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javaspringhibernatespring-data-jpathymeleaf

Even if the form fields are left blank, empty strings are submitted and new entity is created in Spring

I have two entities: Student and StudentDetails. A Student can have only one or no StudentDetails. When I submit a form to save a Student, a StudentDetails is also being saved. That's okay if I send data for StudentDetails entity. But it's happening even if I don't send any data for StudentDetails entity. Images after saving three Students:

student table:

enter image description here

student_details table:

enter image description here

I want row 1,3 would not be saved in student_details table. And in student table student_details_id would be null for these two.

How can I implement @OneToOne relationship where parent/owner entity can have optional (One if exists, Zero if doesn't exist) child entity?

Here are my codes:

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
}

StudentDetails.java

@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
}

StudentController.java

@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";
    }
}

student_add_form.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>
Solution

  • You state that you are not sending any details for StudentDetails however your form clearly has fields for this data e.g:

    <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>

    Even if the form fields are left blank, empty strings will be submitted for these values and Spring will therefore bind a new StudentDetails instance on the Student model attribute and set the bound fields accordingly i.e. to empty strings.

    To prevent this tell Spring to trim empty Strings to null: if there are then, at the time of binding, no non-null properties in the request pertaining to StudentDetails then the StudentDetails instance on the Student model attribute will not be set by Spring.

    You can do this globally or on a per controller basis. See, for example:

    Can spring mvc trim all strings obtained from forms?

    I am not sure that Spring has always behaved like this i.e. auto instantiating non-simple nested properties however I have tested in Boot 2.1.8 (MVC 5.1.9) and this is what is happening.