procession/procession — pull request #47 by jaypipes (2014-02-21 06:57:14+00:00)
Title: More efficient _exists implementation

Closes Issue #42

This patch changes the _exists implementation to produce a more
efficient SQL query. The query goes from:

SELECT COUNT(some_field) FROM (
SELECT FROM model
WHERE expr
)

to

SELECT search_field FROM model WHERE expr LIMIT 1