Create New Method in Rails

Question

How do I create a method in Rails that queries the database in a given table and shows in View, and how I do to call this method and where to create?

def somar    
  @value = Registro.sum('saldo')
end

How do I call this method in view and put into a label ?

Answer 1

Good I will consider that you already have Rails properly installed and configured on your machine.

It is unclear whether your method is really a method of Model or a action (a method of Controller), but I think it’s a action, because you are calling a method that is probably a method of a Model. Good considering these correct assumptions we can perform the following steps to make it work.

We created our Controller and our action (we will use generator to expedite the procedure)

Rails g controller operations sum

That will beget our controller in app/controllers/operacoes_controler.rb

class OperacoesController < ApplicationController
  def somar
  end
end

And it will generate our view on app/views/operacoes/somar.html.erb

<h1>Operacoes#somar</h1>
<p>Find me in app/views/operacoes/somar.html.erb</p>

Okay now we’re almost there, I don’t know your model Registro, nor what you wish to add, I will consider that he has a field saldo and you want to add up the value of each saldo in all the records.

*** For test I managed the model Registro, but you probably won’t need to take this step, I’ll put it here to demonstrate how I performed the procedure.

Rails g model record balance:integer

*** In the console I created 3 records to test the logic, which you probably won’t need to do either.

2.3.1 :001 > Registro.create(saldo: 1)
 => #<Registro id: 1, saldo: 1, created_at: "2016-07-14 23:56:46", updated_at: "2016-07-14 23:56:46"> 

2.3.1 :002 > Registro.create(saldo: 2)
 => #<Registro id: 2, saldo: 2, created_at: "2016-07-14 23:56:50", updated_at: "2016-07-14 23:56:50"> 

2.3.1 :003 > Registro.create(saldo: 3)
 => #<Registro id: 3, saldo: 3, created_at: "2016-07-14 23:56:53", updated_at: "2016-07-14 23:56:53"> 

Resolution of the question

Place the value assignment on action of OperacoesController

class OperacoesController < ApplicationController
  def somar
    @valor = Registro.sum('saldo')
  end
end

And put the @valor amid tags erb <%= @valor =%> in your View (app/views/operacoes/somar.html.erb). Example:

<h1>A soma dos saldos de todos os registros é <%= @valor %>  </h1>

Access: http://localhost:3000/operacoes/somar

And the result will be something like this:

EDIT: Case wanted to re-use this method in several Views one can use a Helper as Rafael quoted. That is, remove from the OperacoesController and add to ApplicationHelper, ex:

# /app/helpers/application_helper.rb
module ApplicationHelper
  def saldo_total
    Registro.sum('saldo')
  end
end

in your View would look like this

#app/views/operacoes/index.html.erb
 <h1>A soma dos saldos de todos os registros é <%= saldo_total %>  </h1>

Answer 2

In this case you will need to define your method in a helper. Helpers are classes with auxiliary methods available in views and also in controllers (through #helpers), as shown in table 1.

module ApplicationHelper
    def identity(user)
        return "#{user.name} - #{user.email}"
    end
end

Table 1. Code with an auxiliary example method.

No one will explain better than their own helper session in the official Ruby on Rails documentation, follow the link, recommend a complete reading (even if English, reading is easy).