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
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
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
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
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.
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: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: Creates a db/schema_cache.yml file.
db:schema:dump: Creates a database schema file (either
db/structure.sql, depending on
db:schema:load: Loads a database schema file (either
db/structure.sql, depending on
config.active_record.schema_format) into the database.
db:seed: Loads the seed data from
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
db:structure:load: Deprecated. It was used to load the
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!