Validation, error message and helper method in Sinatra/Ruby

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To start with, what I am writing here is based on my Sinatra project, but since Sinatra is just a framework of Ruby, this article works for whoever is looking for references on setting up validation, error message and helper method in ruby too.

This Sinatra project not only helps me clarify some concepts about Sinatra but also motivates me to learn new stuff when I need to implement a new feature in my app. I appreciate such a chance to organize and review my knowledge and would love to share what I learn from my project to you.

How do I use validation in my app?

Validation is useful when we persist data to the database. For example, in my User.rb, where I define class User, I have codes like this:

class User < ActiveRecord::Base
has_many :reviews
has_many :centers, through: :reviews
validates :username, presence: true
validates :password_digest, :email, presence: true
validates :email, uniqueness: true

Those sentences starting with the word validates are the tradition you use validation. Following validates, you put the attributes name as a target, and then after, you use a validation helpers. In another word, in the first part of the validation, it tells the model which attribute needs to be validated, and the second part tells the model how will that attribute get validated.

For instance, look at validates :email, uniqueness: true. This statement tells the class User: “Hey, I want the email address to be unique on the creation of every User instance.” In this way, when you use the same email address to create a new user (or, in this case, sign up), the user instance is invalid and thus cannot be saved into the database, which guarantees the uniqueness of the email address in the database.

Uniqueness is not the only keyword I have used in this app. I used presence, validates_associated too. Presence is very common. When I say validates :username, presence: true, that means I require that username attribute is provided when I create an instance from that model. In another word, if that attribute is missing, I won’t be able to create an object successfully. So if I do this statement:


I get false back, which means it is not valid and will not be saved into database.

Validates_associated helper is very helpful too. I use it to validate the user instance associated with the review when creating the review. It makes sure that when the review is created, it has a valid user, or itself won’t be considered as valid either and thus won’t be saved. That makes sense right? If the producer (the user, in this case) does not exist in the database, the production (the review, in this case ) won’t either.

To implement these function, since validation is Active record’s feature. the model that is using that has to inherit from ActiveRecord::Base. Also, one thing I want to mention especially here is, to be careful about the User class, or any other class that will have password attribute and use has_secure_password method. Here is my story: at first, I want to make sure that a password is presented when people sign up. So I put this statement under User class:

validates :password, presence: true

And then, I tried to use this following statement to create a user instance:

User.create(:username=>"John", :password=>"12345", :email=>"")

However, out of my expectation, I fail. I keep trying and trying but still fail even a username, a password, and an email are all provided as they are needed. Why is that?

Finally, I figure out the reason. As I explained before, the validation will look for password attribute every time a user instance is instantiated. If the attribute can’t be found, the instance is not valid.

“But you did provide the password!” You might be thinking. Yes, I did. However, because I use gem bcrypt and has_secure_password method in Active Record, in the user table, I have to set the column name, which is supposed to be password, to password_digest. Because bcrypt will access the attribute of password and store a salted, hashed version of password into a column called password_digest to better protect users’ password information. Therefore, a password is required but not found because only password_digest is there.

After I change the validation to:

validates :password_digest, presence: true

It works! So do be careful when you use gem bcrypt and password_digest together with validation in Active Record. Plus, if you want to know more about validations and helpers, check this out:

Error message

Sometimes the app might break due to users’ inappropriate operations. Of course, there are ways you can stop them. But, once you stop them, how do you tell them “Hey, what you just did is wrong. Now, you should do this or that “? That is where error messages become useful. For my app, I use the gem sinatra-flash. Basically, after setting up, you only have to put the message in the controller file and then leave a statement in the view file to make sure the message will show up if there exists any. The setup and how to use this are on this website:

It is not difficult. However, I just want to share one thing with you when using this gem: The flash message only works on a next request. What does that mean? I will show you in my story. At first, to display the error, I write this following codes:

flash[:error]="You have no right to check this user's file."
erb :"users/error"

It is an error message I left in my /users/:id route, to make sure that a user cannot check on other users’ profiles. And if it does, it will load an error page and display the error message. It does navigate me to the error.erb, but it doesn’t show the error message I expect. Instead, I see totally blank message. I don’t know why, so I test another error message to see if there are more clues:

flash[:error]="The user doesn't exist."
erb :"users/error"

This message is supposed to show up when I try to view a user’s file when that user doesn’t even exist. Guess what? I am navigated to the error page and get “You have no right to check this user’s file.”, I get the error message from the last request! I try many times and it still does the same thing--giving me error message from the last request. Finally, after reading the document about that gem, and with the help of Jennifer, I find out that that is because the flash[:error] message only gets assigned at the end of the request. In another word, the first error message only get assigned after the erb :”users/error”` statement when this request is done and can only be assessed in the next request.

Accordingly, I change the codes from erb :"/users/error" to redirect to "...". Since redirect to is actually another request, my error message will get assigned before that statement and successfully show up on the page whichever I redirect to!

Helper method

Last but not least, I want to talk about helper methods. Sometimes we need to wrap some repetitive codes into a single method in order to save some work and also make the codes look more semantically clear but at the same time, these methods don’t actually belong to any models we already have. So, we will have to wrap them into a helper method.

In my app, I need two helpers methods: current_user and log_in?. I need to use them quite often to verify the user or if they already log in before a review is created or edited. I try two different ways to use helper methods this time in my app and they have their own pros and cons.

put it in helper.rb in models directory

One of the choices is to give the methods their own home! Since they don’t belong to any models, I create a new file called helper.rb, and then write both methods there within class Helper. Since we will not instantiate any Helper instances because we only want to use methods there, we will write all the methods as class methods instead of instance methods. Here are my codes:

class Helper  def self.current_user(session)
User.find_by :id=>session[:user_id]

def self.log_in?(session)

Next time when I try to use these methods, I will just do Helper.current_user(session) or Helper.log_in?(session), which also makes reading codes easier.

put it in the applicationcontroller.rb under controllers directory

The second way is to leave it in the controller document. Within class ApplicationController, on the very bottom, we can add these following codes:

helpers do 

def current_user
User.find_by :id=>session[:user_id]
def log_in?

And when we want to use these methods, I just put current_user or log_in?, then they will be called right away.

From the two versions above, maybe you already see their differences. the second example is simpler: no need to pass a session argument because when methods are within ApplicationController, session is enabled and can be reached everywhere in the controller; no need to build another class; no need to call it as a class method. That is the reason I choose the second one. However, I believe when there are more and more helpers methods, the first one will be easier to maintain and be taken care of.

Thanks for reading!

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