Generating Class Diagram from Models

Hi all!

There are several softwares which read a database and shows the
tables graphically on the screen (now I`m using Power Architect: Is there something which
beyond to read the tables, can understand the relationship beetween it
from app/models files? I say, has_many, belongs_to, etc...

Ok, I could use Power Architect to read the tables and make the arrows
by hand, but in a constant growing project, it is not a good way.

Thank You
Tom Lobato

Hi Tom,

You read my mind, I just was about to post identical question... when
I stumped upon some complicated models legacy models today.

Is there something like that out there?


Oh, alright. I guess it's way past time to get my updates to my
model_graph code ( packaged
up and posted. This reflects on the AR associations and builds a DOT
file that can be visualized with, e.g., Graphviz. (From there you can
export as PNG, PDF, etc.)


Thanks Rob!

That is great script, I didn't use Graphviz before so this was more
trouble than installing yor gem ;).

However, not sure if it's my fault - or library works like that,
generated graph was hard to read and analyze, it also didn't include
model attributes.

Googling for "ruby graphviz" was more successful:

Is really nice plugin, generates cool graphs. I just had to make
little fix for Rails 2.2 to work, but it's easy.


model_graph doesn't do the attributes on purpose. My need was to avoid redrawing the associations at a time on a particular project where they were driving me a bit crazy. The use of decorated edges to denote the kind of association is one thing that I didn't find elsewhere.

If you download the test file (or find it in the gem directory, I think)

and open it with Graphviz, you see the edge types that mean:

         class A < ActiveRecord::Base # :nodoc:
           has_many :bs
           has_one :c
         class B < ActiveRecord::Base # :nodoc:
           belongs_to :a
         class C < ActiveRecord::Base # :nodoc:
           belongs_to :a
         class One < ActiveRecord::Base # :nodoc:
           has_and_belongs_to_many :twos
         class Two < ActiveRecord::Base # :nodoc:
           has_and_belongs_to_many :ones
         class Alpha < ActiveRecord::Base # :nodoc:
           has_many :betas
           has_many :gammas, :through => :betas
         class Beta < ActiveRecord::Base # :nodoc:
           belongs_to :alpha
           belongs_to :gamma
         class Gamma < ActiveRecord::Base # :nodoc:
           has_many :betas
           has_many :alphas, :through => :betas
         class Selfish < ActiveRecord::Base # :nodoc:
           has_many :selfishes, :foreign_key => :solo_id

So a brief legend (in ASCII) would be:

  -| belongs_to
  -|o has_one
  -o< has_many
       dotted edge => has_many :through
  -o<<>>o- has_and_belongs_to_many
     (where <> is a small, unlabeled, diamond-shaped node)

Please do forward your fix for Rails 2.2!

Glad it helps a bit,


You can also try using RrailRoad ( I
find it pretty simple and neat. Note: It does not pick belongs_to
relationships and uses the has_many from the other direction for
figuring out relationships.