zoukankan      html  css  js  c++  java
  • 04、MyBatis DynamicSQL(Mybatis动态SQL)

    1.动态SQL简介

      动态 SQL是MyBatis强大特性之一.

      动态 SQL 元素和使用 JSTL 或其他类似基于 XML 的文本处理器相似.

      MyBatis 采用功能强大的基于 OGNL 的表达式来简化操作.

     

    2.if

     

    1).实现DynamicSQL

     

    public interface EmployeeMapperDynamicSQL {
    	public List<Employee> getEmpsByCondtionIf(Employee employee);
    }
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- 查询员工:携带指定字段查询条件就带上该字段的值 -->
    	 <!-- public List<Employee> getEmpsByCondtionIf(Employee employee) -->
    	 <select id="getEmpsByCondtionIf" resultType="com.atguigu.mybatis.bean.Employee">
    	 	select * from tbl_employee
    	 	<!-- where:根据条件包含 where 子句 -->
    	 	where
    		 	<!-- test:判断表达式(OGNL) -->
    		 	<!-- OGNL语法参照PPT或者官方文档:http://commons.apache.org/proper/commons-ognl/language-guide.html -->
    		 	<!-- 从参数中取值进行判断,如果遇到特殊符号去写转义字符,查W3C HTML ISO-8859-1 参考手册 -->
    		 	<if test="id!=null">
    		 		id=#{id}
    		 	</if>
    		 	<!-- <if test="lastName!=null and lastName!="""> -->
    		 	<!-- <if test="lastName!=null && lastName!=''"> -->
    		 	<if test="lastName!=null && lastName!=""">
    		 		and last_name like #{lastName}
    		 	</if>
    		 	<if test="email!=null and email.trim()!=""">
    		 		 and email=#{email}
    		 	</if>
    		 	<!-- ognl会进行字符串与数字的转换判断  "0"==0 -->
    		 	<if test="gender==0 or gender==1">
    		 		and gender=#{gender}
    		 	</if>
    	 </select>
    </mapper>
    

      

    //			select * from tbl_employee WHERE id=? and last_name like ? and email=?
    //			Employee employee  = new Employee(3, "%e%","atguigu@atguigu.com", null);
    			//select * from tbl_employee WHERE id=? and last_name like ?
    			Employee employee  = new Employee(null, "%e%",null, null);
    			List<Employee> emps = mapper.getEmpsByCondtionIf(employee);
    			for(Employee emp:emps) {
    				System.out.println(emp);
    			}
    

      

    2.choose

      有时候,我们不想使用所有的条件,而只是想从多个条件中选择一个使用.针对这种情况,MyBatis 提供了 choose 元素,它有点像 Java 中的 switch 语句.

     

    	public List<Employee> getEmpByConditionChoose(Employee employee);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- public List<Employee> getEmpByConditionChoose(Employee employee) -->
    	 <select id="getEmpByConditionChoose" resultType="com.atguigu.mybatis.bean.Employee">
    	 	select * from tbl_employee 
    	 	<where>
    	 		<!-- 如果带了id就用id查,如果带了lastName就用lastName查;只会进入其中一个 -->
    	 		<choose>
    	 				 			<when test="id!=null">
    	 				id=#{id}
    	 			</when>
    	 			<when test="lastName!=null">
    	 				last_name like #{lastName}
    	 			</when>
    	 			<when test="email!=null">
    	 				email = #{email}
    	 			</when>
    	 			<otherwise>
    	 				gender = 0
    	 			</otherwise>
    	 		</choose>
    	 	</where>
    	 </select>
    </mapper>
    

      

    			//测试choose
    			Employee employee  = new Employee(3, "%e%",null, null);
    			List<Employee> list = mapper.getEmpByConditionChoose(employee);
    			for(Employee emp:list) { 
    				System.out.println(emp); 
    			}
    

      

    3.trim

    1).where

     

    	public List<Employee> getEmpsByCondtionTrim(Employee employee);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- public List<Employee> getEmpsByCondtionTrim(Employee employee) -->
    	 <select id="getEmpsByCondtionTrim" resultType="com.atguigu.mybatis.bean.Employee">
    	 	select * from tbl_employee
    	 	<!-- 后面多出的and或者or where标签不能解决,我们使用trim定制where元素功能  -->
    	 	<!-- 自定义字符串的截取规则 -->
    	 	<!-- trim:根据条件包含 where 子句 -->
    	 	<!-- trim标签体中是整个字符串拼串 后的结果 -->
    	 	<!-- 通过自定义 trim 元素来定制 where 元素的功能 -->
    	 	<!-- prefix:前缀;prefix给拼串后的整个字符串加一个前缀  如:where <===> <trim prefix="where"> -->
    	 	<!-- prefixOverrides:前缀覆盖;去掉整个字符串前面多余的字符 -->
    	 	<!-- suffix:后缀;suffix给拼串后的整个字符串加一个后缀 -->
    	 	<!-- suffixOverrides:后缀覆盖;去掉整个字符串后面多余的字符 -->
    	 	<trim prefix="where" suffixOverrides="and">
    		 	<if test="id!=null">
    		 		 id=#{id} and
    		 	</if>
    		 	<if test="lastName!=null && lastName!=""">
    		 		 last_name like #{lastName} and
    		 	</if>
    		 	<if test="email!=null and email.trim()!=""">
    		 		 email=#{email} and
    		 	</if>
    		 	<!-- ognl会进行字符串与数字的转换判断  "0"==0 -->
    		 	<if test="gender==0 or gender==1">
    		 		gender=#{gender}
    		 	</if>
    		 </trim>
    	 </select>
    </mapper>
    

      

    	@Test
    	public void testDynamicSql() throws IOException {
    		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
    		SqlSession openSession = sqlSessionFactory.openSession();
    		try {
    			EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
    //			select * from tbl_employee WHERE id=? and last_name like ? and email=?
    //			Employee employee  = new Employee(3, "%e%","atguigu@atguigu.com", null);
    			//select * from tbl_employee WHERE id=? and last_name like ?
    			Employee employee  = new Employee(3, "%e%",null, null);
    			List<Employee> emps = mapper.getEmpsByCondtionIf(employee);
    			for(Employee emp:emps) {
    				System.out.println(emp);
    			}
    			
    			//查询的时候如果某些条件没带可能sql拼装会有问题
    			//1、给where后面加上1=1,以后的条件都and xxx.
    			//2、mybatis使用where标签来将所有的查询条件包括在内。
    				//mybatis就会将where标签中拼装的sql,多出来的and或者or去掉
    				//where只会去掉第一个多出来的and或者or。
    
    			//测试Trim
    			List<Employee> emps2 = mapper.getEmpsByCondtionTrim(employee);
    			for(Employee emp:emps2) {
    				System.out.println(emp);
    			}
    			
    		} finally {
    			//  : handle finally clause
    			openSession.close();
    		}
    	}
    

      

    2).set

    ①.使用set更新

    	public void  updateEmp(Employee employee);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <update id="updateEmp">
    	 	<!-- set:更新拼串  -->
    	 	<!-- set标签的使用 -->
    	 	update tbl_employee 
     	 	<set>
    	 		<if test="lastName!=null">
    				last_name=#{lastName},
    			</if>
    			<if test="email!=null">
    				email=#{email},
    			</if>
    			<if test="gender!=null">
    				gender=#{gender}
    			</if>
    	 	</set>  
    	 	where id=#{id} 
    	 </update>
    </mapper>
    

      

    			//调试set标签 
    			Employee employee = new Employee(1, "Adminn",null, null); 
    			mapper.updateEmp(employee);
    			openSession.commit();
    

      

    ②.使用trim拼串更新

    	public void  updateEmp(Employee employee);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- public void  updateEmp(Employee employee) -->
    	 <update id="updateEmp">
    	 	<!-- Trim:更新拼串  -->
    		update tbl_employee 
    		<trim prefix="set" suffixOverrides=",">
    			<if test="lastName!=null">
    				last_name=#{lastName},
    			</if>
    			<if test="email!=null">
    				email=#{email},
    			</if>
    			<if test="gender!=null">
    				gender=#{gender}
    			</if>
    		</trim>
    		where id=#{id} 
    	 </update>
    </mapper>
    

      

    			//调试set标签 
    			Employee employee = new Employee(1, "Adminn",null, null); 
    			mapper.updateEmp(employee);
    			openSession.commit();
    

      

    4.foreach

     

      动态 SQL 的另外一个常用的必要操作是需要对一个集合进行遍历,通常是在构建 IN 条件语句的时候.

     

      当迭代列表、集合等可迭代对象或者数组时;index是当前迭代的次数,item的值是本次迭代获取的元素.

      当使用字典(或者Map.Entry对象的集合)时,index是键,item是值.

    1).MySQL

    (1).遍历记录

    	//查询员工id'在给定集合中的
    	public List<Employee> getEmpsByConditionForeach(@Param("ids")List<Integer> ids);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- public List<Employee> getEmpsByConditionForeach(List<Integer> ids) -->
    	 <select id="getEmpsByConditionForeach" resultType="com.atguigu.mybatis.bean.Employee">
    	 	<!-- collection:指定要遍历的集合;list类型的参数会特殊处理封装在map中,map的key就是list -->
    	 	<!-- item:当前遍历出的元素赋值给指定的变量 -->
    	 	<!-- separator:每个元素之间的分隔符 -->
    	 	<!-- open:遍历出所有结果拼接一个开始的字符 -->
    	 	<!-- close:遍历出所有结果拼接一个结束的字符 -->
    	 	<!-- index:索引;遍历list的时候是index就是索引,item就是当前值;遍历map的时候index表示的就是map的key,item就是map的值 -->
    	 	<!-- #{变量名}:能取出变量的值也就是当前遍历出的元素 -->
    	 	select * from tbl_employee
    	 	<foreach collection="ids" item="item_id" separator="," open="where id in(" close=")">
    	 		#{item_id}
    	 	</foreach>
    	 </select>
    </mapper>
    

      

    			//测试foreach
    			List<Employee> list = mapper.getEmpsByConditionForeach(Arrays.asList(1,2,3,4));
    			for(Employee emp : list) {
    				System.out.println(emp);
    			}
    

      

    (2).批量保存记录1

    	public void addEmps(@Param("emps")List<Employee> emps);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- 批量保存数据 -->
    	 <!-- MySQL下批量保存:可以foreach遍历   mysql支持values(),(),()语法 -->
    	 <!-- public void addEmps(@Param("emps")List<Employee> emps) -->
    	 <!-- insert 方式一 -->
    	 <!-- 推荐使用inert 方式一 -->
     	 <insert id="addEmps">
    	 	insert into tbl_employee(last_name,email,gender,d_id)
    		values
    		<foreach collection="emps" item="emp" separator=",">
    			(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
    		</foreach>
    	 </insert> 
    </mapper>
    

      

    			List<Employee> emps = new ArrayList<>();
    			emps.add(new Employee(null, "smith", "smith@atguigu.com", "1",new Department(1)));
    			emps.add(new Employee(null, "allen", "allen@atguigu.com", "0",new Department(1)));
    			mapper.addEmps(emps);
    			openSession.commit();
    

      

    (3).批量保存记录2

    	public void addEmps(@Param("emps")List<Employee> emps);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- insert 方式二 -->
    	 <!-- public void addEmps(@Param("emps")List<Employee> emps) -->
    	 <!-- 这种方式需要数据库连接属性allowMultiQueries=true;
    	 	这种分号分隔多个sql可以用于其他的批量操作(删除,修改) -->
    	  <insert id="addEmps">
    	 	<foreach collection="emps" item="emp" separator=";">
    	 		insert into tbl_employee(last_name,email,gender,d_id)
    	 		values(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
    	 	</foreach>
    	 </insert> 
    </mapper>
    

      

    			List<Employee> emps = new ArrayList<>();
    			emps.add(new Employee(null, "smith", "smith@atguigu.com", "1",new Department(1)));
    			emps.add(new Employee(null, "allen", "allen@atguigu.com", "0",new Department(1)));
    			mapper.addEmps(emps);
    			openSession.commit();
    

      

    2).Oracle

    (1).批量保存1

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <insert id="addEmps" databaseId="oracle">
    	 	<!-- oracle第一种批量方式 -->
    	 	<!-- <foreach collection="emps" item="emp" open="begin" close="end;">
    	 		insert into employees(employee_id,last_name,email) 
    			    values(employees_seq.nextval,#{emp.lastName},#{emp.email});
    	 	</foreach> 
    	 </insert>
    </mapper>
    

    (2).批量保存2

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <insert id="addEmps" databaseId="oracle">
    	 	<!-- oracle第二种批量方式  -->
    	 	insert into employees(
    	 		<!-- 引用外部定义的sql -->
    	 		<include refid="insertColumn">
    	 			<property name="testColomn" value="abc"/>
    	 		</include>
    	 	)
    	 			<foreach collection="emps" item="emp" separator="union"
    	 				open="select employees_seq.nextval,lastName,email from("
    	 				close=")">
    	 				select #{emp.lastName} lastName,#{emp.email} email from dual
    	 			</foreach>
    	 </insert>
    </mapper>
    

      

    5.bind

      bind 元素可以从 OGNL 表达式中创建一个变量并将其绑定到上下文.

     

    1).bind

      若在 mybatis 配置文件中配置了 databaseIdProvider , 则可以使用 “_databaseId”变量,这样就可以根据不同的数据库厂商构建特定的语句.

    	public List<Employee> getEmpsTestInnerParameter(Employee employee);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- public List<Employee> getEmpsTestInnerParameter(Employee employee) -->
    	 <!-- mybatis默认还有两个内置参数:_parameter|_databaseId -->
    	 <!-- _parameter:代表整个参数;单个参数:_parameter就是这个参数;多个参数:参数会被封装为一个map,_parameter就是代表这个map -->
    	 <!-- _databaseId:如果配置了databaseIdProvider标签;_databaseId就是代表当前数据库的别名 -->
    	 <select id="getEmpsTestInnerParameter" resultType="com.atguigu.mybatis.bean.Employee">
    		<!-- bind:可以将OGNL表达式的值绑定到一个变量中,方便后来引用这个变量的值 -->
    	  		<if test="_databaseId=='mysql'">
    	  			select * from tbl_employee
    	  			<if test="_parameter!=null">
    	  				where last_name like #{lastName}
    	  			</if>
    	  		</if>
    	  		<if test="_databaseId=='oracle'">
    	  			select * from employees
    	  			<if test="_parameter!=null">
    	  				where last_name like #{_parameter.lastName}
    	  			</if>
    	  		</if>
    	  </select>
    </mapper>
    

      

    	@Test
    	public void testInnerParam() throws IOException{
    		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
    		SqlSession openSession = sqlSessionFactory.openSession();
    		try{
    			EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
    			Employee employee2 = new Employee();
    			employee2.setLastName("%e%");
    			List<Employee> list = mapper.getEmpsTestInnerParameter(employee2);
    			for (Employee employee : list) {
    				System.out.println(employee);
    			}
    		}finally{
    			openSession.close();
    		}
    	}
    

      

    2).SQL片段

    	public void addEmps(@Param("emps")List<Employee> emps);
    

      

    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL">
    	 <!-- insert 方式三 -->
    	<insert id="addEmps">
    		insert into tbl_employee(
    			<include refid="insertColumn"></include>
    	 	) 
    		values
    		<foreach collection="emps" item="emp" separator=",">
    			(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})
    		</foreach>
    	</insert>
    	<!-- 抽取可重用的sql片段;方便后面引用  -->
    	<!-- 1、sql抽取:经常将要查询的列名,或者插入用的列名抽取出来方便引用 -->
    	<!-- 2、include来引用已经抽取的sql -->
    	<!-- 3、include还可以自定义一些property,sql标签内部就能使用自定义的属性 -->
    	<!-- include-property:取值的正确方式${prop} #{不能使用这种方式} -->  			
    	<sql id="insertColumn">
    		<if test="_databaseId=='oracle'">
    			employee_id,last_name,email
    		</if>
    		<if test="_databaseId=='mysql'">
    			last_name,email,gender,d_id
    		</if>
    	</sql>
    </mapper>
    

      

    	@Test
    	public void testBatchSave() throws IOException {
    		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
    		SqlSession openSession = sqlSessionFactory.openSession();
    		try {
    			EmployeeMapperDynamicSQL mapper = openSession.getMapper(EmployeeMapperDynamicSQL.class);
    			List<Employee> emps = new ArrayList<>();
    			emps.add(new Employee(null, "smith", "smith@atguigu.com", "1",new Department(1)));
    			emps.add(new Employee(null, "allen", "allen@atguigu.com", "0",new Department(1)));
    			mapper.addEmps(emps);
    			openSession.commit();
    		}finally {
    			openSession.close();
    		}
    	}
    

    6.OGNL

     

    参考文档:http://commons.apache.org/proper/commons-ognl/language-guide.html

    https://mybatis.org/mybatis-3/zh/dynamic-sql.html

  • 相关阅读:
    JavaScript讲义(三)
    jQuery学习(五)
    jQuery学习(七)
    JavaScript讲义(一)
    jQuery学习(六)
    这些东西不宜空腹吃[转]
    pexpect实现的ssh连接(pexpect可从sourceforge下载)
    Using the commandline connection tool Plink
    【转】系统管理类DOS命令汇总
    挺有意思的QQ资料
  • 原文地址:https://www.cnblogs.com/CSAH/p/13150179.html
Copyright © 2011-2022 走看看