Mongo isNull check and null values

Hello,

I am using Spring Boot with QueryDSL & MongoDB using querydsl-mongodb version 3.7.4. I have a MongoRepository and am using a QueryDSL Predicate to check if a field contains a null value like:

repository.findAll(QPerson.person.personId.isNull())

However, this isn’t retrieving results where the value of the field is null as expected.

Looking at the code for MongodbSerializer, it appears the isNull operation is translated to an $exists check in MongoDB which checks if the property exists. Instead, I need to check if the value of the field is null, which was what I was expecting isNull to do.

Is there a way to check if a field (that exists) has a null value using QueryDSL Predicates & MongoDB?

Thank you!

[butzy92]

Found a workaround: `public class NullConstant implements Constant<Object> {

public static final NullConstant NULL_CONSTANT = new NullConstant();

private NullConstant() {
}

@Override
public Object getConstant() {
	return null;
}

@Nullable
@Override
public Object accept(Visitor v, @Nullable Object context) {
	return null;
}

@Override
public Class getType() {
	return Object.class;
}

}`

and use it: qEntity.field.eq(NullConstant.NULL_CONSTANT)

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.