Query for a null-valued nullable attribute

[Jonathan Baxter]

I am getting an NPE when attempting to do an equal query for a null value of a nullable attribute. Is this supported? Looking at com.googlecode.cqengine.query.simple.Equal.java it appears not. I can always replace the nulls with a non-null object representing null, but maybe I am doing it wrong?

protected int calcHashCode() {

      int result = attribute.hashCode();       <----- Ok, attribute knows it is nullable

result = 31 * result + value.hashCode(); <----- NPE - value being compared is null

return result;

    }

       

[Niall Gallagher]

Hi Jonathan. You need to use a has() query instead.

[Jonathan Baxter]

Ah - did not notice that existed. Helps to rtfm. Thanks! Great package btw. Very easy to use.

[Jonathan Baxter]

For anyone who comes across the same issue, a clean way to handle equal for nullable attributes is to rewrite the query:

  /** The equal query for a nullable attribute. */
  public static <A, O> Query<A> equal(Attribute<A, O> attribute, O value) {
    return value == null ? not(has(attribute)) : QueryFactory.equal(attribute, value);
  }