TIL

Want to change database connections from inside psql? You can! Psql, the REPL for Postgres, has a useful meta-command called \connect, or \c. This lets you establish a new connection to a Postgres server, while closing the current connection. Here is the required format: \c or \connect [ dbname [ username ] [ host ] [ port ] ] | conninfo Only \c [my_database] is required; omitted parameters are taken from the previous connection. ...

To maintain data integrity, certain actions like rake db:drop will not execute when there are active sessions on a Postgres database. You’ll get an error like this: ERROR: database "database_name" is being accessed by other users DETAIL: There are 2 other session(s) using the database. Sessions can be killed from the command line, but a safer route is to kill them with a database method. First, revoke all public access from the database: ...

The Ruby keyword not and the unary ! aren’t the same. They have a different precedence, and therefore are not interchangeable, despite seeming very similar. irb > not 3 == 4 => true irb > !3 == 4 => false The first example is evaluated as not (3 == 4), or not false, which is true. The second example is evaluated as (not 3) == 4, or false == 4, which is false. ...

Ruby has a few interesting old keywords that use the underscore, or ‘skid’, to convey meta information about the file. Here they are in action: # test.rb puts __ENCODING__ puts __FILE__ puts __LINE__ __END__ Because this is after 'end', it should not be executed Running this file produces: $ ruby test.rb UTF-8 test.rb 3 Pretty cool!

The not null constraint is a great way to ensure data integrity. If a Rails model validates_presence_of an attribute, that column should be not null in the database. Rails has a special migration method for setting this constraint. change_column_null :users, :mandatory_attribute, false You could also use the change_column method. The reason change_column_null is a better choice is that change_column requires you to state the type of the column; change_column_null does not. change_column(table_name, column_name, type, options) change_column_null(table_name, column_name, null, default = nil)

Metaprogramming! Today I created a variable event that calls a serializer unique to the value of event. Along the way I learned about the Rails methods classify and constantize. classify takes a plural table name and returns a class name. > 'some_things'.classify => "SomeThing" constantize tries to find a constant with the name specified in the argument string. > "Module".constantize => Module > "Nothing".constantize NameError: uninitialized constant Nothing Here’s a sample of how I used these methods today (on the ‘Today I Learned’ app itself): ...

The Rails find_or_create_by method is great for bringing something into existence only once. I like to use it for database seeds, so you get the basic objects you need to make your development site useable, but don’t keep creating them over and over again. One feature I recently learned is that this method takes a block. User.find_or_create_by(first_name: 'Jake') do |user| user.last_name = 'Worth' end This lets you find the object, and if it doesn’t exist, create it with whatever attributes you need.

The Vim command :e edits a file. Add a bang, :e!, to edit the current file ‘always’, discarding any changes to the current buffer. This is useful if you rename a file with a new file extension (i.e. .txt to .rb). :e! reloads the file in Vim, picking up any customizations you have in your configuration files such as syntax highlighting.

I use HTTP Basic auth in non-production environments because it ships with Rails and is easy to implement. The first time I used it, I set it up like this: # app/controllers/application_controller.rb if ENV['http_basic_auth'] http_basic_authenticate_with name: ENV['username'], password: ENV['password'] end I used environmental variables so that no credentials were hard-coded, and so I could toggle it without deploying. Today I learned you can also implement it like this: # app/controllers/application_controller.rb if creds = ENV['basic_auth_credentials'] username, password = creds.split(':', 2) http_basic_authenticate_with name: username, password: password end This requires an environmental variable called basic_auth_credentials, set to <username>:<password>. I prefer this because it allows one variable to serve two purposes: it toggles the feature and also contains the information the feature needs to work. ...

Ruby’s puts can take multiple arguments! 2.2.0 :002 > puts 'so', 'many', 'statements', 'to', 'puts' so many statements to puts => nil