single custom serializer for all embedded annotated objects that replaces them with their ids

Question

I have entities like those:

@Entity
public Product {
   @Id
   public int id;

   public String name;

   @ManyToOne(cascade = {CascadeType.DETACH} )
   Category category

   @ManyToMany(cascade = {CascadeType.DETACH} )
   Set<Category> secondaryCategories;


}

and

@Entity
public Category {
   @Id
   public int id;

   public String name;

    @JsonCreator
    public Category(int id) {
        this.id = id;
    }

    public Category() {}
}

is it possible to annotate either just Category class or category and secondaryCategories properties with an annotation that will serialize them to be just their ids when they are embedded.

right now I am getting from the server when I make a GET for product with id=1:

{ 
  id: 1,
  name: "product 1", 
  category: {id: 2, name: "category 2" }, 
  secondaryCategories: [{id: 3, name: "category 3" }, 
                        {id: 4, name: "category 4" }, 
                        {id: 5, name: "category 5" }] 
}

is it possible to get back:

{ 
  id: 1,
  name: "product 1", 
  category: 2, 
  secondaryCategories: [3, 4, 5]
}

Annotating Category class with @JsonIdentityReference(alwaysAsId = true) works generally but also returns just ids when I am fetching one or a list of Categories. I need id conversion only when Category is embedded.

Thanks!

Sachin Gupta · Answer 1 · 2017-10-10T09:09:44.427

0

You need to use @JsonIdentityReference(alwaysAsId = true) on the category variable only.

E.g.:

@Entity
public Product {
   @Id
   public int id;

   public String name;

   @ManyToOne(cascade = {CascadeType.DETACH} )
   @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope=Category.class)
   @JsonIdentityReference(alwaysAsId = true)
   Category category;

   @ManyToMany(cascade = {CascadeType.DETACH} )
   Set<Category> secondaryCategories;


}

edited Oct 10 '17 at 09:09

answered Oct 09 '17 at 05:01

Sachin Gupta

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oh I didnt try that annotation on the property! I will give it a try and tell you! One more question since the FetchType is LAZY will this cut the join with the category table? – Michail Michailidis Oct 09 '17 at 09:31
I tried it and I still get embedded objects - anything that I am missing? – Michail Michailidis Oct 09 '17 at 17:45
I have updated code to specify property name using `@JsonIdentityInfo`. I think this would work. – Sachin Gupta Oct 10 '17 at 04:06
while it worked for Serialization (GET) it probably clashed with @JsonCreator constructor of Category during deserialization (PUT/POST) - I am getting: `org.springframework.http.converter.HttpMessageNotReadableException","message":"JSON parse error: Unresolved forward references for: ; nested exception is com.fasterxml.jackson.databind.deser.UnresolvedForwardReference` – Michail Michailidis Oct 10 '17 at 08:40
I removed @JsonCreator and still my PUT/POST fails (I am sending just ids for category and secondaryCategories) – Michail Michailidis Oct 10 '17 at 08:52
Have you added default constructor in `Category` class – Sachin Gupta Oct 10 '17 at 09:05
when I removed @JsonCreator constructor I removed the default one too – Michail Michailidis Oct 10 '17 at 09:06
try to add default one too – Sachin Gupta Oct 10 '17 at 09:06
and add scope param in `@JsonIdentityInfo`, as described in updtaed answer – Sachin Gupta Oct 10 '17 at 09:07
you know that in a Java class a default constructor is always implied if you don't define your own right? https://stackoverflow.com/a/4488766/986160 - so I don't need to try that – Michail Michailidis Oct 10 '17 at 09:08
scope param? I don't see it – Michail Michailidis Oct 10 '17 at 09:09
same issue: com.fasterxml.jackson.databind.deser.UnresolvedForwardReference: Unresolved forward references for: \n at [Source: java.io.PushbackInputStream@692bc560; line: 1, column: 371]Object id [1] – Michail Michailidis Oct 10 '17 at 09:18
Chk this https://stackoverflow.com/questions/44007188/deserialize-json-with-spring-unresolved-forward-references-jackson-exception – Sachin Gupta Oct 10 '17 at 09:23
Thanks! Though this goes back to the comments of the anser of my other question that involves IdentityInfo and IdGenerators.. I then will have the issue that one of the objects in the list will be embedded and the rest will just be ids https://stackoverflow.com/a/46610026/986160 – Michail Michailidis Oct 10 '17 at 09:33

single custom serializer for all embedded annotated objects that replaces them with their ids

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