dm-mapping (0)

Manipulate an existing database.

from Lin Jen-Shin
to DataMapper
cc godfat
date Sun, Jul 27, 2008 at 5:40 PM
subject Manipulate an existing database.
mailed-by gmail.com

Greetings,

DataMapper looks very promising for me, so I am thinking of
using it in the near future. I hate separate my domain objects into
two parts in Rails, writing migration and switching to ActiveRecord,
vice versa, is very annoying to me.

But there's a very convenient feature to me in ActiveRecord,
that is ActiveRecord automatically mapping all fields in a table.
It makes me easily control an existing database without any domain object.

For example,

  require 'active_record'

  ActiveRecord::Base.establish_connection(
    :adapter => 'sqlite3',
    :database => 'db/development.sqlite3'
  )

  clsas User < ActiveRecord::Base
  end

  User.find 1
  => #<User id: 1, account: "admin", created_at: "2008-05-18 20:08:37", etc.>

Some people would use database admin such as phpMyAdmin to
accomplish this kind of task, but I prefer anything in Ruby,
calling Ruby function, manipulating data without SQL and
any domain object. (i.e. I didn't have to load up entire environment.)

In DataMapper, I didn't find an easy way to accomplish this.
I am sorry if there's one but I didn't find it, please point out,
many thanks. In short, I would like to do this in DataMapper:

  class User
    include DataMapper::Resource
    mapping :account, :created_at
  end

or

  class User
    include DataMapper::Resource
    mapping All
  end

  class User
    include DataMapper::ResourceAll
  end

or

  class User
    include DataMapper::Resource
    mapping *storage_fields
  end

The above User.storage_fields should return an Array,
telling all the fields in the table, e.g. [:account, :created_at, :etc]
or a Hash includes data type, e.g. {:account => String,
                                    :created_at => DateTime}
then mapping *storage_fields should change to:

  mapping *storage_fields.each_key.to_a

If it's possible, a feature returning the database schema as well:

  DataMapper.repository.storages
  # => [:users, :posts, :etc]

  DataMapper.repository.storages_and_fields
  # => {:users => {:account => String},
        :posts => {:title => String, :content => Text}}

or returning DataObject::Field, DataObject::Storage, etc.

  DataMapper.repository.storage
  # => [#<DataObject::Storage @name='users' @fields=
         [#<DataObject::Field @name='account' @type=String>]>]

If you feel this kind of feature is indeed needed or not bad for
adding it, I could try to provide a patch for it. Though I didn't
read the source code deeply, not knowning it's easy or not.

sincerely,