Glitch in the Matrix Lab

Initialize a new Rails project

• Use rails new to make a new Rails project called matrix_app_api
• You'll also want to push this homework to your Github Enterprise account; be sure to commit often when prompted.
• Do it now!

Glitch?

• You forgot to use the --api flag? Can't really fix that.

Solution: Don't worry about it for now, just keep going!

Glitch?

• You forgot to make postgres the db with the -d flag? If you forget this, sqlite will be the default, and we don't want that. You could fix this by installing the pg gem and altering the database.yml file, but since you just made the app it would be easier to start over.

Solution: Delete your folder, do rails new again, and this time use postgresql.

Commit your work
The commit message should read:
"Commit 1: Initialized Rails server".

Run the Rails server

We haven't done this yet, but in Terminal, run the Rails server with rails s. The output in Terminal should look like:

In your browser, go to localhost:3000

You should see an error page:

If you remembered to set it up with the --api flag:

If you forgot the --api flag:

Glitch!

• The database does not exist

Solution: Quit the server with ctrl + c. Make the database with rails db:create

Commit your work
The commit message should read:
"Commit 2: Created the db".

Run migrations

Run your migrations with rails db:migrate.

Glitch!

• Nothing happens. That's because we did not first generate any migrations.

Solution: Generate migrations (instructions below)

Generate migrations

We are going to make a table for the database. The table will eventually hold information about characters from the Matrix movies.

Generate a migration to make the table:

rails g migration CreateCharacter

Even though Character is singular, go ahead and press enter to generate the migration.

Glitch!

• I realized that I don't want a table called character. I want a table called characters. It's proper to name the table with a plural of the resource.

Solution: Rails solved this for us automagically!

The migration file should look like this:

You can see that it's going to name the table characters anyway! Thanks, Rails.

Commit your work
The commit message should read:
"Commit 3: Created table migration".

Give details to migration file

I want my Matrix characters to have a name, description, and image url. All three will be strings. I'm going to try this in the migration file:

I'm going to ignore the fact that I spelled description wrong (desciption).

Run migrations

Run the migration to create the table:

rails db:migrate

Glitch!

• When I check the schema.rb file, I am disgusted to learn that I spelled description wrong.

Solution: Run another migration to change the column name (instructions below)

Make a corrective migration

I want to change the column in the schema called "desciption" to "description".

• Run a migration rails g migration FixDescriptionColumnTypo

The migration file should be an empty change method:

Good! No glitches, even though we called our migration FixSomething rather than ChangeSomething. It's all good, mates.

Add in rename_column:

def change
  rename_column :characters, :desciption, :description
end

Run the migration

Check migrations

• Check the schema.rb file.
• Check the db with rails dbconsole
• SELECT * FROM characters;

• \q to quit dbconsole.

Glitch?

• If other columns are not spelled correctly, run more migrations to fix the column names.

Commit your work
The commit message should read:
"Commit 4: Renamed the column".

Change table

Glitch!

I decided I want to name my entire table something other than characters. I want to call it matrix_characters because I might add in more movies to my app later, and want to be specific about which movie's characters I'm referencing.

Solution: Create another migration

rails g migration ChangeTableName

I can use a method called rename_table in the migration file:

class ChangeTableName < ActiveRecord::Migration[6.0]
  def change
    rename_table :characters, :matrix_characters
  end
end

Run the migration

• Check the schema.rb

Commit your work
The commit message should read:
"Commit 5: Changed table name".

Um, I changed my mind

Glitch!

I don't want the table to be called matrix_characters. I just want it to be called characters. I don't want or need the last migration, so can I get rid of it?

Solution:

• Undo the last migration with rails db:rollback
• Check that the schema.rb has "characters" as the table name, not "matrix_characters".

Glitch!

• If I ever run migrations again, it will rename my table again, because that migration file is sitting there ready to go. Ugh! I need to get rid of it!

Solution:

Destroy the migration with rails destroy migration <migration name>

Now the unnecessary migration should be gone. In the future, you could shorten the command to:

rails d migration <migration name>

Commit your work
The commit message should read:
"Commit 6: Rolled back and destroyed migration".

Seed the database

Open the file db/seeds.rb

The pattern for making a single entry is:

Model.create({ column: data, column: data })

Note that the Model name is capitalized and singular.

We can create many of a given Model using an array of entries. Copy this data into your seeds.rb file, an array of Matrix characters for our Character model (our table is called 'characters', so our model should be called 'Character' ... right?

Character.create([
	{ name: "Neo", description: false },
	{ name: "Trinity", description: false },
	{ name: "Morpheus", description: false },
	{ name: "Agent Smith", description: false },
])

To run the seed file:

rails db:seed

Glitch! 👾 Glitch! 👾 Glitch! 👾 Glitch! 👾 Glitch!

• We haven't defined what Character is, yet.
• Solution: Make a Character model to relate to our database (instructions below). Then, we can make ActiveRecord entries for the Character model.

Commit your work
The commit message should read:
"Commit 7: Failed to seed database"

Make a model

To make a model, first we need a model file.

Make a file in app/models called characters.rb

Can we seed our model yet? Run rails db:seed

Glitch!

• Character is still not recognized

Solution:

• Make a Character class. In characters.rb write in:

class Character

end

Can we seed our model yet? Run rails db:seed.

Glitch!

• Character is still not recognized.

Solution:

• Make the Character class inherit from ApplicationRecord (which, if you look in the application_record.rb file, you'll see that it inherits from ActiveRecord)

class Character < ApplicationRecord

end

Can we seed our model yet? Run rails db:seed

Glitch!

• Nope! Character is still an unrecognized constant.

Solution:

• Rename our model file. Remember, Rails favors convention over configuration. We have to stick to Rails' conventions or we'll be doomed. Rails wants the model files to be singular not plural.
• Rename characters.rb to character.rb.

Can we seed our model yet? Run rails db:seed.

Glitch?

• There should be no glitch! In fact, there should be nothing printed at all.

If you did get an error, keep trying to fix the glitch.

Check seed data in the db

Open rails dbconsole

SELECT * FROM characters;

Expected output:

If you have any glitches, fix them!

Commit your work
The commit message should read:
"Commit 8: Successfully seeded database"

The seed data is all wrong

Glitch!

• I don't like the seed data. There is an 'f' in the description columns instead of a description, and no data in the imgurl columns. _But if I run more seeds the old data will still be there. I kind of want to reset the whole db with new seed data.

Solution:

• This is kinda overkill, but you never know when you'll need to do this. Drop the databases, run all the migrations all over again and then re-seed the database from scratch. (Instructions below)

Change your seed data to have a (very) brief description of each Matrix character

Don't worry about the img_url for now

• Neo on Wikipedia
• Morpheus on Wikipedia
• Trinity on Wikipedia
• Agent Smith on Wikipedia
• Then, run rails db:reset

Expected output:

reset has dropped the databases, re-run the migrations, and re-seeded the databases.

Check that the db has seeded correctly inside rails dbconsole

SELECT * FROM characters;

\q to quit

Commit your work
The commit message should read:
"Commit 9: Reset database"

Active Record Queries

Open the Rails console:

rails c

Using Active Record queries, do the following:

• add an img_url to each of the Matrix characters
• delete Agent Smith
• add a new character: The Oracle

Commit your work
The commit message should read:
"Commit 10: Active Record queries"

Relations

• Make a second model, vehicles that has a column for name and style
• Seed a vehicle with a style "Spaceship", and name "Nebuchadnezzar"
• Change the characters table to have an integer field called vehicle_id
• In Rails console, associate Morpheus and Trinity with the Nebuchadnezzar

Commit your work
The commit message should read:
"Commit 11: Relations"

Hungry For More?

• Read through the documentation on Migrations Active Record Migrations
• Read about controllers to prepare you for your next lesson Rails controllers
• Implement an Index route that displays the JSON of all Matrix characters
• Implement a Show route that displays the JSON of a single Matrix character

Commit your work
The commit message should read:
"Commit 12: Implemented controller"