rake function in ruby-on-rails - ruby-on-rails

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.

Answer 2

Simply put, db:migrate doesn't destroy existing data you have in your database. so running migrations and that rake task allows your data to exist from changes you make.
Workflow in words
You create an empty data base.
You will want to add a table of data for your first model into the database. This is done by editing a file in db/migrate
Now you want a second model, so you create your model and edit the migration file in db/migrate that was created for you
The easiest way to update your database without destroy any of the existing data, is to run bundle exec rake db:migrate. This adds the contents of the second migration file into the db and won't hurt existing data.
Example workflow after creating a project:
bundle exec rake db:create:all
bundle exec rails generate scaffold Users name:string email:string
bundle exec rake db:migrate
At this stage, bundle exec rails s and go to localhost:3000/users/new and create a new user.
bundle exec rails generate scaffold Posts title:string body:text
bundle exec rake db:migrate
Back in your browser go to localhost:3000/users and you should still see the user you created.