Persisting JSON object properly

Question

I have following classes:

public class Entity {

@Id 
@GeneratedValue(strategy = GenerationType.AUTO)
private Long Id;
private String name;

@JsonManagedReference
@ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private Category category;

//Constructors, getters and setters
}


public class Category {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long Id;
private String name;

@JsonBackReference
@OneToMany(mappedBy = "category", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<Entity> entity;

//Constructors, getters and setters
}

I have a form where when I submit the form I get following JSON:

{
 id: "1"
 name: "EntityA"
 category: {    
    id: "4"
    name: "categoryA"
 }
}

CategoryA is already in database. When I persist EntityA object (main object) to database BOTH objects will be persisted.

What's wrong with it?

Problem is that category is going to be persisted again with same information but with different id. So when I persist the above object EntityA is persisted fine in database, but category is persisted again with different id even if it exist in database.

So here's the steps with databse point of view.

Initial database:

Entity table (empty)

|id | name | category_id |
--------------------------
|   |      |             |

Category table

| id | name    |
----------------
|  4 |categoryA|

Entity_category table (empty)

| entity_id | category_id |
---------------------------
|           |             |

After persisting

Entity table (empty)

id | name  | category_id |
--------------------------
 1 |EntityA| 5           |

Entity_category table (should not be empty, but is empty)

| entity_id | category_id |
---------------------------
|           |             |

Category table

id | name    |
--------------
 4 |categoryA|
 5 |categoryA|

What I want is simply when I persist the object of EntityA it won't persist category, but instead it updates it's relationship with EntityA. After persisting the category_id of the second view should be 4 instead of 5.

I use entity manager's persist() method to persist the objects.

Technologies I use are jackson 2.0, Hibernate, Postgres as database.

I have also tested @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id") annotation above both classes but it doesn't help.

What I'm doing wrong here? Any help is appreciated.

Nonika · Accepted Answer · 2015-02-16 13:50:39Z

2

You have not marked Id as primary key (@Id) into your entities. In your case it seems that id is an auto-increment column (that's why id is different from what you have inserted) and JPA is not able to detect that the object is the same one. Try to mark ID fields with annotation @Id @GeneratedValue and try again.

edited Feb 16, 2015 at 13:50

answered Feb 16, 2015 at 13:45

Nonika

2,56014 silver badges15 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

Nonika Over a year ago

Also I have noticed that you have ManyToOne-OneToMany relationship with these entities. I don't think that U need extra join table (Entity_category) with this kind of relationship. JPA will not use it either

Amir Over a year ago

sorry I forgot to add that. It is already in my code. I will add it now here. Thanks for pointing it out.

Amir Over a year ago

Those annotations won't help. Same problem still occurs.

Nonika Over a year ago

Why don't U use merge instead of persist? In this case It will act as SaveOrUpdate

Amir Over a year ago

Same problem occures, it won't help with merging either.

|

Amir · Accepted Answer · 2015-02-28 11:04:22Z

0

Okay so I finally found the solution. The whole problem was because I had in the json category object key "id" which was written with small "I" letter, which means that it can't find the category id, because it doesn't match the Id field of entity class thus producing a category with null id. This is why it persisted the category as new entity because it couldn't find such object in database after deserialization process.

Make sure that when you persist your json object, every key in the json must match exactly your entity class fields or attributes.

edited Feb 28, 2015 at 11:04

answered Feb 27, 2015 at 17:50

Amir

1,0614 gold badges19 silver badges43 bronze badges

Comments

aifa · Accepted Answer · 2015-02-16 14:59:31Z

-1

Try getting a reference to the category and set the reference manually before committing/merging (if it is found in the database):

Category category = em.find(Category.class, entity.getCategory().getId());
if (category!=null){
  entity.setCategory(category);
}

This way category will be an attached object.

edited Feb 16, 2015 at 14:59

answered Feb 16, 2015 at 13:53

aifa

5345 silver badges6 bronze badges

4 Comments

Amir Over a year ago

This doesn't help anything.

Amir Over a year ago

Yes but remember that you get the object in json form which means that the code you have added above need deserialization of the json object in order to use it properly in java. Which again means that more logic for desrialization is required. For example you search for proper category by using its id. Category id is in the json object.

aifa Over a year ago

I agree with you, this is what I had in mind when I posted the solution. The specific solution has to be done in two steps. Deserialise and then attach the category object. It is not a one step solution.

aifa Over a year ago

Check this link for tips: stackoverflow.com/questions/17874688/….

Collectives™ on Stack Overflow

Persisting JSON object properly

3 Answers 3

10 Comments

Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

10 Comments

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related