Spring Boot Adding Model to the View with Thymeleaf and MVC

问题

Ok, so I'm trying to put an attribute of an object from the model to the view as a list using thymeleaf, spring boot and jpa, I've been reading over the code for hours and I can't seem to spot my problem, also in the same application I have a very similar function working so I sort of know how to do it, but I just cannot seem to figure out this one. I keep getting an error Property or field 'question' cannot be found on null. I have no idea where I'm going wrong. The object I'm have is called QuestionAnswerSet, and I have a question string and an answer string in the database, that I can submit through the app, so it's not a problem with the database. Also everything is good with my pom file because as I said earlier I have done a very similar function.

Here's my controller.

@Controller
public class QuestionAnswerSetController 
{

private QuestionAnswerSetRepository questionAnswerSetRepo;

@RequestMapping("sets")
public String sets (ModelMap model)
{
    List<QuestionAnswerSet> questionAnswerSets = questionAnswerSetRepo.findAll();
    model.put("questionAnswerSets", questionAnswerSets);
    return "sets";
}

@RequestMapping(value="editSet/{questionAnswerSetId}", method=RequestMethod.GET)
public String editSetGet (@PathVariable Long questionAnswerSetId, ModelMap model)
{
    return "editCourse";
}

@RequestMapping(value="createSet", method=RequestMethod.GET)
public String createSetGet (ModelMap model)
{
    QuestionAnswerSet questionAnswerSet = new QuestionAnswerSet();
    model.put("questionAnswerSet", questionAnswerSet);
    return "createSet";
}

@RequestMapping(value="createSet", method=RequestMethod.POST)
public String createSetPost (@ModelAttribute QuestionAnswerSet questionAnswerSet, ModelMap model)
{
    questionAnswerSetRepo.save(questionAnswerSet);

    return "redirect:/sets";
}

@Autowired
public void setQuestionAnserSetRepo(QuestionAnswerSetRepository questionAnserSetRepo) {
    this.questionAnswerSetRepo = questionAnserSetRepo;
}


}

Here's my html

<div th:each="Set : ${questionAnswerSets}"   th:object="${questionAnswerSet}">
        <span th:text="${questionAnswerSet.question}"></span>
    </div>

    <div th:if="${#lists.isEmpty(questionAnswerSets)}">
        There is no sets to display.
    </div>

Here's my repository, it's pretty standard, just though I would include it

public interface QuestionAnswerSetRepository extends JpaRepository<QuestionAnswerSet, Long> {

}

And here's my QuestionAnswerSet.java object, which is what I'm trying to return as a list

@Entity
public class QuestionAnswerSet {

private Long id;
private String question;
private String answer;
private User user;

@Id
@GeneratedValue
public Long getId() {
    return id;
}
public void setId(Long id) {
    this.id = id;
}
public String getQuestion() {
    return question;
}
public void setQuestion(String question) {
    this.question = question;
}
public String getAnswer() {
    return answer;
}
public void setAnswer(String answer) {
    this.answer = answer;
}
@ManyToOne
public User getUser() {
    return user;
}
public void setUser(User user) {
    this.user = user;
}
}

And Here's the error in my console

org.springframework.expression.spel.SpelEvaluationException: EL1007E:(pos    0): Property or field 'question' cannot be found on null

回答1:

Yup, that should be pretty straightforward, here is the exception :

Property or field 'question' cannot be found on null

Spring EL tries to evaluate the below :

   <div th:each="Set : ${questionAnswerSets}"   th:object="${questionAnswerSet}">
       <span th:text="${questionAnswerSet.question}"></span>
   </div>

And it is unable to find questionAnswerSet ,which is null hence the error.

Use something like this :

<div th:each="questionAnswerSet : ${questionAnswerSets}">
        <span th:text="${questionAnswerSet.question}"></span>
</div>

Refer Doc : http://www.thymeleaf.org/doc/tutorials/2.1/usingthymeleaf.html#using-theach

来源：https://stackoverflow.com/questions/33685660/spring-boot-adding-model-to-the-view-with-thymeleaf-and-mvc

标签

spring-boot

thymeleaf

spring-el