Mybatis持久层框架 | Lombok搭建

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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

importlombok.*;@Data@AllArgsConstructor@NoArgsConstructorpublicclassUser{privateint id;privateString name;privateString 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

packagecom.wei.pojo;importlombok.Data;@DatapublicclassTeacher{privateint id;privateString name;//学生关联一个老师privateTeacher teacher;}

Student类

packagecom.wei.pojo;importlombok.Data;//多对一@DatapublicclassStudent{privateint id;privateString name;//学生需要关联一个老师privateTeacher teacher;}

• 建立Mapper接口

TeacherMapper接口

packagecom.wei.dao;importcom.wei.pojo.Teacher;importorg.apache.ibatis.annotations.Param;importorg.apache.ibatis.annotations.Select;publicinterfaceTeacherMapper{@Select("select * from mybatis_03.teacher where id = #{tid}")TeachergetTeacher(@Param("tid")int id);}

StudentMapper接口

packagecom.wei.dao;publicinterfaceStudentMapper{}

• 建立Mapper.xml文件

TeacherMapper.xml

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPEmapperPUBLIC"-//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--><mappernamespace="com.wei.dao.TeacherMapper"></mapper>

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPEmapperPUBLIC"-//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--><mappernamespace="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><mapperresource="com/wei/dao/StudentMapper.xml"/><mapperresource="com/wei/dao/TeacherMapper.xml"/></mappers>

• 测试

publicclassMyTest{@Testpublicvoidtest(){//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

packagecom.wei.pojo;importlombok.Data;//多对一@DatapublicclassStudent{privateint id;privateString name;//学生需要关联一个老师privateTeacher teacher;}

• Teacher实体类

packagecom.wei.pojo;importlombok.Data;@DatapublicclassTeacher{privateint id;privateString name;//学生关联一个老师privateTeacher 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--><mappernamespace="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
    --><selectid="getStudent"resultMap="StudentTeacher">
        select * from mybatis_03.student;
    </select><resultMapid="StudentTeacher"type="Student"><resultproperty="id"column="id"/><resultproperty="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
        --><associationproperty="teacher"column="tid"javaType="Teacher"select="getTeacher"/></resultMap><selectid="getTeacher"resultType="Teacher">
        select * from mybatis_03.teacher where id=#{tid};
    </select></mapper>

• Test测试类

@TestpublicvoidtestStudent(){//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--><selectid="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><resultMapid="StudentTeacher2"type="Student"><resultproperty="id"column="sid"/><resultproperty="name"column="sname"/><associationproperty="teacher"javaType="Teacher"><resultproperty="name"column="tname"/></association></resultMap>

• Test测试类

@TestpublicvoidtestStudent2(){//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

packagecom.wei.pojo;importlombok.Data;//多对一@DatapublicclassStudent{privateint id;privateString name;privateint tid;}

• Teacher实体类

packagecom.wei.pojo;importlombok.Data;importjava.util.List;@DatapublicclassTeacher{privateint id;privateString name;//一个老师拥有多个学生privateList<Student> students;}

查询嵌套处理

• StudentMapper类

packagecom.wei.dao;importcom.wei.pojo.Student;importjava.util.List;publicinterfaceStudentMapper{//查询所有的学生信息，以及对应的老师的信息publicList<Student>getStudent2();}

• TeacherMapper.xml映射文件

<selectid="getTeacher2"resultMap="TeacherStudent2">
    select * from mybatis_03.teacher where id=#{tid};
</select><!--resultMap结果映射--><resultMapid="TeacherStudent2"type="Teacher"><resultproperty="id"column="tid"/><resultproperty="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
   --><collectionproperty="students"javaType="ArrayList"ofType="Student"select="getStudentByTeacherId"column="id"/></resultMap><selectid="getStudentByTeacherId"resultType="Student">
    select * from mybatis_03.student where tid=#{tid};
</select>

• 测试

@Testpublicvoidtest2(){//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

packagecom.wei.dao;importcom.wei.pojo.Student;importjava.util.List;publicinterfaceStudentMapper{//查询所有的学生信息，以及对应的老师的信息publicList<Student>getStudent();}

• TeacherMapper.xml映射文件

<!--按照结果嵌套查询--><selectid="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
--><resultMapid="TeacherStudent"type="Teacher"><resultproperty="id"column="tid"/><resultproperty="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
    --><collectionproperty="students"ofType="Student"><resultproperty="id"column="sid"/><resultproperty="name"column="sname"/><resultproperty="tid"column="tid"/></collection></resultMap>

• 测试

publicclassMyTest{@Testpublicvoidtest(){//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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