DataMapper
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Matt
Aimonetti Me
irc: m a t t e t t i

Consultant Me
based in San Diego, CA

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

DataMapper
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DM
=
Object Relational Mapper

DataMapper ORM
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Databases
scalar values
da
ta
objects
Object Oriented
Languages

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

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

DataMapper
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Book.find( :all,
:conditions => [\"price > ?\", 100.00],
:order => \"title\" )
¿SQL/Ruby FAIL?

DataMapper
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DM is MORE THAN THAT

DataMapper identity map
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@parent = Parent.find_by_name(\"Bob\")
@parent.children.each do |child|
@parent.object_id.should == child.parent.object_id
end
FAILS with ActiveRecord
PASSES with DataMapper

DataMapper
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Does what ActiveRecord does
but differently

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

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

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

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

DataMapper Lazy loading + SEL
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SELECT * FROM \"zoos\"
SELECT * FROM \"exhibits\" WHERE
(\"exhibits\".zoo_id = 1)
SELECT * FROM \"exhibits\" WHERE
(\"exhibits\".zoo_id = 2)
SELECT * FROM \"exhibits\" WHERE
(\"exhibits\".zoo_id = 3)
4 requests
ActiveRecord

DataMapper Lazy loading + SEL
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SELECT \"id\", \"name\" FROM \"zoos\" ORDER BY \"id\"
SELECT \"id\", \"name\", \"zoo_id\" FROM \"exhibits\"
WHERE (\"zoo_id\" IN (1, 3, 2)) ORDER BY \"id\"
2 requests
DataMapper

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

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

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

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

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 => \"title\"
end

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

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

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

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

DataMapper Migrations
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automigrate
autoupdate
migration

DataMapper Custom Types
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Load / Dump

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

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 =>
\"%street%\" )
SELECT \"people\".\"id\", \"people\".\"name\" FROM \"people\"
INNER JOIN \"addresses\" ON (\"people\".\"id\" = \"addresses\".\"person_id\")
WHERE (\"addresses\".\"street\" LIKE '%street%')
ORDER BY \"people\".\"id\"

DataMapper Query::Path
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Find all people
with an address that
has street in the street name
Person.all(\"addresses.street.like\" =>
\"%street%\" )
SELECT \"people\".\"id\", \"people\".\"name\" FROM \"people\"
INNER JOIN \"addresses\" ON (\"people\".\"id\" = \"addresses\".\"person_id\")
WHERE (\"addresses\".\"street\" LIKE '%street%')
ORDER BY \"people\".\"id\"

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