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Mybatis快速入门——Mybatis的映射文件(4)

Eric
2022-02-04 / 0 评论 / 0 点赞 / 154 阅读 / 44,161 字 / 正在检测是否收录...
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Mybatis的映射文件

1 增删改查

  • 示例:
  • 导入相关jar包的Maven坐标:
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.5</version>
</dependency>
<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.21</version>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13</version>
    <scope>test</scope>
</dependency>
  • db.properties
jdbc.url=jdbc:mysql://192.168.134.100:3306/test?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&serverTimezone=GMT%2B8&allowPublicKeyRetrieval=true
jdbc.driverClass=com.mysql.cj.jdbc.Driver
jdbc.username=root
jdbc.password=123456
  • log4j.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
 
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
 
 <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
   <param name="Encoding" value="UTF-8" />
   <layout class="org.apache.log4j.PatternLayout">
    <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) \n" />
   </layout>
 </appender>
 <logger name="java.sql">
   <level value="debug" />
 </logger>
 <logger name="org.apache.ibatis">
   <level value="info" />
 </logger>
 <root>
   <level value="debug" />
   <appender-ref ref="STDOUT" />
 </root>
</log4j:configuration>
  • Employee.java
package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    public Employee() {
    }

    public Employee(Integer id, String lastName, String email, String gender) {
        this.id = id;
        this.lastName = lastName;
        this.email = email;
        this.gender = gender;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
}
  • EmployeeMapper.java
package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

    /**
     * 根据id查询员工的信息
     *
     * @param id
     * @return
     */
    Employee findById(Integer id);

    /**
     * 增加员工信息
     *
     * @param employee
     */
    void addEmp(Employee employee);

    /**
     * 修改员工信息
     *
     * @param employee
     */
    void updateEmp(Employee employee);


    /**
     * 根据id删除员工信息
     *
     * @param id
     */
    void deleteEmpById(Integer id);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">
    <select id="findById" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{id,jdbcType=INTEGER}
    </select>

    <insert id="addEmp">
        INSERT INTO employee (last_name,email,gender)
        VALUES (#{lastName,jdbcType=VARCHAR},#{email,jdbcType=VARCHAR},#{gender,jdbcType=VARCHAR})
    </insert>

    <update id="updateEmp">
        UPDATE employee
        SET last_name = #{lastName,jdbcType=VARCHAR},email = #{email,jdbcType=VARCHAR},gender=#{gender,jdbcType=VARCHAR}
        WHERE id = #{id,jdbcType=INTEGER}
    </update>
    <delete id="deleteEmpById">
        DELETE FROM employee
        WHERE id = #{id,jdbcType=INTEGER}
    </delete>
</mapper>
  • mybatis-copnfig.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>

    <properties resource="db.properties"></properties>
    <settings>
        <!-- 开启自动驼峰命名规则映射 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!-- 使用${}引入db.properties属性文件中的内容 -->
                <property name="driver" value="${jdbc.driverClass}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <mappers>
        <package name="top.open1024.mapper"/>
    </mappers>

</configuration>
  • 测试:
package top.open1024;

import top.open1024.domain.Employee;
import top.open1024.mapper.EmployeeMapper;
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.After;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;


public class EmployeeTest {
    SqlSessionFactory sqlSessionFactory = null;
    SqlSession sqlSession = null;
    EmployeeMapper employeeMapper = null;

    @Before
    public void before() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession(true);
        employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
    }

    @After
    public void after() {
        if (null != sqlSession) {
            sqlSession.close();
        }
    }

    @Test
    public void testFindById() {

        Employee employee = employeeMapper.findById(1);
        System.out.println("employee = " + employee);
    }

    @Test
    public void testAddEmp() {
        Employee employee = new Employee();
        employee.setEmail("jerry@qq.com");
        employee.setGender("男");
        employee.setLastName("jerry");

        employeeMapper.addEmp(employee);
    }

    @Test
    public void testUpdateEmp(){

        Employee employee = employeeMapper.findById(2);
        employee.setGender("女");

        employeeMapper.updateEmp(employee);
    }

    @Test
    public void testDeleteEmpById(){
        employeeMapper.deleteEmpById(2);

    }

}

2 INSERT获取自增主键的值

  • MySQL等数据库支持自增主键,自增主键的值是通过statement.getGenerateKeys()方法获取的。

  • 通过使用useGeneratedKeys="true"开启自增主键获取主键值的策略。

  • 通过使用keyProperty="id"指定对应的主键属性,Mybatis获取主键值以后,将这个值封装给JavaBean的哪个属性。

  • 示例:

<?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="top.open1024.mapper.EmployeeMapper">
    <!--
        MySQL支持自增主键,自增主键值的获取,Mybatis是利用statement.getGeneratedKeys()
            useGeneratedKeys="true":使用自增主键获取主键值策略
            keyProperty="id":指定对应的主键属性,Mybatis获取主键值以后,将这个值封装给JavaBean的哪个属性
    -->
    <insert id="addEmp" useGeneratedKeys="true" keyProperty="id" parameterType="top.open1024.domain.Employee">
        INSERT INTO employee (last_name,email,gender)
        VALUES (#{lastName,jdbcType=VARCHAR},#{email,jdbcType=VARCHAR},#{gender,jdbcType=VARCHAR})
    </insert>
</mapper>

3 INSERT获取非自增主键的值

  • Oracle不支持自增主键,Oracle是使用序列来模拟自增的。

  • 每次插入的数据的主键都是从序列中拿到的值。

  • 示例:

<?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="top.open1024.mapper.EmployeeMapper">
    <!--
        Oracle不支持自增主键,Oracle是使用序列来模拟自增的。
        每次插入的数据的主键都是从序列中拿到的值。
    -->
    <insert id="addEmp" useGeneratedKeys="true" keyProperty="id" parameterType="top.open1024.domain.Employee">
        <!--
            插入时的主键是从序列中拿到的
                keyProperty:查询的主键封装给JavaBean的哪个属性
                order:
                    - BEFORE:当前的SQL在插入SQL之前运行
                        - 运行顺序:先运行selectKey中的SQL语句,查询出id,然后将id封装给JavaBean中的id属性,在运行插入SQL的时候,就可以取出id属性对应的值
                    - AFTER: 先运行插入SQL,再运行当前的SQL 
                        - 运行顺序:先运行插入的SQL(会从序列中取出新值作为id),再运行selectKey查询id,然后将id封装给JavaBean的id属性,并发情况下可能有问题。
                resultType:查出的数据的返回值类型
        -->
        <selectKey keyProperty="id" order="BEFORE" resultType="java.lang.Integer">
            <!--
                编写查询主键的SQL语句
            -->
            SELECT employee_seq.nextval FROM dual
        </selectKey>

        INSERT INTO employee (id,last_name,email,gender)
        VALUES (#{id,jdbcType=INTEGER},#{lastName,jdbcType=VARCHAR},#{email,jdbcType=VARCHAR},#{gender,jdbcType=VARCHAR})

    </insert>
</mapper>
  • 示例:
<?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="top.open1024.mapper.EmployeeMapper">
    <!--
        Oracle不支持自增主键,Oracle是使用序列来模拟自增的。
        每次插入的数据的主键都是从序列中拿到的值。
    -->
    <insert id="addEmp" useGeneratedKeys="true" keyProperty="id" parameterType="top.open1024.domain.Employee">
        <!--
            插入时的主键是从序列中拿到的
                keyProperty:查询的主键封装给JavaBean的哪个属性
                order:
                    - BEFORE:当前的SQL在插入SQL之前运行
                        - 运行顺序:先运行selectKey中的SQL语句,查询出id,然后将id封装给JavaBean中的id属性,在运行插入SQL的时候,就可以取出id属性对应的值
                    - AFTER: 先运行插入SQL,再运行当前的SQL
                        - 运行顺序:先运行插入的SQL(会从序列中取出新值作为id),再运行selectKey查询id,然后将id封装给JavaBean的id属性,并发情况下可能有问题。
                resultType:查出的数据的返回值类型
        -->
        <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
            <!--
                编写查询主键的SQL语句
            -->
            SELECT employee_seq.currval FROM dual
        </selectKey>

        INSERT INTO employee (id,last_name,email,gender)
        VALUES (employee_seq.nextval},#{lastName,jdbcType=VARCHAR},#{email,jdbcType=VARCHAR},#{gender,jdbcType=VARCHAR})

    </insert>
</mapper>

4 参数处理

4.1 单个参数

  • Mybatis不需要经过任何处理,Mybatis可以直接使用#{参数名}取出参数值。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

    /**
     * 根据id查询员工的信息
     *
     * @param id
     * @return
     */
    Employee findById(Integer id);
    
}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">
    
    <select id="findById" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{abc,jdbcType=INTEGER}
    </select>
</mapper>

4.2 多个参数

  • 任意多个参数,都会被Mybatis重新包装成一个Map传入。Map中的key就是param1,param2,…,value是传入的参数值。

  • #{}就是从map中获取指定的key的值。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

    /**
     * 根据id和lastName查询员工信息
     *
     * @param id
     * @param lastName
     * @return
     */
    Employee findByIdAndLastName(Integer id, String lastName);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <select id="findByIdAndLastName" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{param1,jdbcType=INTEGER} AND last_name = #{param2,jdbcType=VARCHAR}
    </select>

</mapper>

4.3 命名参数

  • 当多个参数的时候,可以使用@Param注解明确指定Mybatis中传入参数Map中的key,Map中的key就是使用@Param注解指定的值,value就是传入的参数值。

  • #{指定的key}就可以取出对应的参数值。

  • 示例:

  • Employee.java

package top.open1024.mapper;

import top.open1024.domain.Employee;
import org.apache.ibatis.annotations.Param;

public interface EmployeeMapper {

    /**
     * 根据id和lastName查询员工信息
     *
     * @param id
     * @param lastName
     * @return
     */
    Employee findByIdAndLastName(@Param("id") Integer id,@Param("lastName") String lastName);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <select id="findByIdAndLastName" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{id,jdbcType=INTEGER} AND last_name = #{lastName,jdbcType=VARCHAR}
    </select>

</mapper>

4.4 POJO

  • 如果多个参数正好是业务逻辑的数据模型,我们就可以直接传入POJO。#{属性名}取出传入POJO的属性值。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {
    
    Employee findByPOJO(Employee employee);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <select id="findByPOJO" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{id,jdbcType=INTEGER} AND last_name = #{lastName,jdbcType=VARCHAR}
    </select>

</mapper>

4.5 Map

  • 如果多个参数不是业务模型的数据,没有对应的POJO,不经常使用,为了方便,我们可以传入Map。

  • #{key}取出传入map中对应的值。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

import java.util.Map;

public interface EmployeeMapper {

    Employee findByMap(Map<String, Object> map);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">
    
    <select id="findByMap" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{id,jdbcType=INTEGER} AND last_name = #{lastName,jdbcType=VARCHAR}
    </select>

</mapper>

4.6 TO

  • 如果多个参数不是业务模型中的数据,但是经常使用,推荐编写一个TO(Transfer Object)数据传输对象。

  • 示例:

  • Page.java

package top.open1024.to;/** * 分页的参数 */public class Page {    /**     * 每页显示条数     */    private Integer pageSize;    /**     * 起始页码     */    private Integer pageNum;    public Integer getPageSize() {        return pageSize;    }    public void setPageSize(Integer pageSize) {        this.pageSize = pageSize;    }    public Integer getPageNum() {        return pageNum;    }    public void setPageNum(Integer pageNum) {        this.pageNum = pageNum;    }    @Override    public String toString() {        return "Page{" +                "pageSize=" + pageSize +                ", pageNum=" + pageNum +                '}';    }}
  • EmployeeMapper.java
package top.open1024.mapper;

import top.open1024.domain.Employee;
import top.open1024.to.Page;

import java.util.List;

public interface EmployeeMapper {

    List<Employee> findByPage(Page page);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">


    <select id="findByPage" resultType="top.open1024.domain.Employee">

        SELECT id,last_name as lastName,email,gender
        FROM employee
        LIMIT #{pageNum},#{pageSize}

    </select>
</mapper>

4.7 Collection类型(List类型、Set类型)数组类型

  • 如果传入的参数是Collection类型(List类型、Set类型)或数组类型,那么Mybatis会针对这些类型进行特殊处理:如果是Collection类型,那么Mybatis内部封装参数的Map的key就是collection;如果是List类型,那么Mybatis内部封装参数的Map的key可以是list;而如果是数组类型,Mybatis内部封装参数的Map的key是array。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

import java.util.List;
import java.util.Set;

public interface EmployeeMapper {

   List<Employee> findBySet(Set<Integer> id);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">
    
    <select id="findBySet" resultType="top.open1024.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{collection}
    </select>
</mapper>

4.8 #和$取值区别

  • #{}获取参数的值,预编译到SQL中,安全。

  • ${}获取参数的值,拼接到SQL中,有SQL注入问题。

  • 注意:

  • 大多数情况下,我们取参数的值的时候使用#{}

  • 原生JDBC不支持占位符的地方,我们就可以使用${}

    • 比如:排序
Order BY ${name}
    • 比如:财务系统在设计之初按照年份分表,查询的时候应该这样写:
SELECT * FROM ${year}_salary WHERE xxx;
  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

import java.util.Map;

public interface EmployeeMapper {
   
   Employee findByMap(Map<String,Object> map);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <select id="findByMap" resultType="top.open1024.domain.Employee" parameterType="java.util.Map">
        SELECT id,last_name as lastName,email,gender
        FROM ${tableName}
        WHERE id = #{id}
    </select>

</mapper>
  • 测试:
package top.open1024;

import top.open1024.domain.Employee;
import top.open1024.mapper.EmployeeMapper;
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.After;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;


public class EmployeeTest {
    SqlSessionFactory sqlSessionFactory = null;
    SqlSession sqlSession = null;
    EmployeeMapper employeeMapper = null;

    @Before
    public void before() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession(true);
        employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
    }

    @After
    public void after() {
        if (null != sqlSession) {
            sqlSession.close();
        }
    }

    @Test
    public void testFindById() {
        Map<String, Object> map = new HashMap<>();
        map.put("id",1);
        map.put("tableName","employee");

        Employee employee = employeeMapper.findByMap(map);
        System.out.println("employee = " + employee);

    }   
}

4.9 #取值时指定参数的相关规则

  • Mybatis在参数位置支持如下的属性:

    • javaType

    • jdbcType

    • mode(用于存储过程)

    • numericScale

    • resultMap

    • typeHandler

    • jdbcTypeName

    • expression

  • 在某种特定的条件下,jdbcType通常需要被设置。

    • 在我们的数据为null的时候,有些数据库可能不能识别Mybatis对null的默认处理,比如Oracle。

    • Mybatis对null的默认处理时的jdbcType是OTHER,这种类型MySQL能正确识别,但是Oracle不能。

      • ①我们在使用Oracle保存null的时候,需要设置jdbcType为NULL。

      • ②在全局配置文件mybatis-config.xml中设置jdbcTypeForNull的值是NULL(推荐这种,Oracle和MySQL都支持)。

  • 示例:修改Mybatis对Oracle的NULL值的默认处理

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {
   
   int addEmp(Employee employee);
}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">
   
    <insert id="addEmp" useGeneratedKeys="true" keyProperty="id" parameterType="top.open1024.domain.Employee">
        <selectKey>
            SELECT employee_seq.nextval FROM dual
        </selectKey>

        INSERT INTO employee (id,last_name,email,gender)
        <!--
            在Oracle数据库中,如果是null值,需要设置jdbcType=NULL
        -->
        VALUES (#{id,jdbcType=INTEGER},#{lastName,jdbcType=VARCHAR},#{email,jdbcType=NULL},#{gender,jdbcType=VARCHAR})
    </insert>
</mapper>

5 select元素

5.1 概述

  • select元素用于定义查询操作。

  • id:唯一标识符。用来引用这条语句,需要和接口的方法名一致。

  • parameterType:参数类型。可以不传,Mybatis会根据TypeHandler自动推断。

  • resultType:返回值类型。别名或者全类名,如果返回的是集合,定义集合中元素的类型。不能和resultMap同时使用。

  • resultMap:实现高级结果集映射。不能和resultType一起使用。

5.2 resultType

5.2.1 返回List

  • 对于resultType来说,如果返回的是一个集合,需要写集合中的类型。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

import java.util.List;

public interface EmployeeMapper {

   List<Employee> findByGender(String gender);
}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <!--
        resultType:如果返回的是一个集合,需要写集合里面的类型
    -->
    <select id="findByGender" resultType="top.open1024.domain.Employee">
        SELECT * FROM employee
        WHERE gender = #{gender,jdbcType=VARCHAR}
    </select>

</mapper>

5.2.2 返回Map

  • 返回一条记录封装Map,key就是列名,值就是对应的值。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;

import java.util.Map;

public interface EmployeeMapper {

   Map<String, Object> findById(Integer id);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <select id="findById" resultType="java.util.Map">
        SELECT * FROM employee
        WHERE id = #{id,jdbcType=INTEGER}
    </select>

</mapper>
  • 返回多条记录将其封装为Map<主键类型,对象类型>,key是这条记录的主键,值是这条记录。

  • 示例:

  • EmployeeMapper.java

package top.open1024.mapper;import top.open1024.domain.Employee;import org.apache.ibatis.annotations.MapKey;import java.util.Map;public interface EmployeeMapper {   @MapKey("id")   Map<Integer, Employee> findById(Integer id);}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <select id="findById" resultType="java.util.Map">
        SELECT id,last_name as lastName,gender,email FROM employee
        WHERE id = #{id,jdbcType=INTEGER}
    </select>

</mapper>

5.3 resultMap

5.3.1 自定义结果映射规则

  • 示例:

  • EmplyeeMapper.java

package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

  Employee findById(Integer id);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <!--
        resultMap 自定义关系结果映射规则
            id:唯一方便引用的id
            type:自定义规则的JavaBean类型
    -->
    <resultMap id="emp" type="top.open1024.domain.Employee">
        <!--
            id:指定主键列的封装规则
                column:指定哪一列
                property:指定column对应的JavaBean属性
         -->
        <id property="id" column="id"/>
        <!--
            result:定义普通列的封装规则
               column:指定哪一列
               property:指定column对应的JavaBean属性
        -->
        <result property="lastName" column="last_name"/>
        <!-- 其它不指定的列会自动封装 -->
        <result property="email" column="email"/>
        <result property="gender" column="gender"/>
    </resultMap>

    <select id="findById" resultMap="emp">
        SELECT * FROM employee
        WHERE id = #{id,jdbcType=INTEGER}
    </select>

</mapper>

5.3.2 关联查询

5.3.2.1 环境搭建

  • SQL脚本:
DROP TABLE IF EXISTS `department`;
CREATE TABLE `department`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `department` VALUES (1, '开发部');
INSERT INTO `department` VALUES (2, '测试部');

DROP TABLE IF EXISTS `employee`;
CREATE TABLE `employee`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `last_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `gender` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `department_id` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `fk_department_id`(`department_id`) USING BTREE,
  CONSTRAINT `fk_department_id` FOREIGN KEY (`department_id`) REFERENCES `department` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `employee` VALUES (1, 'tom', '男', 'tom@qq.com', 1);
INSERT INTO `employee` VALUES (2, 'aa', '女', NULL, 2);

5.3.2.2 级联属性封装查询结果

  • 示例:查询一个员工信息以及其所在部门信息

  • Department.java

package top.open1024.domain;public class Department {    private Integer id;    private String name;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    @Override    public String toString() {        return "Department{" +                "id=" + id +                ", name='" + name + '\'' +                '}';    }}
  • Employee.java
package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    private Department department;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                ", department=" + department +
                '}';
    }
}
  • EmployeeMapper.java
package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

 Employee findEmpAndDeptById(Integer id);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">
    
    <resultMap id="emp" type="top.open1024.domain.Employee">
        <id property="id" column="id"/>
        <result property="lastName" column="last_name"/>
        <result property="email" column="email"/>
        <result property="gender" column="gender"/>
        <result property="department.id" column="did"/>
        <result property="department.name" column="dept_name"/>
    </resultMap>

    <select id="findEmpAndDeptById" resultMap="emp">
        SELECT e.id as id,e.last_name as last_name,e.gender as gender,e.email as email,d.id as did,d.name as dept_name
        FROM employee e INNER JOIN department d
        ON e.department_id = d.id
        WHERE e.id = #{id,jdbcType=INTEGER}
    </select>

</mapper>

5.3.2.3 association定义关联对象

  • 示例:查询一个员工信息以及其所在部门信息

  • Department.java

package top.open1024.domain;

public class Department {

    private Integer id;

    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Department{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
  • Employee.java
package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    private Department department;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                ", department=" + department +
                '}';
    }
}
  • EmployeeMapper.java
package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

 Employee findEmpAndDeptById(Integer id);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <resultMap id="emp" type="top.open1024.domain.Employee">
        <id property="id" column="id"/>
        <result property="lastName" column="last_name"/>
        <result property="email" column="email"/>
        <result property="gender" column="gender"/>
        <!--
            association:可以指定联合的JavaBean对象
                property:指定哪个属性是联合的对象
                javaType:指定联合对象的类型
        -->
        <association property="department" javaType="top.open1024.domain.Department">
            <id property="id" column="did"/>
            <id property="name" column="dept_name"/>
        </association>
    </resultMap>

    <select id="findEmpAndDeptById" resultMap="emp">
        SELECT e.id as id,e.last_name as last_name,e.gender as gender,e.email as email,d.id as did,d.name as dept_name
        FROM employee e INNER JOIN department d
        ON e.department_id = d.id
        WHERE e.id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

5.3.2.4 association分步查询

  • 示例:查询一个员工信息以及其所在部门信息

  • Department.java

package top.open1024.domain;

public class Department {

    private Integer id;

    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Department{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
  • Employee.java
package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    private Department department;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                ", department=" + department +
                '}';
    }
}
  • DepartmentMapper.java
package top.open1024.mapper;

import top.open1024.domain.Department;

public interface DepartmentMapper {

    Department findById(Integer id);

}
  • DepartmentMapper.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="top.open1024.mapper.DepartmentMapper">

    <select id="findById" resultType="top.open1024.domain.Department">
        SELECT *
        FROM department
        WHERE id = #{id,jdbcType=INTEGER}
    </select>
</mapper>
  • EmployeeMapper.java
package top.open1024.mapper;import top.open1024.domain.Employee;public interface EmployeeMapper {    Employee findEmpAndDeptById(Integer id);}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <resultMap id="emp" type="top.open1024.domain.Employee">
        <!--
            分步查询:
                ①按照员工id查询员工信息
                ②根据查询员工信息中的department_id去部门表中查询部门信息
                ③部门设置到员工中
        -->
        <id property="id" column="id"/>
        <result property="lastName" column="last_name"/>
        <result property="email" column="email"/>
        <result property="gender" column="gender"/>
        <!--
            association 定义关联对象的封装规则
                property:关联对象的属性
                select:表明当前属性是调用select查询的结果
                column:指定将那一列的值传给这个方法

             流程:使用select指定的方法(传入column指定的这列参数的值)查出对象,并封装给property指定的关联对象的属性
        -->
        <association property="department" select="top.open1024.mapper.DepartmentMapper.findById" column="did" />
    </resultMap>

    <select id="findEmpAndDeptById" resultMap="emp">
        SELECT e.id as id,e.last_name as last_name,e.gender as gender,e.email as email,e.department_id as did
        FROM employee e
        WHERE e.id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

分步查询中使用延迟加载:需要在mybatis-config.xml中配置如下的全局设置

<settings>
 <!-- 开启自动驼峰命名规则映射 -->
 <setting name="mapUnderscoreToCamelCase" value="true"/>
 <!-- 开启对jdbcType的NULL的支持 -->
 <setting name="jdbcTypeForNull" value="NULL"/>
 <!-- 开启延迟加载 -->
 <setting name="lazyLoadingEnabled" value="true"/>
 <!-- 开启按需加载 -->
 <setting name="aggressiveLazyLoading" value="false"/>
</settings>

5.3.2.5 collection定义关联集合封装规则

  • 示例:查询一个部门信息的同时并查询下面的所有员工信息

  • Employee.java

package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
}
  • Department.java
package top.open1024.domain;

import java.util.List;

public class Department {

    private Integer id;

    private String name;

    private List<Employee> employees;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }

    @Override
    public String toString() {
        return "Department{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", employees=" + employees +
                '}';
    }
}
  • DepartmentMapper.java
package top.open1024.mapper;

import top.open1024.domain.Department;

public interface DepartmentMapper {

    Department findById(Integer id);

}
  • DepartmentMapper.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="top.open1024.mapper.DepartmentMapper">

    <resultMap id="dept" type="top.open1024.domain.Department">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
         <!--
            collection 定义关联集合类型的属性的封装规则
                ofType 定义集合中元素的类型
         -->
        <collection property="employees" ofType="top.open1024.domain.Employee">
            <!-- 定义这个集合中元素的封装规则 -->
            <id property="id" column="eid"/>
            <result property="lastName" column="lastName"/>
            <result property="gender" column="gender"/>
            <result property="email" column="email"/>
        </collection>
    </resultMap>

    <select id="findById" resultMap="dept">
        SELECT d.id as id,d.name as name,e.id as eid,e.last_name as lastName,e.email as email,e.gender as gender
        FROM department d
        INNER JOIN employee e
        ON d.id = e.department_id
        WHERE d.id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

5.3.2.6 collection定义分步查询

  • 示例:查询一个部门信息的同时并查询下面的所有员工信息

  • Employee.java

package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
}
  • Department.java
package top.open1024.domain;

import java.util.List;

public class Department {

    private Integer id;

    private String name;

    private List<Employee> employees;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }

    @Override
    public String toString() {
        return "Department{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", employees=" + employees +
                '}';
    }
}
  • EmployeeMapper.java
package top.open1024.mapper;

import top.open1024.domain.Employee;

import java.util.List;

public interface EmployeeMapper {

    List<Employee> findByDepatmentId(Integer departmentId);

}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <resultMap id="emp" type="top.open1024.domain.Employee">

        <id property="id" column="id"/>
        <result property="lastName" column="last_name"/>
        <result property="email" column="email"/>
        <result property="gender" column="gender"/>
    </resultMap>

    <select id="findByDepatmentId" resultMap="emp">
        SELECT e.id as id,e.last_name as last_name,e.gender as gender,e.email as email,e.department_id as did
        FROM employee e
        WHERE e.department_id = #{departmentId,jdbcType=INTEGER}
    </select>
</mapper>
  • DepartmentMapper.java
package top.open1024.mapper;

import top.open1024.domain.Department;

public interface DepartmentMapper {

    Department findById(Integer id);

}
  • DepartmentMapper.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="top.open1024.mapper.DepartmentMapper">

    <resultMap id="dept" type="top.open1024.domain.Department">
        <id property="id" column="id"/>
        <result property="name" column="name"/>

        <collection property="employees" select="top.open1024.mapper.EmployeeMapper.findByDepatmentId" column="{id}">
        </collection>
    </resultMap>

    <select id="findById" resultMap="dept">
        SELECT d.id as id,d.name as name
        FROM department d
        WHERE d.id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

5.2.3.7 分步查询传递多列值

  • 有的时候,分步查询不是传递一个值,而是传递多列值,这个时候我们需要使用{key1=column1,key2=clomn2…}的形式来多列值封装map传递。

  • 示例:

  • DepartmentMapper.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="top.open1024.mapper.DepartmentMapper">

    <resultMap id="dept" type="top.open1024.domain.Department">
        <id property="id" column="id"/>
        <result property="name" column="name"/>

        <collection property="employees" select="top.open1024.mapper.EmployeeMapper.findByDepatmentId" column="{departmentId=id}">
        </collection>
    </resultMap>

    <select id="findById" resultMap="dept">
        SELECT d.id as id,d.name as name
        FROM department d
        WHERE d.id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

5.2.3.8 fetchType

  • 在collection和association标签的fetchType属性有eager和lazy属性,其中eager属性表示立即加载,而lazy属性表示延迟加载。一旦指定了fetchType可以覆盖全局的延迟加载策略。

5.2.3.9 discriminator鉴别器

  • Mybatis可以使用discriminator判断某列的值,然后根据某列的值改变封装行为。

  • 示例:判断Employee,如果查出的是女生,就把部门信息查询出来,否则不查询;如果查询出来的是男生,就把last_name这一列的值赋值给email

  • Department.java

package top.open1024.domain;

public class Department {

    private Integer id;

    private String name;
    
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Department{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
  • Employee.java
package top.open1024.domain;

import org.apache.ibatis.type.Alias;

@Alias("emp")
public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    private Department department;


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                ", department=" + department +
                '}';
    }
}
  • DepartmentMapper.java
package top.open1024.mapper;

import top.open1024.domain.Department;

public interface DepartmentMapper {

    Department findById(Integer id);

}
  • DepartmentMapper.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="top.open1024.mapper.DepartmentMapper">

    <resultMap id="dept" type="top.open1024.domain.Department">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
    </resultMap>

    <select id="findById" resultMap="dept">
        SELECT d.id as id,d.name as name
        FROM department d
        WHERE d.id = #{id,jdbcType=INTEGER}
    </select>
</mapper>
  • EmployeeMapper.java
package top.open1024.mapper;

import top.open1024.domain.Employee;

public interface EmployeeMapper {

    Employee findById(Integer id);
    
}
  • EmployeeMapper.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="top.open1024.mapper.EmployeeMapper">

    <resultMap id="emp" type="top.open1024.domain.Employee">

        <id property="id" column="id"/>
        <result property="lastName" column="last_name"/>
        <result property="email" column="email"/>
        <result property="gender" column="gender"/>
        <!--
            discriminator 鉴别器
             column:指定要判断的列名
             javaType:指定要判断的列对应的java类型
        -->
        <discriminator javaType="string" column="gender">
            <case value="女" resultType="top.open1024.domain.Employee">
                <association property="department" javaType="java.lang.Integer" select="top.open1024.mapper.DepartmentMapper.findById" column="did"/>
            </case>
            <case value="男" resultType="top.open1024.domain.Employee">
                <id property="id" column="id"/>
                <result property="lastName" column="last_name"/>
                <result property="email" column="last_name"/>
                <result property="gender" column="gender"/>
            </case>
        </discriminator>

    </resultMap>


    <select id="findById" resultMap="emp">
        SELECT e.id as id,e.last_name as last_name,e.gender as gender,e.email as email,e.department_id as did
        FROM employee e
        WHERE e.department_id = #{departmentId,jdbcType=INTEGER}
    </select>
</mapper>
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