Introduction and Definition While learning how to build a rails application at Microverse remote school, there were numerous times where my coding partner and I were required to test if our rails association methods were working. We had to learn how to use the rails console to test this because it’s quicker than running a browser or creating tests on a separate file. Rails console is an irb session that is built into the rails environment and is accessed by typing into the terminal. It can be used to test , and when building a rails app. rails c association methods validations check error messages Let’s build a sample blog app to see how it works. We will start by explaining what association methods, validations and error messages are. in rails are used to show the relationship that exists between two models. It shows how models are connected. What is a rails model? It is a Ruby class that adds records to the database through a rails migration file. Association methods Generating a rails model automatically generates a migration file. The migration file creates tables where none existed and adds or deletes columns in the schema. Rails associations methods make it is easy to capture the relationships between models . provide validation helpers that ensure only valid data gets saved to the database. For example, in our sample blog app, we require a user to input their name to be saved to the database. By placing validation helpers in the user.rb file, a user cannot be saved if a name isn’t provided. Active Records Validations If a user fails to save, rails provide to explain why through . These instance methods return an array of error messages if any exist or an empty array if no error is found. error messages error messages instance methods The returns a list of error messages that’s easy to read and that can be displayed in the view page for the user to see. errors.full_messages method Creating a new rails app and generating rails models. We are going to build a blog with two models, a user with a and an article with To get started, open your terminal and enter the command . name attribute a title attribute and a body attribute. rails new blog_app This generates folders and files that are needed by a new rails app. command Next, and let’s create our models. First, we create a User model, then an Article Model. cd into the blog_app folder The command used to create models in rails begins with followed by the (e.g ) then the (e.g ) rails g model model’s name User column name: type of data name: string rails g model (the model name) (nameofcolumn1:data-type) (nameofcolumn2:data-type) In our case:- rails g model User name: string This command creates a migration file, test for the model and fixtures used to add data when testing your models. We created a user model with one attribute which is the user’s name. This is the same process that we will use to create the Article model which will have two columns, title and body, both of type string :- rails g model Article title: string body: string To view your migration file, navigate to This gives you a glimpse of what tables and columns your migration file will create in your database schema. The files appear in the order in which they were generated. Note that I said this meaning the tables haven’t been created yet. app/db/migrate. is a glimpse of what will be created To create them simply type the command which migrates your files and creates the user table with the name column and the articles table with the title and body columns in the database. rails db: migrate In case a mistake is made while generating the rails model then the command can be used to undo the rails g model command. It reverses the rails g model command and removes the migration files that had been generated is run. rails destroy model (model name) before a rails db: migrate command If you had then simply do a to in the schema, delete the migration file in the app/db/migrate folder then destroy the rails model with the rails destroy command above. already run the rails db: migration command rails db: rollback drop the table Relationship between User and Article models. In a blog application, a user can write many articles but an article can only belong to one User. Developers use ERB diagrams to visually show this relationship while designing databases for their apps. A good tool to use is LUCID Chart . Connecting the models by adding the has_many association method. Next, add the to your model. Go to and add This method is made available through inheritance from the Application Record class in rails. has_many association method blog_app/app/models/user.rb has_many :articles. Testing has_many method using Rails Console At this point, we can start testing our models and association methods. 1. Type into your terminal to access your irb session rails c 2. Check if a user has already been created using User.all This command uses SQLite queries through active records to check if any user exists in the users' table. Nothing is returned since we haven’t created a user for our application. 3. Create a user, use the command. For ease of use, we will use a variable to store the data of our new user. Create a and assign it to e.g T User.new user variable User.new user = User.new. he return value will be a user with no attributes i.e user_id = nil, name =nil e.t.c.This is another way to check if the columns a.k.a attributes in the database are correct. Fill in the attributes as follows user = User.new(name: “Zoe”) This command creates a user called Zoe. If you type the output will be because the user has been created but to the database. Therefore, we must do to the user to the database. Now try query for the user’s id by typing the command , the output will be 1. user.id nil not saved user.save save user.id Congratulations, you have created your first user. In the image above, begin transaction indicates that the process of saving the user to the database has begun. If everything is ok the transaction is committed and the boolean value true is returned. 4. A faster way to create and save a new user to the database is to use the method create as follows This method does the double work of the object to the database. user = User.create(name: ‘Henry’). creating and saving Adding Validations to Models An important aspect of creating rails models is the presence of those model’s attributes. This prevents invalid objects from being saved to the database. The image below shows a user without a name attribute being saved successfully to the database. validating I can't think of an instance where we would want to build an app that doesn't require a particular attribute, yet the attribute exists in the database as an empty column. 5. Open your file add the following user.rb validates : name, presence: true. This validation helper ensures that nothing is saved to the database if a name attribute is not present. Create another user with Don't fill in the user’s name, then do a The output result should be meaning our user failed to save. User.new. user. save. false Checking for errors when our models fail to save To check why our database save was false, do user.errors.any? Output on the terminal should be the boolean value indicating that errors were found. To list the errors do which returns a list of errors as below: true user.errors.full_messages Adding the belongs_to association method Now, we add a belongs_to method to the Article model. Without it, the relationship between the user and article models is half complete. Open and add inside the class, add validations as well i.e and article.rb belongs_to: user validates: title, presence: true validates: body, presence: true Create a new article using the new method and save it to the database. The article saves successfully. Rails console can also be used to query the database for all the articles that have been created or all the users that exist in the database using the . count method If we want a list of articles created by the first user, we can do to get the user whose user_id == 1 then do which returns an array of articles created by the first user. user = User.first user.articles In our case, we get an error saying that there is no column in the database with the column name articles.user_id Having a doesn’t show which user authored which article. A is needed in the to map each article to a particular user. This is done by adding a as a in the article’s table. belongs_to method user_id article table user_id column foreign key In rails 5 and above use the command rails generate migration add_references_to_articles user: references Do a to migrate the file that was generated. If you open the schema, you will see that a of type integer has been added. The schema will be modified as below: rails db: migrate new column user_id We can set the first article we created in the console to belong to the first user as follows: which gets the first article in the database and stores it in the article variable. article = Article.first shows us which this article belongs to which is currently. article.user_id user’s id null sets the article to belong to the first user’s id. article.user_id = 1 saves the article article. save Now we can type then to give us a list of articles created by the first user. You can also query the database for the total number of articles owned by the first user with user = User.first user.articles user.articles.count Conclusion I believe you now have a better understanding of the rails console and I hope that it doesn’t feel as scary to open your terminal, do . Start playing with your app models and methods. a rails c There are other methods that can be used in the console to test for different things such as the but I hope this inspires you to learn more about the rails console. find method , The source code for this tutorial can be found on my , leave an ⭐️ on the repo if you like the tutorial or found it helpful. GitHub Previously published at https://medium.com/@lukoyedith/a-step-by-step-guide-to-using-the-rails-console-to-test-rails-models-associations-and-validations-986f4825aadf

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