chore: clean up some warnings and comments

samples/python/django/create_data_model.sql

@@ -33,7 +33,7 @@ CREATE TABLE IF NOT EXISTS tracks (
     PRIMARY KEY(id, track_number)
 ) INTERLEAVE IN PARENT albums ON DELETE CASCADE;
 
-CREATE UNIQUE INDEX IF NOT EXISTS unique_idx_id ON tracks(track_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_tracks_track_id ON tracks(track_id);
 
 CREATE TABLE IF NOT EXISTS venues (
   id character varying NOT NULL,

samples/python/django/drop_data_model.sql

@@ -2,4 +2,4 @@ drop table if exists concerts;
 drop table if exists venues;
 drop table if exists tracks;
 drop table if exists albums;
-drop table if exists singers;
+drop table if exists singers;

samples/python/django/sample.py

@@ -1,3 +1,18 @@
+""" Copyright 2022 Google LLC
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+"""
+
 import os
 import sys
 import datetime
@@ -300,8 +315,8 @@ def jsonb_filter():
 
 if __name__ == "__main__":
 
+  tables_created: bool = False
   try:
-    tables_created = False
 
     # setting up django
     os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'setting')

samples/python/django/sample_app/model.py

@@ -1,4 +1,4 @@
-''' Copyright 2022 Google LLC
+""" Copyright 2022 Google LLC
 
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
@@ -11,20 +11,19 @@
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-'''
+"""
 
 from django.db import models
 from django.db.models import Q, F
-from django.contrib.postgres.fields import JSONField
 
 class BaseModel(models.Model):
-  class Meta():
+  class Meta:
     abstract = True
   created_at = models.DateTimeField()
   updated_at = models.DateTimeField()
 
 class Singer(BaseModel):
-  class Meta():
+  class Meta:
     db_table = 'singers'
 
   id = models.CharField(primary_key=True, null=False)
@@ -34,7 +33,7 @@ class Meta():
   active = models.BooleanField()
 
 class Album(BaseModel):
-  class Meta():
+  class Meta:
     db_table = 'albums'
 
   id = models.CharField(primary_key=True, null=False)
@@ -45,16 +44,22 @@ class Meta():
   singer = models.ForeignKey(Singer, on_delete=models.DO_NOTHING)
 
 class Track(BaseModel):
-  class Meta():
+  class Meta:
     db_table = 'tracks'
 
-  # Here, track_id is a column that is supposed to be primary key by Django.
-  # But id column will just have a unique index in the actual table.
-  # In the actual table, (id, track_number) will be the primary key.
-  # This is done because Django doesn't support composite primary keys,
-  # but we need to have a composite primary key due to the fact that
-  # the "tracks" table is interleaved in "albums".
-
+  # Track is interleaved in the parent table Album. Cloud Spanner requires that
+  # a child table includes all the primary key columns of the parent table in
+  # its primary key, followed by any primary key column(s) of the child table.
+  # This means that a child table will always have a composite primary key.
+  # Composite primary keys are however not supported by Django. The workaround
+  # that we apply here is to create a separate field `track_id` and tell Django
+  # that this is the primary key of the table. The actual schema definition
+  # for the `tracks` table does not have this as its primary key. Instead, the
+  # primary key of this table is (`id`, `track_number`). In addition, there is a
+  # unique index defined on `track_id` to ensure that Track rows can efficiently
+  # be retrieved using the identifier that Django thinks is the primary key of
+  # this table.
+  # See create_data_model.sql file in this directory for the table definition.
   track_id = models.CharField(primary_key=True, null=False)
   album = models.ForeignKey(Album, on_delete=models.DO_NOTHING, db_column='id')
   track_number = models.BigIntegerField(null=False)
@@ -63,17 +68,19 @@ class Meta():
 
 
 class Venue(BaseModel):
-  class Meta():
+  class Meta:
     db_table = 'venues'
   id = models.CharField(primary_key=True, null=False)
   name = models.CharField(null=False)
   description = models.JSONField()
 
 
 class Concert(BaseModel):
-  class Meta():
+  class Meta:
     db_table = 'concerts'
-    constraints = [models.CheckConstraint(check = Q(end_time__gte=F('start_time')), name='chk_end_time_after_start_time' )]
+    constraints = [models.CheckConstraint(
+      check = Q(end_time__gte=F('start_time')),
+      name='chk_end_time_after_start_time' )]
   id = models.CharField(primary_key=True, null=False)
   venue = models.ForeignKey(Venue, on_delete=models.DO_NOTHING)
   singer = models.ForeignKey(Singer, on_delete=models.DO_NOTHING)