All the Database Tasks in Rails

#rails

Once you start programming in Rails, you inevitably come across db:migrate, which applies the migration to your database. Then you make a mistake and learn about db:rollback to revert the previous migration.

After programming for a while, you stumble upon db:reset, to drop and recreate your database, running all the migrations on this fresh database. Finally, you realize that you lost all your sample data after the last reset, and discover db:seed, which inserts the sample data in the database, so your rails app looks realistic, and you can go back to a clean slate by running db:reset frequently.

Now it's easy to be a competent Rails programmer and get by with these four tasks. However, if you truly want to master Rails (which is one of my goals as a new Rails developer) and make the most use of its magic to make your life easy, it's worth knowing about the remaining database tasks Rails provides to manage the database and migrations.

How to find all db tasks

You can find all the database tasks Rails provides by running the following command from a Rails application directory.

➜  blog (main) ✗ bin/rails help | grep db:

  db:create
  db:drop
  db:environment:set
  db:fixtures:load
  db:migrate
  db:migrate:down
  db:migrate:redo
  db:migrate:status
  db:migrate:up
  db:prepare
  db:reset
  db:rollback
  db:schema:cache:clear
  db:schema:cache:dump
  db:schema:dump
  db:schema:load
  db:seed
  db:seed:replant
  db:setup
  db:structure:dump
  db:structure:load
  db:system:change
  db:version

You can also find the source code for these tasks in the database_tasks.rb file in the Rails repository and the databases.rake file under the ActiveRecord/Railties directory. The ActiveRecord::Tasks::DatabaseTasks utility class encapsulates the logic behind the common tasks used to manage the database and migrations.

Here's a brief summary of each database task.

db:create: Creates the database unless it already exists.

db:drop: Drops the database if it exists.

db:environment:set: Fixes the EnvironmentMismatchError or NoEnvironmentInSchemaError, raised if the environment data is not found in the schema, by setting the current environment in the internal table.

db:fixtures:load: It loads the fixtures, i.e., the sample data that you want to test against. They are stored in the YAML file under the test/fixtures/ directory.

db:migrate: Runs all the migrations that have not run yet, for the current environment.

db:migrate:down: Reverts the transformations performed by the last migration's up method by running the down method.

db:migrate:redo: Rolls back the database one migration and re-migrates up.

db:migrate:status: Displays the status of migrations.

db:migrate:up: Runs the up method for a given migration.

db:prepare: Runs setup if the database does not exist. Otherwise, it runs the migrations.

db:reset: Resets your database using your migrations for the current environment. It does this by running the db:drop, db:create, db:migrate tasks.

db:rollback: Rolls the schema back to the previous version, undoing the migration that you just ran. If you want to undo previous n migrations, pass STEP=n to this task.

db:schema:cache:clear: Clears the db/schema_cache.yml file generated by the db:schema:cache:dump task.

db:schema:cache:dump: Creates a db/schema_cache.yml file.

db:schema:dump: Creates a database schema file (either db/schema.rb or db/structure.sql, depending on config.active_record.schema_format).

db:schema:load: Loads a database schema file (either db/schema.rb or db/structure.sql, depending on config.active_record.schema_format) into the database.

db:seed: Loads the seed data from db/seeds.rb file.

db:seed:replant: Truncates tables of each database for the current environment and loads the seeds

db:setup: Creates all databases db:create, loads all schemas db:schema:load, and initializes with the seed data db:seed. However, it won't drop the database first if it exists. Use db:reset to also drop all databases first.

db:structure:dump: Deprecated. It was used to dump the structure.sql file.
db:structure:load: Deprecated. It was used to load the structure.sql file.

For some history behind why these tasks were deprecated, check out this wtf. No, seriously.

db:system:change: Running rails new generator without specifying a database sets your app with sqlite. It's a hassle to change the database later. This task helps you easily change the database by delegating to the rails db:change SYSTEM=postgresql|mysql|whatever generator.

db:version: Prints the current schema version number.

There you go. Rails gives you so much power. Use it wisely.

Until next time!