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I'm not understanding why when I attempt to use a modelAttributed form in with spring it's attempting to convert my String type variable to a Long type variable when it should just remain a String type. Only thing I suspect it's trying to do is fill the Id variable.

Failed to convert value of type 'java.lang.String' to required type'javaSpring.DojoOverflow.models.Questions'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'Why?'; nested exception is java.lang.NumberFormatException: For input string: "Why?"

//--------------------------------------------------- // My Model @Entity @Table(name="questions") public class Questions { // Attributes @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @NotEmpty(message = "Ask a question!") private String question; @Column(updatable=false) private Date createdAt; private Date updatedAt; @OneToMany(mappedBy="question", fetch = FetchType.LAZY) private List<Answer> answers; @ManyToMany(fetch = FetchType.LAZY) @JoinTable ( name="questions_tags", joinColumns = @JoinColumn(name="question_id"), inverseJoinColumns = @JoinColumn(name="tag_id") ) @Size (max=3) @NotEmpty(message="Tag your question!") private List<Tag> tags; // ------------------------------------- // My Controller Mapping @PostMapping("/questions/new") public String processQuestion(@Valid @ModelAttribute("question")Questions question, BindingResult result) { if(result.hasErrors()) { return "newQuestion.jsp"; } questionService.createQuestion(question); return "redirect:/"; } //----------------------------------------------- // My jsp <body> <div class="container"> <h1>What is your question?</h1> <form:form action="/questions/new" method="post" modelAttribute="question"> <div class="form-group"> <form:label path="question">Question</form:label> <form:textarea rows="5" class="question form-control" path="question"/> <span class="error"><form:errors path="question"/></span> </div> <div class="form-group"> <form:label path="tags">Tags</form:label> <form:input class="tags form-control" placeholder="Tags" path="tags"/> <span class="error"><form:errors path="tags"/></span> </div> <button class="btn btn-secondary" type="submit">Submit</button> </form:form> <a href="/questions">Go Back</a> </div> </body>
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  • Are you sure that types of columns in database match types of your properties in entity class? Commented Oct 13, 2018 at 19:54
  • Database type for the question field where the error occurs is listed as varchar(255) in mysql. Commented Oct 13, 2018 at 19:57
  • So how could Java convert varchar to long? Either change column to NUMBER (or any other numeric integer type specific for your database) or change type for property to String Commented Oct 13, 2018 at 19:59
  • If you look at my entity, the question field is listed as a String and the corresponding field in MySql is varchar(255) so the types do match in those regards. I just don't understand why it's trying to convert when it shouldn't need to. Commented Oct 13, 2018 at 20:01
  • For some reason it's attempting to convert when processing the post. Commented Oct 13, 2018 at 20:02

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Looks like an incompletely initialized object. Check your createQuestion service method, and be sure each required field for Question is set before you pass it to the controller. That form alone doesn't have all the necessary fields.

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I currently have a service for each of my three models which use functions from three corresponding repositories that use the CrudRepository. Based on my model the only field that can be empty is the question field, so I don't think that is the issue. All tables have been instantiated accordingly as I can view them with MySql Workbench. Am I misunderstanding what you mean by each field being set?
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I suggest to apply MVVC pattern to separate your business object from your view object.

You expect to receive only strings from the view in your model attribute object.

Your entity object contains a list of tags and a list of answers => they are modeled differently and the usage of the same class is difficult, with many potential bugs.

In your case it is better to create.a separate view class only with strings and convert them to your entity object.

Example :

public class QuestionModelAttribute { private String tags; private String answers; ..... }

and your method will receive:

@PostMapping("/questions/new") public String processQuestion(@Valid @ModelAttribute("question") QuestionModelAttribute questionModelAttribute, BindingResult result) { Questions question = questionsService.convertQuestion(questionModelAttribute); questionService.save(question); .. }

Your view will receive in the model a QuestionModelAttribute

<form:form action="/questions/new" method="post" modelAttribute="questionModelAttribute">

This pattern offers a healthy decoupling between the view and model.

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Currently I do have two other entities; one for answers and one for tags that look similar to this model. Are you trying to say not to do joining relationships within the entity?
It is normal to have relationships between entities. I am saying to let your Questions object as it is (with OneToMany and ManyToMany relationships) and to use another class for the view - a simplified version of Questions object. In this way you will have control of the conversion and will not receive conversion errors.

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