Returning a QueryDSL BooleanExpression that evaluates to true

Question

Say I have CustomerQueryInfo bean with the following properties:

• String firstName
• String lastName
• StatusEnum status

I want to perform a "QueryDSL" search using this an object of this type that will return a list of customers List<Customer>.

If one of the fields of CustomerQueryInfo is null, I don't want to use it in the search. Thus a CustomerQueryInfo object with all three fields set to null will return all customers.

I am looking for best practices to perform such a search with QueryDSL.

Is something like this OK:

private BooleanExpression isFirstNameLike(String firstName){
    if(firstName==null)
        return true BooleanExpression somehow;
    return QCustomer.customer.firstName.like(firstName);
}

private BooleanExpression isStatutEq(StatusEnum status){
    if(status==null)
        return true BooleanExpression somehow;
    return QCustomer.customer.status.eq(status);
}

then:

return query.from(customer).where(isFirstNameLike(customerQueryInfo.getFirstName).and(isLastNameLike(customerQueryInfo.getLastName).and(isStatusEq(customerQueryInfo.getStatus))).list;

1. How do I return a BooleanExpression that evaluates to true?
2. If the above approach is not advisable, then what is the recommended best practice?

Answer 1

You can safely use null predicates like this

private BooleanExpression isFirstNameLike(String firstName){
    return firstName != null ? customer.firstName.like(firstName) : null;        
}

private BooleanExpression isStatusEq(StatusEnum status){
    return status != null ? customer.status.eq(status) : null;
}

And use the varargs aspect of where

query.from(customer)
     .where(
         isFirstNameLike(customerQueryInfo.getFirstName()),
         isLastNameLike(customerQueryInfo.getLastName()),
         isStatusEq(customerQueryInfo.getStatus()))
     .list(customer);