cheat datamapper

DataMapper, the ruby object relational mapper
website: http://www.datamapper.org
git: git://github.com/sam/dm-core.git
mail: http://groups.google.com/group/datamapper
now: http://www.twitter.com/datamapper

Setting up a Connection
DataMapper.setup(:default, “adapter://user:password@hostname/dbname”)
supported adapters: mysql, sqlite3, postgres, sqlite3::memory:
additional adapters are in dm-more, (couchdb, rest, imap, file, saleforce…)

Creating a Model (with properties)
class Zoo
include DataMapper::Resource
property :id, Serial
end

Properties
property :id, Serial # auto-incrementing PK
property :name, String, :key => true # natural key
# you must specify >= 1 key, CPK support 100%

# available data-types
property :description, Text # (lazy by default)
property :created_at, DateTime
property :open, Boolean
property :admission, BigDecimal

# require dm-types for Csv, Enum, EpochTime, FilePath, Flag,
# IPAddress, URI, Yaml

Property Options (pass as hash)
:default, :nullable, :field (column name), :size, :length, :format,
:index, :unique_index, :ordinal, :auto_validate, :precision,
:scale, :accessor, :reader, :writer, :lazy

Finders
Zoo.get(PK_HERE)
Zoo.first({see_below})
Zoo.all({see_below})

Finder Options (pass as hash)
:conditions => ["property = ? and property = ?", 'value', 'value']
:conditions => {:property => ‘value’, …}
:property => ‘ZooNameHere’
# any non-standard key => value pair is assumed a condition if not
# otherwise recognized
:property.lte => 12.00 # <=
.gte # >=
.gt # >
.lt # <
.not # NOT =
.like # LIKE
.in # IN ()
'class.property' => ‘value’
Class.relationship.property => ‘value’ # will automatically issue JOINS

Finder Gotcha
:order => [:created_at.desc, ...] # descending sort
.asc # ascending

Associations
has 1 # has_one
has n # has_many
belongs_to :things
has n, :things, :through => :more_things
has n, :things, :through => Resource # has_and_belongs_to_many

Association Options
(any Finder Options)
:class_name => ‘ClassNameHere’
:order => [:property.desc]
:child_key => [:property, ...]
:through => :other_association

Validations (require ‘dm-validations’)
validates_present :title
validates_is_number :rating
validates_format :email, :as => :email_address
validates_length :summary, :in => (1..100)
validates_is_unique :slug
validates_with_method (do…end, :method_name)

Callbacks AKA “Hooks”
Object-level
before :method_name, (do…end, :another_method_name)
after :method_name, (do…end, :another_method_name)
Class-level
before_class_method :method_name, (do…end, :another_method_name)
after_class_method :method_name, (do…end, :another_method_name)

Callbacks Gotcha
Hooks act on ’self’ and aren’t passed an arguement
’self’ for object-level hooks are the instance
’self’ for class-level hooks are the class itself

Misc. Stuff & Gotchas
Single Table Inheritance
property :type, Discriminator # then inherit from this model

Paranoia
property :deleted_at, ParanoidDateTime
property :deleted, ParanoidBoolean

Multiple DB Connections
DataMapper.setup(:external, “adapter://username:password@hostname/dbname”)
repository(:external) do…end
Association: has n, :things, :repository => repository(:external)
Finder: Thing.all(:repository => repository(:external))