SSM 实战项目①丨图书管理系统 丨(3) MyBatis Generator 拓展：支持多表联合操作

本篇隶属于《SSM 实战项目①丨图书管理系统 》

详情请见：SSM 实战项目①丨图书管理系统 丨(0) 项目概要及本系列介绍

---

1. 使用 MBG 生成相关文件

SSM 实战项目①丨图书管理系统 丨(2) MyBatis Generator 的基本使用

2. 明确目标

• 查看数据库表

  reader_tbl 中有 operator_id 属性，对应到 manager_tbl，我们希望在查询 reader 信息的时候，顺带把 manager 的信息也查询到。

3. 对 Reader 实体类进行改造

//1. 添加一个 Manager 属性，用作联合查询
private Manager manager;


//2. 为 manger 属性生成 getter 和 setter 方法
public Manager getManager() {
    return manager;
}

public void setManager(Manager manager) {
    this.manager = manager;
}


//3. 生成无参构造函数
public Reader() {
}

//4. 生成有参构造函数（不要带上 manager）
public Reader(Integer readerId, String readerName, String readerGender, String readerBarcode, String readerProfession, Date readerBirth, String readerDocumentType, String readerDocumentNumber, String readerEmail, Date readerRegisterDate, Integer borrowedBookCount, Integer remainingBookCount, Integer operatorId) {
    this.readerId = readerId;
    this.readerName = readerName;
    this.readerGender = readerGender;
    this.readerBarcode = readerBarcode;
    this.readerProfession = readerProfession;
    this.readerBirth = readerBirth;
    this.readerDocumentType = readerDocumentType;
    this.readerDocumentNumber = readerDocumentNumber;
    this.readerEmail = readerEmail;
    this.readerRegisterDate = readerRegisterDate;
    this.borrowedBookCount = borrowedBookCount;
    this.remainingBookCount = remainingBookCount;
    this.operatorId = operatorId;
}
//5. 生成 toString()方法：带上 manager（注意，manager实体类也要加上 toString()方法）
@Override
public String toString() {
  return "Reader{" +
    "readerId=" + readerId +
    ", readerName='" + readerName + '\'' +
    ", readerGender='" + readerGender + '\'' +
    ", readerBarcode='" + readerBarcode + '\'' +
    ", readerProfession='" + readerProfession + '\'' +
    ", readerBirth=" + readerBirth +
    ", readerDocumentType='" + readerDocumentType + '\'' +
    ", readerDocumentNumber='" + readerDocumentNumber + '\'' +
    ", readerEmail='" + readerEmail + '\'' +
    ", readerRegisterDate=" + readerRegisterDate +
    ", borrowedBookCount=" + borrowedBookCount +
    ", remainingBookCount=" + remainingBookCount +
    ", operatorId=" + operatorId +
    ", manager=" + manager +
    '}';
}

4. 改造 ReaderMapper.xml

PS：这里进行改造的时候，我们可以参考 MBG 自动生成的部分，然后进行添加改造既即可，如下：

[1] 新增一个带 manager 的结果集

<resultMap id="ResultMapWithManager" type="com.bean.Reader">
  <id column="reader_id" jdbcType="INTEGER" property="readerId" />
  <result column="reader_name" jdbcType="VARCHAR" property="readerName" />
  <result column="reader_gender" jdbcType="VARCHAR" property="readerGender" />
  <result column="reader_barcode" jdbcType="VARCHAR" property="readerBarcode" />
  <result column="reader_profession" jdbcType="VARCHAR" property="readerProfession" />
  <result column="reader_birth" jdbcType="TIMESTAMP" property="readerBirth" />
  <result column="reader_document_type" jdbcType="VARCHAR" property="readerDocumentType" />
  <result column="reader_document_number" jdbcType="VARCHAR" property="readerDocumentNumber" />
  <result column="reader_email" jdbcType="VARCHAR" property="readerEmail" />
  <result column="reader_register_date" jdbcType="TIMESTAMP" property="readerRegisterDate" />
  <result column="borrowed_book_count" jdbcType="INTEGER" property="borrowedBookCount" />
  <result column="remaining_book_count" jdbcType="INTEGER" property="remainingBookCount" />
  <result column="operator_id" jdbcType="INTEGER" property="operatorId" />
  
  <association property="manager" javaType="com.bean.Manager">
    <id column="manager_id" property="managerId">id>
    <result column="manager_name" property="managerName">result>
  association>
resultMap>

[2] 新增一个带管理员信息的属性集

<sql id="Column_List_With_Manager">
  r.reader_id, r.reader_name, r.reader_gender, r.reader_barcode, r.reader_profession, r.reader_birth,
  r.reader_document_type, r.reader_document_number, r.reader_email, r.reader_register_date,
  r.borrowed_book_count, r.remaining_book_count, r.operator_id, m.manager_id, m.manager_name
sql>

[3] 新增两个查询信息附带管理员的方法

<select id="selectByExampleWithManager" parameterType="com.bean.ReaderExample" resultMap="ResultMapWithManager">
  select
  <if test="distinct">
    distinct
  if>
  <include refid="Column_List_With_Manager" />
  FROM reader_tbl r
  LEFT JOIN manager_tbl m ON r.operator_id = m.manager_id
  <if test="_parameter != null">
    <include refid="Example_Where_Clause" />
  if>
  <if test="orderByClause != null">
    order by ${orderByClause}
  if>
select>
<select id="selectByPrimaryKeyWithManager" parameterType="java.lang.Integer" resultMap="ResultMapWithManager">
  select
  <include refid="Column_List_With_Manager" />
  FROM reader_tbl r
  LEFT JOIN manager_tbl m ON r.operator_id = m.manager_id
  where reader_id = #{readerId,jdbcType=INTEGER}
select>

5. 在 dao 层接口 ManagerMapper.java 添加对应的方法

//新增两个方法：带上管理员
List<Reader> selectByExampleWithManager(ReaderExample example);
Reader selectByPrimaryKeyWithManager(Integer readerId);

这里就改造完成了。

6. 测试

编写一个测试类，调用 mapper 接口中的方法即可测试，下面举例：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:applicationContext.xml"})
public class MapperTest {

    @Autowired
    ReaderMapper readerMapper;

    @Test
    public void mapperTest(){
      //调用 readerMapper 中的 selectByPrimaryKeyWithManager，查看控制台信息，检查是否实现了联合查询
        Reader reader = readerMapper.selectByPrimaryKeyWithManager(10);
        System.out.println(reader);
    }
}

输出结果：

Reader{readerId=10, readerName='邱筹妈', readerGender='男', readerBarcode='ab1eb7a', readerProfession='学生', readerBirth=Sun Oct 05 11:00:00 CST 2003, readerDocumentType='学生证', readerDocumentNumber='2018302178736', readerEmail='[email protected]', readerRegisterDate=Fri May 29 11:00:00 CST 2020, borrowedBookCount=0, remainingBookCount=10, operatorId=4, manager=Manager{managerId=4, managerName='张XX', managerPwd='null'}}

测试成功。

---

有纰漏之处，还望不吝指出~

---