An introduction to DataMapper

1. DataMapper
An Introduction

2. Similarities
• Associations
• Validations
• Migrations

3. Identity Map

4. @parent = Parent.first(:name => 'John')
@parent.children.each do |child|
child.parent.should == @parent
end
# => true

5. Properties

6. class User
include DataMapper::Resource
property :name, String, :index => true,
:nullable => false, :length => 30
property :email, String, :nullable => false,
:length => 255, :format => :email_address
property :password, String, :nullable => false
property :remarks, Text
end

7. Custom Types

8. Custom Data-types
• Csv
• Enum
• EpochTime
• FilePath
• Flag
• IPAddress
• URI
• Yaml
• Regex

9. Lazy Loading

10. class Post
..
property :body, Text, :lazy => false
property :summary, Text, :lazy => [:show]
property :subtitle, String, :lazy => [:show]
property :views, Integer, :lazy => [:count]
..
end

11. Multiple Repositories

12. class Page
include DataMapper::Resource
property :id, Serial
property :name, String
repository(:legacy) do
property :name, String, :field => 'title'
end
end
Page.all(:repository => :legacy)

13. Auto Validations

14. property :email, String, :length => 255, :nullable => false
# => email varchar(255) not null (create table SQL)
# => validate_present :email
# => validate_length :email, :max => 255

15. Migrations

16. • Auto Migrate
• Auto Upgrade
• Migration

17. Finding Records

18. exhibitions = Exhibition.all(:run_time.gt => 2, :run_time.lt => 5)
# => SQL conditions: 'run_time > 1 AND run_time < 5'

19. class Zoo
# all the keys and property setup here
def self.open
all(:open => true)
end
def self.big
all(:animal_count.gte => 1000)
end
end
big_open_zoos = Zoo.big.open

20. big_open_zoos = Zoo.all(:open => true).all(:animal_count.gte =>
1000)

21. big_open_zoos = Zoo.all(:open =>
true).all(:animal_count.gte => 1000)
# => This line of code generate zero sql
big_open_zoos.each do |zoo|
puts zoo.name
end
# => This generates one sql.

22. Kicker methods
• #each
• #first
• #last
• #count
• #map
• etc

23. Strategic Eager Loading

24. Query Path

25. Person.all(quot;addresses.street.likequot; => '%marina%')
SELECT quot;peoplequot;.quot;idquot;, quot;peoplequot;.quot;namequot;
FROM quot;peoplequot; INNER JOIN quot;addressesquot; ON
(quot;peoplequot;.quot;idquot; = quot;addressesquot;.quot;person_idquot;)
WHERE (quot;addressesquot;.quot;streetquot; LIKE '%marina%')
ORDER BY quot;peoplequot;.quot;idquot;

26. Questions?