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.

I think there is no such thing as `truncate` in JPQL, you can write a native query for that or use JPQL "delete". — Edwin Dalorzo, Apr 24 '14 at 13:10

wypieprz · Accepted Answer · 2017-12-08T10:14:18.563

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.

What do you mean by "_made to work from the class_"? Could you please elaborate the question? — wypieprz, Apr 25 '14 at 08:16
I have a reference to `MyEntity.class` I don't have the string `"MyEntity"` in fact I mutated this so that `CriteriaDelete` is just a cast `(CriteriaDelete)` because it didn't like me further paramaterizing it with `ENTITY` — xenoterracide, Apr 25 '14 at 16:10
You might try to use Java generics, thus you wouldn't need to cast and parametrize a given query, see the updated answer above... — wypieprz, Apr 26 '14 at 19:51
it didn't seem to like my generics in this case, something about the extends in the generic — xenoterracide, Apr 27 '14 at 17:10
CriteriaDelete 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. — enes.acikoglu, Dec 08 '17 at 07:49

truncate/delete from given the entity class

1 Answers1