Generic check_media_slug_used db utility.

In two cases (generating a new slug and editing the slug)
it is nice to know in advance (before the db gets angry)
that the slug is used/free. So created a db utility
function to check for this on mongo and sql:
check_media_slug_used()

mediagoblin/db/mongo/util.py

@@ -301,3 +301,12 @@ def atomic_update(table, query_dict, update_values):
     table.collection.update(
         query_dict,
         {"$set": update_values})
+
+
+def check_media_slug_used(db, uploader_id, slug, ignore_m_id):
+    query_dict = {'uploader': uploader_id, 'slug': slug}
+    if ignore_m_id is not None:
+        query_dict['_id'] = {'$ne': ignore_m_id}
+    existing_user_slug_entries = db.MediaEntry.find(
+        query_dict).count()
+    return existing_user_slug_entries

mediagoblin/db/sql/util.py

@@ -17,7 +17,7 @@
 
 import sys
 from mediagoblin.db.sql.base import Session
-from mediagoblin.db.sql.models import Tag, MediaTag
+from mediagoblin.db.sql.models import MediaEntry, Tag, MediaTag
 
 
 def _simple_printer(string):
@@ -285,6 +285,15 @@ def atomic_update(table, query_dict, update_values):
     Session.commit()
 
 
+def check_media_slug_used(dummy_db, uploader_id, slug, ignore_m_id):
+    filt = (MediaEntry.uploader == uploader_id) \
+        & (MediaEntry.slug == slug)
+    if ignore_m_id is not None:
+        filt = filt & (MediaEntry.id != ignore_m_id)
+    does_exist = Session.query(MediaEntry.id).filter(filt).first() is not None
+    return does_exist
+
+
 def clean_orphan_tags():
     q1 = Session.query(Tag).outerjoin(MediaTag).filter(MediaTag.id==None)
     for t in q1:

mediagoblin/db/util.py

@@ -21,7 +21,7 @@ except ImportError:
 
 if use_sql:
     from mediagoblin.db.sql.fake import ObjectId, InvalidId, DESCENDING
-    from mediagoblin.db.sql.util import atomic_update
+    from mediagoblin.db.sql.util import atomic_update, check_media_slug_used
 else:
     from mediagoblin.db.mongo.util import \
-        ObjectId, InvalidId, DESCENDING, atomic_update
+        ObjectId, InvalidId, DESCENDING, atomic_update, check_media_slug_used