Mybatis

Mybatis

配置文件

依赖

<!-- Mybatis依赖-->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.2</version>
</dependency>
<!-- Mysql依赖 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>

核心配置文件

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="571240."/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
		<!-- 使用相对于类路径的资源引用 -->
        <mapper resource="com/gorilla/dao/userMapper.xml"/>
		<!-- 使用完全限定资源定位符（URL） -->
		<mapper url="file:///var/mappers/AuthorMapper.xml
        <!-- 使用映射器接口实现类的完全限定类名,需要配置文件名称和接口名称一致，并且位于同一目录下 -->
		<mapper class="org.mybatis.builder.AuthorMapper"/>
    </mappers>
</configuration>

Mapper.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.gorilla.dao.UserMapper">
  <select id="selectUser" resultType="com.gorilla.pojo.User">
    select * from user
  </select>
</mapper>

ResultMap

<resultMap id="UserMap" type="User">
    <!-- id为主键 -->
    <id column="id" property="id"/>
    <!-- column是数据库表的列名 , property是对应实体类的属性名 -->
    <result column="name" property="name"/>
    <result column="pwd" property="password"/>
</resultMap>
 
<select id="selectUserById" resultMap="UserMap">
    select id , name , pwd from user where id = #{id}
</select>

Maven静态资源过滤问题

<resources>
    <resource>
        <directory>src/main/java</directory>
        <includes>
            <include>**/*.properties</include>
            <include>**/*.xml</include>
        </includes>
        <filtering>false</filtering>
    </resource>
    <resource>
        <directory>src/main/resources</directory>
        <includes>
            <include>**/*.properties</include>
            <include>**/*.xml</include>
        </includes>
        <filtering>false</filtering>
    </resource>
</resources>

Mybatis工具类

public class MybatisUtils {
 
    private static SqlSessionFactory sqlSessionFactory;
 
    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    //获取SqlSession连接
    public static SqlSession getSession(){
        return sqlSessionFactory.openSession();
    }
 
}

动态SQL

if

<!--
根据作者名字和博客名字来查询博客！
如果作者名字为空，那么只根据博客名字查询，反之，则根据作者名来查询
select * from blog where title = #{title} and author = #{author}
-->
<select id="queryBlogIf" parameterType="map" resultType="blog">
    select * from blog where
    <if test="title != null">
        title = #{title}
    </if>
    <if test="author != null">
        and author = #{author}
    </if>
</select>
<!--如果title为空,查询语句为 select * from user where and author=#{author}，这是错误的 SQL 语句-->

where

<!--“where”标签会知道如果它包含的标签中有返回值的话，它就插入一个‘where’。此外，如果标签返回的内容是以AND 或 OR 开头的，则它会剔除掉-->
<select id="queryBlogIf" parameterType="map" resultType="blog">
    select * from blog
    <where>
        <if test="title != null">
            title = #{title}
        </if>
        <if test="author != null">
            and author = #{author}
        </if>
    </where>
</select>

set

<!--注意set是用的逗号隔开-->
<update id="updateBlog" parameterType="map">
    update blog
      <set>
          <if test="title != null">
              title = #{title},
          </if>
          <if test="author != null">
              author = #{author}
          </if>
      </set>
    where id = #{id};
</update>

choose

<!--有时候不想用到所有的查询条件，只想选择其中的一个，查询条件有一个满足即可，使用 choose 标签-->
<select id="queryBlogChoose" parameterType="map" resultType="blog">
    select * from blog
    <where>
        <choose>
            <when test="title != null">
                 title = #{title}
            </when>
            <when test="author != null">
                and author = #{author}
            </when>
            <otherwise>
                and views = #{views}
            </otherwise>
        </choose>
    </where>
</select>

foreach

<select id="queryBlogForeach" parameterType="map" resultType="blog">
    select * from blog
    <where>
        <!--
        collection:指定输入对象中的集合属性
        item:每次遍历生成的对象
        open:开始遍历时的拼接字符串
        close:结束时拼接的字符串
        separator:遍历对象之间需要拼接的字符串
        select * from blog where 1=1 and (id=1 or id=2 or id=3)
      -->
        <foreach collection="ids"  item="id" open="and (" close=")" separator="or">
            id=#{id}
        </foreach>
    </where>
</select>