# File activerecord/lib/active_record/relation/spawn_methods.rb, line 57
def except(*skips)
  relation_with values.except(*skips)
end

Removes from the query the condition(s) specified in skips.

Post.order('id asc').except(:order)                  # discards the order condition
Post.where('id > 10').order('id asc').except(:where) # discards the where condition but keeps the order

# File activerecord/lib/active_record/relation/spawn_methods.rb, line 31
def merge(other)
  if other.is_a?(Array)
    records & other
  elsif other
    spawn.merge!(other)
  else
    raise ArgumentError, "invalid argument: #{other.inspect}."
  end
end

Merges in the conditions from other, if other is an ActiveRecord::Relation. Returns an array representing the intersection of the resulting records with other, if other is an array.

Post.where(published: true).joins(:comments).merge( Comment.where(spam: false) )
# Performs a single join query with both where conditions.

recent_posts = Post.order('created_at DESC').first(5)
Post.where(published: true).merge(recent_posts)
# Returns the intersection of all published posts with the 5 most recently created posts.
# (This is just an example. You'd probably want to do this with a single query!)

Procs will be evaluated by merge:

Post.where(published: true).merge(-> { joins(:comments) })
# => Post.where(published: true).joins(:comments)

This is mainly intended for sharing common conditions between multiple associations.

# File activerecord/lib/active_record/relation/spawn_methods.rb, line 65
def only(*onlies)
  relation_with values.slice(*onlies)
end

Removes any condition from the query other than the one(s) specified in onlies.

Post.order('id asc').only(:where)         # discards the order condition
Post.order('id asc').only(:where, :order) # uses the specified order