I'm new to Ruby on Rails and I'm looking at an application that has a variable called current_teacher. I cannot seem to find where this is set. Everywhere I look the code seems to read from it but where is it set. Is this one of those things that Rails does for you. There is a mode and a table called teachers, so I'm sure this has something to do with it.
I'm very confused by statements like the following, can someone tell me how Rails does this?
if current_teacher.can_request_fieldtrip
Suppose you have a controller like :
class ClientsController < ApplicationController
def new
if current_teacher.can_request_fieldtrip
# code
end
end
end
Here is debugging tips :
(a) put this in your Gemfile and do bundle install :
`gem 'pry-rails', :group => :development`
(b) Put the line binding.pry just before the if statement.
(c) Start rails server using rails s.
(d) Hit the browser like http://localhost:3000/new
(e) Now you will be in the Pry console. Just do in the console,
method(:current_teacher).source_location
And the above line tell you where the method has been defined.
Documentation of Method#source_location
Returns the Ruby source filename and line number containing this method or nil if this method was not defined in Ruby (i.e. native)
Rails does not support authentication by itself, however there are a lot of 'add-ons' that rails can use. These 'add-ons' are called gems. This can be a little confusing because you can't actually see their code inside your project folder.
If you open a file called "Gemfile" (it should be in your project folder) you can see a list of gems that you use. Try searching their names on google, you will probably find official web page that contains it's documentation. That way can learn what they do and how to use them.
current_teacher method smells like "Devise" gem
https://github.com/plataformatec/devise
I'm not sure about can_request_fieldtrip, this could be a custom method defined in Teacher model.
Related
I have a Rails app that uses a gem called ActsAsTaggableOnSteroids, which is a Rails Engine. Specifically, I'm using PavelNartov's fork of the gem. But nevermind that.
I need to add specific functionality to the Tag model, which is supplied by the engine.
But, according to my understanding of Rails engines and the magical loading functionality in Rails, if I put a file called "tag.rb" in my models directory, then it will completely replace the one from the Engine.
Ideally, I would be able to do something like:
class Tag < ActsAsTaggable::Tag
# my stuff
end
...but alas, that doesn't work because the model supplied by the engine is not namespaced.
So, I came up with this nightmare, which I put in app/models/tag.rb:
path = ActsAsTaggable::Engine.config.eager_load_paths.grep(/models/).first
require File.join(path, 'tag')
Tag.class_eval { include TagConcern }
But there has to be a better way! I feel like I'm missing something. I'd prefer not to add this strangeness to my app if possible.
Just require the file by looking up the path of the gem's model:
require File.join(Gem::Specification.find_by_name("bborn-acts_as_taggable_on_steroids").gem_dir, 'app/models/tag')
Tag.class_eval do
# ...
end
Ok, I have a rails gem that I am working on and I want it to override a specific method in sprockets.
The method I want to override is: Sprockets::Base.digest so that I can base the fingerprint off my gem version when compiling the app's assets.
How would I go about doing that?
In my gem I create a file lib/sprockets/base.rb and place the following code:
class Sprockets::Base
def digest
#digest = digest_class.new.update(MyGem::VERSION)
#digest.dup
end
end
When I run bundle exec rake assets:precompile I get:
undefined method 'logger=' for #<Sprockets::Environment:0x1315b040>
So it almost seems to me like the entire class is getting overridden somehow (this losing that, and the other methods), instead of just overriding the one method.
If I include that snippet of code directly into the app's rakefile that's using both gems, things work perfectly.
It's impossible to override an entire Ruby class in that manner, but I think it is possible to prevent the original class from loading...if it's using autoload. I was curious, so I checked out https://github.com/sstephenson/sprockets/blob/master/lib/sprockets.rb, and yes, Sprockets is using autoload.
autoload :Base, "sprockets/base"
Importantly, that doesn't load the code. It simply tells Ruby that if/when an undefined constant called "Sprockets::Base" is ever encountered, to load it from the specified file. Your patch defines Sprockets::Base before it is ever called anywhere, thus preventing the original file from loading.
When you moved your patch to the Rakefile, something in Rails had already referenced Sprockets::Base, loading the original code. Your patch then applied cleanly on top.
I've never actually used autoload, so I'm not sure how cases like this are supposed to be handled. I'm betting though, that this would work:
Sprockets::Base
class Sprockets::Base
def digest
...
By referencing the class first, you should force Ruby to load the original class. Then you can safely go about the business of overriding one of its methods.
Ok, I marked your answer correct, but it really only led me to figure out the problem.
Anyway, the rails app was requiring my base file instead of the one in the gem itself. Which is what you said. However, the reason it was happening seems to have been caused by the path itself. The path to the file was basically the same as the gem's (lib/sprockets/base.rb).
Moving that file into my gem's "namespace" (lib/my_gem instead of lib/sprockets) and renaming it to sprockets_base.rb fixed the problem! Weird, huh?
In other words, me trying to keep the directory structure nice actually seems to have confused Rails into thinking it was the gem itself or something.
Pretty self explanatory.
I use array_name.first to get the first element. How do you extend it to get second, third, random, etc?
Thanks.
In Ruby you can just reopen any existing class and add your own functions.
In rails, you already have those methods defined in activesupport
See the source at github: https://github.com/rails/rails/blob/master/activesupport/lib/active_support/core_ext/array/access.rb
I discovered it is already there, in Ruby 1.9.2 at least.
If it weren't there, I would create a file in config/initializers called array_helper.rb (or whatever) and add the following code:
class Array
def second
self[1]
end
end
Why? Because all classes in Ruby are open and you can extend anything you want.
Here's some tricks to know:
When working in the console, if you want to test the file, be sure to use rails console and not irb. Also, do reload! after creating or updating the above file. Finally, all objects must be recreated to use the new code after reload!.
I'm using the Rails gem SimpleForm, but I think my question may be applicable to any gem.
https://github.com/plataformatec/simple_form
It has a lot of great features and customization, but I'm looking to go a bit further. For example, I really wish the markup generated had no default classes inserted into it, but I'd still like the ability to insert my own manually. I found that I could remove some of the classes by commenting out lines in the gem files. However this is outside of my project-- I would want a DRY solution that will stay with my project when I deploy to production, preferably without having to pack all of my gems.
I imagine this is a common situation that could apply to any gem, and I should be able to override any gem wholly or partially probably by adding customs files in my project that override the gem... but I'm not sure how.
Any help would be appreciated! Thanks.
Are you talking about monkey patching? Say your gem has a class in a file
# simple_form_gem/lib/some_file.rb
class A
def some_method
puts 'A'
end
end
If you want to change the output of #some_method then you can create an initializer file and do
# config/initializers/my_monkey_patch_for_simple_form_gem.rb
class A
def some_method
puts 'duck punching'
end
end
Your monkey patch will only affect A#some_method, and not other methods in A. Just make sure the output of your monkey patch won't break something else in the gem.
I'm messing around with rails 2.3 templates and want to be able to use the app name as a variable inside my template, so when I use...
rails appname -m path/to/template.rb
...I want to be able to access appname inside template.rb. Anyone know how to do this?
Thanks
I was looking for an answer to this question. unfortunately the answer above (#root) doesn't seem to work in Rails 3.
Here's the variables you can access in Rails 3 app templates (even easier):
#app_name
#app_path
Thanks for the answers. Mike Woodhouse, you were so close. Turns out, all you need to do to access the appname from inside your rails template is...
#root.split('/').last
The #root variable is the first thing created when initializing templates and is available inside your rails templates. RAILS_ROOT does not work.
In Rails 3, use the app_name attribute.
See the documentation for the Rails::Generators::AppGenerator.
I ran into a similar problem, none of the variables listed above were available to me in Rails 4. I found that #name was available while running
rails plugin new engines/dummy -m my_template.rb
There are other useful variables available from within the template. You can see for yourself and play around by utilizing pry. Inside my template I added
require 'pry'; binding.pry
and then ran ls to show a list of available instance variables
ls -i
instance variables:
#_initializer #app_path #behavior #destination_stack #extra_entries #name #output_buffer #shell
#_invocations #args #builder #dummy_path #gem_filter #options #rails_template #source_paths
#after_bundle_callbacks #author #camelized #email #in_group #original_name #shebang
There's probably a more straightforward way, but this seems to work:
RAILS_ROOT.split('/').last
EDIT: Bleah - this got voted down once, and the voter was right. If I'd read the question more carefully, I'd have noticed the 2.3 and template.rb elements. Apologies.
I suspect that RAILS_ROOT won't have been created at the point that you need the app name. Looking at ruby\lib\ruby\gems\1.8\gems\rails-2.2.2\bin\rails, however, almost the first thing that happens is this:
app_path = ARGV.first
It's used at the end of the script to allow a chdir and freeze to be done if needed - I didn't know I could insta-freeze at creation, so I learned something new at least. ARGV then gets used here:
Rails::Generator::Scripts::Generate.new.run(ARGV, :generator => 'app')
which quickly gets us to the place where ARGV is really handled:
rails-2.3.1\lib\rails_generator\scripts.rb
where I see
Rails::Generator::Base.instance(options[:generator], args, options).command(options[:command]).invoke!
Somewhere below here is probably where the templating gets handled. I'm afraid I'm at a very early stage with 2.3 and templating is an area that I haven't looked at yet.
Does that help any better than my first effort?
RAILS_ROOT will give you the absolute path to your root directory. Your app name will be the portion of the string after the final '/' which you can grab in any number of ways.
EDIT: Not quite enough to get the job done. Mike and Dan iron it out below.
I believe the preferred way now is to call Rails.root and no longer RAILS_ROOT. Apparently someone on planet rails has an aversion to uppercase or some similar important reason. As of 2.3.5 they both appear to work.
I was getting error
`template': undefined local variable or method `app_name'
ruby 1.9.2p290, rails 3.2.11, thor 0.18.0, Windows
but with rails 2.3 generator:
class DynanavGenerator < Rails::Generators::Base
(can't be sure whether this error happened under rails 3.0.9 or earlier)
changed class definition to be:
class DynanavGenerator < Rails::Generators::NamedBase
which then gave:
No value provided for required arguments 'name'
I then added a 'name' ("something" below):
rails generate dynanav something --force
which gave the original error, so I then added:
def app_name
#name.titleize
end
to the class and all was well.
As of Rails 4 (maybe earlier versions?), use Rails.application.class to get the application name. For example, if your app is named Fizzbuzz, here are a few ways you might access it:
rails(development)> Rails.application.class
=> Fizzbuzz::Application
rails(development)> Rails.application.class.name
=> "Fizzbuzz::Application"
rails(development)> Rails.application.class.parent
=> Fizzbuzz
rails(development)> Rails.application.class.parent.to_s
=> "Fizzbuzz"