1.前言
Springboot 的使用已经越来越广泛了，目前使用的主流持久层框架有JPA+Hibernate,Mybatis等，JPA不用说api封装的很完善，一切面向对象，基本上不用写啥sql就可以完成大部分增删改查功能，据统计目前国内使用mybaits的表较多，JPA国外使用的比较多。话说写的一手好sql才能成为一个合格的后台，所以。。。 我还是比较喜欢mybatis,毕竟自己写出来的sql才能有灵魂，Springboot+mybatis 有两种写法，mapper.xml文件或者注解，这里主要讲mybatis注解的用法，持久化层无外乎增删改查，从这篇文章你可以学到90%的注解使用方法，举一反三可以完成各种需求的业务。
1.准备
友情链接：mybatis-3 github项目地址：github项目环境：springboot+mybatis+mysql配置文件如下
application.properties：
server.port=8081
server.servlet.context-path=/mybatis
spring.main.banner-mode=off
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/root?characterEncoding=utf8
spring.datasource.username=root
spring.datasource.password=123456
##时间格式化
spring.jackson.date-format=yyyy-MM-dd HH:mm:ss
spring.jackson.time-zone=GMT+8
##mybatis
##开启驼峰发命名
mybatis.configuration.mapUnderscoreToCamelCase=true
## 分页插件
pagehelper.helperDialect=mysql
pagehelper.reasonable=false
##去掉这个配置 否则出现分页异常
#pagehelper.supportMethodsArguments=true
pagehelper.params=count=countSql
pagehelper.returnPageInfo=check
##redis 地址
实体类一对多关系
@Data
@ToString
public class Teacher implements Serializable {
public final static String SEX_BOY = "1";
public final static String SEX_GIRL = "2";
private Long id;
private String name;
private String sex;
private String phoneNumber;
private Date createTime;
private List<Student> students;
}
@Data
@ToString
public class Student implements Serializable {
public final static String SEX_BOY = "1";
public final static String SEX_GIRL = "2";
private Long id;
private String name;
private String sex;
private Integer age;
private String phoneNumber;
private Long teacherId;
private Date createTime;
private Teacher teacher;
}
创建Mapper接口类 方式一：在Mapper类增加注解 @Mapper 需要每个文件都加 方式二：在MybatisApplication启动类增加注解：@MapperScan(“com.springboot.mybatis.mapper”) 这样spring 就可以扫描Mapper类
@Mapper
public interface StudentMapper {
public static final String TABLE_NAME = "t_student";
}
2.Mapper下的增删改查
2.1 增
增加一条数据
@Insert("insert into " + TABLE_NAME + "(name,sex,age,phone_number,teacher_id,create_time) " +
"values(#{name},#{sex},#{age},#{phoneNumber},#{teacherId},#{createTime})")
int insertOne(Student student);
批量增加数据
@Insert({"<script> insert into "+TABLE_NAME+"(name,sex,age,phone_number,teacher_id,create_time) " +
"values " +
"<foreach collection='list' open='' item='item' separator=','> " +
"(#{item.name},#{item.sex},#{item.age},#{item.phoneNumber},#{item.teacherId},#{item.createTime}) " +
"</foreach> </script>"})
//批量增加数据
int insertList(List<Student> list);
2.2 删
删除数据
@Delete("delete from " + TABLE_NAME + " where id = #{id}")
int delete(Long id);
2.3 改
@Update("update " + TABLE_NAME + " set create_time = #{time} where id = #{id}")
int updateTime(@Param("id") long id, @Param("time") Date time);
2.4 查
查找一条数据
@Select("select * from " + TABLE_NAME + " where id = #{id} ")
Student getOneById(Long id);
查找一条数据（一对一）
@Select("select * from " + TABLE_NAME + " where id = #{id} ")
@Results({
@Result(column = "teacher_id", property = "teacher",
one = @One(select = "com.springboot.mybatis.mapper.TeacherMapper.getOneById"))
})
Student getOneWithTeacherById(Long id);
查找一条数据（一对多）
@Select("select * from " + TABLE_NAME + " where id = #{id} ")
@Results({
@Result(column = "id", property = "students",
many = @Many(select = "com.springboot.mybatis.mapper.StudentMapper.getListByTeacherId"))
})
Teacher getOneWithStudentsById(long id);
查找列表数据
@Select("select * from " + TABLE_NAME + " order by create_time desc ")
List<Teacher> getList();
@Select("select * from " + TABLE_NAME + " order by create_time desc ")
@Results({
@Result(column = "id", property = "students",
many = @Many(select = "com.springboot.mybatis.mapper.StudentMapper.getListByTeacherId"))
})
List<Teacher> getTeacherWithStudentsList();
灵活配置返回的参数
@Select("select COUNT(*) AS age_total,SUM(IF(age<14 = 1, 1, 0)) AS age_a,SUM(IF(age>14 and age < 17, 1, 0)) AS age_b,SUM(IF(age >17, 1, 0)) AS age_c from t_student")
@Results({
@Result(column = "age_total", property = "ageTotal"),
@Result(column = "age_a", property = "ageA"),
@Result(column = "age_b", property = "ageB"),
@Result(column = "age_c", property = "ageC"),
})
StudentAgeInfo getStudentAgeInfo();
动态sql (如果mapper sql 无法满足你的需求，动态sql才是考验你技术的时候) 创建 StudentMapperProvider 在这里你可以写出你想要的各种sql
package com.springboot.mybatis.mapper.provider;
import com.springboot.mybatis.entity.Student;
import com.springboot.mybatis.mapper.StudentMapper;
import org.apache.ibatis.jdbc.SQL;
import org.springframework.util.StringUtils;
/**
* @author wudyy
* @date 2019/4/1 16:31
* @Description: TODO
*/
public class StudentMapperProvider {
/**
* API拼装sql
*
* @param student
* @return
*/
public String queryAll(Student student) {
return new SQL() {
{
SELECT("*");
FROM(StudentMapper.TABLE_NAME);
if (student.getId() == null) {
WHERE("id = #{id}");
} else {
if (StringUtils.isEmpty(student.getName())) {
AND();
WHERE("name = #{name}");
} else if (StringUtils.isEmpty(student.getPhoneNumber())) {
AND();
WHERE("phone_number = #{phoneNumber}");
}
ORDER_BY("create_time desc");
}
}
}.toString();
}
/**
* 手动拼装sql(个人比较喜欢这种，感觉一切都在掌握中)
*
* @param student
* @return
*/
public String queryAllByNativeSql(Student student) {
StringBuilder sb = new StringBuilder();
sb.append("select * from ");
sb.append(StudentMapper.TABLE_NAME);
if (student.getId() == null) {
sb.append(" where id = #{id} ");
return sb.toString();
} else {
sb.append(" where 1 = 1 ");
}
if (StringUtils.isEmpty(student.getName())) {
sb.append("and name = #{name}");
} else if (StringUtils.isEmpty(student.getPhoneNumber())) {
sb.append("and phone_number = #{phoneNumber}");
}
sb.append("order by create_time desc");
return sb.toString();
}
}
使用：
//动态sql 查询
@SelectProvider(type = StudentMapperProvider.class, method = "queryAll")
List<Student> queryAll(Student student);
//动态sql 查询
@SelectProvider(type = StudentMapperProvider.class, method = "queryAllByNativeSql")
List<Student> queryAllByNativeSql(Student student);
当然增删改也可以使用动态sql， mybatis就是那么灵活，你想怎么玩就可以怎么玩，前提是你能写出一手good sql.
