ActiveRecord Mechanics

NB If you don't know the schema of your app, you don't know your app!

Object Relational Mapper
Model class
ORM means we have to keep the database and the Objects “in sync”
Rails/Sinatra server “modes” (technically they are environments)
rails server -e production (for Rails)
`set :environment, :development (for Sinatra)
Actually these modes are ActiveRecord modes!
Modes will affect what database to use, whether caching is enabled or not, and numerous other things
- development - working on your own computer, developing
- test - running tests
- production - working on Heroku for example

Library from Ruby on Rails which is the connection between the rails application and the underlying database
For advanced designs, there are options other than ActiveRecord
ActiveRecord is also often used by itself, especially in Sinatra
Naming
- Model.rb file is named singular, e.g. User
- Corresponding db table is plural and lower case, e.g. users
Correspondences
- Each instance of the class (e.g. User) corresponds to a single record in the database
- When a query returns a bunch of records, you get a collection of instances of the class
- (this is classic Active Record model)

Attributes
- Rails will automagically create the methods to access each field (column) of the record in the database
Two copies!
- Instance of the class, in memory
- Corresponding record in database
- One or the other or both may exist!
- Need to save, need to query, etc.
Datatypes supported by ActiveRecord
- ActiveRecord Datatypes
- ActiveRecord Migrations

NB: memory vs. persisted copy of the object
Create: create record and persist it
New: create model object without persisting it
Queries and other ways to access the database
- Rails ActiveRecord Queries
- ActiveRecord Guide for Queries
Updating
- Retrieve the object (.where etc), modify the attribute, and save it
Deleting
- Retrieve the object and .destroy (also class method .destroy_all)
Validations
- Rails Guide on ActiveRecord Validations