cheat sheets.

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
  wiki:     http://github.com/sam/dm-core/wikis

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_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))