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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