DRb and ActiveRecord


#1

Friends-

I am trying to make a drb server publish an ActiveRecord model so it

can be used by remote clients. It looks like I am getting close but
no cigar. Can some kind soul enlighten me as to how to make this
work? It seems like it is communicating with the remote AR model. And
I am able to create records and find records. But I am unable to
display the contents of the records on the client side. It seems like
drb is not unmarshaling them correctly. Do I need to use DRbUndumped
or something similar? Any help is greatly appreciated!

Here is my code and irb session:

server.rb

#!/usr/local/bin/ruby
require ‘rubygems’
require ‘drb/drb’
require_gem ‘activerecord’

ActiveRecord::Base.establish_connection(
:adapter => “mysql”,
:username => “root”,
:host => “localhost”,
:password => “reversal”,
:database => “switchboard_development”
)

class RemoteRecord < ActiveRecord::Base
end

DRb.start_service(“druby://:3500”, RemoteRecord)
puts DRb.uri
DRb.thread.join

And my irb session trying to access the remote model.

ezra:~ ez$ irb
irb(main):001:0> require ‘rubygems’
=> true
irb(main):002:0> require ‘drb/drb’
=> true
irb(main):003:0> require_gem ‘activerecord’
=> true
irb(main):005:0* DRb.start_service
=> #<DRb::DRbServer:0x137d3b0 @uri=“druby://ezra.local:61668”,
@idconv=#DRb::DRbIdConv:0x410d88, @front=nil, @config=
{:idconv=>#<DRb::DRbIdConv:
0x410d88>, :argc_limit=>256, :verbose=>false, :tcp_acl=>nil, :load_limit
=>26214400}, @thread=#<Thread:0x137d324 sleep>, @grp=#<ThreadGroup:
0x137d374>, @protocol=#<DRb::DRbTCPSocket:0x137d02c @uri=“druby://
ezra.local:61668”, @acl=nil, @config={:idconv=>#<DRb::DRbIdConv:
0x410d88>, :argc_limit=>256, :verbose=>false, :tcp_acl=>nil, :load_limit
=>26214400}, @msg=#<DRb::DRbMessage:0x137d004 @argc_limit=256,
@load_limit=26214400>, @socket=#TCPServer:0x137d0a4>>

irb(main):006:0> test = DRbObject.new(nil, ‘druby://ezra.local:3500’)
=> #<DRb::DRbObject:0x1379990 @ref=nil, @uri=“druby://ezra.local:3500”>

irb(main):009:0> test.create(:title => ‘Foo’, :desc => ‘Bar’)
=> #<DRb::DRbUnknown:0x13727f8 @buf="\004\010o:\021RemoteRecord\010:
\020@new_recordF:\f@errorso:\031ActiveRecord::Errors\a;\a{\000:
\n@base@\000:\020@attributes{\010"\ntitle"\010Foo"\aidi\010"\tdesc
“\010Bar”, @name=“RemoteRecord”>

irb(main):011:0> a = test.find :first
=> #<DRb::DRbUnknown:0x136dce4 @buf="\004\010o:\021RemoteRecord\006:
\020@attributes{\010"\ntitle"\010foo"\aid"\0061"\tdesc
“\010bar”, @name=“RemoteRecord”>

irb(main):012:0> p a
#<DRb::DRbUnknown:0x136dce4 @buf="\004\010o:\021RemoteRecord\006:
\020@attributes{\010"\ntitle"\010foo"\aid"\0061"\tdesc
“\010bar”, @name=“RemoteRecord”>
=> nil

irb(main):013:0> a.title
NoMethodError: undefined method `title’ for #DRb::DRbUnknown:0x136dce4
from (irb):13

So you can see it is almost working! title and desc are columns in
the database table. The records do get created fine in the db and it
seems to get the right records when I run a find on the model. I just
can’t figure out how to use the found object like a normal active
record. I mean I need to be able to display the attributes of the
record after I do a find and thats the part that is not working for me.

Thoughts? Clues? Derision?

Thanks-
-Ezra


#2

On 1/25/06, Ezra Z. removed_email_address@domain.invalid wrote:

 :username => "root",

DRb.thread.join
irb(main):005:0* DRb.start_service

=> #<DRb::DRbUnknown:0x136dce4 @buf="\004\010o:\021RemoteRecord\006:
NoMethodError: undefined method `title’ for #DRb::DRbUnknown:0x136dce4
from (irb):13

So you can see it is almost working! title and desc are columns in
the database table. The records do get created fine in the db and it
seems to get the right records when I run a find on the model. I just
can’t figure out how to use the found object like a normal active
record. I mean I need to be able to display the attributes of the
record after I do a find and thats the part that is not working for me.

Just a shot in the dark: does
a.send :title
work?


#3

Ezra Z. wrote:

Friends-

Advance warning: I am not a drb or ActiveRecord expert. I’m not much of
an expert on anything, come to think of it :slight_smile:

I am trying to make a drb server publish an ActiveRecord model so 

it can be used by remote clients.

class RemoteRecord < ActiveRecord::Base

You need to make this class undumped:

  include DRb::DRbUndumped

irb(main):009:0> test.create(:title => ‘Foo’, :desc => ‘Bar’)
=> #<DRb::DRbUnknown:0x13727f8 @buf="\004\010o:\021RemoteRecord\010:
\020@new_recordF:\f@errorso:\031ActiveRecord::Errors\a;\a{\000:
\n@base@\000:\020@attributes{\010"\ntitle"\010Foo"\aidi\010"\tdesc
“\010Bar”, @name=“RemoteRecord”>

DRbUnknown is your clue here. See:

http://www.ruby-doc.org/stdlib/libdoc/drb/rdoc/classes/DRb/DRbUnknown.html


irb(main):013:0> a.title
NoMethodError: undefined method `title’ for #DRb::DRbUnknown:0x136dce4
from (irb):13

Since “a” is a DRbUnknown object, it doesn’t have a title method; hence
the exception. You need drb to send over a proxy for the object so you
can send methods back to it. That’s what DRb::DRbUndumped does. After
you make that change, “a” will be a DRb::DRbObject, and the method calls
will be sent back to the server.

Or something like that…


#4

Bob-

Thank you very much. That was exactly what I needed and now it works

fine.

I appreciate it
-Ezra