Overview of DataMapper and the differences between DM and other Ruby ORMs. Presentation given by Matt Aimonetti during MerbCamp 2008 in San Diego, CA.

1. DataMapper
i n 2 0 m i n

2. Matt
Aimonetti Me
irc: m a t t e t t i

3. Consultant Me
based in San Diego, CA

4. Blogs:
http://merbist.com
http://railsontherun.com

5. DataMapper
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DM
=
Object Relational Mapper

6. DataMapper ORM
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Databases
scalar values
da
ta
objects
Object Oriented
Languages

7. DataMapper
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SELECT *
FROM Book
WHERE price > 100.00
ORDER BY title;
Raw SQL statements FTL

8. DataMapper
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Book.all( :price.gt => 100.00,
:order => [:title.asc] )
Pure Ruby FTW

9. DataMapper
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Book.find( :all,
:conditions => [quot;price > ?quot;, 100.00],
:order => quot;titlequot; )
¿SQL/Ruby FAIL?

10. DataMapper
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DM is MORE THAN THAT

11. DataMapper identity map
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@parent = Parent.find_by_name(quot;Bobquot;)
@parent.children.each do |child|
@parent.object_id.should == child.parent.object_id
end
FAILS with ActiveRecord
PASSES with DataMapper

12. DataMapper
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Does what ActiveRecord does
but differently

13. DataMapper Data Objects
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Copyright - Merb in Action - Manning
db drivers using 1 unified interface

14. DataMapper Lazy loading
+
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Strategic Eager
Loader
Procrastination
becomes an
ORM value

15. DataMapper Lazy loading + SEL
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#first, #each, #count, #map...
DM only generates a query when encountering a kicker

16. DataMapper Lazy loading + SEL
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zoos = Zoo.all
zoos.each do |zoo|
zoo.exhibits.map{|e| e.name}
end

17. DataMapper Lazy loading + SEL
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SELECT * FROM quot;zoosquot;
SELECT * FROM quot;exhibitsquot; WHERE
(quot;exhibitsquot;.zoo_id = 1)
SELECT * FROM quot;exhibitsquot; WHERE
(quot;exhibitsquot;.zoo_id = 2)
SELECT * FROM quot;exhibitsquot; WHERE
(quot;exhibitsquot;.zoo_id = 3)
4 requests
ActiveRecord

18. DataMapper Lazy loading + SEL
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SELECT quot;idquot;, quot;namequot; FROM quot;zoosquot; ORDER BY quot;idquot;
SELECT quot;idquot;, quot;namequot;, quot;zoo_idquot; FROM quot;exhibitsquot;
WHERE (quot;zoo_idquot; IN (1, 3, 2)) ORDER BY quot;idquot;
2 requests
DataMapper

19. DataMapper Lazy load
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DM doesn’t load all properties for each request
unless required

20. DataMapper Multiple Repos
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production:
adapter: mysql
encoding: utf8
database: production-app
username: root
database.yml
password: top-s3ckit
host: localhost
repositories:
nightly_backup:
adapter: sqlite3
database: shared/nightly.db
weekly_backup:
adapter: sqlite3
database: shared/weekly.db

21. DataMapper Multiple Repos
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Article.copy(:default, :nightly_backup,
:created.gt => 1.day.ago )

22. DataMapper Multiple Repos
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Article.copy(:nightly_backup, :weekly_backup,
:created.gt => 1.week.ago )

23. DataMapper Legacy Data
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class Page
include DataMapper::Resource
property :id, Serial
property :name, String
repository(:legacy) do
property :name, String,
:field => quot;titlequot;
end

24. DataMapper Adapters
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Provide an interface between your
models
and
a data store.

25. DataMapper Adapters
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imap
file system
salesforce API
REST
couchdb
ferret
google video - http scraper

26. DataMapper Lazy Attributes
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google video - http scraper
DM adapter
80 LOC
only required to implement
- a read method
- handling query conditions

27. DataMapper Lazy Attributes
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Sales Force read-write
DM adapter
200 LOC

28. DataMapper Migrations
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automigrate
autoupdate
migration

29. DataMapper Custom Types
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Load / Dump

30. DataMapper Plugins
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modular structure
migration, validation, model factory, state
machine, constraints, lists, tagging...
DM facilitates extensions by offering nice hooks

31. DataMapper Query::Path
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Find all people
with an address that
has street in the street name
Person.all(Person.addresses.street.like =>
quot;%street%quot; )
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 '%street%')
ORDER BY quot;peoplequot;.quot;idquot;

32. DataMapper Query::Path
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Find all people
with an address that
has street in the street name
Person.all(quot;addresses.street.likequot; =>
quot;%street%quot; )
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 '%street%')
ORDER BY quot;peoplequot;.quot;idquot;

33. DataMapper
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Credits
people who helped with this presentation:
dbussink, dkubb, afrench, wycats