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Active Record Warmup: Movie Buff In Training!

This homework is a chance to dip your toes into Active Record and explore the data before you have to handle more complicated queries tomorrow.

How to Run the Project

  • Clone the skeleton repo accessed through the Download Project button below.
  • Navigate to your local version of the skeleton.
  • Make sure Postgres is running.
  • Run bundle install and ./setup.
    • If you get a permission error, run chmod +x setup and then ./setup again.

Do your work in movie_novice/queries.rb. Information on the tables you will be querying can be found at the top of the file.

Run bundle exec rspec to test.

You can manually test queries in the rails console. All queries should be written in Active Record. If you want to test some SQL code directly, run rails dbconsole to pull up a psql session with your development database loaded. (See below for an example.)

Note:

  • Active Record queries have two methods, to_sql and as_json, that you might find helpful for debugging.

    • to_sql outputs the raw SQL query that Rails will generate from your Active Record query. You can then use this SQL query in your psql console for testing. When using to_sql in pry, precede your query with puts: this will remove formatting characters for easy copy-pasting and will allow you to paste multi-line, chained expressions. So, e.g., you could run the following command in the Rails console (rails c):

      [1] pry(main)> puts Actor.where(name: "Harrison Ford").to_sql
SELECT "actors".* FROM "actors" WHERE "actors"."name" = 'Harrison Ford'
=> nil

      You could then copy the SELECT line, run rails dbconsole, and paste it in:

      movie_buff_in_training_development=# SELECT "actors".* FROM "actors" WHERE "actors"."name" = 'Harrison Ford';
 id |     name      |         created_at         |         updated_at         
----+---------------+----------------------------+----------------------------
  6 | Harrison Ford | 2021-12-02 05:30:59.543374 | 2021-12-02 05:30:59.543374
(1 row)

    • as_json converts query results into more readable Arrays and Hashes; the specs use this method -- feel free to refer to them while writing your queries.

  • find, find_by, find_by_#{attribute}, etc., all return the first matching instance from the database; where returns a collection of instances, regardless of the number. Be careful about whether you are expecting the object itself or a collection-wrapped object / set of objects.