DRYing out Rails

Question 1

Add Validation to this..
Class Person < ApplicationRecord
end
Then call the validation.

Answer 1

Class Person < ApplicationRecord
     validates :name, presence: true
end
Person.create(name: "John Doe").valid? #True
Person.create(name: nil).valid? #False

Question 2

Spot the Error
class Library < ApplicationRecord
     has_many :books
     validates_association :books
end

class Book < ApplicationRecord
has_many :libraries
validates_association :libraries
end

Answer 2

The validations create an infinite loop.

Question 3

Name the Validations you would use for these scenarios:

1. A check box being marked
2. I am creating a book which is of association library. I want to validate what is in library as well as book when creating a book.
3. Two Text Fields should receive the same values, like password and confirm password.
4. Validate that certain values are not included in a set.

Answer 3

1. Acceptance Validation.
   validates :terms_of_service, acceptance :true
2. Validates Associated
   validates_associated :books
3. Confirmation:
   validates :email, confirmation: true
4. Exclusion
   validates :subdomain, exclusion: { in : w%(www}

Question 4

What is Dry?

Answer 4

Don’t Repeat Yourself

Question 5

How is validation Dry?

Answer 5

Well we would have to have a validity constraint and that could be put anywhere. SO we DRY it out by putting it in just the Model.

Question 6

How can I see what didn’t pass validation?

Answer 6

m.errors[:release_date] will show me the errors of release data validation.

Question 7

What are Lifecycle Callbacks?

Answer 7

Before you talk to the database, you can have these callbacks run. Like you can uppercase some of these things before the value hits the server. There are control on validations before the create. Or maybe an audit record or log entry after the validation. The point cuts are set though.

Question 8

Can we put validations anywhere?

Answer 8

No we have certain places for validation and we must follow them. We also have to be cautious that we don’t know where the validation comes from

Question 9

What are constraints on a controller action?

Answer 9

Typical is that you want to only be able to do stuff when you are logged in per say.

Question 10

Setup a Filter in an application

Answer 10

class applicationController ‘login’
protected
def set_current_user
@current_user=Moviegoer.find_by_id(session[:user_id])
redirect to ‘/login’ and return unless @current_user
end
end

The Redirect terminates the default execution that would happen after the filter. The filter could unexpectedly get triggered though.

Question 11

What does Protected do in the controller?

Answer 11

Prevents method from being called by any routes.

Question 12

I have a route that I made in my controller, but it seems to not be working. When I debug I see that my controller method pertaining to that route never gets called. What could be happening?

Answer 12

I am not calling the right route. I am not calling the right redirect.

It is more likely that I have a before_filter somewhere in the code that is preventing the controller method from being called in the first place.

Question 13

What is the scope a before_filter? of the ApplicationController before_filters?

Answer 13

The Filters declared in a controller also apply to all of its subclasses. That means the filters in ApplicationController apply EVERYWHERE.

Question 14

Can a filter change the flow of execution?

Answer 14

Yes by calling redirect or render it can prevent the default controller method from a route from ever being called.

Question 15

Compare Validations and Filters

Answer 15

Both Are Dry
Both are point cuts, but rails gets to determine where these point cuts are.
Only Filters can change execution flow
Filters capture errors in flash, validation captures errors in its errors object.

Question 16

Which Ruby Language Features support Dryness enabled by validations?

Answer 16

Higher Order Functions, Closures, and Metaprogramming.
Metaprogramming cause you can turn the function name into a function reference at run time. Closures and higher order are usually together. Pass a function to validator is an example of higher order and closure.

Question 17

What is Metaprogramming?

Answer 17

When you can write programs and treat them as your data. Write code as you run them is another plus. Modify itself while running.

Question 18

What is the general rule of Third Party Application?

Answer 18

You never reveal the password and login.

Question 19

Tamper-evident secure token?

Answer 19

String that when some of the characters are manipulated we can tell and we can invalidate them. You use a secret string that only I can decode. Then the tampered version won’t decode properly. Only someone with secret can make the code. The string doesn’t contain the actual password, just enough information for it.

Question 20

Explain Process of 3rd Party Validation

Answer 20

1. Tell the app you want to login with Twitter.
2. Redirect to Twitter Login Page
3. You OK to authorize the app
4. User Agrees
5. Twitter then provides an access token as a tamper-evident secure token. Use the token to make sure I authorize that the app does what user agrees to.

Session should centralize the logic that talks with the third party application. Session remembers the primary key. Session is also tamper-evident string.

Question 21

Which is True with Authentication?
Requester can do anything you can do on a provider.

If your credentials on the requester are compromised. your credentials on the provider are compromised.

If provider revokes access, the requester no longer has information.

Access can be time-limited to expire on a pre-set date.

Answer 21

That last is true, Notice that the others are false.

Question 22

What do you have to tell Omni-Auth?

Answer 22

1. Where are you trying to authenticate to? Twitter, Facebook, Google, etc.
2. Omniauth gem provides the routes to Twitter authentication. It then provides the logic and such for you. You just have to tell omni auth what site I want to authenticate.
3. Then you have to get a developer key from the third party software. Then you put your auth key in a xaml file.
4. Once you authenticate on Twitter it will redirect to something in my app and it will include the token. We need to provide the end route for the third party.
5. Create ‘auth/:provider/callback’ route and ‘auth/failure/ routes

Question 23

How do I get all the parameters sent back by the omniauth provider?

Answer 23

You just have to call request.env[“omniauth.auth”].
Example:
def create
auth = request.env[“omniauth.auth”]
user = Moviegoer.find_by_provider_and_uid(auth[“provider”], auth[“uid”]
or Moviegoer.create_with_omniauth(auth)

“provider” we know from omniauth, like Twitter.
“uid” we look and see this is what Twitter sends us.

Question 24

What are reusable scopes in rails?

Answer 24

A movie that have some average score/rating. Movies with some certain rating. There are ways to prevent having to call a bunch of join statements.
Movie.for_kids
Movie.average_reviews

Example:
scope :for_kids, :conditions => [‘rating IN (:ratings)’, :ratings => %w(g PG)]

Question 25

What is happening here?
scope :with_good_reviews, lambda{ |cutoff|
joins(:reviews).
group(:movie_id).
having(“AVG(reviews.potatoes) > #{cutoff}”)
}
end

Answer 25

This is in a lambda expression because I need to be able to evaluate this for a particular argument value, right. Instantiate at run time the right value for the cutoff.

The scopes are stackable as well.

If you call with_good_reviews then you get an error since you HAVE to call it with parameters.

Question 26

When does the Query Happen?

Answer 26

The Query is deferred until the view because it can then check the cache to see if had been called earlier and then just render that value again without calling the query.

Question 27

Query is Horizontal or Vertical Bottleneck?

Answer 27

Horizontal

Question 28

When does the Database Query Happen?
Controller?
View?
Controller:
   @m = Movie.for_kids_with_reviews

View:
@m.each do |movie|

Answer 28

In the View!