Populate a drop down with a list using Thymeleaf and Spring Boot

Question

I'm trying to add an HTML select with data from a Database using Spring Boot and Thymeleaf. I can't get it what I'm doing wrong. This is the Code that is connected to this Problem:

My Model:

@Entity // This tells Hibernate to make a table out of this class
@Table(name = "Skill")
public class Skill {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="skillID")
    private int skillID;
    
    @Column(name="skillname")
    private String skillname;

    @OneToMany(mappedBy = "skill")
    private Collection<UserSkill> UserSkills = new ArrayList<>();

    public Skill() {
    }
    
      // constructors

    public Skill(int skillID, String skillname, Collection<UserSkill> userSkills) {
        this.skillID = skillID;
        this.skillname = skillname;
        this.UserSkills = userSkills;
    }
    
    // getter and setter

    public int getSkillID() {
        return skillID;
    }


    public void setSkillID(int skillID) {
        this.skillID = skillID;
    }

    public String getSkillname() {
        return skillname;
    }

    public void setSkillname(String skillname) {
        this.skillname = skillname;
    }

    public Collection<UserSkill> getUserSkills() {
        return UserSkills;
    }

    public void setUserSkills(Collection<UserSkill> userSkills) {
        UserSkills = userSkills;
    }
    
      @Override
      public String toString() {
          return "Skill [skillID=" + skillID + ", skillname=" + skillname + ", UserSkills=" + UserSkills + "]"; }
     
}

My Controller:

@Controller
public class SkillController {

    @Autowired
    private SkillService skillService;

    public SkillController(SkillService skillService) {
        this.skillService = skillService;
    }

      @GetMapping("/skill")
      public String skill(Model theModel) {
          Skill theSkill = new Skill();
         // add existing users to the spring model
        theModel.addAttribute("skills", skillService.getSkills());
        return "skill";
        }

My HTML Thymeleaf (View):

<div class="form-group col-md-8">
<label  class="col-form-label">Category </label>
<select  id="category" name="category" th:field="*{skill.skillID}" >
<option th:each="skill : ${skills}" th:value="${skill.skillID}" th:utext="${skill.skillname}"/>
</select>
</div>

My Repo:

@Repository
public interface SkillRepository extends JpaRepository<Skill, Integer> {
    Skill findSkillBySkillname(String skillname);
}

My Service (Interface):

@Service
public interface SkillService {

    Skill getSkill(String skillname);
    Iterable<Skill>getSkills();
    Skill findBySkillId(int theSkillID);
}

My ServiceImpl (Interface):

@Service
public class SkillServiceImpl implements SkillService {

    private final SkillRepository skillRepository;
    
    /*
     * @Autowired SkillRepository skillRepository;
     */

    @Autowired
    public SkillServiceImpl(SkillRepository theSkillRepository) {
        skillRepository = theSkillRepository;

    }

    @Override
    public Iterable<Skill> getSkills() {
        System.out.println("Abrufen aller Skills.");
        return skillRepository.findAll();
    }

    @Override
    public Skill getSkill(String skillname) {
        System.out.println("Abrufen des Skills "+ skillname);
        return skillRepository.findSkillBySkillname(skillname);
    }


    @Override
    public Skill findBySkillId(int theSkillID) {
        Optional<Skill> result = skillRepository.findById(theSkillID);
        Skill theSkill = null;
        if (result.isPresent()) {
            theSkill = result.get();
        }
        else {
            // we didn't find the vaccination state
            throw new RuntimeException("Did not find user id - " + theSkillID);
        }
        return theSkill;
    }

and I get this Error:

ERROR 94396 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[.[dispatcherServlet]      : Servlet.service() for servlet [dispatcherServlet] in context with path [/webapp] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/skill.html]")] with root cause

java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'skill' available as request attribute

Answer 1

In your controller add theSkill to your model. You created it but didn't add it to the model. The error indicates you are making references to the form backing object but it doesn't exist in your model.