Review and Edit Generated Scripts
Fix autogenerated migrations before applying.
Review and Edit Generated Scripts is a free Flask Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Flask Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Autogenerate Is Not Perfect
Autogenerate is a great first draft, not a final answer. Always review the script before you apply it anywhere. 🔍
Open the Versions File
Each script lives in the versions folder. Open it and read the upgrade and downgrade functions like any other code.
The op Object
Inside the functions you will see calls on the op object, like op.create_table and op.add_column, each describing one schema change.
op.add_column("user", sa.Column("age", sa.Integer()))What Alembic Misses
Autogenerate often misses renames, seeing them as a drop plus an add. That would silently delete the column data.
Fix Renames by Hand
When a column is really being renamed, replace the drop and add with a single alter_column that preserves the data.
op.alter_column("user", "name", new_column_name="full_name")Check the downgrade
Confirm the downgrade truly reverses the upgrade. A broken downgrade leaves you stuck if you ever need to roll back.
Watch NOT NULL Columns
Adding a non-nullable column to a table with rows will fail. Add it nullable first, fill values, then make it required.
Add Data Steps Yourself
Need to backfill values? Add an op.execute call with raw SQL between the schema steps to migrate existing data safely.
op.execute("UPDATE user SET age = 0")Test on a Copy First
Before touching production, run the migration on a copy of real data. It surfaces failures while they are still cheap to fix.
One Change per Migration
Keep each migration focused on one logical change. Small scripts are far easier to review, test, and roll back cleanly.
Commit the Final Script
Once edited and tested, commit the script. Never change a migration that has already shipped to production history.
Quick Check
You renamed a column, but autogenerate wrote a drop and an add. What is the danger?
Recap
You learned to review generated scripts, fix renames with alter_column, handle non-null columns, and test before shipping. 🎉
Frequently asked questions
Is the “Review and Edit Generated Scripts” lesson free?
Yes — the full text of “Review and Edit Generated Scripts” is free to read here on the web, and the Flask Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Flask Academy course, upgrade to CoddyKit PRO.
What will I learn in “Review and Edit Generated Scripts”?
Fix autogenerated migrations before applying. You practise Flask Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Flask Academy?
No prior experience is required. Flask Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Review and Edit Generated Scripts” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Flask Academy lesson?
Yes. Every Flask Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Why You Need Migrations, Not create_all
- Init and Autogenerate a Migration
- Apply and Roll Back with upgrade
- Review and Edit Generated Scripts