How can I "initialize" instance variable?

Question

I am just trying to study about Rails.

Everytime I send the get request through postman, initialize method is called, so I cannot maintain @data Array because @data is initialized at every request. Is there any way to initialize @data once, and let create, update, destroy methods work properly?

class BooksController < ApplicationController
    skip_before_action :verify_authenticity_token

    def initialize
        super
        @data = [
            { title: "Harry Potter", author: "J.K Rowling" },
            { title: "Name of the wind", author: "Patrick Rothfuss" }
        ]
    end

    def index
        render json: @data
    end

    def create
        @data.push(params[:book])
        render json: @data
    end
end

Yes, you need to save it to a database. An instance variable only applies to that instance of the class, every time you make a new request, you create a new instance of your BooksController class, which has no variables associated with it — Mark
– Mark, Commented Apr 9, 2020 at 8:17
Thanks @Mark. I just realized that every request created a new instance. This was just for the purpose of study before I get into the database. — Jason KIM
– Jason KIM, Commented Apr 9, 2020 at 8:24

max · Accepted Answer · 2020-04-10 12:30:32Z

2

If you want to persist anything between requests you need to store it somewhere:

Database
Memory based storage (Redis, Memcached)
File system

You can also pass state back and forth between the client and server without actually storing it with:

HTTP cookies
Query string parameters

Using a class variable is not really going to solve anything. It will only hold the variable as long as the class is held in memory. Every time the class is reloaded it will be reset.

Multi-threading is another huge issue here as Rails servers are commonly multi-threaded and class variables are not thread safe.

edited Apr 10, 2020 at 12:30

answered Apr 9, 2020 at 10:41

max

103k15 gold badges113 silver badges177 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Jason KIM · Accepted Answer · 2020-04-09 08:30:50Z

0

Because I just didn't want to use any database yet, and knew that every request created a new instance of BooksController. To make this code work, the following changes could solve it.

class BooksController < ApplicationController
    skip_before_action :verify_authenticity_token

    @@data = [
        { title: "Harry Potter", author: "J.K Rowling" },
        { title: "Name of the wind", author: "Patrick Rothfuss" }
    ]

    def index
        render json: @@data
    end

    def create
        @@data.push(params[:book])
        render json: @@data
    end
end

answered Apr 9, 2020 at 8:30

Jason KIM

1471 silver badge9 bronze badges

2 Comments

Roland Studer Over a year ago

This is ok as a learning experience, but what you should take away from this exercise, is that really your data should live outside of your classes. Rails helps you a lot with that, it will actually be easier, if you create an Active Record Model.

Jason KIM Over a year ago

Thanks @Roland. I am sure I will do that in a couple of days.

Collectives™ on Stack Overflow

How can I "initialize" instance variable?

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related