What have you found for these years?


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


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'

:adapter => 'sqlite3',
:database => 'db/development.sqlite3'

clsas User < ActiveRecord::Base

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


class User
include DataMapper::Resource
mapping All

class User
include DataMapper::ResourceAll


class User
include DataMapper::Resource
mapping *storage_fields

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:

# => [:users, :posts, :etc]

# => {:users => {:account => String},
:posts => {:title => String, :content => Text}}

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

# => [#<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.


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