Question

I am very new in ruby-on-rails. I have doubt in rake. create function is create a new db. After that, we want to run some commands like

rake db:load
rake db:data:load
rake db:schema:load
rake db:migrate
rake db:seed

But why we want to run this cmds after create the db and what function of the about cmd.

Thanks for your advice.

Answer 1

You can use rake -T to get the description of each task:

$ rake -T | grep db
rake db:create                                # Create the database from config/database.yml for the current Rails.env (use db:create:all to create all dbs in the config)
rake db:drop                                  # Drops the database for the current Rails.env (use db:drop:all to drop all databases)
rake db:fixtures:load                         # Load fixtures into the current environment's database.
rake db:migrate                               # Migrate the database (options: VERSION=x, VERBOSE=false).
rake db:migrate:status                        # Display status of migrations
rake db:rollback                              # Rolls the schema back to the previous version (specify steps w/ STEP=n).
rake db:schema:dump                           # Create a db/schema.rb file that can be portably used against any DB supported by AR
rake db:schema:load                           # Load a schema.rb file into the database
rake db:seed                                  # Load the seed data from db/seeds.rb
rake db:setup                                 # Create the database, load the schema, and initialize with the seed data (use db:reset to also drop the db first)
rake db:structure:dump                        # Dump the database structure to db/structure.sql. Specify another file with DB_STRUCTURE=db/my_structure.sql
rake db:version                               # Retrieves the current schema version number

I this what you were asking about?

EDIT:

You can read more about what migrations are for here: http://guides.rubyonrails.org/migrations.html

EDIT 2:

rake db:migrate allows you to update the DB schema in a “sane” way: you can create a new migration (read the guides!) and add a new column for example, add an index, rename a column, etc. – migrations allow you to “travel” back and forth in “time” – you can run the migration and rollback it later.

When you generate a new migration:

$ rails g migration add_new_column_to_some_table you will be able to run rake db:migrate later on to apply to changes you want (of course you have to write the body of this generated migration).

I STRONLY advise you to read the guides though 🙂

EDIT 3:

add_column :users, :price, :float, for example, will add price column to the users table, the type of the column will be float (float isn’t a best idea to store money related things BTW!). This column will be NULL by default.

EDIT 4:

Information about which migrations were run is stored in schema_migrations table: running migration for the first time will add a new record in this table with version of this migration (date + some random numbers from the name of the file). Rollbacking a migration will remove this record. Running a migration twice will not have any effect.