Question

So I have an example I came across in some reading where we define in a rails model

has_many :some_tablename

Then later they reference it by saying

if some_tablename.empty?
  #do something
end

I am new to Ruby, so the magic isn’t quite clear to me why I wouldn’t do

if :some_tablename.empty?
  #do something
end

Now, I understand that .empty can be called on a number of types, Symbol not being one of them. So, I am expecting that the answer is going to be something like….the .inspect or .to_s is being called on the symbol :some_tablename (behind the scenes) and returning a string representation which then we’re calling .empty on it.

is that correct, or can someone set me straight of how it is lining up :some_tablename to some_tablename?

Answer 1

ActiveRecord makes extensive use of Ruby as a metaprogramming language to perform much of the queries you can make over a model.

When you call if some_table you are calling a some_table method which in fact does’t exists, so the method_missing method of ActiveRecord::Base is called (if your model extends it) and it looks in an attributes hash which is built with your has_many, belongs_to directives and then builds a query over that missing method, specifically an inner join in your case as some_table is a has_many.

Check http://apidock.com/rails/ActiveRecord/Base/method_missing.