Why has_many update does not work on children?

The reason it doesn't automatically save the children is because a save
operation is very expensive, and Rails doesn't keep track of which
children you have updated (which in and of itself would be very ugly
and perform poorly). The solution is to explicitly save any children
you have modified.

I would certainly avoid looping over and saving the children unless you
are modifying all the children. Otherwise you should only be saving
the ones you updated.

Inanc Gumus wrote: