Question

I have two classes, Person and Company, derived from another class Contact. They are represented as polymorphically in two tables (Person and Company). The simplified classes look like this:

public abstract class Contact {

  Integer id;

  public abstract String getDisplayName();

}

public class Person extends Contact {

  String firstName;
  String lastName;

  public String getDisplayName() {
    return firstName + " " + lastName;
  }

}

public class Company extends Contact {

  String name;

  public String getDisplayName() {
    return name;
  }

}

The problem is that I need to make a query finding all contacts with displayName containing a certain string. I can’t make the query using displayName because it is not part of either table. Any ideas on how to do this query?

Answer 1

Because you do the concatenation in the Java class, there is no way that Hibernate can really help you with this one, sorry. It can simply not see what you are doing in this method, since it is in fact not related to persistence at all.

The solution depends on how you mapped the inheritance of these classes:

If it is table-per-hierarchy you can use this approach: Write a SQL where clause for a criteria query, and then use a case statement:

s.createCriteria(Contact.class)
 .add(Restrictions.sqlRestriction("? = case when type='Person' then firstName || ' '|| lastName else name end"))
 .list();

If it is table per-concrete-subclass, then you are better of writing two queries (since that is what Hibernate will do anyway).