Thanks to all.
I did try the Collection<String> approach but OpenJPA generates an error and
complains about the underlying type (ArrayList, HashSet, etc.) being an
invalid type for th expression. Not being familiar with the OpenJPA source
I took a quick look at fisheye for
org.apache.openjpa.persistence.query.ArrayExpression and it seems to suggest
that it expects an String[]. That failed to produce the expect results.
In the end I fell back to generating the sql string manually and abandoning
NamedQuery, e.g:
private static String mostRefersType = "select count(e.eid), e.* from Entity
e, Property p where e.eid=p.refersTo and p.type IN ( #### ) group by e.eid
order by count(e.eid) desc;";
public static List<EntityHolder> findMostUsed(Registry registry,
Collection<String> types, int limit) {
...
sql = mostRefersType.replace("####", asString(types));
q = registry.getEntityManager().createNativeQuery(sql, "MostUsedResults");
list = (List<Object[]>) q.getResultList();
...
}
private static String asString(Collection<String> types) {
StringBuffer typesAsString = new StringBuffer();
int i = 0;
for (String type : types) {
if ( typesAsString.length() > 0 ) typesAsString.append(",");
typesAsString.append("'"+type+"'");
}
return typesAsString.toString();
}
This approach works fine. I have to assume that there is either a bug in
the Native Named Query processing or some requirement that isnt very well
documented.
Regards....
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