Improve query efficiency when calculating ref_counts

sir/schema/__init__.py

@@ -76,7 +76,7 @@
     F("iso2", "iso_3166_2_codes.code"),
     F("iso3", "iso_3166_3_codes.code"),
     F("sortname", "aliases.sort_name"),
-    F("ref_count", ["labels.id", "places.id"] , transformfunc=len, trigger=False),
+    F("ref_count", ["place_count", "label_count", "artist_count"], transformfunc=tfs.integer_sum, trigger=False),
     F("tag", "tags.tag.name"),
     F("type", "type.name")
 ],

sir/schema/modelext.py

@@ -8,8 +8,8 @@
                            Instrument, Label, LinkAttribute, LinkAttributeType,
                            MediumCDTOC, Place, Recording, Release, ReleaseGroup,
                            ReleaseRaw, ReleaseTag, Series, Work, URL)
-from sqlalchemy import exc as sa_exc
-from sqlalchemy.orm import relationship
+from sqlalchemy import exc as sa_exc, func, select
+from sqlalchemy.orm import relationship, column_property
 from warnings import simplefilter
 
 # Ignore SQLAlchemy's warnings that we're overriding some attributes
@@ -35,8 +35,9 @@ class CustomArea(Area):
     area_links = relationship("LinkAreaArea",
                               primaryjoin="Area.id == LinkAreaArea.entity1_id")
     tags = relationship("AreaTag")
-    places = relationship("Place")
-    labels = relationship("Label")
+    place_count = column_property(select([func.count(Place.id)]).where(Place.area_id == Area.id))
+    label_count = column_property(select([func.count(Label.id)]).where(Label.area_id == Area.id))
+    artist_count = column_property(select([func.count(Artist.id)]).where(Artist.area_id == Area.id))
 
 class CustomArtist(Artist):
     area = relationship('CustomArea', foreign_keys=[Artist.area_id])

sir/schema/transformfuncs.py

@@ -33,6 +33,10 @@
 }
 
 
+def integer_sum(values):
+    return int(sum(values))
+
+
 def ended_to_string(ended):
     """
     :param ended: