Properly get latest update for ofxaccount

I had done it lazily before and was getting erroneous results when
querying as soon as I had more than one OFXUpdate for an account. Now I
properly do a subselect. Come to think of it, I could also use a limit,
I think...

vanth/platform/ofxaccount.py

@@ -1,13 +1,22 @@
+import logging
 import uuid
 
 import chryso.connection
 import sqlalchemy
+import sqlalchemy.sql.functions
 
 import vanth.platform.ofxsource
 import vanth.tables
 
+LOGGER = logging.getLogger(__name__)
 
 def _select():
+    subselect = sqlalchemy.select([
+        vanth.tables.OFXUpdate.c.ofxaccount,
+        sqlalchemy.sql.functions.max(vanth.tables.OFXUpdate.c.created),
+    ]).group_by(
+        vanth.tables.OFXUpdate.c.ofxaccount
+    ).alias('ofxupdates')
     return sqlalchemy.select([
         vanth.tables.OFXAccount.c.account_id,
         vanth.tables.OFXAccount.c.name,
@@ -18,11 +27,11 @@ def _select():
         vanth.tables.OFXAccount.c.uuid,
         vanth.tables.OFXSource.c.name.label('source.name'),
         vanth.tables.OFXSource.c.uuid.label('source.uuid'),
-        vanth.tables.OFXUpdate.c.created,
-    ]).where(
-        vanth.tables.OFXAccount.c.source == vanth.tables.OFXSource.c.uuid
+        subselect,
+    ]).select_from(
+        subselect
     ).where(
-        vanth.tables.OFXAccount.c.uuid == vanth.tables.OFXUpdate.c.ofxaccount
+        vanth.tables.OFXAccount.c.uuid == subselect.c.ofxaccount
     )
 
 def _execute_and_convert(query):
@@ -31,7 +40,7 @@ def _execute_and_convert(query):
     return [{
         'account_id'    : result[vanth.tables.OFXAccount.c.account_id],
         'name'          : result[vanth.tables.OFXAccount.c.name],
-        'last_updated'  : result[vanth.tables.OFXUpdate.c.created],
+        'last_updated'  : result['max_1'],
         'password'      : result[vanth.tables.OFXAccount.c.password],
         'source'        : {
             'name'      : result[vanth.tables.OFXSource.c.name.label('source.name')],