truncate/delete from given the entity class

Question

I have my entity class available via a method. I'm trying to figure out, how via the JPA JPQL or Criteria API's I could issue a truncate or delete from. I think that the criteria API is more natural for working with classes, and truncate is a faster operation so these are preferred. This is what I put together so far, but not sure what to add/change about it.

CriteriaBuilder cb = this._em().getCriteriaBuilder();
cb.createQuery( _entityClass() ).from( _entityClass() );

note: _entityClass returns MyEntity.class, I have no other references to MyEntity this is a more generalized implementation.

Erythroblastosis

I think there is no such thing as truncate in JPQL, you can write a native query for that or use JPQL "delete". – Automatic

Answer 1

Assuming that MyEntity refers to the table you want to drop you can proceed as follows:

// Criteria API (JPA 2.1 and above)
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaDelete<MyEntity> query = builder.createCriteriaDelete(MyEntity.class);
query.from(MyEntity.class);
em.createQuery(query).executeUpdate();

or with a generalized approach:

public <T> int deleteAllEntities(Class<T> entityType) {
    CriteriaBuilder builder = em.getCriteriaBuilder();
    CriteriaDelete<T> query = builder.createCriteriaDelete(entityType);
    query.from(entityType);
    return em.createQuery(query).executeUpdate();
}

Similarly for JPQL/SQL queries:

// JPQL
em.createQuery("DELETE FROM MyEntity e").executeUpdate();

// SQL
em.createNativeQuery("TRUNCATE TABLE MyEntity").executeUpdate();

or with a generalized approach:

public static <T> int deleteAllEntities(Class<T> entityType) {
    String query = new StringBuilder("DELETE FROM ")
                            .append(entityType.getSimpleName())
                            .append(" e")
                            .toString();
    return em.createQuery(query).executeUpdate();
}

public static <T> int truncateTable(Class<T> entityType) {
    String query = new StringBuilder("TRUNCATE TABLE ")
                            .append(entityType.getSimpleName())
                            .toString();        
    return em.createNativeQuery(query).executeUpdate();
}

With Criteria API you can only use SELECT, UPDATE, DELETE statements therefore TRUNCATE is not possible.

Grantham

What do you mean by "made to work from the class"? Could you please elaborate the question? – Grantham

I have a reference to MyEntity.class I don't have the string "MyEntity" in fact I mutated this so that CriteriaDelete<MyEntity> is just a cast (CriteriaDelete) because it didn't like me further paramaterizing it with ENTITY – Erythroblastosis

You might try to use Java generics, thus you wouldn't need to cast and parametrize a given query, see the updated answer above... – Grantham

it didn't seem to like my generics in this case, something about the extends in the generic – Erythroblastosis

CriteriaDelete<MyEntity> is not a truncate operation.Please do not mess delete and truncate with each others.Especially,using oracle as a DB it can cause a really big performance issue using delete instead of truncate with big tables. – Deter