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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

org.projectlomboklombok1.18.24

• 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

org.projectlomboklombok1.18.24

• 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

StudentMapper.xml

• 核心配置文件mybatis-config.xml绑定注册接口

• 测试

public class MyTest {@Testpublic 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

select * from mybatis_03.student;select * from mybatis_03.teacher where id=#{tid};

• Test测试类

    @Testpublic 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 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 s.id sid, s.name sname,t.name tname from mybatis_03.student s , mybatis_03.teacher t where t.id=s.tid;

• 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 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 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 getStudent2();
}

• TeacherMapper.xml映射文件

select * from mybatis_03.teacher where id=#{tid};



select * from mybatis_03.student where tid=#{tid};

• 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 getStudent();
}

• TeacherMapper.xml映射文件

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};

• 测试

public class MyTest {@Testpublic 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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