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ActiveRecord and Database Design

1) FilmFile and ActiveRecord (~1-2 hours)

  1. Using a migration, add a new table to Film File for directors. The only attribute of a director is a name. A film belongs to a director and a director can have many films. Don't forget to add a foreign key of director_id to the films table.

  2. Run your migration. Check to see that schema.rb was updated properly.

  3. From the command line, start Tux:

$ tux

Tux gives you an interactive console for your app. Go ahead and add some data to your database:

james = Director.create(name: "James Cameron")
colin = Director.create(name: "Colin Trevorrow")
joss = Director.create(name: "Joss Whedon")
christopher = Director.create(name: "Christopher Nolan")
george = Director.create(name: "George Lucas")
lee = Director.create(name: "Lee Unkrich")

Associate the existing films in your database with their respective directors. If you don't know any movie directors (like me), check out IMDB All-Time Box Office: USA.

Experimenting with Built-in ActiveRecord Methods

What does this do? What table is affected?

>> genre = Genre.find(2)
>> genre.films.create(title: "Avengers: Age of Ultron", year: 2015, box_office_sales: 458991599, director_id: 3)

What about this?

>> director = Director.first
>> film = Film.create(title: "Terminator 2: Judgment Day", year: 1991, box_office_sales: 204843350, genre_id: 2)
>> director.films << film

  • What's the difference between Genre.new(name: "Anime") and Genre.create(name: "Anime")? Play around with Tux and your development environment (use shotgun to see your web interface) to investigate the difference. How does the save method play into the relationship between new and create? What about the new_record? method? You may also want to do some Googling.

  • What kind of object does Genre.all return?

  • How can you get a count of all of the Directors?

  • How do you grab the first Film? What about the last?

  • Can you select all films where the director_id is 3? Try Film.where(... or Director.find(...

  • What's the difference between the query above and Film.find_by(director_id: 3)?

  • Can you select the genre with a specific id? Try Genre.find(...

  • What does Director.find_or_create_by(name: "James Cameron") do? What about Director.find_or_create_by(name: "Mel Gibson")?

  • Try calling .to_sql on the end of the query Genre.where(name: "Romance").to_sql. What happens?

  • What does Film.pluck(:title) do? Can you generate a query to return only the task titles?

  • Go through the ActiveRecord docs and find three other methods to try out.

Calculations

  • Create a route in your controller for /directors/:id. This should prepare an instance variable for the director @director = Director.find(id) and render a view with all films associated with that director.
  • In this view, display the total gross box office sales for that director's films. Hint: Use the ActiveRecord Calculations Documentation
  • Display the average gross box office sales for that director's films. Use the documentation linked above.
  • I'm not judging, but you probably wrote these calculations right in your view. Can you extract these out to a class method in film so that you can call something more beautiful like @director.films.total_sales? (Yes, total_sales will be a class method on Film. Any class methods defined in a class that inherits from ActiveRecord::Base are also available on associations.)

Extension

  • Change out the sqlite database for a postgres database.

2) FilmFile and CRUD

Add the CRUD functionality for films. A user should be able to see all the films, create a new film, see an individual film, update a film, and delete a film.