Mybatis持久层框架 | Lombok搭建

怼烎@ 2024-04-22 19:14 91阅读 0赞

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> [?wei\_shuo的个人主页][wei_shuo]
> 
> ?[wei\_shuo的学习社区][wei_shuo 1]
> 
> ?Hello World ！

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### Lombok ###

![在这里插入图片描述][af805bdd712044dbb878fba509574aa0.png_pic_center]

> 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">
>     
>     
>     <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">
>     
>     
>     <mapper namespace="com.wei.dao.StudentMapper">
>     
>     </mapper>
> 
>  *  核心配置文件mybatis-config.xml绑定注册接口
> 
>     
>     <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
> 
>     
>     <mapper namespace="com.wei.dao.StudentMapper">
>     
>     
>     
>         
>         <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"/>
>             
>             <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
> 
>     
>     <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 id="TeacherStudent2" type="Teacher">
>         <result property="id" column="tid"/>
>         <result property="name" column="tname"/>
>         
>         <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
> 
>     
>     <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 id="TeacherStudent" type="Teacher">
>         <result property="id" column="tid"/>
>         <result property="name" column="tname"/>
>         
>         <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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[wei_shuo]: https://blog.csdn.net/weixin_62765017
[wei_shuo 1]: https://bbs.csdn.net/forums/wei_shuo_study
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