Dm Intro

DataMapperAn Introduction

Similarities

• Associations

• Validations

• Migrations

Identity Map

@parent = Parent.first(:name => 'John')

@parent.children.each do |child| child.parent.should == @parentend

# => true

Properties

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

Custom Types

Custom Data-types

• Csv

• Enum

• EpochTime

• FilePath

• Flag

• IPAddress

• URI

• Yaml

• Regex

Lazy Loading

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

Multiple Repositories

class Page include DataMapper::Resource property :id, Serial property :name, String

repository(:legacy) do property :name, String, :field => 'title' endend

Page.all(:repository => :legacy)

Auto Validations

property :email, String, :length => 255, :nullable => false

# => email varchar(255) not null (create table SQL)# => validate_present :email# => validate_length :email, :max => 255

Migrations

• Auto Migrate

• Auto Upgrade

• Migration

Finding Records

exhibitions = Exhibition.all(:run_time.gt => 2, :run_time.lt => 5)

# => SQL conditions: 'run_time > 1 AND run_time < 5'

class Zoo # all the keys and property setup here def self.open all(:open => true) end

def self.big all(:animal_count.gte => 1000) endend

big_open_zoos = Zoo.big.open

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

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.nameend# => This generates one sql.

• #each

• #first

• #last

• #count

• #map

• etc

Kicker methods

Strategic Eager Loading

Query Path

Person.all("addresses.street.like" => '%marina%')

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

Questions?