Aliasing the source table - ruby-on-rails

Question

Is there a way to alias the source table in the context of a single scope ?
I tried this :
scope = User.all
scope.arel.source.left.table_alias = "toto"
scope.where(firstname: nil) => "SELECT `toto`.* FROM `users` `toto` WHERE `toto`.`firstname` IS NULL"
The problem is that the model class keeps the alias for all subsequent queries :
User.all => "SELECT `toto`.* FROM `users` `toto`"
Edit
I added this method to ApplicationRecord
def self.alias_source(table_alias)
klass = Class.new(self)
klass.all.source.left.table_alias = table_alias
klass
end
Now, I can do :
User.alias_source(:toto).where(firstname: nil) => "SELECT `toto`.* FROM `users` `toto` WHERE `toto`.`firstname` IS NULL"

Answer 1

I added this method to ApplicationRecord
def self.alias_source(table_alias)
klass = Class.new(self)
klass.all.source.left.table_alias = table_alias
klass
end
Now, I can do :
User.alias_source(:toto).where(firstname: nil) => "SELECT `toto`.* FROM `users` `toto` WHERE `toto`.`firstname` IS NULL"

Answer 2

Since creating Anonymous Classes that inherit from ActiveRecord::Base will cause memory bloat, I am not sure I would recommend it (See Here: https://github.com/rails/rails/issues/31395).
Maybe a better implementation would be to execute in a block form instead e.g. yield the aliased table to the block then set it back afterwards?
e.g.
def self.with_table_alias(table_alias, &block)
begin
self.all.source.left.table_alias = table_alias
block.call(self)
ensure
self.all.source.left.table_alias = nil
end
end
Usage
User.with_table_alias(:toto) do |scope|
puts scope.joins(:posts).where(firstname: "Ruur").to_sql
end
# "SELECT `toto`.*
# FROM
# `users` `toto`
# INNER JOIN `posts` ON `posts`.`user_id` = `toto`.`id`
# WHERE
# `toto`.`firstname` = 'Ruur'"
puts User.all.to_sql
# "SELECT `users`.* FROM `users`
WARNING: THIS HAS NOT BE TESTED BEYOND WHAT IS SHOWN HERE AND I WOULD NOT RECOMMEND THIS IN A PRODUCTION ENVIRONMENT WITHOUT EXTENSIVE TESTING FOR EDGE CASES AND OTHER GOTCHAS
Update To address desired implementation
module ARTableAlias
def alias_table_name=(val)
#alias_table_name = val
end
def alias_table_name
#alias_table_name ||= "#{self.table_name}_alias"
end
def alias_source
#alias_klass ||= Class.new(self).tap do |k|
k.all.source.left.table_alias = alias_table_name
end
end
end
Then usage as:
class User < ApplicationRecord
extend ARTableAlias
alias_table_name = :toto
end
User.alias_source.where(first_name = 'Ruur')
#=> SELECT `toto`.* FROM `users` `toto` WHERE `toto`.`first_name` = 'Ruur'
User.where(first_name = 'Ruur')
#=> SELECT `users`.* FROM `users` WHERE `users`.`first_name` = 'Ruur'
User.alias_source === User.alias_source
#=> true