Query preprocessor interface?

[Christopher Nelson]

I have a need to augment the core query logic with extra keywords.
For example, "goal=<ticketID>" goes through logic in my Project
Management plugin to find all the tickets required to satisfy a goal
(that is, all the predecessors of the ticket ID and all their
predecessors, etc.). I currently do that with a wrapper which
processes application-specific keywords and adds standard Query
parameters something like:

def preQuery(self, options, this_ticket = None):
ids = ''

if options.get('goal'):
...
nodes = options['goal'].split('|')
...
# Loop getting all the predecessors of the tickets
...
ids += '|'.join(nodes)

return ids

....

# Expand (or set) list of IDs to include those specified by PM
# query meta-options (e.g., root)
pm_id = preQuery(options, self._this_ticket())
if pm_id != '':
if 'id' in query_args:
query_args['id'] += '|' + pm_id
else:
query_args['id'] = pm_id

...

# Make the query argument
query_args['col'] = "|".join(fields)

# Construct the querystring.
query_string = '&'.join(['%s=%s' %
(f, unicode(v)) for (f, v) in
query_args.iteritems()])

# Get the Query Object.
query = Query.from_string(self.env, query_string)

# Get all tickets
tickets = query.execute(self.req)

But this is kind of awkward and requires editing every piece of code
that I want to be PM-aware. I can't, for example, do
`trac/query?goal=1234` in my address bar. What I'd like is to define
an interface for a Query preprocessor. Something like:

class IQueryHelper(Interface):
# Preprocess query arguments
# @param options hash of query options
# @return options after handling application-specific options
def preProcess(self, options):
""""Expand and remove application-specific options
For example {"id" : "1|3", "goal" : "7"} transformed into
{"id" : "1|3|4|5|6"} because 4, 5, and 6 are required for 7"""

and then have the core Query handler call any registered preprocessors.

Is there a way to do that now? A better way to approach it?


Chris