Converting string to active record query statement

Question

inside one of my view pages I'm using old fashion way of presenting data but I have problem in converting a string like "User.country.name" to a query statement. I'm using a loop like below :

@columns = ['id','email','name','country.name']

table = User.all

<% table.each do |row| %>
    <% @columns.each do |field| %>
         <%= row[field] %>
    <% end %>
<% end %>

The table shows almost all data except for column "country.name". I can't use constantize for country.name it gives me error. Any solution ? Thanks

if I write row[field].constantize it shows : NoMethodError in Table#show_table , undefined method `constantize'. Without constantize it shows the id, email and name fields of each row except last one with empty field — Soheil
– Soheil, Commented Jan 28, 2014 at 11:06

Stefan · Accepted Answer · 2014-01-28 11:26:06Z

2

Your User doesn't have an attribute country.name, it has an association country and that association has an attribute name.

You could set up a delegate:

 class User < ActiveRecord::Base
   delegate :name, to: :country, prefix: true
   # ...
 end

This creates a method User#country_name, returning country.name.

Now you can adapt your loop, using public_send to call the methods: (I've changed the variable names to make it clearer)

@methods = [:id, :email, :name, :country_name]

records = User.all

<% records.each do |record| %>
  <% @methods.each do |method| %>
    <%= record.public_send(method) %>
  <% end %>
<% end %>

answered Jan 28, 2014 at 11:26

Stefan

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Comments

nikolayp · Accepted Answer · 2014-01-28 11:22:12Z

0

@users = User.select(:id, :email).joins(:countries)

<% @users.each do |user| %>
  <%= user.id %>
  <%= user.email %>
  <%= user.countries %>
<% end %>

http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-joins

Wish it helps

answered Jan 28, 2014 at 11:22

nikolayp

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