Add option to limit the number of matches

This is useful if the user already expects a lot of matches but is only
interested in a limited number of them. An upcoming commit will
introduce the option to have quarg list matches in ascending or
descending order (currently we do not pick a default - effectively
listing matches in ascending timestamp order), making it possible to
select the first or last N matches.

1 files changed, 8 insertions, 3 deletions

diff --git a/quarg/main.py b/quarg/main.py
index 82474b8..8b9987b 100644
--- a/quarg/main.py
+++ b/quarg/main.py
@@ -18,6 +18,7 @@ cli = argparse.ArgumentParser()
 cli.add_argument('keyword', nargs='*', help='match messages containing this keyword')
 cli.add_argument('-d', action='store_true', dest='debug', help='print debug and SQL query information')
 cli.add_argument('-e', action='store_true', dest='expr', help='interpret keywords as LIKE expression')
+cli.add_argument('-l', dest='limit', metavar='NUM', type=int, help='limit the number of matches')
 matchers = cli.add_argument_group('matching message context')
 matchers.add_argument('-b', action='append', dest='buffer', help='match this buffer')
 matchers.add_argument('-B', action=actions.ParseBufferType, dest='buftype', help='match buffers of this type')
@@ -94,7 +95,7 @@ def collect_predicates(args):
         else:
             yield fun(value)
 
-def run_query(session, predicates):
+def run_query(session, predicates, limit):
     start = timer()
 
     query = session.query(Backlog).join(Sender).join(Buffer).join(Network).join(QuasselUser)
@@ -102,7 +103,11 @@ def run_query(session, predicates):
     for predicate in predicates:
         query = query.filter(predicate)
 
-    rows = query.order_by(Backlog.time).all()
+    query = query.order_by(Backlog.time)
+    if limit:
+        query = query.limit(limit)
+
+    rows = query.all()
 
     end = timer()
 
@@ -125,7 +130,7 @@ def main():
     if not predicates:
         errx('Nothing to match.')
 
-    rows, time = run_query(session, predicates)
+    rows, time = run_query(session, predicates, args.limit)
 
     for row in rows:
         print(format_from(row))