RFE: BlitzGateway.getObjects(???, []) returns an unhelpful error

[spli]

It would be nice if the following could return a clearer exception message or even better, return an empty list (which would be the same behaviour as when a non-existent ID is passed to getObjects).

list(conn.getObjects('Image', []))

    serverExceptionClass = ome.conditions.ApiUsageException
    message = unexpected end of subtree [select obj from ome.model.core.Image obj join fetch obj.details.owner as owner join fetch obj.details.group join fetch obj.details.creationEvent where obj.id in ()]; nested exception is org.hibernate.hql.ast.QuerySyntaxException: unexpected end of subtree [select obj from ome.model.core.Image obj join fetch obj.details.owner as owner join fetch obj.details.group join fetch obj.details.creationEvent where obj.id in ()]

[jamoore]

This is a very long-standing Hibernate issue: ​https://hibernate.atlassian.net/browse/HHH-2045

• #9187
• #1061
• #9136
• #2611
• #1582

which has *amazingly* recently been fixed. We won't be upgrading to that version of Hibernate soon, and especially not on the stable line. The background issue is that the server can't know a priori (without parsing the queries) know if the user is intending the list to be us in a "in (:ids)" style query.

A method like getObjects() though can definitely check for an empty list of IDs and return immediately.

[wmoore]

Since getObjects() actually returns a generator, so we want to return an "empty" generator, or is it OK to return [].
Both will be handled identically in most cases, E.g.

list(conn.getObjects('Image', []))
# or 
for i in conn.getObjects('Image', []): 
    print i

To get an "empty" generator I think you have to do something like this (which seems a bit contrived!).

def emptyGen():
    for i in []:
        yield i

return emptyGen()

[jamoore]

if False: yield would work, too. I don't know if any assumptions would be violated with "return []". Probably best to use a generator.