mybatis动态sql之修改（学习set标签）

EmployeeMapperDynamicSql.java

package com.gong.mybatis.mapper;

import java.util.List;
import java.util.Map;

import org.apache.ibatis.annotations.MapKey;

import com.gong.mybatis.bean.Employee;

public interface EmployeeMapperDynamicSql {
    public List<Employee> getEmpByConditionIf(Employee employee);

    public void updateEmp(Employee employee);
}

EmployeeMapperDynamicSql.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.gong.mybatis.mapper.EmployeeMapperDynamicSql">
    <!-- 查询，要查那个就带上那个条件 -->
    <select id="getEmpByConditionIf" resultType="com.gong.mybatis.bean.Employee">
        select * from tbl_employee
        <where>
            <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>
                </otherwise>
            </choose>
        </where>
    </select>

    <update id="updateEmp">
        update tbl_employee
        set
        <if test="lastName!=null">
            last_name=#{lastName},
        </if>
        <if test="gender!=null and gender == 0 or gender == 1">
            gender=#{gender},
        </if>
        <if test="email!=null">
            email=#{email}
        </if>
        where id=#{id}
    </update>
</mapper>

结合之前的知识，我们在这里不使用set标签：

进行测试：

package com.gong.mybatis.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.gong.mybatis.bean.Employee;
import com.gong.mybatis.mapper.EmployeeMapperDynamicSql;

public class TestMybatis3 {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(is);
    }

    @Test
    public void test() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession();
        try {
            EmployeeMapperDynamicSql mapper = openSession.getMapper(EmployeeMapperDynamicSql.class);
            Employee employee = new Employee();
            employee.setId(1);
            employee.setLastName("hanbin");
//            employee.setGender("0");
//            employee.setEmail("[email protected]");
            mapper.updateEmp(employee);
            List<Employee> es = mapper.getEmpByConditionIf(new Employee());
            for(Employee e:es) {
                System.err.println(e);
            }
            openSession.commit();
        } finally {
            openSession.close();
        }

    }

}

我们先对Id=1的记录修改last_name=hanbin，结果：会报错，因为sql最后面多了个逗号

DEBUG 01-21 14:31:18,323 ==>  Preparing: update tbl_employee set last_name=?, where id=?   (BaseJdbcLogger.java:145)
DEBUG 01-21 14:31:18,366 ==> Parameters: hanbin(String), 1(Integer)  (BaseJdbcLogger.java:145) 

解决方法有两种：

第一种：使用set标签，会自动过滤掉多余的逗号

    <update id="updateEmp">
        update tbl_employee
        <set>
            <if test="lastName!=null">
                last_name=#{lastName},
            </if>
            <if test="gender!=null and gender == 0 or gender == 1">
                gender=#{gender},
            </if>
            <if test="email!=null">
                email=#{email}
            </if>
        </set>
        where id=#{id}
    </update>

结果：

DEBUG 01-21 14:46:11,726 ==>  Preparing: select * from tbl_employee   (BaseJdbcLogger.java:145)
DEBUG 01-21 14:46:11,727 ==> Parameters:   (BaseJdbcLogger.java:145)
DEBUG 01-21 14:46:11,756 <==      Total: 4  (BaseJdbcLogger.java:145)
Employee [id=1, lastName=hanbin, gender=0, email[email protected], dept=null]

第二种：使用之前学过的trim标签

    <update id="updateEmp">
        update tbl_employee
        <trim prefix="set" suffixOverrides=",">
            <if test="lastName!=null">
                last_name=#{lastName},
            </if>
            <if test="gender!=null and gender == 0 or gender == 1">
                gender=#{gender},
            </if>
            <if test="email!=null">
                email=#{email}
            </if>
        </trim>
        where id=#{id}
    </update>

并修改id=1的last_name为dema，gender为1，email为[email protected]

            employee.setId(1);
            employee.setLastName("dema");
            employee.setGender("1");
            employee.setEmail("[email protected]");

结果：

DEBUG 01-21 14:53:38,851 ==>  Preparing: select * from tbl_employee   (BaseJdbcLogger.java:145)
DEBUG 01-21 14:53:38,852 ==> Parameters:   (BaseJdbcLogger.java:145)
DEBUG 01-21 14:53:38,885 <==      Total: 4  (BaseJdbcLogger.java:145)
Employee [id=1, lastName=dema, gender=1, email[email protected], dept=null]
Employee [id=2, lastName=jack, gender=1, email[email protected], dept=null]
Employee [id=3, lastName=小红, gender=0, email[email protected], dept=null]
Employee [id=4, lastName=小明, gender=0, email[email protected], dept=null]

原文地址：https://www.cnblogs.com/xiximayou/p/12221761.html