Can I add to an existing value in a Rails DB, instead of replacing it?

Question

I've been trying to add to a value in my DB, rather than replace it.

If you were to input 5 as the value in the update/edit form, I want the DB to be 5 plus whatever is already in the DB. So, if the DB already has 1 refill, entering 5 in the form would result in 6 in the DB.

When putting different :values into the update form I have been breaking the form, and a rails error comes up. Not sure if/how to pass a function in the input of a ruby form. This project is mainly written in Ruby(2.4.1p111) on Rails (5.1.5). Below is the Controller

def update
    @waterbottle = Waterbottle.find(params[:id])
    if @waterbottle.update(waterbottle_params)
        redirect_to "/users/#{current_user.id}"
    end
end

Schema

create_table "waterbottles", force: :cascade do |t|
  t.integer "volume"
  t.integer "user_id"
  t.integer "refills"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

And the update form is.

<%= form_for @waterbottle, :url => waterbottle_path(@waterbottle.id) do |f| %>
  <p> How many times did you refill your bottle today? </p>
  <%= f.text_field :refills, :value => @waterbottle.refills %>
  <%= f.hidden_field :user_id, :value => current_user.id %></br>
  <%= f.hidden_field :volume, :value => @waterbottle.volume %></br>
  <%= f.submit "Refill Waterbottle" %>
<% end %>

Any help is greatly appreciated.

Post the code you're trying that gives you an error, and also post the error. — Nathan
– Nathan, Commented Apr 4, 2018 at 0:30
also: hidden_field can be easily hacked/modified, so you should do anything you need with current_user.id in the controller, instead of passing the value with the form. — court3nay
– court3nay, Commented Apr 4, 2018 at 0:38
finally; you don't need the :url => waterbootle_path either, just form_for @waterbottle do |f| - again, rails magic. — court3nay
– court3nay, Commented Apr 4, 2018 at 0:39
I took the liberty of editing your post to make it more clear what you're asking. — Nathan
– Nathan, Commented Apr 4, 2018 at 0:52

Буянбат Чойжилсүрэн · Accepted Answer · 2018-04-04 01:41:28Z

1

Offering you to use before_update callback in your model. And you can get old values by refills_was method.

class Waterbottle < ApplicationRecord
  before_update :increase_fills

  def increase_fills
    if self.refills_changed?
      self.refills = self.refills + self.refills_was
    end 
  end
end

Hope this will help you to solve problem.

answered Apr 4, 2018 at 1:41

Буянбат Чойжилсүрэн

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Comments

court3nay · Accepted Answer · 2018-04-04 00:40:59Z

1

you can easily do math or other functions inline in the value part:

<%= f.text_field :refills, :value => (@waterbottle.refills + 1) %>

Bear in mind, generally you don't need to specify the value if you're not changing it. (I made a few other stylistic and security comments, above, about your other rails code. good luck!)

answered Apr 4, 2018 at 0:40

court3nay

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1 Comment

Nathan Over a year ago

I believe you misunderstood the OP's intent.

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