rake db：迁移，源和目标

Question

I'm new to ruby and mysql.

I was told to execute two commands below:

1. mysql -u root; then CREATE DATABASE sd

2. rake db:migrate .

The sd database was empty when created. After I ran the 2nd command, sd is full of items.

I'm wondering how rake knows that the destination is sd and what the source is.

I know that there are some scripts under db/migrate folder, so I guess rake knows who the destination is from such newly-created(I assume, 'cause I'm new to ruby) scripts. But how about the source?

Thanks!

Answer 1

It looks like you are trying to work with a Rails application. I would suggest looking at config/database.yml. That file holds configuration data for test, development, and production environments. By default, rails uses the development environment. You will likely find the answer in config/database.yml under development section.

• Duck

Answer 2

All information about your database is on the file config/database.yml . This doc can help you: http://guides.rubyonrails.org/configuring.html#configuring-a-database

And you can change this:

mysql -u root; then CREATE DATABASE sd

for that:

rake db:create

Answer 3

The source of the data will normally be controlled by the db/migrate/*.rb files as you are aware of.

But they may have hooked another task onto db:migrate via the Rakefile or lib/tasks/*.rake files so "rake db:mirgrate" may also runs some extra tasks. A common task that adds seed information is the rake db:seed task, which normally runs db/seeds.rb .

When I use db/seeds.rb I typically put my seed data in db/fixtures/*.yml, but others may have different places.

on newer rails you can also use rake db:create to do the database creation (assuming the user in database.yml has sufficient privileges). rake -T db will tell you wnat tasks have been named with db in them, eg:

$ rake -T db
rake db:create          # Create the database from DATABASE_URL or 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 using DATABASE_URL or 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:seed_fu         # Loads seed data for the current environment.
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:test:seed       # seed the test database
rake db:version         # Retrieves the current schema version number