From 119d4a005234477894df569a992d142b699288c9 Mon Sep 17 00:00:00 2001
From: forest <forest.n.johnson@gmail.com>
Date: Sat, 9 May 2020 19:22:25 -0500
Subject: [PATCH] correctly handle when the desiredSchemaVersion <
 schemaVersion

---
 README.md         |  4 +++-
 capsulflask/db.py | 13 +++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index b3ff279..b9ea148 100644
--- a/README.md
+++ b/README.md
@@ -7,10 +7,12 @@ Python Flask web application for capsul.org
 capsulflask has a concept of a schema version. When the application starts, it will query the database for a table named
 `schemaversion` that has one row and one column (`version`). If the `version` it finds is not equal to the `desiredSchemaVersion` variable set in `db.py`, it will run  migration scripts from the `schema_migrations` folder one by one until the `schemaversion` table shows the correct version.
 
-For example, the script named `02_up_xyz.sql` should contain code that migrates the database in a reverse-able fashion from schema version 1 to schema version 2. Likewise, the script `02_down_xyz.sql` should contain code that migrates from schema version 2 back to schema version 1.
+For example, the script named `02_up_xyz.sql` should contain code that migrates the database from schema version 1 to schema version 2. Likewise, the script `02_down_xyz.sql` should contain code that migrates from schema version 2 back to schema version 1.
 
 **IMPORTANT: if you need to make changes to the schema, make a NEW schema version. DO NOT EDIT the existing schema versions.**
 
+In general, for safety, schema version upgrades should not delete data. Schema version downgrades will simply throw an error and exit for now. 
+
 ## how to run locally
 
 Ensure you have the pre-requisites for the psycopg2 Postgres database adapter package
diff --git a/capsulflask/db.py b/capsulflask/db.py
index 214ce88..a987b38 100644
--- a/capsulflask/db.py
+++ b/capsulflask/db.py
@@ -60,8 +60,13 @@ def init_app(app):
 
   cursor.execute("SELECT Version FROM schemaversion")
   schemaVersion = cursor.fetchall()[0][0]
-  
-  # print(schemaVersion)
+
+  if schemaVersion > desiredSchemaVersion:
+    print("schemaVersion ({}) > desiredSchemaVersion ({}). schema downgrades are not supported yet. exiting.".format(
+      schemaVersion, desiredSchemaVersion
+    ))
+    exit(1)
+
   while schemaVersion < desiredSchemaVersion:
     migrationKey = "%02d_up" % (schemaVersion+1)
     print("schemaVersion ({}) < desiredSchemaVersion ({}). running migration {}".format(
@@ -94,8 +99,8 @@ def init_app(app):
 
   app.config['PSYCOPG2_CONNECTION_POOL'].putconn(db)
 
-  print("schema migration completed. {}current schemaVersion: \"{}\"".format(
-    ("" if actionWasTaken else "(no action was taken). "), schemaVersion
+  print("{} current schemaVersion: \"{}\"".format(
+    ("schema migration completed." if actionWasTaken else "schema is already up to date. "), schemaVersion
   ))
 
   app.teardown_appcontext(close_db)