
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