@ManyToOne and @BatchSize

Question

I found in some old code strange thing (at least for me).

The field which is annotated @ManyToOne is also annotated with @BatchSize.

Answer 1

Solving N+1 query problem with Hibernate

1 Using Criteria queries with fetchMode

Criteria criteria = session.createCriteria(Customer.class); criteria.setFetchMode("contact", FetchMode.EAGER);

2 HOL fetch join

3 @BatchSize

The @BatchSize annotation can be used to define how many identical associations to populate in a single database query. If the session has 100 customers attached to it and the mapping of the 'contact' collection is annotated with @BatchSize of size n. It means that whenever Hibernate needs to populate a lazy contact collection it checks the session and if it has more customers which their contact collections need to be populated it fetches up to n collections.

@OneToMany(mappedBy="customer",cascade=CascadeType.ALL, fetch=FetchType.LAZY)
    @BatchSize(size=25)
    private Set contacts = new HashSet();