Question

为什么在使用JPA注释时不能将String作为主键？

我正在尝试创建具有字符串类型作为ID的注册页面。并获取IdentifierGenerationException异常：

org.hibernate.id.IdentifierGenerationException：此类的ID必须在调用save（）之前手动分配

HomeController.java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class HomeController
{
    @Autowired
    StudRepo repo;
    @RequestMapping("/home")
    public void addStud(@ModelAttribute("students") Students students) 
    {
        repo.save(students);
    }
}



POJO :
import javax.persistence.Entity;
import javax.persistence.Id;
@Entity
public class Students 

{       
        @Id
    private String name;
    private String grade;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public String getGrade() {
        return grade;
    }
    public void setGrade(String grade) {
        this.grade = grade;
    }

    @Override
    public String toString() {
        return "Students [name=" + name + ", grade=" + grade + "]";
    }
}


Repo:
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Component;

@Component

public interface StudRepo extends JpaRepository<Students, String>
{

}



JSP :
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>

<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
    <form action="students" method="get">
        Student Name : <input type="text" name="name" /> <br> Student
        Grade : <input type="text" name="grade" /> <br> 
        <input type="submit" name="Log Me In" />
        </form>

</body>
</html>

Error :

ids for this class must be manually assigned before calling save(): com.example.demo.Students; nested exception is org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.example.demo.Students

为什么在使用JPA注释时不能将String作为主键？

我希望将String作为创建的主键表。

在调用save（）之前，必须手动分配此类的ID：com.example.demo

0 个答案: