Hibernate - How to persist a new item in a Collection without loading the entire Collection

Question

I have a collection in my model that contains a set of \'previous versions\' of my root domain object. The previous versions are therefore \'immutable\' and we will never wa

Answer 1

When you have a List or Set-based collection and you add a new object into your collection, Hibernate will always hit the database because it compare one by one object by using equals implementation before saving or updating - when using a Set - or by comparing a index column when using a List. This behavior is needed because of the Set and List semantic. Because of that, the performance of your application can decrease significantly whether you have a bunch of records.

Some workaround to overcome this issue

1º Conversion pattern by using a encapsuled Bag collection plus your desired Set or List exposed as a property

@Entity
public class One {

    private Collection<Many> manyCollection = new ArrayList<Many>();

    @Transient
    public Set<Many> getManyCollectionAsSet() { return new HashSet<Many>(manyCollection); }
    public void setManyCollectionAsSet(Set<Many> manySet) { manyCollection = new ArrayList<Many>(manySet); }

    /**
      * Keep in mind that, unlike Hibernate, JPA specification does not allow private visibility. You should use public or protected instead
      */
    @OneToMany(cascade=ALL)
    private Collection<Many> getManyCollection() { return manyCollection; }
    private void setManyCollection(Collection<Many> manyCollection) { this.manyCollection = manyCollection; }

}

2º Use ManyToOne instead of OneToMany

@Entity
public class One {

    /**
      * Neither cascade nor reference
      */

}

@Entity
public class Many {

    private One one;

    @ManyToOne(cascade=ALL)
    public One getOne() { return one; }
    public void setOne(One one) { this.one = one }

}

3º Caching - when applied because of, depending on your requirements, your configuration can increase or decrease the performance of your application. See here

4° SQL constraint - If you want a collection that behaves like a Set, you can use a SQL constraint, which can be applied to a column or set of columns. See here

Answer 2

The way I typically do this is to define the collection as "inverse".

That roughly means: the primary definition of the 1-N association is done at the "N" end. Tf you want to add something to the collection you alter the associated object of the detail data.

A small XML example:

<class name="common.hibernate.Person" table="person">
    <id name="id" type="long" column="PERSON_ID">
        <generator class="assigned"/>
    </id>
    <property name="name"/>
    <bag name="addresses" inverse="true">
        <key column="PERSON_ID"/>
        <one-to-many class="common.hibernate.Address"/>
    </bag>
 </class>

 <class name="common.hibernate.Address" table="ADDRESS">
    <id name="id" column="ADDRESS_ID"/>
    <property name="street"/>
    <many-to-one name="person" column="PERSON_ID"/>
   </class>

then the update is done exclusively in Address:

Address a = ...;
a.setPerson(me);
a.setStreet("abc");
Session s = ...;
s.save(a);

Done. You did not even touch the collection. Consider it read-only, which may be very practical for querying with HQL, and iterating and displaying it.

Answer 3

If I understand well your need:

• you have an in-memory add-only collection of immutable objects
• how to add an item to that collection without initializing the entire collection (in the current Session)?

Did you consider maintaining your collection disconnected?

• Load it once when the application starts
• Adding an element would mean two operations, done by a single service in only one place:
  • save the element (fast database operation, no cascading is done to the parent)
  • add the element to the existing disconnected collection (no database operation)

Answer 4

I used to create a native query for this cases, like below:

    @Modifying
    @Transactional
    @Query(nativeQuery = true, value = "INSERT INTO categorytopic_topic(category_id, topic_id) VALUES (?1, ?2)")
    public void addTopic(long categoryId, long topicId);

It's very fast because does not need load the collection.