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ActiveRecord is an ORM. It's a layer of Ruby code that runs between your database and your logic code. When you need to make changes to the database, you'll write Ruby code, and then run "migrations" which makes the actual changes to the database.
The Relation Class. Having queries return an ActiveRecord::Relation object allows us to chain queries together and this Relation class is at the heart of the new query syntax. Let's take a look at this class by searching through the ActiveRecord source code for a file called relation.
ActiveRecord::Base indicates that the ActiveRecord class or module has a static inner class called Base that you're extending.
Active Record uses naming conventions for the columns in database tables, depending on the purpose of these columns. Foreign keys - These fields should be named following the pattern singularized_table_name_id (e.g., item_id , order_id ).
An ActiveRecord object lifecycle:
1.new record
item = Item.new
item.new_record? #=> true
2.persisted
item.save
item.persisted? #=> true
3.changed
item.name = "other"
item.changed? #=> true
4.destroyed
item.destroy
item.destroyed? #=> true
#new_record? does just that:
object.new_record?
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