How can I convert all migration files into a single file in Rails?

Question

I have been developing a project in Ruby on Rails. During the development I have generated tons of migration files for my project. Sometimes I have added and deleted columns from different tables.

Is there a way that I could consolidate all the migrations from multiple files into a single file?

Answer 1

TL;DR

What you need isn't a consolidated set of migrations; it's a single schema file and an optional seeds.rb file. Rails generally maintains the schema automagically when you run migrations, so you already have most of what you should need with the possible exception of seed data as described below.

Use the Schema, Not Migrations

In general, you shouldn't be maintaining a large pool of migrations. Instead, you should periodically clear out your migrations, and use schema.rb or schema.sql to (re)create a database. The Rails guides specifically state:

There is no need (and it is error prone) to deploy a new instance of an app by replaying the entire migration history. It is much simpler and faster to just load into the database a description of the current schema...Because schema dumps are the authoritative source for your database schema, it is strongly recommended that you check them into source control.

You should therefore be using bin/rails db:schema:load rather than running migrations, or run the associated Rake task on older versions of Rails.

Data Migrations

While you can use migrations to fix or munge data related to a recent schema change, data migrations (if used at all) should be temporary artifacts. Data migrations are almost never idempotent, so you shouldn't be maintaining data migrations long-term. The guide says:

Some people use migrations to add data to the database...However, Rails has a 'seeds' feature that should be used for seeding a database with initial data. It's a really simple feature: just fill up db/seeds.rb with some Ruby code, and run rake db:seed...This is generally a much cleaner way to set up the database of a blank application.

Database seed data should be loaded with bin/rails db:seed (or the associated Rake task) rather than maintaining the data in migrations.

Answer 2

There is a gem that purports to do exactly what you describe in the question - check out Squasher.

From the README: "Squasher compresses old migrations in a Rails application. ... Squasher removes all the migrations and creates a single migration with the final database state of the specified date (the new migration will look like a schema)."

Answer 3

You'll have to do the merge manually.

But if you want only a single file, there is db/schema.rb. It contains a snapshot of current database schema. You can load it directly in database if you want.