Mybatis介绍
MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架。MyBatis 避免了几乎所有的 JDBC 代码和手工设置参数以及抽取结果集。MyBatis 使用简单的 XML 或注解来配置和映射基本体，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。
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优点
1.简单易学：mybatis本身就很小且简单。没有任何第三方依赖，最简单安装只要两个jar文件+配置几个sql映射文件易于学习，易于使用，通过文档和源代码，可以比较完全的掌握它的设计思路和实现。
2.灵活：mybatis不会对应用程序或者数据库的现有设计强加任何影响。 sql可以写在xml里，便于统一管理和优化。
3.提供映射标签，支持对象与数据库的orm字段关系映射。
4.提供对象关系映射标签，支持对象关系组建维护。
5.提供xml标签，支持编写动态sql。
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缺点
1、编写SQL语句时工作量很大，尤其是字段多、关联表多时，更是如此。
2、SQL语句依赖于数据库，导致数据库移植性差，不能更换数据库。
3、框架还是比较简陋，功能尚有缺失，虽然简化了数据绑定代码，但是整个底层数据库查询实际还是要自己写的，工作量也比较大，而且不太容易适应快速数据库修改。
导入项目依赖
org.mybatis.spring.boot
mybatis-spring-boot-starter
2.1.1
mysql
mysql-connector-java
runtime
编写配置文件
# 数据库相关配置
spring.datasource.username=root
spring.datasource.password=yzhroot
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&serverTimezone=CTT
# mybatis相关配置
# 支持驼峰式与下划线转换
mybatis.configuration.map-underscore-to-camel-case=true
数据库建表语句
CREATE TABLE `department` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8
CREATE TABLE `user` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`create_date` date DEFAULT NULL,
`username` varchar(255) DEFAULT NULL,
`department_id` bigint(20) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `department_foreign` (`department_id`)
) DEFAULT CHARSET=utf8
编写实体类
/**
* 用户实体类
*/
public class User {
private Long id;
private String username;
private Date createDate;
private Department department;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getCreateDate() {
return createDate;
}
public void setCreateDate(Date createDate) {
this.createDate = createDate;
}
public Department getDepartment() {
return department;
}
public void setDepartment(Department department) {
this.department = department;
}
}
/**
* 部门实体类
*/
public class Department {
private Long id;
private String name;
private List users;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List getUsers() {
return users;
}
public void setUsers(List users) {
this.users = users;
}
}
编写持久层
由于SQL并不复杂，所以这里我使用注解的形式实现持久层代码。
@Mapper
public interface UserDao {
//根据department_id查询user
@Select("Select * from user where department_id = #{departmentId}")
List queryUserByDepartmentId(@Param("departmentId")Long departmentId);
//根据userId查询user信息
@Select("Select * from user where id = #{userId}")
@Results({
@Result(column = "department_id",property = "department",javaType = Department.class,one = @One(select = "training.springboot.mybatis.dao.DepartmentDao.queryDepartmentById"))
})
User queryUserbyUserId(@Param("userId")Long id);
}
@Mapper
public interface DepartmentDao {
//查询所有部门信息
@Select("Select * from department")
@Results({
@Result(column = "id",property = "users",javaType = List.class,many = @Many(select = "training.springboot.mybatis.dao.UserDao.queryUserByDepartmentId"))
})
List queryAllDepartment();
//根据部门ID查询部门信息
@Select("Select * from department where id = #{id}")
Department queryDepartmentById(@Param("id")Long id);
//插入一条部门记录
@Insert("Insert into department(name) values(#{name})")
Integer addDepartment(Department department);
//删除一条部门记录
@Delete("delete from department where id = #{id}")
Integer deleteDepartmentById(@Param("id")Long id);
}
实现一对多和多对一的关系只需要使用@Results注解即可。
测试
@SpringBootTest
class MybatisApplicationTests {
@Autowired
DepartmentDao departmentDao;
@Autowired
UserDao userDao;
@Test
public void testQueryUser(){
System.out.println(userDao.queryUserbyUserId((long) 1));
}
@Test
public void testQueryUserByDepartmentId(){
System.out.println(userDao.queryUserByDepartmentId((long) 1));
}
@Test
public void testQueryDepartmentById(){
System.out.println(departmentDao.queryDepartmentById((long) 1));
}
@Test
public void testQueryAllDepartments(){
System.out.println(departmentDao.queryAllDepartment());
}
@Test
public void testInsertDepartment(){
Department department = new Department();
department.setName("市场部");
departmentDao.addDepartment(department);
}
@Test
public void testDeleteDepartment(){
departmentDao.deleteDepartmentById((long) 2);
}
}
完整的工程代码链接：https://github.com/youzhihua/springboot-training