README

This is a simple Rails project to demonstrate an issue with using an existing database in Rails.

If you have an existing database with data in it (but without a schema_migrations table), and load your schema into a new Rails application via bin/rails db:schema:dump, then the first migration will drop all the data in your database.

I prepared this application by setting up a database using the prep environment, inserting some data, and then generated the "real" schema via bin/rails db:schema:dump. From there, if you run bin/rails db:migrate, all the data gets dropped.

You can see a real time demonstration of this by cloning this project, bundling, and running:

bin/rails demo

The demo task will do the following:

• Drop the database by running prep:reset
• Create, migrate, drop the schema_migrations table (and ar_internal_metadata to make it more like a DB that came from a non-Rails project), and insert some dummy data via prep:setup
• Show the dummy data via data:show
• Run db:migrate, which truncates the data
• Shows the now deleted data via data:show

I have created a temporary fix via a monkeypatch. You can run the demo with the fix applied using the APPLY_FIX=true environment variable:

APPLY_FIX=true bin/rails demo