How to Use a Variable as Object Attribute in Rails

How to use a variable as object attribute in rails?

• Reading AR attribute

  @payment_detail.send("#{address_type}_address_country")
  

  OR

  @payment_detail.read_attribute("#{address_type}_address_country")
  

• Writing AR attribute

  @payment_detail.send("#{address_type}_address_country=", value)
  

  OR

  @payment_detail.write_attribute("#{address_type}_address_country", value)
  

• Setting instance variable

  @payment_detail.instance_variable_set("@#{address_type}_address_country", value)
  

• Getting instance variable

  @payment_detail.instance_variable_get("@#{address_type}_address_country")
  

Reference

• send method documentation
• read_attribute method documentation
• write_attribute method documentation
• instance_variable_get method documentation
• instance_variable_set method documentation

Using variable to access object values like Javascripts object[var] in Ruby

Ruby has more classical heritage, so objects are not extensible in the same way as in JavaScript. Depending on your use case, you would use a hash object or an open struct.

person = {
  "name": "John Smith"
}

puts person["name"]

Most of the time you'll see symbols be used instead of string literals.

person = {
  :name => "John Smith",
}

puts person[:name]

Finally you could use a struct or open struct if you really want to the same type of semantics as in JavaScript.

person = OpenStruct.new
person.name    = "John Smith"
person.age     = 70
person.pension = 300

Using a Variable Name as Attribute in Rails

If you want to assign to an attribute, you need the method name with the equal sign:

f.send("#{percent_field}=", 5)

Also, this:

rank_class = (klass.name).constantize

is equivalent to this:

rank_class = klass

Ruby on Rails variables, object attributes, and methods that use a : before or after them

:symbol

{key: value}

When the colon is before the variable / object, it denotes a "symbol", meaning a piece of data to be placed there. The symbol can typically be used in the likes of calling an attribute (key) or in part of a hash: @user.comment[:created_at]

When the colon is after the variable / object, it means you're setting or getting some sort of value in a key: value pair. {key: value} pairs are used mostly in hashes, kind of like an array except you can call the specific keys. This is how the attributes of models are invoked in Rails. EG:

@user = {name: "joe", email: "joe@email.com"}
@user.name #-> "joe"

Referencing an object attribute by a string

{
  picture:       Picture,
  picture_for_x: PictureForX,
  picture_for_y: PictureForY
}.each do |name,klass|
  if !@item.send(name).blank?
    copy = klass.new
    copy.save!
    item_copy.send("#{name}=",copy)
  end
end

Remember that in Ruby there are no properties or attributes available externally, just methods (which you may choose to call without parentheses so that it looks like you're accessing a property, and which sometimes might be just returning the value of an instance variable).

Object#send is the magic method that lets you invoke a method based on a name stored in a variable.

Ruby add variables to an existing object?

To create temporary custom Objects without add new attributes to database Struct solve my problem.

I can create a Struct with chat room info and total users

chat_info = Struct.new(:name, :total_users, :messages)
chat_temp = []
chats = ChatRoom.where(condition)
chats.each do |chat|
  chat_temp << chat_info.new("nome", 100, messages)
end

How do I add an attribute to an instance variable in rails 4?

The type of @foo_users is ActiveRecord::Relation. Trying to add age_sum as a new attribute to an ActiveRecord::Relation object doesn't make sense because semantically age_sum is not an attribute of ActiveRecord::Relation objects. It's better to store the sum of ages in a new instance variable, for example @user_age_sum.

UPDATE
Try the following

class HotelStatistic < ActiveRecord::Base
  belongs_to :hotel
end

class Hotel < ActiveRecord::Base
  has_many :hotel_statistics

  def last_30_days_check_ins
    self.hotel_statistics.where("date >= ?", 30.days.ago).sum(:check_ins)
  end

end

Keep the existing code for building @recent_stats in the controller

In the view

<% @recent_stats.each do |statistic| %>
    Hotel Id: <%= statistic.hotel_id %>
    Daily check-ins: <%= statistic.check_ins %>
    Last 30 days check-ins: <%= statistic.hotel.last_30_days_check_ins %>     
<% end %>

More elegant way of setting an object attribute dynamically from string in Ruby

You can do

[:@web, :@mobile, :@accessible].each do |stylesheet|
  @theme.instance_variable_set(stylesheet, "some dynamic value"))      
end

This saves the string concatenation and string->symbole conversion, so theoretically it's should be a bit faster.

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