write sample migration structure

app/migrations/__init__.py

@@ -1,3 +1,20 @@
 """
-Migrations module
+Migrations module.
+
+Reads and applies the latest database migrations.
 """
+from .main import main_db_migrations
+from .userdata import userdata_db_migrations
+
+
+def apply_migrations():
+    userdb_version = 0
+    maindb_version = 0
+
+    for migration in main_db_migrations:
+        if migration.version > maindb_version:
+            migration.migrate()
+
+    for migration in userdata_db_migrations:
+        if migration.version > userdb_version:
+            migration.migrate()

app/migrations/main/__init__.py

@@ -0,0 +1,4 @@
+from .sample import SampleMigrationModel
+
+main_db_migrations = [SampleMigrationModel]
+

app/migrations/main/sample.py

@@ -0,0 +1,6 @@
+class SampleMigrationModel:
+    version = 1
+
+    @staticmethod
+    def migrate():
+        print("executing sample main db migration")

app/migrations/userdata/__init__.py

@@ -0,0 +1,4 @@
+from .sample import SampleMigrationModel
+
+userdata_db_migrations = [SampleMigrationModel]
+

app/migrations/userdata/sample.py

@@ -0,0 +1,6 @@
+class SampleMigrationModel:
+    version = 1
+
+    @staticmethod
+    def migrate():
+        print("executing sample userdata db migration")