# Updating Child Records **URL:** \ **Category:** Rails\ **Created:** [January 7, 2008, 12:15am UTC](https://www.ruby-forum.com/t/updating-child-records/125200 "2008-01-07T00:15:52Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 12:15am UTC](https://www.ruby-forum.com/t/updating-child-records/125200/1 "2008-01-07T00:15:52Z")
I have a 3 level hierarchical data structure, for this example lets say it’s Bike (has many) Wheels (has many) Spokes. Here’s what I want to do, update a bunch of Spokes that all belong to one Bike but do it all with one Save! method call. I’ve tried loading the Bike, accessing, changing, and adding Spokes through the Bike.wheels.spokes collections then doing Bike.save! but it doesn’t work (the database remains unchanged). It DOES work however when I create a new bike record, add the wheels and spokes then save that. So is there any way to have all the Spoke records saved with one call to save? I’m attempting to limit the number of individual SQL calls, cause there are a lot of spoke records and it will happen often. Thanks in advance, Danny ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 1:59am UTC](https://www.ruby-forum.com/t/updating-child-records/125200/2 "2008-01-07T01:59:19Z")
The problem with bike.wheels.spokes is because bike has many wheels, and _each wheel_ has many spokes. With bike.wheels.spokes, you’re trying to call spokes on the collection of all wheels for that bike, so it isn’t going to work! What you need to do is to find a single wheel, something a simple as @ bike.wheels.first will do, or do @wheel = Wheel.find(id) and just find the one wheel. To add spokes: @bike.wheels.first.spokes.build(:spoke\_field\_1 =\> “blah”) To remove a spoke: @bike.wheels.first.spokes - Spoke.find(spoke\_id) To edit a spoke: @bike.wheels.first.spokes.find(id).update\_attributes(params[:spoke]) ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 2:46am UTC](https://www.ruby-forum.com/t/updating-child-records/125200/3 "2008-01-07T02:46:04Z")
I wouldn’t think that would work, because you’re not changing the associations themselves (i.e. adding/removing records), but you’re editing instances of the single records. I can’t think of another way to do this, sorry. If it’s one value you could loop through and do update\_attribute(“field”,“value”), and update\_attributes which I guess you know about already. ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 2:42am UTC](https://www.ruby-forum.com/t/updating-child-records/125200/4 "2008-01-07T02:42:34Z")
Sorry, I should have been more clear, I’m aware of how the collections work, that was pseudo-code. I’m doing it properly in my real code. #Pseudo code b = bike.find(id) then I loop through b.wheels loop through wheel.spokes spoke.thing = “newvalue” end end b.save! ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 9:13am UTC](https://www.ruby-forum.com/t/updating-child-records/125200/5 "2008-01-07T09:13:11Z")
It was a hypothetical example, things in my real DB are all correct and don’t break any of the normal forms, one pk and one foreign key to link each record to it’s parent. According to Ryan’s reply above, Save’s are only propagated (to descendents) in Ruby model objects when there are insertions or deletions, not when the fields have been changed. Thanks, Danny ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 3:58am UTC](https://www.ruby-forum.com/t/updating-child-records/125200/6 "2008-01-07T03:58:43Z")
On Jan 6, 3:14 pm, Daniel B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Here’s what I want to do, update a bunch of Spokes that all belong to > one Bike but do it all with one Save! method call. I recommend (as I have in another thread) that you not do this. Third normal form states that every column in a table should be dependent on the primary key. Well, in this case, one of the columns in the spokes table appears to be dependent not on its primary key, but on its associated bike’s primary key. Just my $.02. ///ark ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 11:46pm UTC](https://www.ruby-forum.com/t/updating-child-records/125200/7 "2008-01-07T23:46:11Z")
It’s true - they’re done automatically on create, but not on update. Ryan B. covers this in his screencast on managing multiple models with 1 form ([#75 Complex Forms Part 3 - RailsCasts](http://railscasts.com/episodes/75)). It’s relatively simple to iterate through the child records using something like def save\_wheels wheels.each do |w| w.save(false) end end It assumes of course that you have updated their attributes and have a has\_many :wheels in the Bike model. and calling this method (of the Bike model) with a callback in the Bike model after\_update :save\_wheels This way, the children are automatically saved when the parent is saved. MC ---
**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\ **Post date:** [January 7, 2008, 11:49pm UTC](https://www.ruby-forum.com/t/updating-child-records/125200/8 "2008-01-07T23:49:06Z")
eeew @ .save(false) Take this as a warning to be very careful when using .save(false), passing in false skips all validations and you might not get desired results. On Jan 8, 2008 9:15 AM, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > end > > > deletions, not when the fields have been changed. > > > > > > one Bike but do it all with one Save! method call. > > > > ///ark – Ryan B. > **[frozenplague.net](http://www.frozenplague.net)** > > This domain may be for sale! Feel free to add me to MSN and/or GTalk as this email.