Monkeypatching "left" in String conflicts with Active Record

[norman]

I recently had to track down a problem with a Rails application where a query was failing and isolated it to this code in Active Record:

counts = table_joins.map do |join|
  if join.is_a?(Arel::Nodes::StringJoin)
    # Table names + table aliases
    join.left.downcase.scan(
      /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
    ).size
  elsif join.respond_to? :left
    join.left.table_name == name ? 1 : 0
  else
    0
  end
end

Since terminal_table aliases String#ljust, to left, any instance of String responds to left when using this gem. In the example above this leads to an ArgumentError. This happens to me on Rails 4.0.12, but I've verified that similar code exists in Rails 4.2.0 as well. To reproduce, create a scope with a manual join, and then invoke the exists? method on the scope. For example:

class Foo < ActiveRecord::Base
  belongs_to :bar
  scope :baz, -> {joins('INNER JOIN bars on bars.id = foos.bar_id')}
end

Foo.baz.exists?(1)

I would suggest removing the aliases in String completely and using the ljust and rjust methods internally instead; left is a very generic method name to add to a core class like String and is likely to conflict with other libraries as well.

[desheikh]

+1 Just traced down the same issue when installing a gem in our app. terminal-table also breaks group_by queries.

[nateberkopec]

Fixed by #45.

[norman]

Excellent, thanks @nateberkopec!