@Column AnnotationThe nullable attribute of the @Column annotation has two purposes:
The HBM2DDL schema generation tool translates the @Column(nullable = false) entity attribute to a NOT NULL constraint for the associated table column when generating the CREATE TABLE statement.
As I explained in the Hibernate User Guide, it's better to use a tool like Flyway instead of relying on the HBM2DDL mechanism for generating the database schema.
When flushing the Persistence Context, Hibernate ORM also uses the @Column(nullable = false) entity attribute:
new Nullability( session ).checkNullability( values, persister, true );
If the validation fails, Hibernate will throw a PropertyValueException, and prevents the INSERT or UPDATE statement to be executed needesly:
if ( !nullability[i] && value == null ) {
//check basic level one nullablilty
throw new PropertyValueException(
"not-null property references a null or transient value",
persister.getEntityName(),
persister.getPropertyNames()[i]
);
}
@NotNull AnnotationThe @NotNull annotation is defined by Bean Validation and, just like Hibernate ORM is the most popular JPA implementation, the most popular Bean Validation implementation is the Hibernate Validator framework.
When using Hibernate Validator along with Hibernate ORM, Hibernate Validator will throw a ConstraintViolation when validating the entity.