Creating Model Classes

In this demonstration, I will show how to create model classes to store and manage data in the database. We will continue to build upon the QuizMe project from the previous demos.

Since we are building a quizzing application, we will need to store questions in the database. At first, the app will only allow multiple choice questions but in a later demo we will see that it’s pretty easy to add other kinds of questions too (e.g., fill in the blank). For multiple choice questions, we need to store the question, answer, and a couple of incorrect options (distractors). Figure 1 shows the corresponding class diagram.

1. Creating the McQuestion Model Class

First, generate the McQuestion model class shown in the above class diagram by running the following command:

rails generate model McQuestion question:string answer:string distractor_1:string distractor_2:string

This command generates several key files:

• app/models/mc_question.rb: The Rails model class.
• db/migrate/20190926192541_create_mc_questions.rb: The database migration that is used to set up the database schema (timestamp will vary based on creation time).
• test/models/mc_question_test.rb: Unit test code skeleton where tests for the models can be defined.
• test/fixtures/mc_questions.yml: Test fixtures skeleton where McQuestion objects for use in the tests can be defined.

Next, set up the mc_questions table in the database and regenerate the db/schema.rb file, which holds the Rails app’s representation of the database, by running the following command:

rails db:migrate

Finally, confirm that the database was set up correctly by

• inspecting the db/schema.rb file to see that the mc_questions table is defined correctly, and

• inspecting the Postgres database quiz_me_development with pgAdmin to see that mc_questions table is present and that its columns are correct by navigating as follows, starting from the pgAdmin sidebar:

  Servers > SoftwareEng > Databases > quiz_me_development > Schemas > public > Tables > (right-click) mc_questions > View/Edit Data > All Rows

We have now created our first model class and corresponding database table; however, we have not yet saved any McQuestion records in the database—that will be coming soon!

Code changeset for this part