How do I sub in data in a variable name, Ruby?

Question

So I've got

LanRole.where("lan_id = ?", requestable.id).each do |lan_role| %>
    <% @lan_??? = Lan.find(lan_role.lan_id) %>
    <li><a data-toggle="tab" href="#lan_info_<%= lan.id %>"><%= lan.name %> INFO</a></li>

Where ??? should be lan_role.id so that i can put it in the tab later

<div class="tab-content">
  <div id="lan_info_<%= lan.id %>" class="tab-pane fade">
    <h4><%= @lan_???.name %> INFO</h4>
    etc
  </div>

But I don't know how to make a variable variable name, sub it in there.

If it was a string, I could do

#{lan_role.id}

but it's not a string.

... I misread the error, it's on <div id="lan_info_<%= lan.id %>" class="tab-pane fade">

ActionView::Template::Error (undefined local variable or method `lan' for #<#<Class:0x007f7afb9e98a0>:0x007f7afb28aeb0>):

Answer 1

For "variable" variables:

{one: 1, two: 2, three: 3}.each do |name, id|
  instance_variable_set("@lan_#{name}", [id, name])
  p @lan_one, @lan_two, @lan_three
end

[1, :one]
nil
nil
[1, :one]
[2, :two]
nil
[1, :one]
[2, :two]
[3, :three]

But since you're making tabs, just have two loops, one for links and one for bodies:

collection = LanRole.where("lan_id = ?", requestable.id)

# make tabs
collection.each do |role|
  role.name
end

# make tab contents
# collection is now loaded it won't hit the database again, at least it shouldn't
collection.each do |role|
  role.description
end

Answer 2

you can do it bu using instance_variable_set and instance_variable_get like this:

<% LanRole.where("lan_id = ?", requestable.id).each do |lan_role| %>
    <% instance_variable_set(:"@lan_#{lan_role.lan_id}", Lan.find(lan_role.lan_id)) %>
<% end %>

Then when you try to get it out use:

<h4><%= instance_variable_get(:"@lan_#{lan_role.lan_id}").name %> INFO</h4>

Answer 3

You can use instance_variable_set and instance_variable_get to set and get instance variables with dynamic names, but the is cumbersome. And unless you are doing meta-programming (and especially in your example) I would call using those methods a code-smell.

Instead, the go-to data structure to store data by a key is using a Hash. In your example, utilizing a Hash to store data by its id could look like this:

<% @lans_by_id = {} %>
<% LanRole.where("lan_id = ?", requestable.id).each do |lan_role| %>
  <% @lans_by_id[lan_role.lan_id] = Lan.find(lan_role.lan_id) %>
  # ...

And you can read the data similarly later in your code:

<h4><%= @lans_by_id[lan_role.lan_id].name %> INFO</h4>

But: You tagged your question with Ruby on Rails and instances of LanRole have a lan_id attribute already. Therefore, I suggest that you take advantage of Ruby on Rails and configure proper Active Record Associations between your models.

When you configure the associations between LanRole and Lan like this:

# in app/models/lan_role.rb
class LanRole < ApplicationRecord
  belongs_to :lan
  # ... 

#in app/models/lan.rb
class LanRole < ApplicationRecord
  has_many :lan_roles # or just `has_one :lan_role`?

When you have those associations set up in your models, then you can get the lan for a given lan_role by calling lan_role.lan instead of Lan.find(lan_role.lan_id). And to avoid loading one lan in each block of the each iteration, I recommend eager loading all associated lanswith includes at once.

Putting is all together: Loading and iterating

LanRole.where(lan_id: requestable.id).includes(:lan).each do |lan_role| %>

And then later using the associated lan like this:

<h4><%= lan_role.lan.name %> INFO</h4>