[experiments][model] Fixed BlockInput backup/restore

Database hash doesn't exists anymore and rather than generating
natural keys that trigger the creation of get_by_natural_key
methods with way too many parameters, use tuples in tuples. This
make the code clearer to read as well as easier to maintain if the
natural key of a related field changes.

beat/web/experiments/models/block_input.py

@@ -33,25 +33,26 @@ from ...databases.models import DatabaseSetOutput
 from .block import Block
 
 
-#----------------------------------------------------------
+# ----------------------------------------------------------
 
 
 class BlockInputManager(models.Manager):
 
-    def get_by_natural_key(self, name, experiment_author, toolchain_author,
-                           toolchain_name, toolchain_version, experiment_name,
-                           cache_hash, database_hash):
-        block = Block.objects.get_by_natural_key(name, experiment_author,
-                                                 toolchain_author, toolchain_name, toolchain_version,
-                                                 experiment_name)
+    def get_by_natural_key(self, block_natural_key,
+                           cache_hash, database_natural_key):
+        if block_natural_key:
+            block = Block.objects.get_by_natural_key(*block_natural_key)
+        else:
+            block = None
 
         if cache_hash:
             return self.get(cache__hash=cache_hash, block=block)
         else:
-            return self.get(database__hash=database_hash, block=block)
-
+            database = DatabaseSetOutput.objects.get_by_natural_key(
+                *database_natural_key)
+            return self.get(database=database, block=block)
 
-#----------------------------------------------------------
+# ----------------------------------------------------------
 
 
 class BlockInput(models.Model):
@@ -68,12 +69,16 @@ class BlockInput(models.Model):
                                  null=True, on_delete=models.CASCADE)
 
     channel = models.CharField(max_length=200, default='', blank=True,
-                               help_text="Synchronization channel within the toolchain")
+                               help_text="Synchronization channel within "
+                                         "the toolchain")
 
     objects = BlockInputManager()
 
-
     def natural_key(self):
+        if self.block:
+            block_natural_key = self.block.natural_key()
+        else:
+            block_natural_key = None
         cache_hash = self.cache and self.cache.hash
-        database_hash = self.database and self.database.hash
-        return self.block.natural_key() + (cache_hash, database_hash)
+        database_natural_key = self.database and self.database.natural_key()
+        return (block_natural_key, cache_hash, database_natural_key)