WideFix tech post

Simple form array text input

Since Rails 4 supports PostgreSQL array type out of the box it would be great to have an opportunity to use it for getting from a form on client side an array of text fields (it may be collection of zips, for example) and pass it to a model. I love SimpleForm gem to generate a form in Rails but it allows to generate only collection of radio buttons or checkboxes and unfortunately it doesn’t support the functionality. In this post I will show how to solve the problem.


This screenshot will explain what I have to do without any words:

Account and User relation

In database I’m going to use PostgreSQL arrays in ActiveRecord for saving the data. But in the view we don’t have some tool to generate the fields with Rails out of the box. So let’s do it with SimpleForm.

SimpleForm and custom inputs

It may not be surprise for you, but SimpleForm gives us possibility to define our own custom input. It’s very easy to do it: just define your own class inherited from base SimpleForm’s input and call when generating inputs.

This is the custom attribute for the array input:

class ArrayInput < SimpleForm::Inputs::StringInput
  def input
    input_html_options[:type] ||= input_type

    Array(object.public_send(attribute_name)).map do |array_el|
      @builder.text_field(nil, input_html_options.merge(value: array_el, name: "#{object_name}[#{attribute_name}][]"))

  def input_type

In the form use this example to generate a collection of text fields:

form_for @location do |f|
  f.input :zips, as: :array

One note here is that the @location object must have the zips attributes and it should be an array. If you have not empty array of zips this peace of code will generate them in a form. I you have an empty array of zips you will have to worry about how to initialize the attribute on the server before rendering a form.

All the generated inputs will get name like this: location[zips][]. And all of them will have the same name. Browser will join them together before sending to a server. Rails will understand that this is an array of inputs because their names ending with []. Finally you will get a parameter of an array in params controllers’ object. It means that you will be able to get the values in a controller with this code: params[:location][:zips].

We’ve just being said that the browser will join parameters in one line with the same name and this is an example how they will go to the server: "location[zips][]=11111&location[zips][]=22222". Rails will parse their into a hash with Rack::Utils.parse_nested_query method. Let’s summarize to understand the process and to see the results of the parsing attributes:

$irb --simple-prompt
>> require 'rack'
=> true
>> Rack::Utils.parse_nested_query "location[zips][]=11111&location[zips][]=22222"
=> {"location"=>{"zips"=>["11111", "22222"]}}

If you use StrongParameters to filter out parameters going from a client you may be interested how to manage this. It’s very simple task - just don’t forget to identify that you are expecting array rather than one attribute:

params.require(:location).permit(zips: [])

Note the [] is after the zips: - it’s necessary to not forget to write it like this. In other case (if you write permit(:zips), for example) you will get an exception because an array goes from server but StrongParameters expects a single object in such definition.

Implementing “+Add another” link won’t be described in this post because it’s rather trivial task. You will have to write a little JavaScript and it’s up to you.

Hope this article will help somebody.

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