Rails DRY Up Your Database Configuration

由于database.yml十分小巧，我们很容易忘掉它是用YAML这种非常健壮的标记语言来写的。

YAML有一个叫"merge keys"的特性，它可以merge one Hash into another。

例如:

development:
  adapter: mysql
  database: DRYUpYourDatabaseConfig_development
  username: root
  password: secret
  socket: /tmp/mysql.sock

test:
  adapter: mysql
  database: DRYUpYourDatabaseConfig_test
  username: root
  password: secret
  socket: /tmp/mysql.sock

production:
  adapter: mysql
  database: DRYUpYourDatabaseConfig_production
  username: root
  password: secret
  socket: /tmp/mysql.sock

development:   adapter: mysql   database: DRYUpYourDatabaseConfig_development   username: root   password: secret   socket: /tmp/mysql.sock  test:   adapter: mysql   database: DRYUpYourDatabaseConfig_test   username: root   password: secret   socket: /tmp/mysql.sock  production:   adapter: mysql   database: DRYUpYourDatabaseConfig_production   username: root   password: secret   socket: /tmp/mysql.sock 

我们可以利用YAML的"merge keys"特性简化配置和减少冗余:

defaults: &defaults
  adapter: mysql
  username: root
  password: secret
  socket: /tmp/mysql.sock

development:
  database: DRYUpYourDatabaseConfig_development
  <<: *defaults

test:
  database: DRYUpYourDatabaseConfig_test
  <<: *defaults

production:
  database: DRYUpYourDatabaseConfig_production
  <<: *defaults

defaults: &defaults   adapter: mysql   username: root   password: secret   socket: /tmp/mysql.sock  development:   database: DRYUpYourDatabaseConfig_development   <<: *defaults  test:   database: DRYUpYourDatabaseConfig_test   <<: *defaults  production:   database: DRYUpYourDatabaseConfig_production   <<: *defaults