Models represent database tables and contain business logic and object rules. A model is generated using a generator command and tied into the Rails infrastructure using migrations and the schema file. Models allow CRUD (create, read, update, delete) actions on data through ActiveRecord methods. Validations add rules to ensure data integrity.

1. Model Basics
Business Logic Goes Here

2. What is a Model?
It’s a Ruby Object
Home of your business logic and object rules
ActiveRecord
The layer in Rails that talks to the database
Gives you a lot of conventional tools to make manipulating data easy
Home of CRUD
create, read, update and delete

3. Think Model - Think Table
id Name Age
1 Gypsy 12
2 Storm 14

4. Think Model - Think Table
The Model as a whole
id Name Age
is an object
Calling a method on the
model effects all data in the
model 1 Gypsy 12
2 Storm 14

5. Think Model - Think Table
The Model as a whole
id Name Age
is an object
Calling a method on the
model effects all data in the
model 1 Gypsy 12
A record in the model
is also an object
Calling a method on a record 2 Storm 14
effects only that record

7. How do I
get one?

8. How do I
get one?
Easy!
Become one with
ruby script/generate
in your console!

9. Tell the generate
command what you
How do I want to generate and
get one? you can even add in
fields.
Easy!
Become one with $ ruby script/generate model
user name:string
ruby script/generate address:string age:integer
admin:boolean
in your console!

10. class CreateUsers < ActiveRecord::Migration
def self.up
create_table :users do |t|
t.string :name
t.integer :age
t.string :address
t.boolean :admin
t.timestamps
end
end
def self.down
drop_table :users
end
end
What happens after generate?
Rails creates a file representing the new model
you just created called a migration.

11. class CreateUsers < ActiveRecord::Migration
def self.up
create_table :users do |t|
t.string :name
t.integer :age
t.string :address
t.boolean :admin
t.timestamps
end
end
def self.down
drop_table :users
end
end
What happens after generate?
Rails creates a file representing the new model
you just created called a migration.

12. Magic Fields

13. Magic Fields
Rails adds a few magic fields to your model

14. Magic Fields
Rails adds a few magic fields to your model
id - this is the record’s unique id. Every model has
one, even though it doesn’t appear in the migration

15. Magic Fields
Rails adds a few magic fields to your model
id - this is the record’s unique id. Every model has
one, even though it doesn’t appear in the migration
timestamps

16. Magic Fields
Rails adds a few magic fields to your model
id - this is the record’s unique id. Every model has
one, even though it doesn’t appear in the migration
timestamps
created_at - puts a time stamp when a new record
is created

17. Magic Fields
Rails adds a few magic fields to your model
id - this is the record’s unique id. Every model has
one, even though it doesn’t appear in the migration
timestamps
created_at - puts a time stamp when a new record
is created
updated_at - puts a time stamp when a record is
changed

18. So I have this migration.
Now what?
Generating the model
is half the battle
Now you have to tie it
into the Rails
infrastructure
How? Why, run a rake
task, of course!

19. Rake

20. Rake
Infrastructure that helps
you run common tasks
in Rails easily.
migrations, run tests
and many more

21. Rake
Infrastructure that helps
you run common tasks
in Rails easily.
migrations, run tests
and many more
Completely customizable
- create your own rake
tasks

22. Rake
Infrastructure that helps For a list of all the rake
you run common tasks commands, just run
in Rails easily. $ rake -T
migrations, run tests
and many more
Completely customizable
- create your own rake
tasks

23. Rake
Infrastructure that helps For a list of all the rake
you run common tasks commands, just run
in Rails easily. $ rake -T
migrations, run tests
To execute your
and many more
beautifully crafted
Completely customizable migration, just run
- create your own rake
tasks $ rake db:migrate

24. A bit more about Migrations
$ script/generate migration add_email_to_users
add_column() takes
the model name, field
name and data type class AddEmailToUsers <
ActiveRecord::Migration
def self.up
add_column :users, :email, :string
self.down will revert to end
the pre-migrated state def self.down
remove_column :users, :email
end
use the same rake end
db:migrate to execute
command

25. ActiveRecord::Schema.define(:version => 20100301045108) do
create_table "users", :force => true do |t|
t.string "name"
t.integer "age"
t.string "address"
t.boolean "admin"
t.datetime "created_at"
t.datetime "updated_at"
end
end
Meet the Schema file
Rails generates a ‘map’ of your database.This is
the map after the initial model generation

26. create_table "users", :force => true do |t|
t.string "name"
t.integer "age"
t.string "address"
t.boolean "admin"
t.datetime "created_at"
t.datetime "updated_at"
t.string "email"
end
Schema after migration
Each migration updates and replaces the existing
schema

27. create_table "users", :force => true do |t|
t.string "name"
t.integer "age"
t.string "address"
t.boolean "admin"
t.datetime "created_at"
t.datetime "updated_at"
t.string "email"
end
Schema after migration
Each migration updates and replaces the existing
schema

28. Let’s play with some CRUD

29. Let’s play with some CRUD
CRUD stands for Create, Read, Update and Delete

30. Let’s play with some CRUD
CRUD stands for Create, Read, Update and Delete
These are the heart of ActiveRecord and the primary
purpose of the model

31. Let’s play with some CRUD
CRUD stands for Create, Read, Update and Delete
These are the heart of ActiveRecord and the primary
purpose of the model
Between these four actions, you can accomplish pretty
much anything in your database

32. C is for Create

33. C is for Create
Create - adds an
object to the database

34. C is for Create
Create - adds an
object to the database
user = User.new(:name => "Gypsy",
Two common ways of :age => 12)
user.save
achieving this are with
new() and save() or
create()

35. C is for Create
Create - adds an
object to the database
user = User.new(:name => "Gypsy",
Two common ways of :age => 12)
user.save
achieving this are with
new() and save() or user = User.create(:name => "Storm",
create() :age => 14)
create() is a combined
new() and save()

36. R is for Read
Read - Retrieves an
object from the
user = User.find(1) # by id
database => #<User id: 1, name: "Gypsy", age: 12>
user = User.first # first record
You can find virtually => #<User id: 1, name: "Gypsy", age: 12>
anything using user = User.last # last record
=> #<User id: 2, name: "Storm", age: 14>
ActiveRecords find
methods

37. Some more Read methods
user = User.find_by_name("Storm")
You can pass in => #<User id: 2, name: "Storm", age: 14, >
arguments to find_by() users = User.all # returns an array of all users
=> [#<User id: 1, name: "Gypsy", age: 12>,
#<User id: 2, name: "Storm", age: 14>]
You an also use SQL to user = User.all(:order => 'age DESC')
=> [#<User id: 2, name: "Storm", age: 14>,
locate data within #<User id: 1, name: "Gypsy", age: 12>]
specific criteria user = User.first(:conditions => 'age > 12')
=> #<User id: 2, name: "Storm", age: 14>

38. U is for Update
Update - saves existing
object with new data user.update_attributes(
:age => 15,
update_attributes() => true
:email => "storm@gmail.com")
takes in a Hash of => #<User id: 2, name: "Storm", age: 15,
email: "storm@gmail.com">
attributes and saves
them to the database

39. D is for Delete
Delete - removes
object from database user = User.find_by_name("Gypsy")
user.destroy
This is an all or nothing User.find_by_name("Gypsy")
=> nil
deal. Once it’s gone,
it’s really gone.

40. Fetching and updating
individual attributes
>> user = User.find(2)
Rails will let you fetch a => #<User id: 2, name: "Strom",
age: 15>
specific attribute of an >> user.name
=> "Strom"
object >> user.name = "Storm"
=> "Storm"
it will also let you >> user.save
=> true
manipulate that single >> user = User.find(2)
=> #<User id: 2, name: "Storm",
attribute age: 15>

41. Model Objects
id Name Age
1 Gypsy 12
2 Storm 14

42. Model Objects users = User.all
id Name Age
1 Gypsy 12
2 Storm 14

43. Model Objects users = User.all
id Name Age
user = User.first(:conditions => 'age > 12') 1 Gypsy 12
2 Storm 14

44. Model Objects users = User.all
id Name Age
user = User.first(:conditions => 'age > 12') 1 Gypsy 12
user = User.find_by_name("Storm") 2 Storm 14

45. class User < ActiveRecord::Base
###################
### Validations ###
###################
validates_presence_of :name
validates_uniqueness_of :name
end
Validations
Putting rules on the way your data should
behave in Rails

46. Validation Power

47. Validation Power
Adding validations ensures you get the data you are
expecting

48. Validation Power
Adding validations ensures you get the data you are
expecting
Enforces certain rules and expectations so you can
count on them later

49. Validation Power
Adding validations ensures you get the data you are
expecting
Enforces certain rules and expectations so you can
count on them later
Rails has several predefined validations

50. Validation Power
Adding validations ensures you get the data you are
expecting
Enforces certain rules and expectations so you can
count on them later
Rails has several predefined validations
validates_uniqueness_of, validates_presence_of,
validates_numericality_of, validates_format_of, etc

51. validates_format_of :email,
:with => /A[^s@]+@[^s@]+.[^s@]+z/,
:message => "is not a valid address"
validates_presence_of :name, :age
Always call the type of validation followed by the
method or methods and any additional rules,
such as formatting and messages

52. Custom Validations
validate :age_must_be_less_than_30
You can also define
def age_must_be_less_than_30
your own rules. Just if age > 30
errors.add_to_base("Age must be
call validate and the less than 30")
name of the method end
end

53. >> user = User.new(:name => "Tipper", :age => 45)
=> #<User id: nil, name: "Tipper", age: 45>
>> user.save
=> false
>> user.errors.full_messages
=> ["Age must be less than 30"]
Validation explosion
When a record won’t save, calling
errors.full_messages will show you what went wrong

54. Questions?

55. Starting a Database Lab
Your book has instructions for building your first
models with validations and creating some data