Learning Ruby On Rails: Day 10

“Black and Blue: The Invisible Man and the Masque of Blackness” Artist: Zak Ové

In an attempt to learn more, faster, I’m changing the style of these posts a little. I’ll be sharing notes, rather than creating micro tutorials of what I’ve learned each day.

• Action Pack: the Controller and View Rails component.
• We generate dynamic content in our views with Embedded Ruby (erb).
• Ruby is an object oriented programming language.
• Local variables, method names and method parameters should all start with a lower case letter or underscore.
• Instance variables begin with an @.
• Use underscores to separate words.
• Class names are capitalized and CamelCased.
• Symbols are string literals magically made into constants.
• Everything in Ruby is an object.
• Double quotes are used for expression interpolation, and for strings that have single quotes in them. Example: "Let's hang out".
• Arrays are ordered collections of things. To reference an item in an array, you use an item’s index (which is an integer). Example: array_of_things[0].
• Hashes are collections of key/value pairs. To reference an item in a hash, you use its key (which can be a symbol or string). Example: hash_of_things[:some_key].
• nil is an object.
• The << method is used to append a single value to the end of an array.
• Hashes have keys and values.
• The keys can be a symbol, string, or a variable that returns a symbol or string.
• The syntax to separate a key from its value is always a hashrocket (=>).
• The one allowed exception to this rule is if the key is a symbol, in which case the symbol can be immediately followed (no space) by a colon. And then a space.
• That said, a symbol as a key is still allowed to use a hash rocket. (In which case the symbol’s colon goes at the start of the symbol, not the end.)
• The colon separator is completely optional and is syntactical sugar. (ie, it’s nice and cleaner, but not required.)
• unless is like if but it checks for the condition not to be true.
• until is like while, but it continues until the condition evaluates to true.
• We can put the if/unless at the end of a line of code instead of wrapping the line of code in an if/unless block. Like this:

puts “danger will Robinson” if radiation > 3000
distance = distance * 1.2 while distance < 100

• Two organizations for methods: classes and modules.

Class Order < ApplicationRecord
  has_many :line_items
  def self.find_all_unpaid
    self.where(‘paid = 0’)
  end
  def total
    sum = 0
    line_items.each {|li| sum += li.total}
    sum
  end
end

In the above code snippet:

• Order inherits all behavior from ApplicationRecord.
• has_many is a method defined by ActiveRecord. It is called as the Order class is being defined.
• Prefixing a method with self makes it a class method. So it can be called anywhere on the class, instead of on an instance of that class.
• So I could write:to_collect = Order.find_all_unpaid instead of:@order = Order.new and then: @order.find_all_unpaid.

Bai!

Next post, here.