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Lombok

Lombok项目是一个java库，它可以自动插入到编辑器和构建工具中，增强java的性能。不需要再写getter、setter或equals方法，只要有一个注解，你的类就有一个功能齐全的构建器、自动记录变量……

使用步骤：

• IDEA中安装Lombok插件
• 项目中导入Lombok的jar包

<dependencies>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.24</version>
    </dependency>
</dependencies>

• 实体类中添加注解

import lombok.*;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int id;
    private String name;
    private String password;

}

• @Data：无参构造、get/set方法、toString、hashCode、equals
• @AllArgsConstructor：带参构造方法
• @NoArgsConstructor：无参构造方法
• @ToString：toString方法
• @EqualsAndHashCode：equals和hashCode方法
• @Getter：get方法
• @Setter：set方法

复杂查询环境搭建

• 导入lombok

<dependencies>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.24</version>
    </dependency>
</dependencies>

• 新建实体类Teacher、Student

Teacher类

package com.wei.pojo;

import lombok.Data;

@Data
public class Teacher {
    private int id;
    private String name;
    //学生关联一个老师
    private Teacher teacher;
}

Student类

package com.wei.pojo;

import lombok.Data;

//多对一
@Data
public class Student {
    private int id;
    private String name;
    //学生需要关联一个老师
    private Teacher teacher;
}

• 建立Mapper接口

TeacherMapper接口

package com.wei.dao;

import com.wei.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

public interface TeacherMapper {

    @Select("select * from mybatis_03.teacher where id = #{tid}")
    Teacher getTeacher(@Param("tid") int id);
}

StudentMapper接口

package com.wei.dao;

public interface StudentMapper {

}

• 建立Mapper.xml文件

TeacherMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.wei.dao.TeacherMapper">

</mapper>

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.wei.dao.StudentMapper">

</mapper>

• 核心配置文件mybatis-config.xml绑定注册接口

<!--绑定接口-->
<mappers>
    <mapper resource="com/wei/dao/StudentMapper.xml"/>
    <mapper resource="com/wei/dao/TeacherMapper.xml"/>
</mappers>

• 测试

public class MyTest {
    @Test
    public void test(){
        //取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获得TeacherMapper接口类
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);

        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);

        //关闭SqlSession,避免造成内存出现问题
        sqlSession.close();
    }
}

多对一处理

环境搭建

• Student实体类

package com.wei.pojo;

import lombok.Data;

//多对一
@Data
public class Student {
    private int id;
    private String name;
    //学生需要关联一个老师
    private Teacher teacher;
}

• Teacher实体类

package com.wei.pojo;

import lombok.Data;

@Data
public class Teacher {
    private int id;
    private String name;
    //学生关联一个老师
    private Teacher teacher;
}

查询嵌套处理

• Mapper.xml映射文件

<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.wei.dao.StudentMapper">
<!--    - resultType：Sql语句执行的返回值-->
<!--    - parameterMap：参数类型-->

    <!--
    子查询思路：
    1.查询所有的学生信息
    2.根据查询出来的学生的tid，寻找对应的老师
    -->
    <select id="getStudent" resultMap="StudentTeacher">
        select * from mybatis_03.student;
    </select>

    <resultMap id="StudentTeacher" type="Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--
        复杂的属性，我们需要单独处理
        对象：association
        集合：collection
        column：数据库中的字段
        property：实体类中的属性
        javaType：设置对象类型
        -->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>

    <select id="getTeacher" resultType="Teacher">
        select * from mybatis_03.teacher where id=#{tid};
    </select>
</mapper>

• Test测试类

    @Test
    public void testStudent() {
        //取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获得StudentMapper接口类
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        //获取getStudent学生信息
        List<Student> studentList = mapper.getStudent();

        for (Student student : studentList) {
            System.out.println(student);
        }

        //关闭SqlSession,避免造成内存出现问题
        sqlSession.close();
    }
}

结果嵌套查询

• Mapper.xml映射文件

<!--按照结果嵌套处理-->
<select id="getStudent2" resultMap="StudentTeacher2">
    select s.id sid, s.name sname,t.name tname from mybatis_03.student s , mybatis_03.teacher t where t.id=s.tid;
</select>

<resultMap id="StudentTeacher2" type="Student">
    <result property="id" column="sid"/>
    <result property="name" column="sname"/>
    <association property="teacher" javaType="Teacher">
        <result property="name" column="tname"/>
    </association>
</resultMap>

• Test测试类

@Test
public void testStudent2() {
    //取SqlSession对象
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    //获得StudentMapper接口类
    StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
    //获取getStudent学生信息
    List<Student> studentList = mapper.getStudent2();

    for (Student student : studentList) {
        System.out.println(student);
    }

    //关闭SqlSession,避免造成内存出现问题
    sqlSession.close();
}

一对多处理

环境搭建

• Student实体类

package com.wei.pojo;

import lombok.Data;

//多对一
@Data
public class Student {
    private int id;
    private String name;
    private int tid;
}

• Teacher实体类

package com.wei.pojo;

import lombok.Data;

import java.util.List;

@Data
public class Teacher {
    private int id;
    private String name;
    //一个老师拥有多个学生
    private List<Student> students;
}

查询嵌套处理

• StudentMapper类

package com.wei.dao;

import com.wei.pojo.Student;

import java.util.List;

public interface StudentMapper {
    //查询所有的学生信息，以及对应的老师的信息
    public List<Student> getStudent2();
}

• TeacherMapper.xml映射文件

<select id="getTeacher2" resultMap="TeacherStudent2">
    select * from mybatis_03.teacher where id=#{tid};
</select>
<!--resultMap结果映射-->
<resultMap id="TeacherStudent2" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <!--
    复杂的属性，我们需要单独处理
    对象：association
    集合：collection
    javaType：指定的属性类型
    集合中的泛型信息，使用ofType获取
   -->
    <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
</resultMap>

<select id="getStudentByTeacherId" resultType="Student">
    select * from mybatis_03.student where tid=#{tid};
</select>

• 测试

@Test
public void test2() {
    //获取sqlSession对象
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    //获取TeacherMapper接口类
    TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);

    Teacher teacher = mapper.getTeacher2(1);
    System.out.println(teacher);

    //关闭SqlSession,避免造成内存出现问题
    sqlSession.close();
}

结果嵌套查询

• StudentMapper类

package com.wei.dao;

import com.wei.pojo.Student;

import java.util.List;

public interface StudentMapper {
    //查询所有的学生信息，以及对应的老师的信息
    public List<Student> getStudent();
}

• TeacherMapper.xml映射文件

<!--按照结果嵌套查询-->
<select id="getTeacher" resultMap="TeacherStudent">
    select s.id sid, s.name sname, t.name tname, t.id tid from mybatis_03.student s,mybatis_03.teacher t where t.id = s.tid and t.id=#{tid};
</select>
<!--resultMap结果映射-->
<!--
column：数据库中的字段
property：实体类中的属性
-->
<resultMap id="TeacherStudent" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <!--
    复杂的属性，我们需要单独处理
    对象：association
    集合：collection
    javaType：指定的属性类型
    集合中的泛型信息，使用ofType获取
    -->
    <collection property="students" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>

• 测试

public class MyTest {
    @Test
    public void test() {
        //获取sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获取TeacherMapper接口类
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);

        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);

        //关闭SqlSession,避免造成内存出现问题
        sqlSession.close();
    }

总结：

collection & association区别：

• 关联 - association [多对一]
• 集合 - collection [一对多]

javatype & oftype区别：

• javatype：指定实体类中属性的类型
• oftype：指定映射到List或者集合的pojo类型，泛型中的约束类型

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