Helpers in rails

Question

I'm just starting out in Rails and there's a lot I still need to learn so I'm likely to be on Stackoverflow more often than normal asking beginner Rails / Ruby questions.

I'm just trying to figure out how Helpers work in Rails. From what I've seen so far, Helpers are intended to be used with Views and not so much with your Controllers.

However I would like to make a simple function that will validate the user input given in params (check if certain params are defined and optionally check if their value is valid).

Can anyone explain to me what would be the best way of implementing this? (Keeping in mind that I will want to use this in many different controllers so it should be globally available.)

I also noticed that by default Rails does not generate a lib folder in the main application folder. Are developers to place their libs outside the app folder in the main folder, or does Rails use libraries differently?

Answer 1

With regards to your validation issue, it depends on what you are validating.

If the data makes up objects from your problem domain, also known as models, then you should use the built in validators from ActiveModel. This is probably what you should do, but its hard to say without knowing the exact problem. See the Rails Guides on Validations. You can tell if this is the case by asking yourself if the data that needs validation will be stored after you get it. If so, its most definitely a model. An example of this kind of data would be the title and text fields of a blog post being sent to Rails from a browser form.

If the data is something tertiary to your models, or specific to presentation, then you should be fine using helpers. You noticed that helpers are used mostly in the views, and although this is true, theres nothing stopping you from using them in the controllers, you just have to declare that you will use them using the ActiveController#helper method. Inside the ApplicationController class, a lot of devs will put helper :all to just include all the helpers in all the controllers. Once the code has been required once, it doesn't really incur that big a performance hit.

Do note that almost all incoming data can be modeled using a model. A big school of thought in the Rails world subscribes to the Fat Model idea. People say that putting as much code as possible in the model and as little in the controller as possible separates concerns properly and leads to more maintainable code. This suggests that even if you don't think the incoming data is modelable (in the sense that you can create a model to represent it), you should try to make it a model and encapsulate the logic around validating it. However, you may find that making a helper function is faster, and either will work.

Your notion of validating user input is a good one. I get the feeling that as you are new to Rails you are used to doing these things yourself, but that doesn't quite apply here. In the Rails world, a lot of the common stuff like validations is handled by the framework. You don't have to check for presence in the params array, instead you call validates_presence_of on the model and let Rails spit the error out to the user. It makes things easier in the long run if you let the framework do what it is designed to.

With regards to your question about the lib folder, it doesn't really matter. You can put miscellaneous support files and libraries in the lib folder in the root directory and they will be available for use in your application (the files in the app folder). You can also choose to abstract your code into a plugin or a gem and include it that way, which a lot of people opt to do. My suggestion for this would be to read up on the notion of gems and plugins before diving in.

Answer 2

Want you want is probably a custom validator (in Rails3):

http://railscasts.com/episodes/211-validations-in-rails-3

You can either add libs in a lib folder you create, or add them to config/initializers in a file you add. Files in the initializers directory are automatically loaded by Rails.