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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🌼 结语：创作不易，如果觉得博主的文章赏心悦目，还请——点赞👍收藏⭐️评论📝冲冲冲🤞
