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.
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.
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