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学习MyBatis必知必会(7)~注解开发、动态SQL

作者:互联网


一、MyBatis的注解开发

1、配置映射关系【使用注解的方式】:

<!-- 全局的配置文件 --> 
<configuration>
   <!-- 2、关联映射文件/ 关联Mapper接口  -->	
	<mappers>
		<!--  <mapper resource="com/shan/hello/mapper/UserMapper.xml"/>-->
		<mapper class="com.shan.hello.mapper.UserMapper"/>
	</mappers>
  </configuration>

2、通过注解,把sql和映射写到Mapper接口:

public interface UserMapper {

	@Insert("insert into t_user (name, salary) values (#{name}, #{salary});")
	@Options(useGeneratedKeys = true,keyProperty = "id")
	void save(User user);
	
	@Delete("delete from t_user where id = #{id};")
	void delete(Long id);
	
	@Update("update t_user set name = #{name}, salary = #{salary} where id = #{id};")
	void update(User user);
//	void update(User user, Long id);//错误:myBatis默认只能传递一个参数
	
	@Select("select id u_id, name as u_name, salary u_salary from t_user where id = #{id}")
	@Results(id="BaseResultMap", value= {
			@Result(column = "u_id",property = "id"),
			@Result(column = "u_name",property = "name"),
			@Result(column = "u_salary",property = "salary")
	})
	User get(Long id);
	
	@Select("select id u_id, name as u_name, salary u_salary from t_user")
	@ResultMap("BaseResultMap")
	List<User> getListAll();
}

3、测试(这里以测试查询为例):

	/* 测试查询 */
	@Test
	public void testGet() throws IOException {
		SqlSession session = MyBatisUtil.getSession();
		UserMapper userMapper = session.getMapper(UserMapper.class);
		User user = userMapper.get(2L);
		System.out.println(user);
		//5、关闭资源
		session.close();
	}



二、动态SQL 【类似JSTL(java标准标签库)语法】

1、if 举例:

  <!-- 映射文件 -->
  <select id="select" resultType="Employee">
  	select * from employee 
  	<if test="minSalary != null">
  		where salary >= #{minSalary}
  	</if>
  </select>

2、choose (when, otherwise) 举例:

 <!-- 映射文件 -->
 <select id="select" resultType="Employee">
  		select * from employee where 1=1
  	<if test="minSalary != null">
  		and salary >= #{minSalary}
  	</if>
  	<choose>
  		<when test="deptId > 0">and deptId = #{deptId}</when>
  		<otherwise>and deptId is not null</otherwise>
  	</choose>
  </select>

3-1、trim (where, set)- where 举例:

  <!-- 映射文件 -->
  <select id="select" resultType="Employee">
  		select * from employee 
	<where>
		 <if test="minSalary != null">
  				and salary >= #{minSalary}
  	   	</if>
  		<if test="maxSalary != null">
  			and salary &lt;= #{maxSalary}
  		</if>
  		<choose>
  			<when test="deptId > 0">and deptId = #{deptId}</when>
  			<otherwise>and deptId is not null</otherwise>
  			</choose>
	</where>
  </select>

3-2、trim (where, set)-set 举例:

<update id="updateAuthorIfNecessary">
  update Author
    <set>
      <if test="username != null">username=#{username},</if>
      <if test="password != null">password=#{password},</if>
      <if test="email != null">email=#{email},</if>
      <if test="bio != null">bio=#{bio}</if>
    </set>
  where id=#{id}
</update>

3-3、trim (where, set)-trim :

<trim prefix="" prefixOverrides="" suffix="" suffixOverrides="">
	<!--trim 包含的动态 SQL-->
</trim>

prefix – 在这个字符串之前插入 prefix 属性值。

prefixOverrides – 并且字符串的内容以 prefixOverrides 中的内容开头(可以包含管道符号),那么使用 prefix 属性值替换内容的开头。

suffix – 在这个字符串之后插入 suffix 属性值。

suffixOverrides –并且字符串的内容以 suffixOverrides 中的内容结尾(可以包含管道符号),那么使用 suffix 属性值替换内容的结尾。


4、foreach 举例1:

/* Mapper接口 */
void batchDelete(@Param("ids")List<Long> ids);


<!-- 映射文件 -->
 <!-- 
  	foreach 元素: collection属性:表示要迭代的集合或数组【的类型,若是通过Parm注解,可以直接写上Map中的key,而不用填写类型】
  				  open属性:在集合迭代之前,要拼接的符号   close 属性:在集合迭代之后要拼接的符号
  				  separator属性:迭代的元素之间的分割符号
  				  item属性:每个被迭代的元素
  				  index属性:迭代的索引
   -->
  <delete id="batchDelete">
  	delete from employee where id in
  	<foreach collection="ids" open="(" close=")" separator="," item="id">
  		#{id}
  	</foreach>
  </delete>

■ foreach 举例2:

/* Mapper接口 */
void batchSave(@Param("emps")List<Employee>emps);

  <!-- 映射文件 -->
  <insert id="batchSave">
  	insert into employee (name, sn, salary) values 
  	<foreach collection="emps" separator="," item="e">
  		(#{e.name}, #{e.sn}, #{e.salary})
  	</foreach>
  </insert>

5、其他(bind,sql,include) 举例-高级分页查询:

■ sql,include 的例子:

<!-- 映射文件 -->
<mapper namespace="com.shan.hello.mapper.EmployeeMapper">
	<sql id="base_where">
		<where>
			<if test="keyword != null">
				<!--and name like #{%name%}; 要使用字符串函数concat进行拼接呀 -->
				<!-- and name like concat('%', #{name}, '%') or sn like concat('%', #{sn},'%'); qo查询对象,也没有属性name,sn呀 -->
				and (name like concat('%', #{keyword}, '%') or sn like concat('%', #{keyword}, '%'))
			</if>
			<if test="minSalary != null">
				and salary >= #{minSalary}
			</if>
			<if test="maxSalary != null">
				and salary &lt;= #{maxSalary}
			</if>
			<if test="deptId > 0">
				and deptId = #{deptId}
			</if>
		</where>
	</sql>
	
	<select id="queryForList" resultType="Employee">
		select id, name, sn, salary from employee
		<include refid="base_where"/>
	</select>

	<select id="queryForCount" resultType="int">
		select count(id) from employee
		<include refid="base_where"/>
	</select>

</mapper>

■ bind(跟concat一样是用于拼接字符串) 的例子:

<if test="keyword != null">
	<!--and name like #{%name%}; 要使用字符串函数concat进行拼接呀 -->
	<!-- and name like concat('%', #{name}, '%') or sn like concat('%', #{sn},'%'); qo查询对象,也没有属性name,sn呀 -->
	<!-- and (name like concat('%', #{keyword}, '%') or sn like concat('%', #{keyword}, '%')) -->
    
	<bind name="keywordLike" value="'%' + keyword + '%'"/>
			and (name like #{keywordLike} or sn like #{keywordLike})
</if>

标签:salary,deptId,name,必知,user,SQL,MyBatis,where,id
来源: https://www.cnblogs.com/shan333/p/15864333.html