Changed tile lookups to be pk based on views.

raster/const.py

@@ -4,6 +4,7 @@
 EXPORT_MAX_PIXELS = 10000 * 10000
 MAX_EXPORT_NAME_LENGTH = 100
 DEFAULT_LEGEND_BREAKS = 7
+PK_FORMAT = '{layer}-{z}-{x}-{y}'
 README_TEMPLATE = """Django Raster Algebra Export
 ============================
 {description}

raster/models.py

@@ -13,6 +13,7 @@
 from django.db.models import Max, Min
 from django.db.models.signals import post_delete, post_save, pre_save
 from django.dispatch import receiver
+from raster.const import PK_FORMAT
 from raster.mixins import ValueCountMixin
 from raster.tiles.const import WEB_MERCATOR_SRID
 from raster.utils import hex_to_rgba
@@ -371,6 +372,25 @@ def statistics(self):
         return (self.min, self.max, self.mean, self.std)
 
 
+class RasterTileManager(models.Manager):
+
+    def filter_on_pk(self, rasterlayer_id, tilez, tilex, tiley):
+        """
+        A wrapper function that filters on the primary key based on the input
+        parameters, instead of the individual column values directly.
+
+        This is useful for sharded databases, which can be sharded by the
+        verbose primary key.
+        """
+        pk = PK_FORMAT.format(
+            layer=rasterlayer_id,
+            z=tilez,
+            x=tilex,
+            y=tiley,
+        )
+        return self.filter(id=pk)
+
+
 class RasterTile(models.Model):
     """
     Store individual tiles of a raster data source layer.
@@ -387,14 +407,19 @@ class RasterTile(models.Model):
     tiley = models.IntegerField(db_index=True)
     tilez = models.IntegerField(db_index=True, choices=ZOOMLEVELS)
 
+    objects = RasterTileManager()
+
     def __str__(self):
         return '{} {}'.format(self.rid, self.rasterlayer.name)
 
     def save(self, *args, **kwargs):
-        self.id = '{0}-{1}-{2}-{3}'.format(
-            self.rasterlayer_id,
-            self.zoom,
-            self.tilex,
-            self.tiley,
-        )
+        self.id = self.construct_pk()
         super(RasterTile, self).save(*args, **kwargs)
+
+    def construct_pk(self):
+        return PK_FORMAT.format(
+            layer=self.rasterlayer_id,
+            z=self.tilez,
+            x=self.tilex,
+            y=self.tiley,
+        )

raster/tiles/utils.py

@@ -23,11 +23,11 @@ def get_raster_tile(layer_id, tilez, tilex, tiley):
         # Compute multiplier to find parent raster
         multiplier = 2 ** (tilez - zoom)
         # Fetch tile
-        tile = RasterTile.objects.filter(
+        tile = RasterTile.objects.filter_on_pk(
             tilex=tilex / multiplier,
             tiley=tiley / multiplier,
             tilez=zoom,
-            rasterlayer_id=layer_id
+            rasterlayer_id=layer_id,
         )
 
         if tile.exists():