Confusion of Ruby syntax

Question

I am a beginner in Ruby. I am providing below a code snippet which I want to know the meaning of the syntax of. I know the semantics, in a sense that I can run the full length code and see what happens. But I am not clear on the language construct itself.

class Product < ActiveRecord::Base
    include ActsAsTree

    self.primary_key = 'id'
    acts_as_tree foreign_key: 'product_id'

Questions follow:

Is ActiveRecord a module provided by ActiveRecord gem?
Is ActiveRecord::Base a class contained in ActiveRecord module?
Is primary_key an attribute of ActiveRecord::Base class?
The last line of the code confuses me the most. acts_as_tree is the name of the gem. Why does it precede in the statement? And what the heck is foreign_key: 'product_id'? Why is there a colon(:) separator in between? What language construct does the statement represent?

Might I suggest reading the source material and see how many of your questions are answered? — MCBama
– MCBama, Commented May 19, 2015 at 19:53
4) Because it's not just the name of the gem--it's also a class method. It's a map argument to acts_as_tree. I'd strongly consider boning up on some Ruby basics. — Dave Newton
– Dave Newton, Commented May 19, 2015 at 19:59
acts_as_tree foreign_key: 'product_id' is equal to act_as_tree(:foreign_key => 'product_id') — Яois
– Яois, Commented May 19, 2015 at 20:27

Rohan Pujari · Accepted Answer · 2015-05-19 20:52:33Z

Yes ActiveRecord is a module provided by ActiveRecord gem
Base is a class contained in ActiveRecord module.
By default activerecord treats id column in a table as primary key. If we have primary key with different name in table then we use self.primary_key to inform activerecord about the primary key. primary_key is a class method. You can check it here http://apidock.com/rails/ActiveRecord/AttributeMethods/PrimaryKey/ClassMethods/primary_key. You can also check the source code to better understand how the method is written.
acts_as_tree is a gem name and this gem have acts_as_tree class method defined in it. acts_as_tree foreign_key: 'product_id' line is just calling acts_as_tree method with parameter(foreign_key: 'product_id'). Above line is equivalent to acts_as_tree(foreign_key: 'product_id') or acts_as_tree(:foreign_key => 'product_id'). Parameter to the function is a Hash object. Hash is a class in ruby.

Learn some basic stuffs about ruby before starting to write code. You can start here http://www.tutorialspoint.com/ruby/

Mircea · Accepted Answer · 2015-05-19 20:47:13Z

1

https://github.com/rails/rails/blob/master/activerecord/lib/active_record/base.rb

ActiveRecord is a module.
Base is a class inside the module
primary_key is a class level var (see the self. in front). Active Records internals use that if defined to identify the pk for your table (if not defined I think it's using 'id' by default)
as comments say foreign_key: 'blah' is just a fancy notation for :foreign_key=>'blah. the parenthesis are implied, the fact that it's a hash is also implied

answered May 19, 2015 at 20:47

Mircea

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