Passing array of objects as param to rails controller

Question

I have an array of objects on my frontend that I want to pass to my rails controller.

The array of object I'm passing to my controller looks like this:

[ 
  {id: 1, position: 1}, 
  {id: 2, position: 2}
]

In my controller, I'm trying to do something like this:

def map
  params[:items].each do |item|
    todo = @user.todos.new(
      item_id: item.id,
      item_position: item.position
    )
    todo.save!
  end
end

I tried JSON.stringify on my array and then sending it to my controller but everything is a string so a lot of my methods are not working.

What is the correct way to pass in an array of objects to a rails controller?

Well of course you are receiving a string, that's what JSON.stringify does. Did you try to "unstringify" in your controller? Also: stackoverflow.com/questions/38175383/… — Félix Paradis
– Félix Paradis, Commented Jan 17, 2019 at 22:29
After I JSON.parse in rails, I'm getting an error undefined method 'id' for {:id=>1}:Hash — jj008
– jj008, Commented Jan 17, 2019 at 23:10

Thomas · Accepted Answer · 2019-01-18 00:00:51Z

1

If params[:items] is a string ("[{:id=>1, :position=>1}, {:id=>2, :position=>2}]"), then you can use eval(). That will return an array.

Try in your rails console:

pry(main)> eval("[{:id=>1, :position=>1}, {:id=>2, :position=>2}]")
=> [{:id=>1, :position=>1}, {:id=>2, :position=>2}]

So, in your case this should do the trick:

def map
  arr = eval(params[:items])
  arr.each do |item|
    todo = @user.todos.new(
      item_id: item[:id]
    )
    todo.save!
  end
end

Hope it helps.

EDIT: It is perhaps 🤪NOT the most secure thing to do to call eval on a string that has been submitted from outside (see my "mea culpa" comment below").

So I played around with this problem and the only way I can come up with would be to encode the array in the front end and decode it in your controller. It can still rais an error if the value is NOT an array of hashes so you should have an error handler in your controller...

in JS:

let array = [{id: 1, position: 1}, {id: 2, position: 2}]
let yourParamToSendOff = escape(JSON.stringify(array))

And on your back-end:

JSON.parse(CGI.unescape("%5B%7B%22id%22%3A1%2C%22position%22%3A1%7D%2C%7B%22id%22%3A2%2C%22position%22%3A2%7D%5D"))
=> [{"id"=>1, "position"=>1}, {"id"=>2, "position"=>2}]

Sorry about my first answer....

edited Jan 18, 2019 at 0:00

answered Jan 17, 2019 at 22:29

Thomas

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6 Comments

jj008 Over a year ago

I'm getting an error: undefined method 'id' for {:id=>1}:Hash

Thomas Over a year ago

I modified my answer. You used item.id. It should be item[:id]. Sorry, I did not spot it at first glance.

mu is too short Over a year ago

You're proposing that someone eval a string that came from the outside world?

Thomas Over a year ago

😒@muistooshort You are totally right. Now I need to downvote my own answer. What can I say? It's getting late and I totally slipped... EDIT: tried to downvote but can't do it. Feel free 😉

mu is too short Over a year ago

There's always JSON.parse on the Ruby side if the client is using JSON.stringify in JavaScript. Correcting yourself is always an acceptable alternative to downvotes and answer deletion (as you just did while I was writing this comment).

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