How to add values from a column in Ruby/Ror

Question

Loveliness?

I’m trying to build an application in Rails. In it I have a resource where users inform the running time related to a category. Well, I need to perform adding up the total column time running time in order to present to a particular user: "You have already performed a total of X hours of activities".

Another point is that I made the relationship with the model Category by attribute category_id and everything is working perfectly, only that I would like to make it appear in the form through a list of categories (by name) and not have the user type the id of the category to make the relationship.

Answer 1

Sum and other aggregation functions

To add values through the API ActiveRecord, use the method sum(). Example:

Person.sum('age')

List of options

On the second point, to display an element select (Combo Box) and facilitate selection, you can use the collection_select. Example taken from section 3.3 of the guide:

<%= collection_select(:person, :city_id, City.all, :id, :name) %>

In the above section:

• :person is a reference to model
• :city_id is the attribute that makes the relationship
• City.all is the list of possible relationship values
• :id is the value of each item in the list (the :id selected will be assigned to :city_id)
• :name is the label to be displayed in combo for each item

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Updating

The field value may not be being updated in the template. A probable cause is not having defined the attribute as accessible.

Example Rails 3:

class Item < ActiveRecord::Base
  attr_accessible :category_id

Example Rails 4:

class ItemsController <  ApplicationController
  def item_params
    params.require(:item).permit(:category_id)
  end