Difference between rake db:migrate db:reset and db:schema:load
The difference between rake db:migrate and rake db:reset is pretty clear in my head. The thing which I don't understand is how rake db:schema:load different from the former two.
Just to be sure that I am on the same page:
rake db:migrate - Runs the migrations which haven't been run yet. rake db:reset - Clears the database (presumably does a rake db:drop + rake db:create + rake db:migrate ) and runs migration on a fresh database. Please help to clarify, if my understanding has gone wrong.
db:schema:load creates tables and columns within the (existing) database following schema.rb
db:setup does db:create, db:schema:load, db:seed
Typically, you would use db:migrate after having made changes to the schema via new migration files (this makes sense only if there is already data in the database). db:schema:load is used when you setup a new instance of your app.
I hope that helps.
UPDATE for rails 3.2.12:
I just checked the source and the dependencies are like this now:
db:schema:dump dumps the current env's schema (and seems to create the db as well)
db:setup runs db:schema:load, db:seed
For further information please have a look at https://github.com/rails/rails/blob/v3.2.12/activerecord/lib/active_record/railties/databases.rake (for Rails 3.2.x) and https://github.com/rails/rails/blob/v4.0.5/activerecord/lib/active_record/railties/databases.rake (for Rails 4.0.x)
TLDR
Use
rake db:migrate If you wanna make changes to the schema rake db:reset If you wanna drop the database, reload the schema from schema.rb , and reseed the database rake db:schema:load If you wanna reset database to schema as provided in schema.rb (This will delete all data) Explanations
rake db:schema:load will set up the schema as provided in schema.rb file. This is useful for a fresh install of app as it doesn't take as much time as db:migrate
Important note, db:schema:load will delete data on server.
rake db:migrate makes changes to the existing schema. Its like creating versions of schema. db:migrate will look in db/migrate/ for any ruby files and execute the migrations that aren't run yet starting with the oldest. Rails knows which file is the oldest by looking at the timestamp at the beginning of the migration filename. db:migrate comes with a benefit that data can also be put in the database. This is actually not a good practice. Its better to use rake db:seed to add data.
rake db:migrate provides tasks up, down etc which enables commands like rake db:rollback and makes it the most useful command.
rake db:reset does a db:drop and db:setup
It drops the database, create it again, loads the schema, and initializes with the seed data
Relevant part of the commands from databases.rake
namespace :schema do
desc 'Creates a db/schema.rb file that is portable against any DB supported by Active Record'
task :dump => [:environment, :load_config] do
require 'active_record/schema_dumper'
filename = ENV['SCHEMA'] || File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, 'schema.rb')
File.open(filename, "w:utf-8") do |file|
ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
end
db_namespace['schema:dump'].reenable
end
desc 'Loads a schema.rb file into the database'
task :load => [:environment, :load_config, :check_protected_environments] do
ActiveRecord::Tasks::DatabaseTasks.load_schema_current(:ruby, ENV['SCHEMA'])
end
# desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
task :reset => [ 'db:drop', 'db:setup' ]
namespace :migrate do
# desc 'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
task :redo => [:environment, :load_config] do
if ENV['VERSION']
db_namespace['migrate:down'].invoke
db_namespace['migrate:up'].invoke
else
db_namespace['rollback'].invoke
db_namespace['migrate'].invoke
end
end
As far as I understand, it is going to drop your database and re-create it based on your db/schema.rb file. That is why you need to make sure that your schema.rb file is always up to date and under version control.
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