[dak/master] Check for the existance of the function before trying to drop it.

[Allan Lyons <Allan_Lyons@wycliffe.ca>]

At least on my machine, ignoring the error if the function doesn't exist
doesn't work since psycopg2 bombs.  So, we attempt to at least check if
there are any functions with a similar name before trying to drop it.
This way it should work better on an empty database where the function
has never existed.

Signed-off-by: Allan Lyons <Allan_Lyons@wycliffe.ca>
---
 dak/dakdb/update3.py |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/dak/dakdb/update3.py b/dak/dakdb/update3.py
index 406cc89..5a5562f 100755
--- a/dak/dakdb/update3.py
+++ b/dak/dakdb/update3.py
@@ -36,12 +36,15 @@ def do_update(self):
 
     try:
         c = self.db.cursor()
-        try:
-            # This might not exist on a fresh install, so don't fail
-            # needlessly
+        # The reason we try and check to see if it exists is that
+        # psycopg2 might leave the cursor invalid if the drop fails
+        c.execute("SELECT proname from pg_catalog.pg_proc WHERE proname = 'versioncmp'")
+        rows = c.fetchall()
+        if rows:
             c.execute("DROP FUNCTION versioncmp(text, text);")
-        except:
-            pass
+        else:
+            print "function already does not exist"
+
         c.execute("UPDATE config SET value = '3' WHERE name = 'db_revision'")
 
         self.db.commit()
-- 
1.5.6.5