main: Handle SQLAlchemy errors more nicely

Instead of giving the user a screen full of backtraces, catch any errors
SQLAlchemy can run into when preparing or executing the query and report
only the error message to the user.

We include the print loop in the try/except block because an upcoming
commit will add a handler for KeyboardInterrupt.

1 files changed, 9 insertions, 6 deletions

diff --git a/quarg/main.py b/quarg/main.py
index ce72310..9532ba7 100644
--- a/quarg/main.py
+++ b/quarg/main.py
@@ -4,13 +4,13 @@ import os
 import sys
 from timeit import default_timer as timer
 
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, exc
 from sqlalchemy.orm import sessionmaker
 
 import quarg.actions as actions
 import quarg.database.filters as filters
+import quarg.quassel.formatter as formatter
 from quarg.database.tables import Backlog, Buffer, Network, QuasselUser, Sender
-from quarg.quassel.formatter import format_from
 from quarg.utils import errx
 
 # pylint: disable=line-too-long
@@ -136,11 +136,14 @@ def main():
     if not predicates:
         errx('Nothing to match.')
 
-    query = prepare_query(session, predicates, args)
-    rows, time = time_query(query)
+    try:
+        query = prepare_query(session, predicates, args)
+        rows, time = time_query(query)
 
-    for row in rows:
-        print(format_from(row))
+        for row in rows:
+            print(formatter.format_from(row))
+    except exc.SQLAlchemyError as err:
+        errx(err)
 
     print(f'Query returned {len(rows)} lines in {time:.4f} seconds.', file=sys.stderr)