JPA中findBy基本语法规则：
这边需要引入jpa+mysql+web的相关依赖，如果创建的时候没有引入就需要在pom.xml进行配置
新建一个controller包（控制类所在地），entity包（实体类所在地），repository包（dao类所在地）
#数据库驱动
#数据库url地址，其中jpatest是数据库名称
spring.datasource.url=jdbc:mysql://localhost:3308/jpatest?useUnicode=true&characterEncoding=utf-8
#用户名称
#用户密码
#创建数据库表结构（更新的状态下创建）
#显示执行的sql语句
import javax.persistence.*;
/**
* Created by qiang on 2018/1/22.
*/
@Entity
@Table(name="user")
public class User {
@Id
@GenericGenerator(name = "PKUUID", strategy = "uuid2")
@GeneratedValue(generator = "PKUUID")
@Column(length = 36)
protected String id;
/**
* 名字
*/
@Column(name = "name", nullable = true, length = 30)
private String name;
/**
* 身高
*/
@Column(name = "height", nullable = true, length = 10)
private Integer height;
public User() {
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getHeight() {
return height;
}
public void setHeight(Integer height) {
this.height = height;
}
}
关于实体类的注释我会在接下来的章节中具体的介绍给大家，这篇文章先不做介绍。
import java.util.List;
/**
* Created by qiang on 2018/1/22.
*/
public interface UserRepository extends JpaRepository{
/**
* 相当于 select *from user where name=?
* @param name
* @return
*/
public List findByName(String name);
/**
* 相当于select *from user where name like ?
* 但是有一点需要注意的是，%需要我们自己来写
* @param name
* @return
*/
public List findByNameLike(String name);
/**
* 相当于select *from user where name not like ?
* 但是有一点需要注意的是，%需要我们自己来写
* @param name
* @return
*/
public List findByNameNotLike(String name);
/**
* 相当于 select *from user where name ?
* @param name
* @return
*/
public List findByNameNot(String name);
/**
* 相当于 select *from user where id in (?)
* @param ids
* @return
*/
public List findByIdIn(List ids);
/**
* 相当于 select *from user where id not in ()
* @param ids
* @return
*/
public List findByIdNotIn(List ids);
/**
* 相当于 select *from user where name=? order by height desc
* @param name
* @return
*/
public List findByNameOrderByHeightDesc(String name);
/**
* 相当于 select *from user where name=? order by height asc
* @param name
* @return
*/
public List findByNameOrderByHeightAsc(String name);
/**
* 相当于 select *from user where name is null
* @return
*/
public List findByNameIsNull();
/**
* 相当于 select *from user where name is not null
* @return
*/
public List findByNameIsNotNull();
/**
* 相当于 select *from user where name =? and height=?
* @param name
* @param height
* @return
*/
public List findByNameAndHeight(String name,int height);
/**
* 相当于 select *from user where name =? or height=?
* @param name
* @param height
* @return
*/
public List findByNameOrHeight(String name,int height);
/**
* 相当于 select *from user where height between ? and ?
* 需要注意的是mysql是有包含两个端点值的
* @param start
* @param end
* @return
*/
public List findByHeightBetween(int start,int end);
/**
* 相当于 select *from user where height < ?
* 需要注意的是mysql是没有包含端点值的
* @param less
* @return
*/
public List findByHeightLessThan(int less);
/**
* 相当于 select *from user where height > ?
* 需要注意的是mysql是没有包含端点值的
* @param greater
* @return
*/
public List findByHeightGreaterThan(int greater);
}
具体语法规则和对应的sql都在代码中给出来了，这边需要和大家说的是UserRepository接口的特点。我们通过继承JpaRepository《对应的实体类，主键属性值》来编写findBy等相关的函数来查询数据库。继承JpaRepository的接口在使用的时候，通过@Autowired会自动创建接口的实现类，不需要怎么去实现这个接口，这也是jpa最方便的地方。
import org.springframework.web.bind.annotation.RequestMapping;
import java.util.ArrayList;
import java.util.List;
/**
* Created by qiang on 2018/1/22.
*/
@Controller
@RequestMapping(value = "jpa")
public class UserController {
@Autowired
private UserRepository userRepository;
@RequestMapping(value = "findByName",method = RequestMethod.GET)
@ResponseBody
public List findByName(String name){
return userRepository.findByName(name);
}
@RequestMapping(value = "findByHeightBetween",method = RequestMethod.GET)
@ResponseBody
public List findByHeightBetween(int start,int end){
return userRepository.findByHeightBetween(start,end);
}
@RequestMapping(value = "findByHeightLessThan",method = RequestMethod.GET)
@ResponseBody
public List findByHeightLessThan(int less){
return userRepository.findByHeightLessThan(less);
}
@RequestMapping(value = "findByHeightGreaterThan",method = RequestMethod.GET)
@ResponseBody
public List findByHeightGreaterThan(int greater){
return userRepository.findByHeightGreaterThan(greater);
}
@RequestMapping(value = "findByNameAndHeight",method = RequestMethod.GET)
@ResponseBody
public List findByNameAndHeight(String name,int height){
return userRepository.findByNameAndHeight(name,height);
}
@RequestMapping(value = "findByNameOrHeight",method = RequestMethod.GET)
@ResponseBody
public List findByNameOrHeight(String name,int height){
return userRepository.findByNameOrHeight(name,height);
}
@RequestMapping(value = "findByNameIsNull",method = RequestMethod.GET)
@ResponseBody
public List findByNameIsNull(){
return userRepository.findByNameIsNull();
}
@RequestMapping(value = "findByNameIsNotNull",method = RequestMethod.GET)
@ResponseBody
public List findByNameIsNotNull(){
return userRepository.findByNameIsNotNull();
}
@RequestMapping(value = "findByNameOrderByHeightDesc",method = RequestMethod.GET)
@ResponseBody
public List findByNameOrderByHeightDesc(String name){
return userRepository.findByNameOrderByHeightDesc(name);
}
@RequestMapping(value = "findByNameOrderByHeightAsc",method = RequestMethod.GET)
@ResponseBody
public List findByNameOrderByHeightAsc(String name){
return userRepository.findByNameOrderByHeightAsc(name);
}
@RequestMapping(value = "findByNameLike",method = RequestMethod.GET)
@ResponseBody
public List findByNameLike(String name){
return userRepository.findByNameLike("%"+name+"%");
}
@RequestMapping(value = "findByNameNotLike",method = RequestMethod.GET)
@ResponseBody
public List findByNameNotLike(String name){
return userRepository.findByNameNotLike("%"+name+"%");
}
@RequestMapping(value = "findByNameNot",method = RequestMethod.GET)
@ResponseBody
public List findByNameNot(String name){
return userRepository.findByNameNot(name);
}
@RequestMapping(value = "findByIdIn",method = RequestMethod.GET)
@ResponseBody
public List findByIdIn(String ids){
Listlist=new ArrayList();
String[] idsStr=ids.split(",");
for(String id:idsStr){
list.add(id);
}
return userRepository.findByIdIn(list);
}
@RequestMapping(value = "findByIdNotIn",method = RequestMethod.GET)
@ResponseBody
public List findByIdNotIn(String ids){
Listlist=new ArrayList();
String[] idsStr=ids.split(",");
for(String id:idsStr){
list.add(id);
}
return userRepository.findByIdNotIn(list);
}
}
到这里关于jpa中findBy基本的语法就介绍完毕了，下一节将介绍jpa中关联查询的用法。
项目GitHub地址：https://github.com/1913045515/JPA
转载自：https://blog.csdn.net/linzhiqiang0316/article/details/79177077
