MyBatis實(shí)現(xiàn)高級(jí)映射的示例代碼

更新時(shí)間：2024年06月20日 10:23:51 作者：花落隨風(fēng)輕飄舞

高級(jí)映射主要還是映射,只是映射中的數(shù)據(jù)關(guān)系復(fù)雜了,其中就包括一對(duì)一、一對(duì)多、多對(duì)多的關(guān)系,本文主要介紹了MyBatis實(shí)現(xiàn)高級(jí)映射的示例代碼,感興趣的可以了解一下

1 association 和 collection 介紹

在之前的 SQL 映射文件中提及了 resultMap 元素的 association 和 collection 標(biāo)簽，這兩個(gè)標(biāo)簽是用來(lái)關(guān)聯(lián)查詢的，它們的屬性幾乎一致，以下是對(duì)它們屬性的描述，紅色標(biāo)注的是常用屬性。

屬性	描述
property	實(shí)體類屬性名
column	數(shù)據(jù)庫(kù)字段名或者其別名
javaType	實(shí)體類屬性的 Java 類型
jdbcType	數(shù)據(jù)庫(kù)列的數(shù)據(jù)類型
ofType	指定關(guān)聯(lián)對(duì)象的類型。它通常用于泛型類型的情況，以確保正確的類型轉(zhuǎn)換
select	指定一個(gè)子查詢，用于加載關(guān)聯(lián)的對(duì)象
fetchType	用于控制加載策略，比如立即加載還是延遲加載。常見(jiàn)的取值有 lazy（延遲加載）和 eager（立即加載）
resultMap	引用預(yù)定義的結(jié)果映射，以便更靈活地配置關(guān)聯(lián)對(duì)象的映射規(guī)則
resultSet	指定結(jié)果集的名稱，以便在多結(jié)果集的情況下進(jìn)行區(qū)分
autoMapping	是否自動(dòng)映射所有列到目標(biāo)對(duì)象的屬性上。默認(rèn)為 true，表示自動(dòng)映射；設(shè)置為 false 則表示不自動(dòng)映射
columnPrefix	當(dāng)使用內(nèi)連接查詢時(shí)，這個(gè)屬性可以用來(lái)指定前綴，以區(qū)分關(guān)聯(lián)表的列名
foreignColumn	指定外鍵對(duì)應(yīng)的列名
notNullColumn	指定一個(gè)列名，只有當(dāng)該列的值不為 null 時(shí)，才會(huì)執(zhí)行關(guān)聯(lián)查詢
typeHandler	自定義的類型處理器

2 案例分析

以典型的員工 (Employee) 和部門 (Department) 為例

一個(gè)員工只能在一個(gè)部門：Employee -> Department（一對(duì)一）
一個(gè)部門可以包含多個(gè)員工：Department -> Employee（一對(duì)多）

以用戶 (User) 和角色 (Role) 為例，兩者成了一個(gè)雙向的一對(duì)多，從而變成了多對(duì)多，不做介紹

一個(gè)用戶可以擁有多個(gè)角色：User -> Role（一對(duì)多）
一個(gè)角色可以賦予多個(gè)用戶：Role -> User（一對(duì)多）

表 department 和表 employee

# 創(chuàng)建 department 表
drop table if exists department;
create table department(
department_id int(11) primary key auto_increment, #主鍵，自增
department_name varchar(255)
)charset=utf8;

# 插入數(shù)據(jù)
insert into department(department_name) values
('開(kāi)發(fā)部'),
('人力資源部'),
('市場(chǎng)營(yíng)銷部'),
('財(cái)務(wù)部'),
('行政部'),
('監(jiān)察部'),
('客服服務(wù)部');

# 創(chuàng)建 employee 表
drop table if exists employee;
create table employee(
employee_id int(11) primary key auto_increment, #主鍵，自增
employee_name varchar(255),
employee_age int(11),
employee_sex char(32),
employee_email varchar(255),
employee_address varchar(255),
department_id int(11)
)charset=utf8;

# 插入數(shù)據(jù)
insert into employee values
(1, '唐浩榮', 23, 1, '15477259875@163.com', '中國(guó)上海浦東區(qū)', 1),
(2, '黃飛鴻', 32, 1, '86547547@qq.com', '大清廣東', 2),
(3, '十三姨', 18, 0, '520520520@gmail.com', '大清廣東', 3),
(4, '納蘭元述', 28, 1, '545627858@qq.com', '大清京師', 5),
(5, '梁寬', 31, 1, '8795124578@qq.com', '大清廣東', 7),
(6, '蔡徐坤', 20, 0, '4257895124@gmail.com', '四川成都', 4),
(7, '楊超越', 21, 0, '8746821252@qq.com', '中國(guó)北京', 7),
(8, '馬保國(guó)', 66, 1, '6666666666@qq.com', '廣東深圳', 6),
(9, '馬牛逼', 45, 1, 'asdfg45678@163.com', '湖北武漢', 3);

3 一對(duì)一關(guān)聯(lián)和一對(duì)多關(guān)聯(lián)

工程目錄

Department 類

public class Department {
    //部門id
    private Integer deptId;
    //部門名稱
    private String deptName;

    //部門有哪些員工
    private List<Employee> employees;

    // Getter、Setter、toString 方法省略
}

Employee 類

public class Employee {
    //員工id
    private Integer empId;
    //員工名稱
    private String empName;
    //員工年齡
    private Integer empAge;
    //員工性別
    private Integer empSex;
    //員工郵箱
    private String empEmail;
    //員工地址
    private String empAddress;

    //員工所屬部門，和部門表構(gòu)成一對(duì)一的關(guān)系，一個(gè)員工只能在一個(gè)部門
    private Department department;

    // Getter、Setter、toString 方法省略
}

創(chuàng)建 DepartmentMapper

public interface DepartmentMapper {
    //查詢所有數(shù)據(jù)
    @Select("select * from department")
    @Results(id = "deptMap1", value = {
            @Result(property = "deptId", column = "department_id"),
            @Result(property = "deptName", column = "department_name"),
            // 一對(duì)多關(guān)聯(lián)對(duì)象
            // 根據(jù) department_id 來(lái)比較
            @Result(property = "employees", column = "department_id",
                many = @Many(select = "com.mapper.EmployeeMapper.selectEmpByDeptId"))
    })
    List<Department> selectAll();
    // 根據(jù) id 查找部門
    @Select("select * from department where department_id = #{id}")
    @Results(id = "deptMap2", value = {
            @Result(property = "deptId", column = "department_id"),
            @Result(property = "deptName", column = "department_name")
    })
    Department findDepartmentById(int id);
}

創(chuàng)建 EmployeeMapper

public interface EmployeeMapper {
    //查詢所有數(shù)據(jù)
    @Select("select * from employee")
    @Results(id = "empMap1", value = {
            @Result(property = "empId", column = "employee_id", id = true),
            @Result(property = "empName", column = "employee_name"),
            @Result(property = "empAge", column = "employee_age"),
            @Result(property = "empSex", column = "employee_sex"),
            @Result(property = "empEmail", column = "employee_email"),
            @Result(property = "empAddress", column = "employee_address"),
            // 一對(duì)一關(guān)聯(lián)對(duì)象
            // 根據(jù) department_id 來(lái)比較
            @Result(property = "department", column = "department_id",
                    one = @One(select = "com.mapper.DepartmentMapper.findDepartmentById"))}

    )
    List<Employee> selectAll();
    //根據(jù)員工id查詢數(shù)據(jù)
    @Select("select * from employee where employee_id = #{id}")
    @ResultMap("empMap1")
    Employee selectEmpByEmpId(@Param("id") int empId);

    // 根據(jù) department_id 查詢數(shù)據(jù)
    @Select("select * from employee where department_id = #{id}")
    @ResultMap("empMap1")
    Employee selectEmpByDeptId(@Param("id") int deptId);
}

log4j.properties

log4j.rootLogger=DEBUG, Console
#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=INFO
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

mysql.properties

url=jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC
name=root
password=123456
driver=com.mysql.cj.jdbc.Driver

MyBatis 配置文件 mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!-- 通過(guò)properties標(biāo)簽，讀取java配置文件的內(nèi)容 -->
    <properties resource="mysql.properties" />
    <!-- 配置環(huán)境.-->
    <environments default="development">
        <environment id="development">
            <!--配置事務(wù)的類型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--dataSource 元素使用標(biāo)準(zhǔn)的 JDBC 數(shù)據(jù)源接口來(lái)配置 JDBC 連接對(duì)象源 -->
            <dataSource type="POOLED">
                <!--配置連接數(shù)據(jù)庫(kù)的4個(gè)基本信息-->
                <property name="url" value="${url}" />
                <property name="username" value="${name}" />
                <property name="password" value="${password}" />
                <property name="driver" value="${driver}" />
            </dataSource>
        </environment>
    </environments>
    <!--通過(guò)包 package 引入 SQL 映射文件-->
    <mappers>
        <package name="com.mapper"/>
    </mappers>
</configuration>

創(chuàng)建 EmployeeTest 測(cè)試類

public class EmployeeTest {
    //定義 SqlSession
    SqlSession sqlSession = null;
    //定義 EmployeeMapper 對(duì)象
    private EmployeeMapper mapper = null;

    @Before
    public void getSqlSession() throws IOException {
        //加載 mybatis 全局配置文件 Resources
        // 原 InputStream is = MybatisTest.class.getClassLoader().getResourceAsStream("mybatis-config.xml");
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        //創(chuàng)建 SqlSessionFactory 對(duì)象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        //根據(jù) sqlSessionFactory 產(chǎn)生 session
        sqlSession = sqlSessionFactory.openSession();
        // 創(chuàng)建Mapper接口的的代理對(duì)象，getMapper方法底層會(huì)通過(guò)動(dòng)態(tài)代理生成 EmployeeMapper 的代理實(shí)現(xiàn)類
        mapper = sqlSession.getMapper(EmployeeMapper.class);
    }

    //查詢所有員工數(shù)據(jù)
    @Test
    public void testSelectAll() {
        List<Employee> listEmployee = mapper.selectAll();
        for (Employee employee : listEmployee) {
            System.out.println(employee);
        }
        sqlSession.close();
    }

    //根據(jù)員工 id 查詢數(shù)據(jù)
    @Test
    public void testSelectById() {
        Employee employee = mapper.selectEmpByEmpId(1);
        System.out.println(employee);
        sqlSession.close();
    }
}

測(cè)試結(jié)果

查詢所有員工數(shù)據(jù)，包括員工所在部門（一個(gè)員工屬于一個(gè)部門）

創(chuàng)建 DepartmentTest 測(cè)試類

public class DepartmentTest {
    //定義 SqlSession
    SqlSession sqlSession = null;
    //定義 DepartmentMapper 對(duì)象
    private DepartmentMapper mapper = null;

    @Before
    public void getSqlSession() throws IOException {
        //加載 mybatis 全局配置文件 Resources
        // 原 InputStream is = MybatisTest.class.getClassLoader().getResourceAsStream("mybatis-config.xml");
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        //創(chuàng)建 SqlSessionFactory 對(duì)象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        //根據(jù) sqlSessionFactory 產(chǎn)生 session
        sqlSession = sqlSessionFactory.openSession();
        // 創(chuàng)建Mapper接口的的代理對(duì)象，getMapper方法底層會(huì)通過(guò)動(dòng)態(tài)代理生成 DepartmentMapper 的代理實(shí)現(xiàn)類
        mapper = sqlSession.getMapper(DepartmentMapper.class);
    }

    //查詢所有部門數(shù)據(jù)
    @Test
    public void testSelectAll() {
        List<Department> listDepartment = mapper.selectAll();
        for (Department department : listDepartment) {
            System.out.println(department);
        }
        sqlSession.close();
    }

    //根據(jù)部門 id 查詢 數(shù)據(jù)
    @Test
    public void testSelectById() {
        Department department = mapper.findDepartmentById(1);
        System.out.println(department);
        sqlSession.close();
    }
}

測(cè)試結(jié)果

查詢所有部門信息，包括該部門有哪些員工（一個(gè)部門有多個(gè)員工）