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correctly handle when the desiredSchemaVersion < schemaVersion

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forest 2020-05-09 19:22:25 -05:00
parent 4a1924587c
commit 119d4a0052
2 changed files with 12 additions and 5 deletions
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4
README.md
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@ -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

13
capsulflask/db.py
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@ -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)