Rails: modify form parameters before modifying the database

Question

I'm working on a Rails app that sends data through a form. I want to modify some of the "parameters" of the form after the form sends, but before it is processed.

What I have right now

{"commit"=>"Create",
  "authenticity_token"=>"0000000000000000000000000"
  "page"=>{
    "body"=>"TEST",
    "link_attributes"=>[
      {"action"=>"Foo"},
      {"action"=>"Bar"},
      {"action"=>"Test"},
      {"action"=>"Blah"}
    ]
  }
}

What I want

{"commit"=>"Create",
  "authenticity_token"=>"0000000000000000000000000"
  "page"=>{
    "body"=>"TEST",
    "link_attributes"=>[
      {"action"=>"Foo",
       "source_id"=>1},
      {"action"=>"Bar",
       "source_id"=>1},
      {"action"=>"Test",
       "source_id"=>1},
      {"action"=>"Blah",
       "source_id"=>1},
    ]
  }
}

Is this feasible? Basically, I'm trying to submit two types of data at once ("page" and "link"), and assign the "source_id" of the "links" to the "id" of the "page."

Answer 1

Before it's submitted to the database you can write code in the controller that will take the parameters and append different information before saving. For example:

FooController < ApplicationController

  def update
    params[:page] ||= {}
    params[:page][:link_attributes] ||= []
    params[:page][:link_attriubtes].each { |h| h[:source_id] ||= '1' }
    Page.create(params[:page])
  end

end

Answer 2

Edit params before you use strong params

Ok, so (reviving this old question) I had a lot of trouble with this, I wanted to modify a param before it reached the model (and keep strong params). I finally figured it out, here's the basics:

def update
  sanitize_my_stuff
  @my_thing.update(my_things_params)
end

private

def sanitize_my_stuff
  params[:my_thing][:my_nested_attributes][:foo] = "hello"
end

def my_things_params
  params.permit(etc etc)
end

Answer 3

You should also probably look at callbacks, specifically before_validate (if you're using validations), before_save, or before_create.

It's hard to give you a specific example of how to use them without knowing how you're saving the data, but it would probably look very similar to the example that Gaius gave.