Change derived storage to be based on image

Fixes #971

data/database.py

@@ -514,6 +514,7 @@ class ImageStorageSignature(BaseModel):
     )
 
 
+# NOTE: This table is *deprecated* and will be removed in the next PR.
 class DerivedImageStorage(BaseModel):
   source = ForeignKeyField(ImageStorage, null=True, related_name='source')
   derivative = ForeignKeyField(ImageStorage, related_name='derivative')
@@ -596,6 +597,19 @@ class Image(BaseModel):
 _ImageProxy.initialize(Image)
 
 
+class DerivedStorageForImage(BaseModel):
+  source_image = ForeignKeyField(Image)
+  derivative = ForeignKeyField(ImageStorage)
+  transformation = ForeignKeyField(ImageStorageTransformation)
+
+  class Meta:
+    database = db
+    read_slaves = (read_slave,)
+    indexes = (
+      (('source_image', 'transformation'), True),
+    )
+
+
 class RepositoryTag(BaseModel):
   name = CharField()
   image = ForeignKeyField(Image)
@@ -831,4 +845,4 @@ all_models = [User, Repository, Image, AccessToken, Role, RepositoryPermission,
               RepositoryAuthorizedEmail, ImageStorageTransformation, DerivedImageStorage,
               TeamMemberInvite, ImageStorageSignature, ImageStorageSignatureKind,
               AccessTokenKind, Star, RepositoryActionCount, TagManifest, UserRegion,
-              QuayService, QuayRegion, QuayRelease, BlobUpload]
+              QuayService, QuayRegion, QuayRelease, BlobUpload, DerivedStorageForImage]