mybatis动态sql之foreach补充（一）

EmployeeMapperDynamicSql.java

package com.gong.mybatis.mapper;

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

import org.apache.ibatis.annotations.MapKey;
import org.apache.ibatis.annotations.Param;

import com.gong.mybatis.bean.Employee;

public interface EmployeeMapperDynamicSql {
    public List<Employee> getEmpByConditionIf(Employee employee);
    
    public void updateEmp(Employee employee);
    
    public List<Employee> getEmpByForeach(@Param("ids") List<Integer> ids);
    
    public List<Employee> getEmpByForeach2(List<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 
        <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>
    
    <select id="getEmpByForeach" resultType="com.gong.mybatis.bean.Employee">
        select * from tbl_employee where id in
        <foreach collection="ids" item="item_id" separator="," open="(" close=")">
            #{item_id}
        </foreach>
    </select>
    
    <select id="getEmpByForeach2" resultType="com.gong.mybatis.bean.Employee">
        select * from tbl_employee where id in
        <foreach collection="list" item="item" separator="," open="(" close=")">
            #{item.id}
        </foreach>
    </select>
</mapper>

说明，现在我们使用public List<Employee> getEmpByForeach2(List<Employee> employee);，传入的是一个Employee集合，那么此时我们应该怎么使用foreach呢？

我们可以在collection中对应着list类型，即collection="list"。

测试：

package com.gong.mybatis.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
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);
            List<Employee> emps = new ArrayList<Employee>();
            Employee e1 = new Employee();
            e1.setId(1);
            Employee e2 = new Employee();
            e2.setId(2);
            emps.add(e1);
            emps.add(e2);
            List<Employee> es = mapper.getEmpByForeach2(emps);
            for(Employee e:es) {
                System.out.println(e);
            }
            openSession.commit();
        } finally {
            openSession.close();
        }
        
    }
    
}

结果：

DEBUG 01-21 16:21:28,692 ==>  Preparing: select * from tbl_employee where id in ( ? , ? )   (BaseJdbcLogger.java:145) 
DEBUG 01-21 16:21:28,783 ==> Parameters: 1(Integer), 2(Integer)  (BaseJdbcLogger.java:145) 
DEBUG 01-21 16:21:28,813 <==      Total: 2  (BaseJdbcLogger.java:145) 
Employee [id=1, lastName=dema, gender=1, email=dema@qq.com, dept=null]
Employee [id=2, lastName=jack, gender=1, email=675544321@qq.com, dept=null]

成功的通过id将对象取出来。

当然，我们也可以取别名：

public List<Employee> getEmpByForeach2(@Param("emps") List<Employee> employee);

然后在使collection="emps"，其余不变，还是可以达到一样的效果。