The document describes how to create relationships between models in a Model-View-Controller framework. It discusses creating one-to-one, one-to-many, and many-to-many relationships between models using associations like belongs_to, has_many, and has_and_belongs_to_many. It also covers fetching, validating, saving, and deleting data from the database through the model layer.

1. How to create relationships
between models
MeetUP @ Balabit
June 17, 2010
nucc@balabit.com

2. Model View Controller
http://domain/:controller/:action?p1=v1&p2=v2
router
Model Controller View
HTML, XML, JSON, CSV, ...

3. Model & Database
class Product Table products
id name
Product object
1 scb
2 syslog-ng
3 zorp
Mysql, Pgsql, Sqlite,
Model layer Oracle, Mssql
(memory) (hard disk)

4. Creating a new row
1.
product = Product.new class Product
Table products
id name
2.
1 scb
product.name = “ssb”
2 syslog-ng
3. 3 zorp
product.save! / product.save validation 4 ssb
4. ...
error
Model Database
(memory) (disk)

5. Validating
class Product
validates_presence_of :name
validate :my_validator
def my_validator
if name.length < 3
errors.add :name, “is too short”
end
end
end

6. Built-in validators
validates_uniqueness_of :username
validates_presence_of :username, :password, :email
validates_size_of :username, :password, :within => 5..15
validates_format_of :email,
:with => /^([^@s]+)@((?:[-a-z0-9]+.)+[a-z]{2,})$/i
validates_format_of :username, :with => /^w+$/i,
:message => "can only contain letters and numbers."
validates_confirmation_of :password
validates_inclusion_of :gender, :in => %w(male female)
validates_acceptance_of :eula

7. Fetch information
class Product Table products
product = find_by_name(“scb”) id name
1 scb
2 syslog-ng
3 zorp
product.id 4 ssb
#1 ...

8. Find
Product.find :all == Product.all
Product.find :first == Product.first
Product.find :last == Product.last
Product.all( :limit => 10, :offset => 3, :select => “name”, :order => “name desc” )
Product.find(1, 5, 10)
Product.all( :conditions => { :name => ["scb", "zorp"] }, :readonly => true )
Product.find_by_name(“scb”)
Product.find_by_id_and_name(1, “scb”)
Product.find_by_sql(“SELECT * FROM products”)
Product.exists?( :name => “scb” )
Product.all :conditions => [“id = ? or name = ?”, 5, “scb”]
Product.all :conditions => [“id = :id or name = :name”, {:id => 5, :name => “scb”}

9. Destroy
scb = Product.find_by_name “scb”
scb.delete
Product.delete_all

10. How to create relations?

11. Relations
Product Owner
scb marci
ssb
class Product class Owner
belongs_to :product_owner has_many :products
end end
products owner
id name owner_id id name
1 scb 1 1 marci
2 ssb 1

12. Has and belongs to many
Developer Product
tia scb
gyp ssb
class Developer class Product
has_and_belongs_to_many :products has_one :owner
end has_and_belongs_to_many :developers
end
developers developers_products products
id name developer_id product_id id name owner_id
1 gyp 1 1 1 scb 1
2 tia 1 2 2 ssb 1

13. Questions?

14. Thank you!