From: George Moschovitis <gm@...>
Date: 2004-10-08T18:09:49+09:00
Subject: Re: [ANN] ndb Object-Relational Mapper

Kirk Haines wrote:
> On Fri, 8 Oct 2004 01:36:37 +0900, Brian Candler wrote
>>That's another O<->R mapping engine? Looks like there's a big 
>>ecosystem to choose from :-)
> In alphabetical order:
> Active Record, Criteria, Kansas, Lafcadio, ndb are the five that pop to mind 
> immediately.

There are many O<->R libraries out there, but let me point out where ndb 
is different:

ActiveRecord:
this seems to me to be an R->O mapping and not vice versa
i think this doesnt use standard ruby objects but something like OpenStruct.

Criteria:
Uses strange OO query objects

Lafcadio:
R->O again, you have to write sql definitnions

Kansas:
the same.

n/db:
- Uses STANDARD ruby objects ie (O->R mapping)

- You write NO SQL table definitions
(you can finetune the generated sql schema using a simple metalanguage 
in ruby)

- Because the managed objects are standard objects, you can use
inheritance or synthesize your objects using mixins. A number
of usefull mixins are provided (for example Child, SqlTreeTraversable
(graph preorder pattern) etc).

- You can optionally use a unified id space. Ie oids are allocated to
different classes of object from the same space. This allows you for
example code like the following:

class Article
....
end

class User
....
end

class Comment
....
end

a = Article.new
u = User.new

c1 = Comment.new
c1.set_parent(a)
$db << c1

c2 = Comment.new
c2.set_parent(a)
$db << c2

article_comments = $db.children(a, Comment)
user_comments = $db.children(u, Comment)

- you can automatically deserialize to ruby objects or to resultsets,
a future version will support deserialization to OpenStruct objects.

- nice support for SQL JOIN operations.

- moreover there are some optimizations (for example pregenerated 
insert/update/deserialize code for each managed class) and more
are coming in the next version (prepared statements, stored procedures).

- there are some more nice tricks for you to discover until I find time
to write proper documentation.

I hope more people will have a look at the code, and tell me about 
problems, and bugs or give suggestions and ideas for improvement.
Any cool ideas will be integrated in a future version.

regards,
George Moschovitis




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