Java 即使表单字段留空，也会提交空字符串，并在Spring中创建新实体

我有两个实体：

Student

和

StudentDetails

。

学生

只能有一个或没有

学生详细信息

。当我提交表单以保存

学生

时，也会保存

学生详细信息

。如果我发送

StudentDetails

entity的数据，这没关系。但即使我没有为

StudentDetails

实体发送任何数据，这种情况也会发生。保存三个

Student

s后的图像：

学生

表格：

学生详细信息

表格：

我希望第1,3行不会保存在

student\u details

表中。而在

student

表

student\u details\u id

中，这两个变量的

null

我如何实现@OneToOne关系，其中父/所有者实体可以有可选的子实体（如果存在一个，如果不存在则为零）

这是我的密码：

Student.java

@Entity
@Table(name = "student")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "student_name")
    private String studentName;

    @Column(name = "student_roll")
    private String studentRoll;

    @Column(name = "student_class")
    private String studentClass;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "student_details_id")
    private StudentDetails studentDetails;

    // Constructors, Getters and Setters
}

@Entity
@Table(name = "student_details")
public class StudentDetails {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "student_contact")
    private String studentContact;

    @Column(name = "student_email")
    private String studentEmail;

    @Column(name = "student_address")
    private String studentAddress;

    @OneToOne(mappedBy = "studentDetails", cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.DETACH, CascadeType.REFRESH })
    @JsonIgnore
    private Student student;

    // Constructors, Getters and Setters
}

@Controller
@RequestMapping("/students")
public class StudentController {

    @Autowired
    private StudentRepository studentRepository;

    @GetMapping("/add")
    public String add(Model theModel) {
        Student theStudent = new Student();
        theModel.addAttribute("theStudent", theStudent);
        return "student/student_add_form";
    }

    @PostMapping("/create")
    public String create(@ModelAttribute("theStudent") Student theStudent) {
        theStudent.setId((long) 0);
        studentRepository.save(theStudent);
        return "redirect:/students/index";
    }
}

StudentDetails.java

@Entity
@Table(name = "student")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "student_name")
    private String studentName;

    @Column(name = "student_roll")
    private String studentRoll;

    @Column(name = "student_class")
    private String studentClass;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "student_details_id")
    private StudentDetails studentDetails;

    // Constructors, Getters and Setters
}

@Entity
@Table(name = "student_details")
public class StudentDetails {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "student_contact")
    private String studentContact;

    @Column(name = "student_email")
    private String studentEmail;

    @Column(name = "student_address")
    private String studentAddress;

    @OneToOne(mappedBy = "studentDetails", cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.DETACH, CascadeType.REFRESH })
    @JsonIgnore
    private Student student;

    // Constructors, Getters and Setters
}

@Controller
@RequestMapping("/students")
public class StudentController {

    @Autowired
    private StudentRepository studentRepository;

    @GetMapping("/add")
    public String add(Model theModel) {
        Student theStudent = new Student();
        theModel.addAttribute("theStudent", theStudent);
        return "student/student_add_form";
    }

    @PostMapping("/create")
    public String create(@ModelAttribute("theStudent") Student theStudent) {
        theStudent.setId((long) 0);
        studentRepository.save(theStudent);
        return "redirect:/students/index";
    }
}

StudentController.java

@Entity
@Table(name = "student")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "student_name")
    private String studentName;

    @Column(name = "student_roll")
    private String studentRoll;

    @Column(name = "student_class")
    private String studentClass;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "student_details_id")
    private StudentDetails studentDetails;

    // Constructors, Getters and Setters
}

@Entity
@Table(name = "student_details")
public class StudentDetails {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "student_contact")
    private String studentContact;

    @Column(name = "student_email")
    private String studentEmail;

    @Column(name = "student_address")
    private String studentAddress;

    @OneToOne(mappedBy = "studentDetails", cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.DETACH, CascadeType.REFRESH })
    @JsonIgnore
    private Student student;

    // Constructors, Getters and Setters
}

@Controller
@RequestMapping("/students")
public class StudentController {

    @Autowired
    private StudentRepository studentRepository;

    @GetMapping("/add")
    public String add(Model theModel) {
        Student theStudent = new Student();
        theModel.addAttribute("theStudent", theStudent);
        return "student/student_add_form";
    }

    @PostMapping("/create")
    public String create(@ModelAttribute("theStudent") Student theStudent) {
        theStudent.setId((long) 0);
        studentRepository.save(theStudent);
        return "redirect:/students/index";
    }
}

学生添加表单.html

<!doctype html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">

<head>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.3.1/css/bootstrap.css">
<title>Student List</title>
</head>

<body>
    <div class="container">
        <div class="row">
            <div class="col-9">
                <h1 th:text="'Add New Student'"></h1>
            </div>
            <div class="col-3">
                <a th:href="@{/students/index}" class="btn btn-success">View Student List</a>
            </div>
        </div>
        <div class="row">
            <form action="#" th:action="@{/students/create}" th:object="${theStudent}" th:method="POST" class="col-12">
                <div class="row">
                    <div class="form-group col-3">
                        <label for="studentName">Name:</label> <input type="text" class="form-control"
                            id="studentName" name="studentName" placeholder="Enter Student's Name" th:field="*{studentName}">
                    </div>
                    <div class="form-group col-3">
                        <label for="studentClass">Class:</label> <input type="text" class="form-control"
                            id="studentClass" name="studentClass" placeholder="Enter Student's Class" th:field="*{studentClass}">
                    </div>
                    <div class="form-group col-3">
                        <label for="studentRoll">Roll:</label> <input type="text" class="form-control"
                            id="studentRoll" name="studentRoll" placeholder="Enter Student's Roll" th:field="*{studentRoll}">
                    </div>
                    <div class="form-group col-3">
                        <label for="studentContact">Contact:</label> <input type="text" class="form-control"
                            id="studentContact" name="studentContact" placeholder="Enter Student's Contact"
                            th:field="*{studentDetails.studentContact}">
                    </div>
                </div>
                <div class="row">
                    <div class="form-group col-3">
                        <label for="studentEmail">Email:</label> <input type="text" class="form-control"
                            id="studentEmail" name="studentEmail" placeholder="Enter Student's Email"
                            th:field="*{studentDetails.studentEmail}">
                    </div>
                    <div class="form-group col-6">
                        <label for="studentAddress">Address:</label> <input type="text" class="form-control"
                            id="studentAddress" name="studentAddress" placeholder="Enter Student's Address"
                            th:field="*{studentDetails.studentAddress}">
                    </div>
                                        <div class="form-group col-3">
                        <label></label> <input type="submit" class="form-control btn btn-success" id="saveStudent"
                            name="saveStudent" value="Save Student">
                    </div>
                </div>
            </form>
        </div>
    </div>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.3.1/js/bootstrap.js"></script>
    <script>

    </script>
</body>
</html>

学生名单
姓名：
类别：
滚动：
联系人：
电邮：
地址:

您声明您没有发送任何有关StudentDetails的详细信息，但是您的表单中明确包含此数据的字段，例如：

<div class="form-group col-3">
    <label for="studentEmail">Email:</label> <input type="text" class="form-control"
        id="studentEmail" name="studentEmail" placeholder="Enter Student's Email"
        th:field="*{studentDetails.studentEmail}">
</div>

电邮：

即使表单字段留空，也会为这些值提交空字符串，因此Spring会在

Student

模型属性上绑定一个新的

StudentDetails

实例，并相应地设置绑定字段，即空字符串

为了防止这种情况，请告诉Spring将空字符串修剪为null：如果在绑定时，请求中没有与

StudentDetails

相关的非null属性，那么

StudentDetails

模型属性上的

StudentDetails

实例将不会由Spring设置

您可以全局执行此操作，也可以基于每个控制器执行此操作。例如，见：

---

我不确定Spring是否总是这样，即自动实例化非简单嵌套属性，但我在Boot 2.1.8（MVC 5.1.9）中进行了测试，结果就是这样。

列“student\u id”不能为null

是一个数据库约束。您需要更改列以允许空值。对于可选关系，在

@OneToOne

中使用

optional=true

，在whcih表中不清楚您看到的错误。可能是

Student.studentId

可能是

StudentDetails.Student

。它来自哪一张桌子？还有我经常遇到的问题是

cascade=CascadeType。所有的
都是持久化一个新实体。我认为应该首先保存
StudentDetails
，但是
Student
尚未保存。虽然您的问题不清楚，但您是否检查了
StudentDetails
是否设置了
Student
？您发送的请求是什么？正在保存的学生是否有学生详细信息记录？如果是这样，那是因为您没有设置关系的反面。i、 e.StudentDetails没有学生集。在双向关系中，您有责任确保内存模型的两侧设置正确。保存SudentDetails记录的唯一方法是为学生创建一条记录。你说你没有，但你一定弄错了。您发送的请求是什么，因为Student.studentDetails！=保存时为空。