Basic ActiveRecord

Let's write some ActiveRecord! Woo!

Setup

Fork and clone this repository
createdb basic_activerecord
Create a new Tracker project and import the stories in stories.csv
Work through stories

What we are working with

We will be working with four tables: customers, items, orders, and orderitems. These tables should be familiar. In fact, this whole exercise should be familiar, since the stories are the same ones we did when we started working with SQL.

The tables look like this:

customers

Column   |  Type   |                       Modifiers
---------+---------+--------------------------------------------------------
 id      | integer | not null default nextval('customers_id_seq'::regclass)
 name    | text    |
 email   | text    |
 address | text    |
 city    | text    |
 state   | text    |
 zipcode | text    |

items

 Column      |  Type   |                     Modifiers
-------------+---------+----------------------------------------------------
 id          | integer | not null default nextval('items_id_seq'::regclass)
 name        | text    |
 description | text    |

orders

 Column      |  Type   |                      Modifiers
-------------+---------+-----------------------------------------------------
 id          | integer | not null default nextval('orders_id_seq'::regclass)
 customer_id | integer |
 amount      | numeric |

orderitems

   Column  |  Type   |                        Modifiers
 ----------+---------+---------------------------------------------------------
  id       | integer | not null default nextval('orderitems_id_seq'::regclass)
  order_id | integer |
  item_id  | integer |

In the second story, you will insert a bunch of data into these tables so you have some data to work with for the exercise.

Enter ActiveRecord

So far, to talk to a database, we have been writing SQL queries by hand and using the #sql method to send our hand written queries to the database. Now we are going to let ActiveRecord handle the work of not only talking to the database but also generating the SQL to be executed as well.

There is an ActiveRecord model for each of the tables listed above.

lib/customer.rb
lib/item.rb
lib/order.rb
lib/orderitems.rb

Inside each of these files you will see an ActiveRecord class, similar to:

require "active_record"

class Customer < ActiveRecord::Base
end

We will use each of these ActiveRecord models throughout the exercise.

Try this before moving on: open the lib/exercise.rb file, and edit it so that it looks like this:

require "./lib/connection"

require "./lib/customer"
require "./lib/item"
require "./lib/orderitem"
require "./lib/order"

p Customer.all

To try this out, execute the lib/exercise.rb file:

|ruby-2.1.1@gschool| Hunters-MacBook-Pro in ~/gschool/dev/exercises/basic-activerecord
± |master ✗| → ruby lib/exercise.rb
#<ActiveRecord::Relation [#<Customer id: 1, name: "Donato Rempel", email: "ladarius@waelchi.org", address: "890 Ullrich Plains", city: "Janachester", state: "Virginia", zipcode: "77714">, #<Customer id: 2, name: "Tyrell Von DDS", email: "cleo_frami@bartondenesik.name", address: "63337 Abdullah Camp", city: "Verdieborough", state: "Colorado", zipcode: "69882-7027">, #<Customer id: 3, name: "Ms. Sofia Rowe", email: "jacky_funk@bayerprosacco.name", address: "1991 Kyler Village", city: "Opheliaborough", state: "Ohio", zipcode: "15599-5395">, #<Customer id: 4, name: "Evert Pfeffer", email: "alisa.luettgen@hoeger.org", address: "1311 Khalil Shores", city: "Port Ozella", state: "Arizona", zipcode: "34713">, #<Customer id: 5, name: "Elta Dicki", email: "lesly@heaney.org", address: "3878 Alyce Lock", city: "Deckowtown", state: "Montana", zipcode: "42114-6195">, #<Customer id: 6, name: "Zelma Davis", email: "osborne@mohr.biz", address: "184 Hazel Lane", city: "Alport", state: "Ohio", zipcode: "87119">, #<Customer id: 7, name: "Edna Hintz", email: "elisha_mclaughlin@pouros.biz", address: "2550 Hassan Pass", city: "North Kelliestad", state: "California", zipcode: "40909-5637">, #<Customer id: 8, name: "Coleman Prohaska Jr.", email: "taryn.becker@doyle.org", address: "32202 Zemlak Ridge", city: "Rigobertoside", state: "Colorado", zipcode: "95667-8653">, #<Customer id: 9, name: "Wilhelmine Huels", email: "alexander_rice@ornjakubowski.com", address: "44097 Elvie Divide", city: "West Lauryntown", state: "Maine", zipcode: "55164-9178">, #<Customer id: 10, name: "Hulda Will III", email: "ella_sanford@stracke.com", address: "3746 Ashton Divide", city: "Mikeberg", state: "Florida", zipcode: "22826">]>

If you see something similar, then you are good to go for the exercise.

Working through these stories

This exercise is set up so that you can edit the lib/exercise.rb file for each story. Each story should follow these steps:

Write the Ruby code you need to satisfy a story
Make a commit when you are done
Start the next story and erase the code you wrote for the previous story

Here is an example. One of the first stories is "display first 5 customers". There is a #limit method in ActiveRecord that we can use to limit the number of records returned.

require "./lib/connection"

require "./lib/customer"
require "./lib/item"
require "./lib/orderitem"
require "./lib/order"

p Customer.limit(5)

Try running that from the command line.

How do I know I have completed a story

We aren't going to write any automated tests for this exercise. However, you still want to make sure that you have successfully completed each story before moving on to the next one.

Just like when we are writing tests, it is a good idea to have an expectation for what the results for each story should be. If you are having a hard time seeing what results you'd expect for a story, you could try opening psql and writing the SQL by hand. Then when you write your query with ActiveRecord, you would make sure that the results that come back look the same.

What SQL is ActiveRecord executing?

One last tip. When you are debugging a story, you might want to see what SQL ActiveRecord is actually generating. You can do this using the #to_sql method. Here is an example using the "display first 5 customers" story in lib/exercise.rb.

require "./lib/connection"

require "./lib/customer"
require "./lib/item"
require "./lib/orderitem"
require "./lib/order"

puts Customer.limit(5).to_sql

Executing that Ruby script with ruby lib/exercise.rb gives you this output:

|ruby-2.1.1@gschool| Hunters-MacBook-Pro in ~/gschool/dev/exercises/basic-activerecord
± |master ✗| → ruby lib/exercise.rb
SELECT  "customers".* FROM "customers"  LIMIT 5

Because the script called the #to_sql, instead of executing the query we see the SQL string that ActiveRecord generated.

Getting Help

To see what methods are available, check out this ActiveRecord documentation:

http://guides.rubyonrails.org/active_record_querying.html

spencereldred/basic-activerecord