mybatis動態sql之遍歷集合（學習foreach標簽（初探））

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 List<Employee> getEmpByForeach(@Param("ids") List<Integer> ids);
}

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">
    <!-- 查詢，要查那個就帶上那個條件 -->
    <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>
    
    <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>
</mapper>

說明：

• item：集合中元素迭代時的別名，該參數為必選。
• index：在list和數組中,index是元素的序號，在map中，index是元素的key，item是元素的value，該參數可選
• open：foreach代碼的開始符號，一般是(和close=")"合用。常用在in(),values()時。該參數可選
• separator：元素之間的分隔符，例如在in()的時候，separator=","會自動在元素中間用“,“隔開，避免手動輸入逗號導致sql錯誤，如in(1,2,)這樣。該參數可選。
• close: foreach代碼的關閉符號，一般是)和open="("合用。常用在in(),values()時。該參數可選。
• collection: 要做foreach的對象，作為入參時，List對象默認用"list"代替作為鍵，數組對象有"array"代替作為鍵，Map對象沒有默認的鍵。當然在作為入參時可以使用@Param("keyName")來設置鍵，設置keyName后，list,array將會失效。 除了入參這種情況外，還有一種作為參數對象的某個字段的時候。舉個例子：如果User有屬性List ids。入參是User對象，那么這個collection = "ids".如果User有屬性Ids ids;其中Ids是個對象，Ids有個屬性List id;入參是User對象，那么collection = "ids.id"

也就是說整個sql語句是這樣的：select * from tbl_employee where id in (1,2,3)

注意的是我們在接口中定義了傳入參數的名稱，因此在collection中可以傳入該名稱。

進行測試：

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> es = mapper.getEmpByForeach(Arrays.asList(1,2,3));
            for(Employee e:es) {
                System.out.println(e);
            }
            openSession.commit();
        } finally {
            openSession.close();
        }
        
    }
    
}

最終結果：

DEBUG 01-21 15:31:16,176 ==>  Preparing: select * from tbl_employee where id in ( ? , ? , ? )   (BaseJdbcLogger.java:145) 
DEBUG 01-21 15:31:16,241 ==> Parameters: 1(Integer), 2(Integer), 3(Integer)  (BaseJdbcLogger.java:145) 
DEBUG 01-21 15:31:16,335 <==      Total: 3  (BaseJdbcLogger.java:145) 
Employee [id=1, lastName=dema, gender=1, email=[e-mail], dept=null]
Employee [id=2, lastName=jack, gender=1, email=[e-mail], dept=null]
Employee [id=3, lastName=小紅, gender=0, email=[e-mail], dept=null]