Seeding the Database
In this demonstration, I will show how to add seed data to the app’s database. We will continue to build upon the QuizMe project from the previous demos.
In particular, we will update the QuizMe app such that the database can be initially seeded with three sample multiple-choice questions. Having such seed data available is useful for manually testing the app during development.
1. Adding Seed Multiple-Choice Questions to the Database
First, declare a few sample questions in the db/seeds.rb file, like this:
q1 = McQuestion.create!(
question: 'What does the M in MVC stand for?',
answer: 'Model',
distractor_1: 'Media',
distractor_2: 'Mode'
)
q2 = McQuestion.create!(
question: 'What does the V in MVC stand for?',
answer: 'View',
distractor_1: 'Verify',
distractor_2: 'Validate'
)
q3 = McQuestion.create!(
question: 'What does the C in MVC stand for?',
answer: 'Controller',
distractor_1: 'Create',
distractor_2: 'Code'
)
The create! method is part of the Rails model API, and when executed, it has the effect of creating the corresponding model object (in this case McQuestion objects) and saving the object to the database.
The Rails API actually offers both a create (with no !) version and a create! (with a !) version of the method. These two versions are essentially the same, except they behave differently when saving to the database fails. In particular, the create! version throws an exception if saving fails, whereas the create version does not.
Caution! The reason that we use the exception-throwing create! version in the seeds.rb script is so that we will see an error message if a record fails to save to the database. In contrast, if we were to use the create (with no !) version of the method, the script would fail silently, and that can create a lot of confusion for us regarding why certain records are mysteriously missing from the database.
Next, execute the seeds.rb script by running this command:
rails db:seed
Finally, verify that the records were added to the database by using pgAdmin to navigate as follows, starting from the sidebar:
Servers > SoftwareEng > Databases > quiz_me_development > Schemas > public > Tables > (right-click) mc_questions > View/Edit Data > All Rows
You should see the three seed records, as depicted in Figure 1.
Figure 1. The seeded multiple-choice questions, as visualized in pgAdmin.
We have now set up our app such that we can add seed data whenever we reset the database. As we evolve our model in future demos, we will continue to add new seed data, so when we manually test the app, we won’t have to manually enter in all our test data every time.