Thymeleaf #sets.contains() always returning false despite usage according to documentation - spring

Question

Preface
I have a spring boot application with a User entity with a set of Role.
On the edit user template, I am displaying the user's roles with a <select>multiple. When rending the view of a existing User with its set of Role, I am trying to only mark as selected the roles within the set.
Thymeleaf provides two tools for this:
th:selected: Which expects a boolean value (true being selected)
#sets: Which provides a handful of useful methods similar to java.util.Set, the one being used in this case is contains().
The problem
When adding to the model a found User and all the possibles Role in the form of a HashSet, using #sets.contains() always return false when using the found user's roles and all the roles as parameters, therefore not selecting the user's roles when loading the form.
If I use the notation th:selected="${{user.roles}}" notation all the options are selected (even those the user does not posses).
The Code
User
public class User
{
private Long id;
private String username;
private String password;
private String passwordConfirm;
private Set<Role> roles;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
public Long getId()
{
return id;
}
public void setId(Long id)
{
this.id = id;
}
public String getUsername()
{
return username;
}
public void setUsername(String username)
{
this.username = username;
}
public String getPassword()
{
return password;
}
public void setPassword(String password)
{
this.password = password;
}
#Transient
public String getPasswordConfirm()
{
return passwordConfirm;
}
public void setPasswordConfirm(String passwordConfirm)
{
this.passwordConfirm = passwordConfirm;
}
#ManyToMany(fetch = FetchType.EAGER)
#JoinTable(name = "users_role", joinColumns = #JoinColumn(name = "users_id"), inverseJoinColumns = #JoinColumn(name = "role_id"))
public Set<Role> getRoles()
{
return roles;
}
public void setRoles(Set<Role> roles)
{
this.roles = roles;
}
}
Role
public class Role
{
private Long id;
private String name;
private Set<User> users;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
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;
}
#ManyToMany(mappedBy = "roles")
public Set<User> getUsers()
{
return users;
}
public void setUsers(Set<User> users)
{
this.users = users;
}
}
Controller
#Controller
#RequestMapping("/admin")
public class AdminController
{
#Autowired
UserService userService;
#Autowired
RoleService roleService;
#RequestMapping("/user/edit/{id}")
public String editUser(Model model, #PathVariable("id") long id)
{
User user = userService.findByUserId(id);
HashSet<Role> foundRoles = roleService.getAllRoles();
model.addAttribute("user", user);
model.addAttribute("userRoles", foundRoles);
return "admin/adminUserDetail";
}
}
The form
<form role="form" th:action="#{/registration}" method="POST"
th:object="${user}">
<div th:if="${#fields.hasErrors('*')}">
<div class="alert alert-danger" role="alert">
<h3 class="alert-heading">It seems we have a couple problems with your input</h3>
<li th:each="err : ${#fields.errors('*')}" th:text="${err}"></li>
</div>
</div>
<div class="form-group">
<label>Username: </label> <input class="form-control" type="text" th:field="${user.username}"
placeholder="Username" name="username"/>
<label>Password: </label> <input class="form-control" type="password" th:field="${user.password}"
placeholder="Password" name="password"/>
<label>Password Confirm: </label> <input type="password"
th:field="${user.passwordConfirm}" class="form-control"
placeholder="Password Confirm"/>
<select class="form-control" multiple="multiple">
<option th:each="role : ${userRoles}"
th:value="${role.id}"
th:selected="${#sets.contains(user.roles, role)}"
th:text="${role.name}">Role name
</option>
</select>
<button type="submit" class="btn btn-success">Update</button>
</div>
</form>

Answer 1

When using a Set the object in there must implement both hashCode and equals as that is used to determine if an object is already in the Set. Unless it is a SortedSet which uses either a Comparator or the natural order expressed through your object implementing Comparable.
As you don't do either of those using contains will simply always return false even for a seemingly same Role instance. Because according to the contract they aren't.
To fix implement the equals and hashCode method in your User and Role object.
public class Role {
public int hashCode() {
return Objects.hash(this.name);
}
public boolean equals(Object o) {
if (o == this) { return true; }
if (o == null || !(o instanceof Role) ) { return false; }
return Objects.equals(this.name, ((Role) o).name);
}
}
Something along those lines should do the trick.