Module: Without

Defined in:
lib/without.rb,
lib/without/version.rb

Constant Summary collapse

VERSION = 
"0.1.0"

Instance Method Summary collapse

Instance Method Details

#without_a(belongs_to, options = {}) ⇒ Object Also known as: without_an 



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# File 'lib/without.rb', line 5

def without_a(belongs_to, options={})
  options = options.with_indifferent_access
  scope = all
  association = scope.model.reflect_on_association(belongs_to)

  unless association.macro == :belongs_to
    raise ArgumentError, "`without_a` only works on belongs_to associations"
  end

  if association.polymorphic?
    foreign_type = options.fetch(association.foreign_type) do
      raise ArgumentError, "`#{belongs_to}` is a polymorphic association; please " <<
                           "pass :#{association.foreign_type} to `without_a`"
    end

    join_table = foreign_type.constantize.table_name
    scope = scope.where(scope.arel_table[association.foreign_type].eq(foreign_type))
  else
    join_table = association.table_name
  end

  # This technique with the JOINs is a lot more work than simply saying
  #
  #   where("#{association.foreign_key} NOT IN (SELECT id FROM #{association.table_name})")
  #
  # but `NOT IN` is very slow: it requires a sequence scan. On very large
  # tables this thousands (or millions!) of times faster.
  query = scope.joins("LEFT OUTER JOIN #{join_table} ON #{table_name}.#{association.foreign_key}=#{join_table}.id").where("#{join_table}.id" => nil)

  # Postgres does not allow a DELETE statement to also use JOINs.
  # The common technique (that Rails uses) is to
  #
  #   DELETE FROM the_table WHERE primary_key in (the_query)
  #
  # This technique doesn't work with pure join tables which have
  # no primary key.
  #
  # So instead we manually construct a query that moves the JOIN
  # into a subquery and connects the two with a key that will work
  # (the broken foreign_key).
  unless scope.model.primary_key
    query = scope.where(association.foreign_key => query.select(association.foreign_key))
  end

  query
end

#without_any(has_many) ⇒ Object 



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# File 'lib/without.rb', line 53

def without_any(has_many)
  scope = all
  association = scope.model.reflect_on_association(has_many)

  unless association.macro == :has_many
    raise ArgumentError, "`without_any` only works on has_many associations"
  end

  scope.joins("LEFT OUTER JOIN #{association.table_name} ON #{table_name}.id=#{association.table_name}.#{association.foreign_key}").where("#{association.table_name}.#{association.foreign_key}" => nil)
end