Querying ManyToMany relationship with Hibernate Criteria

Question

I'm not sure how to describe this problem, so I think an example is the best way to ask my question:

I have two tables with a manyToMany relationship:

DriversLicence <-> LicenceClass

LicenceClass is things like "Car", "Motorbike", and "Medium Rigid".

Using Hibernate Criteria, how can I find all licences that have both "Car" and "Motorbike" LicenceClasses?

UPDATE 12/11/2008 I have discovered that this can easily be achieved by using a custom ResultTransformer. However the problem is that a result transformer only gets applied AFTER the query returns its results, it does not actually become part of the SQL. So I guess my question is now "Can you do what I initially described in SQL - and is there a Hibernate Criteria analog?"

Answer 1

Here's how I finally achieved it using HQL:

public List<DriversLicence> findDriversLicencesWith(List<LicenceClass> licenceClasses) {
    String hqlString = "select dl from DriversLicenceImpl dl where 1=1 ";
    for (int i = 0; i < licenceClasses.size(); i++) {
        hqlString += " and :licenceClass" + i + " = some elements(dl.licenceClasses)";
    }

    Query query = getSession().createQuery(hqlString);
    for (int i = 0; i < licenceClasses.size(); i++) {
        query.setParameter("licenceClass" + i, licenceClasses.get(i));
    }
    return query.list();
}

Or using Hibernate Criteria with an sqlRestriction:

for (LicenceClass licenceClass : licenceClasses) {               
    criteria.add(Restrictions.sqlRestriction("? = some(select " + LicenceClass.PRIMARY_KEY + " from " +
                    LICENCE_CLASS_JOIN_TABLE + "  where {alias}." +
                    DriversLicence.PRIMARY_KEY + " = " + DriversLicence.PRIMARY_KEY + ")",
                    licenceClass.getId(), Hibernate.LONG));
}

LICENCE_CLASS_JOIN_TABLE is the name of the table that hibernate generates to support the many-to-many relationship between driversLicence and LicenceClass.

Answer 2

You can still use dot notation to work across the relations. For example, assuming you have a DriversLicence.licenceClass property and LicenceClass.type property, then:

session.createCriteria(DriversLicence.class)
   .add(Expression.or(
     Expression.eq("licenceClass.type", "Car"),
     Expression.eq("licenceClass.type", "Motorbike")
   )
).list();

Personally though, I'd simply avoid using criteria in this case because it's not a dynamic query, but instead use:

session.createQuery("from DriversLicence where licenceClass.type in (:types)")
  .setParameterList("types", myListOfTypes)
  .list();

Answer 3

I had a similar issue but fixed up using HQL, I have a class "Enterprise" that is related to class "User" and also related to class "Role", they hay a many to many relationship, when I need all the enterprises related to a specific user I do the following;

Select e from Enterprise As e inner join e.Users As u inner join u.Roles As r 
Where u.UserCode=?

I suppose that in your case you should do something like;

Select dl from LicenceClass As l inner join l.DriversLicences As dl
Where 
l.LicenseClass.Name = ? OR 
l.LicenseClass.Name=? OR 
l.LicenseClass.Name=?

Hope it helps.

Answer 4

Another option is to chain joins (one join per each LicenseClass). I used criteria builder and predicates like this

 List<Predicate> predicates = new ArrayList<>();
 for(Integer lcId : licenceClassIdList) {
     SetJoin<DriversLicence, LicenceClass> dlClasses = dlRoot.join(DriversLicence_.licenceClasses);
     predicates.add(builder.equal(dlClasses.get(LicenseClass_.id), lcId));
 }
 Predicate predicate = builder.and(predicates.toArray(new Predicate[predicates.size()]));

Notice dlRoot is object of Root class and you can get it from CriteriaQuery class. Resulted predicate is what are you looking for...

Answer 5

'I don't think this going to work. I want to find all licences that have both "Car" and "Motorbike" '

User Expression.and(....) instead of Expression.or(....) in the snippet provided by Nick