#196 Nested Model Form (revised)

This was one of the first casts that got me into Railscasts so I'm glad to see an update.
Just a word of caution to new users of this technique: when you have a hammer everything can look like a nail. Dynamic nested forms like this are extremely powerful and can sometimes grant the user too many chances to input bad data.

If you find yourself needing complex validations to regulate the the data coming in from the form, a solution like this might not be what's in order and you might want to limit the scope of what is possible to do. Ryan's simple example here is spot on.

This dynamic nested form technique has worked wonders for me (Thanks, Ryan!) but I've been bitten by applying it to the wrong use cases-- use discretion when deciding on a UX.

I think you should have mentioned Cocoon

thanks Ryan...

@anyone Does anyone have an example carrierwave intregration (file or image upload in in a nested model)

Amazing how much simpler this is, especially since the power shown in the unrevised editions is one of the thing that made me think Ruby was so much better than the alternatives. Thanks, Ryan!

I actually feel good about spending the $9 per month for episodes like this! That's a big statement considering how cheap I am.

How do i get it to work with simple form?

Thank you Ryan. I like this nested model forms that starting from scratch. This is awesome.
+1

If you want more flexibility, try awesome_nested_fields. =)

Does anyone know how you would make the questions answerable (perhaps assuming that you were using Devise for user authentication and had access to current_user)? I'm guessing that you would have a model that stored the ID from a User model as well as an ID from the Answer model. So then on the show page, each answer that was listed would be a link that would allow the user to answer the question.

So i guess my question is: What code would you use to then save this into the database when the user clicked the link?

Also, is this the best way to go about this? should this actually use a form instead? It seems like an easy thing to do but I'm not sure of what the Rails way to approach it is. Thanks!

What is the difference between Cocoon and awesome_nested_fields?

Any reason not to use your nested_form gem anymore?

I'm getting in this episode the same strange thing some other user mentioned in another thread. It seems it's cut off in the end, interrupting Ryan mid-sentence... Probably just a few seconds of video cut off but I think it's worth mentioning.

Great episode as always.

What if you wanted to put a validation on Question to ensure that it's not blank... or maybe validate its uniqueness against all of the other Questions to ensure none of the names are the same?

The validations are easy, but the hard part is correlating those Rails errors to which Question input actually failed in the case of multiple children errors. If you had several questions that each were non-unique or perhaps blank, Rails will simply merge all of those errors into one key, and you have no way of associating those out independently from one another.

Does anyone know a workaround on this problem?

THANK YOU! I wrote my college Software Engineering project using the old version of this video, and this new approach makes it so much simpler! Keep them coming.

Awesome update on this technique, Ryan. And thanks everyone for the additional gem suggestions (cocoon and awesome_nested_fields).

How this would work when the models are associated via a has_many :through association?

I'm trying to follow the same steps, however nothing is displayed in my form.

I remember that the first episode regarding this topic used to build the objects in the controller, e.g. Question.new, so that they would be made available in the view. I found really weird that this wasn't mentioned this time.

Did that behavior changed in Rails?

In order to make it work with has_many :through I need to build "by hand" the associated object in my controller?

Thanks :)

Hi Ryan,

Thanks for all the great RailsCasts - I'm learning a ton of stuff!

I'm using your adding/deleting field partials fairly extensively and ran into a couple of things others may find useful:

1. Your .gsub('\n','') removing newlines causes slight horizontal shifting of fields on inline forms. This was easily fixed by escaping rather than removing newlines using .gsub('\n','&#xA').

2. jQuery won't recognize events from controls created this way. Apparently the solution is to use .on() (formerly .live and .delegate) though I have yet to try this.

Thanks again for all your great tutorials and keep up the good work.

Cheers,
Peter

In Rails 3.0.3 I get "undefined method `klass'" from the application_helper.

This is the syntax I'm using:

def link_to_add_fields(name, f, association)
    new_object = f.object.send(association).klass.new
    id = new_object.object_id
    fields = f.fields_for(association, new_object, :child_index => id) do |builder|
      render(association.to_s.singularize + "_fields", :f => builder)
    end
    
    link_to(name, '#', :class => "add_fields", :data => {:id => id, :fields => fields.gsub("\n", "")})
  end

Is my syntax correct? Does "klass" work with my rails version?

Thanks

Quick Q Ryan - the models I'm working with are connecting using has_many :through, and I'm getting issues with creating the sub-objects via the update method, here's the exception:

ActiveRecord::RecordNotFound
Couldn't find Question with ID=1 for Quiz with ID=9

For context, Quizzes have many questions through a join table.

Anyway, decent chance I'll have this fixed before anyone has a chance to reply, but seemed like something enough people might be trying to do to warrant a comment.

Back to figuring it out.. :D

Great tutorial as always. I did run into a problem though when trying to implement it into my app. When I add an extra field it didn't show up in the params sent to the controller.

I found the problem was I had put the form into a table and it didn't work well with this. I simply removed the table and it all started to work.

This is working great for me except for one issue. I have SEVERAL nested models.

A workout has_many steps, a step has_many actions, an action has_many instructions. When I click to add a new step, I would like that step to be populated with on action fieldset, and that action fieldset, populated with one instruction fieldset. But it just renders the empty step fieldset, I have to click the "add action" and then the "add instruction" buttons for those to render. Does anyone know how to get all the nested fieldsets to render when I add a step?

Data Associations:

• Workout

has_many steps

  has_many actions

     has_many instructions

I am having trouble using auto-complete with multiple fields. The first one works but the second instance does not. Been working on trying to figure out how to make it work for close to a week now. Any help would be great!

Please note I do NOT want to tokenize. Do in face want to set other fields along side the auto-complete text field too.

Thanks!

I'm trying to add an image field to my survey. I can get the image to upload and to show on the Show page. But when I go back to the Edit view, there is no image and I still see the "No file chosen" text next to the Choose File button.

I have this line of code in my Show view:

<%= image_tag question.image_url(:thumb).to_s if question.image? %>

but if I try to put that into the _form view then I get an unknown variable or method error.

I've tried a couple of if statements but haven't gotten it to work.

Thanks to anyone who can help.

I got an error on jquery:
$("form").on is not a function

I upgrated jquery to 1.7.1, but it still error.
Thanks to anyone who can help.

Thanks for this brilliant tutorial! I am new to rails and this one made a few pennies drop.

How can I achieve that destroying a question automatically destroys all associated answers records in the database?

Hi, I followed the tutorial step by step

but my remove function won't work.

add function work fine, remove using checkbox works fine. Why?

i'm trying to render a partial form in a show view but it doesn't render it, do you know why would this be?

I was able to get grandchildren to work in the forms with a special application helper function:

  def special_button_to_add_fields(name, f, association, child_association)
    new_object = f.object.class.reflect_on_association(association).klass.new
    child_object = f.object.class.reflect_on_association(association).klass.reflect_on_association(child_association).klass.new
    new_object.wireless_client = child_object

    fields = f.fields_for(association, new_object, :child_index => "new_#{association}") do |builder|
      render(association.to_s.singularize + "_fields", :f => builder)
    end
    button_to_function(name, h("add_fields(this, \"#{association}\", \"#{escape_javascript(fields)}\")"))
  end

Essentially, you have to create the grandchildren in this helper to have an object for the fields_for to attach to.

How would you do this if your model is not ActiveRecord based? Since I'm not using ActiveRecord, I don't have access to the accepts_nested_attributes_for method.

Great Railcast. There seems to be a problem rendering the nested model fields when implementing this solution with models that have a one-to-one association. One-to-many associations show nested model fields fine, but not one-to-one.

I'm not sure if it's exactly the same thing, but what really saved me (for what I needed) was this https://github.com/moo-li/Simple-parent-child-forms-in-Rails-3.1

Great railcast anyways!

I'm getting a Missing partial in the link_to_add_fields method and can't for the life of me figure out why. I've followed the setup exactly as described in the RailsCast.

It seems to be coming from this line:

render(association.to_s.singularize + "_fields", :f => builder)

This is a great piece of knowlege, thanks!

I encountered one problem.
The dynamic form doesn't work when I added validates :question_id, presence: true to the Answer model class.

Form is not saving and returning error: Questions answers question can't be blank
This happens only in case when you try to add a new question and add a new answer to it.

Why is this happening?

If you, like me, had trouble converting the Coffeescripts to pure Javascripts, this site is very helpful:

http://cs2js.nodejitsu.com/

Anyone got this working with mongoid?

Great tutorial, Ryan!

I was lucky enough to get this working on my machine.

The only problem I have is that the nested attributes are not saved to the database in the order in which I created them.

E.g. sometimes I create 3 answers at once, then click "Update" and the answers do appear on the form, but not in the correct order. I can't see any pattern in there, so I assume that they get saved to the database randomly.

Is there any way to fix this?

Hi guys, nice episode.
Ryan, I think that the following code could help handling validation errors.

<%= f.hidden_field :_destroy, :value => f.object._destroy %>

$("input[type=hidden][id$='_destroy'][value='true']").closest("ITEM SELECTOR").hide();

What do you think?

Thanks,
Mauro

Base on this example, How do we delete an entire survey together with it's questions and answers? Please help...

I would like to add a 'Copy' button that creates a new copy of the question with the same set of answers. I think it will be similar to the link_to_add_fields, but I cannot figure out how to capture user input and create a new nested object with those values on the fly. Any help will be appreciated. Thanks.

in our scenario we need to vary the number of associated records allowed. We have validation in the model i.e

accepts_nested_attributes_for :answers , :limit => 4,:allow_destroy => true

My question is . how do we prevent the Add Answers link from being rendered if we already have reached our limit ?

I'm having some trouble adapting railscasts with nested parameters using strong_parameters. I think this form creates an empty hash in answers_attributes and questions_attributes which cause problems on update for strong_parameters.