How to populate dropdown list from one entity class to another in spring-boot? - spring-boot

Question

Customer.java file
#Entity
#Data
#AllArgsConstructor
#NoArgsConstructor
public class Customer {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String relative;
private String address;
private Long aadhar;
private Long contact;
public Long getAadhar() {
return aadhar;
}
public void setAadhar(Long aadhar) {
this.aadhar = aadhar;
}
#ManyToOne
#JoinColumn(name="town_name",insertable = false,updatable = false)
private Town town;
private String town_name;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getRelative() {
return relative;
}
public void setRelative(String relative) {
this.relative = relative;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public Town getTown() {
return town;
}
public void setTown(Town town) {
this.town = town;
}
public String getTown_name() {
return town_name;
}
public void setTown_name(String town_name) {
this.town_name = town_name;
}
public Long getContact() {
return contact;
}
public void setContact(Long contact) {
this.contact = contact;
}
}
Town.Java
#Entity
#Data
#AllArgsConstructor
#NoArgsConstructor
public class Town {
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Id
private String townname;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getTownname() {
return townname;
}
public void setTownname(String townname) {
this.townname = townname;
}
}
CustomerController.java file
#Controller
public class CutomerController {
#Autowired
private CutomerService customerService;
#GetMapping("/customer")
public String findAllCustomers(Model model) {
model.addAttribute("customers", customerService.findAllCustomers());
return "customer";
}
#PostMapping("/customer/addnew")
public String addNew(Customer customer) {
customerService.saveCustomer(customer);
return "redirect:/customer";
}
}
TownController.java file
#Controller
public class TownController {
#Autowired
private TownService townService;
#GetMapping("/town")
public String findAllTowns(Model model) {
model.addAttribute("towns", townService.findAllTown());
return "town";
}
}
My customer.html file
<!-- Multi Columns Form -->
<form class="row g-3" th:action="#{/customer/addnew}" method="post">
<div class="col-md-4">
<label for="aadhar" class="form-label">Aadhar No.</label>
<input type="number" min="0" max="999999999999" class="form-control" id="aadhar">
</div>
<div class="col-md-8">
<label for="customername" class="form-label">Customer Name</label>
<input type="text" class="form-control" id="name"onKeyup="this.value = this.value.toUpperCase()" required>
</div>
<div class="col-md-6">
<label for="relative" class="form-label">S/O,D/O,C/O</label>
<input type="text" class="form-control" id="relative"onKeyup="this.value = this.value.toUpperCase()" required>
</div>
<div class="col-md-6">
<label for="contact" class="form-label">Contact No.</label>
<input type="number" max="9999999999" class="form-control" id="contact">
</div>
<div class="col-12">
<label for="inputAddress5" class="form-label">Address</label>
<input type="text" class="form-control" id="address"onKeyup="this.value = this.value.toUpperCase()" placeholder="1234 Main St" required>
</div>
<div class="col-md-4">
<label for="inputTown" class="form-label" id="selecttown">Town/Area</label>
<select class="form-control" id="selecttown" name="townname" th:field="*{townname}" required>
<option selected>Choose...</option>
<option th:each="town:${towns}" th:value="${town.towname}" th:text="${town.towname}"></option>
</select>
</div>
<div class="text-center" style="margin-bottom:10px">
<button type="submit" class="btn btn-primary mx-1 my-1">Submit</button>
i am expecting populate the names of towns in dropdown list of customer modal form. But i am getting this error
Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Wed Nov 30 12:18:23 IST 2022
There was an unexpected error (type=Internal Server Error, status=500).
An error happened during template parsing (template: "class path resource [templates/customer.html]")
org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/customer.html]")
Caused by: org.attoparser.ParseException: Error during execution of processor 'org.thymeleaf.spring6.processor.SpringSelectFieldTagProcessor' (template: "customer" - line 473, col 70)
Caused by: org.thymeleaf.exceptions.TemplateProcessingException: Error during execution of processor 'org.thymeleaf.spring6.processor.SpringSelectFieldTagProcessor' (template: "customer" - line 473, col 70)
Caused by: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'townname' available as request attribute

Answer 1

Your are referencing wrong variable.
Modify your CustomerController class like this:
#Autowired
private CutomerService customerService;
#Autowired
private TownService townService;
#GetMapping("/customer")
public String findAllCustomers(Model model) {
model.addAttribute("customers", customerService.findAllCustomers());
model.addAttribute("towns", townService.findAllTown());
return "customer";
}
#PostMapping("/customer/addnew")
public String addNew(Customer customer) {
customerService.saveCustomer(customer);
return "redirect:/customer";
}