How to populate model with primary key when persisting through a controller - spring

Question

I'm quite new to spring and Thymeleaf integration so bear with me:
I'm having trouble getting the data from my Thymeleaf template using a JPA model. I've tried using both sequential and identity generation strategies but It doesn't even let me load the page
I've tried creating a completely new variable as seen before but that's clearly not the problem. I know the problem might come from the Thymeleaf references from the html but I'm quite confused; is there a way to auto generate an ID? It doesn't even let me add a value in the form as an ID
class Admin(#Id #GeneratedValue(strategy = GenerationType.IDENTITY) var id: Long, var firstName: String, var lastName: String, var login: String, var password: String) {
#PostMapping("/addstuff")
fun addAdmin(#ModelAttribute(name = "admin") admin: Admin, result: BindingResult, model: Model): String {
val newAdmin: Admin = Admin(admin.id, admin.firstName, admin.lastName, admin.firstName[0].plus(admin.lastName), encoder.encode("password"))
adminRepository.save(newAdmin)
return "adminadd"
}
form action="#" data-th-action="#{/addstuff}" th:object="${admin}" method="post">
<div class="row justify-content-center" id="mainBody">
<div class="col-8">
<div id="student0">
<div class="row">
<div class="col">
Administrator Information
</div>
</div>
<div class="row">
<div class="col">
<input th:field="*{firstName}" type="text" class="form-control" placeholder="First name">
</div>
<div class="col">
<input th:field="*{lastName}" type="text" class="form-control" placeholder="Last name">
</div>
<div class="col">
<input type="number" class="form-control" placeholder="Administrator ID number">
</div>
</div>
<div class="row">
<div class="col">
<label>Role
<div class="form-check">
<input class="form-check-input" type="radio" name="exampleRadios" id="adminRadio"
value="option1" checked>
<label class="form-check-label" for="adminRadio">
Administrator
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" name="exampleRadios" id="profRadio"
value="option2">
<label class="form-check-label" for="profRadio">
Professor
</label>
</div>
</label>
</div>
</div>
<hr>
</div>
<input id="submitAdmin" type="submit" value="Add Administrator">
<!-- <button id="submitAdmin">Add Administrator</button>-->
</div>
</div>
</form>
The result I expect should be the persisting of the data into my local db but the error i get is this:
'admin' on field 'id': rejected value [null]; codes [typeMismatch.admin.id,typeMismatch.id,typeMismatch.long,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [admin.id,id]; arguments []; default message [id]]; default message [Failed to convert value of type 'null' to required type 'long'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [null] to type [#javax.persistence.Id #javax.persistence.GeneratedValue long] for value 'null'; nested exception is java.lang.IllegalArgumentException: A null value cannot be assigned to a primitive type]]
I know it has to do with the id value but I'm stuck as to how I generate a value for it. I'm using the h2 embedded database if anyone is interested. Thanks in advance

Answer 1

Though your question is about data not getting transferred between template and JPA but exception clearly say the problem with JPA only. You are never required to pass ID while saving a new entity object in database. I suspect your id column in database table is not defined with auto generation strategy. Can you try modifying it and rerunning your code.

Answer 2

I've figured it out! I used the regular old html name tag and thymeleaf parsed and read it.
<div class="col">
<input type="text" name="lastName" class="form-control" placeholder="Last name">
</div>