mybatis如何封裝List<String>類型屬性

更新時(shí)間：2023年12月06日 09:47:45 作者：hhtSeeTheWorld

這篇文章主要介紹了mybatis如何封裝List<String>類型屬性問題,具有很好的參考價(jià)值,希望對(duì)大家有所幫助,如有錯(cuò)誤或未考慮完全的地方,望不吝賜教

數(shù)據(jù)庫

有一個(gè)班級(jí)表

然后還有一個(gè)學(xué)生表

需要封裝成的對(duì)象

/*
 *@author huanghaitao
 *@description
 *@Date 2022/1/27
 */
@Data
public class AClassAndStudent {

    private Integer classId;

    private String className;
    
    private List<String> stuNames;
}

第一種寫法

封裝ResultMap寫法

   <resultMap id="AClassAndStudent" type="com.ruoyi.system.domain.AClassAndStudent">
        <result column="class_id" property="classId"/>
        <result column="class_name" property="className"/>
        <collection property="stuNames" ofType="string">
            <constructor>
                <arg column="stu_name"/>
            </constructor>
        </collection>
    </resultMap>

sql語句

<select id="testSelectSql" resultMap="AClassAndStudent">
    select c.id   class_id,
           c.name class_name,
           s.name stu_name
    from class c
             left join student s on c.id = s.class_id
    where c.id = 1
</select>

打印結(jié)果

AClassAndStudent(classId=1, className=3班, stuNames=[張三, 李四, 王二, 趙六])

第二種寫法

    <resultMap id="AClassAndStudent" type="com.ruoyi.system.domain.AClassAndStudent">
        <result column="class_id" property="classId"/>
        <result column="class_name" property="className"/>
        <collection property="stuNames" column="class_id" ofType="string" select="selectStuName"/>
    </resultMap>
 
    <select id="testSelectSql" resultMap="AClassAndStudent">
        select c.id   class_id,
               c.name class_name
        from class c
        where c.id = 1
    </select>

    <select id="selectStuName" resultType="java.lang.String">
        select name stu_name
        from Student
        where class_id = 1
    </select>

上面那個(gè)爆紅不用管的

sql語句打印有點(diǎn)區(qū)別

但是結(jié)果是一樣的

AClassAndStudent(classId=1, className=3班, stuNames=[張三, 李四, 王二, 趙六])

第三種寫法

修改封裝方式

新建一個(gè)學(xué)生類

/*
 *@author huanghaitao
 *@description
 *@Date 2022/1/27
 */
@Data
public class AStudent {

    private Integer id;
    private Integer classId;
    private String name;

}

一個(gè)班級(jí)類，這個(gè)班級(jí)類包含學(xué)生類

import java.util.List;
@Data
public class AClassContainStudent {

    private Integer id;

    private String name;

    private List<AStudent> studentList;
}

這樣的話，ResultMap寫法是下面這樣的

<resultMap id="AClassContainStudent" type="com.ruoyi.system.domain.AClassContainStudent">
    <id column="class_id" property="id"/>
    <result column="class_name" property="name"/>
    <collection property="studentList" resultMap="AStudent"/>
</resultMap>

<resultMap id="AStudent" type="com.ruoyi.system.domain.AStudent">
    <id column="stu_id" property="id"/>
    <result column="class_id" property="classId"/>
    <result column="stu_name" property="name"/>
</resultMap>

<select id="testSelectSqlTwo" resultMap="AClassContainStudent">
    select c.id   class_id,
           c.name class_name,
           s.id   stu_id,
           s.name stu_name
    from class c
             left join student s on c.id = s.class_id
    where c.id = 1
</select>

打印的結(jié)果

AClassContainStudent(id=1, name=3班, studentList=[AStudent(id=1,
classId=1, name=張三), AStudent(id=2, classId=1, name=李四),
AStudent(id=3, classId=1, name=王二), AStudent(id=4, classId=1,
name=趙六)])