Entity Relationships Break the GET Request - Spring MVC

Question

I've recently added a @ManyToOne & @OneToMany association on two of the @Entitys in my Spring MVC Project.

@Entity
public class Book {

    @ManyToOne
    @JoinColumn(name = "book_id")
    private BookCategory category;

}

@Entity
public class BookCategory{

    @OneToMany(mappedBy = "category")
    private List<Book> books;

}

@RequestMapping(value = "getAllBooks", produces = "application/json")
public @ResponseBody List<Book> getAllBooks(){
    return bookRepo.findAll(); // Native Spring JPA method
}

Before including the joins, I could easily populate a List of Books (without their BookCategories) and send them to the client as a JSON response.

However, after including the joins my asynchronous request fails and I get the following error in Chrome

SyntaxError: Unexpected end of JSON input at JSON.parse (<anonymous>)

On IE:

Unterminated string constant: {description: "...

Also in Chrome I see

Resource interpreted as Document but transferred with MIME type application/json:

The request itself runs fine, returning a 200, and the response looks like normal JSON array of objects. Any ideas why this might be occuring?

Thank you!

@notanormie I haven't defined any FetchType, so whatever the default is — Clay Banks, Aug 24 '17 at 12:13
Do you use POSTMAN, Curl or any REST Client? Try it once and see what output you are getting. — aksappy, Aug 24 '17 at 12:25
@aksappy I ran with Advanced REST Client - Returned a 200 but also returned an unparseable array of objects — Clay Banks, Aug 24 '17 at 12:38
Can you convert your DAO Objects into a simpler DTO structure and send the DTO in the RequestMapping? — aksappy, Aug 24 '17 at 12:48

Oleh Kurpiak · Answer 1 · 2017-08-24T12:49:49.087

1

posible problem could be endless json. each book contains a category, ecach category contains same book, that contains category, that contains the same book and soo on

book: {
  category: {
    book: {
      category: {
        book: {
    .. and so on

so you mapper can convert you object to a json-like string

EDIT: you can fix it using Views.

create BookView class and BookCategoryView class

public class BookCategoryView {

// contains all nessesery fields: id, name ..
// contains getters and setters
// DOESN'T contain book field

}

public class BookView {
  // contains all nessesery fields: id, name ..
  // contains getters and setters

  // here add List<BookCategoryView>
}

if you convert you entity objects to this view object, that does not have endless circle dependencies than you can omit that error

MORE INFO: usually such objects call DTO's(Data Transfer Object). So if you named them BookDTO and BookCategoryDTO everything will be clear

edited Aug 24 '17 at 12:49

answered Aug 24 '17 at 12:41

Oleh Kurpiak

1,339
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This seems like it could be the issue. Is there a way to prevent this? – Clay Banks Aug 24 '17 at 12:44
@KuraiBankusu, in my answer I add the easiest solution – Oleh Kurpiak Aug 24 '17 at 12:50
Thanks for the response. it seems that @JsonIgnore resolved this issue as well (see https://stackoverflow.com/questions/3325387/infinite-recursion-with-jackson-json-and-hibernate-jpa-issue). I'll report back if I find anything missing – Clay Banks Aug 24 '17 at 12:55

score 0 · Answer 2 · answered Aug 24 '17 at 12:54

I fixed this issue by adding @JsonIgnore to my BookCategory Entity.

@JsonIgnore
@OneToMany(mappedBy = "category")
private List<Book> books;

Description:

@JsonIgnore - Marker annotation that indicates that the annotated method or field 
is to be ignored by introspection-based serialization and deserialization functionality.

As Oleh pointed out this response looked like an endless recursive JSON response. Including the annotation prevents this and returns the appropriate response

Entity Relationships Break the GET Request - Spring MVC

2 Answers2