Since the gem appends its root route as the last route here:
https://github.com/amatsuda/erd/blob/master/lib/erd/railtie.rb#L14

It might not be picked up properly if you have other wildcard routes preceding it.
Simply by updating the line to prepend the route into the route list fixes the issue.

FYI, by pulling in that dependency, my understanding is you cannot release this code under the MIT license.

https://github.com/ioquatix/graphviz is an alternative using the MIT license.

Hey Akira!

Got this error on my Mac OS X 10.9.3:
Stack overflow in regexp matcher: /^node ([^ ]+) ([0-9\.]+) ([0-9\.]+) ([0-9\.]+) ([0-9\.]+) <\{?(<((?!^\}?>).)*)^\}?> [^ ]+ [^ ]+ [^ ]+ [^ ]+\n/m
Here is the full stacktrace:
http://pastie.org/9350927

ruby v='1.8.7'
rails v='3.1.12'

I get the following messages with Rails 5.2.2:

DEPRECATION WARNING on line 28 of gems/erd-0.6.0/app/assets/stylesheets/erd/erd.css.scss:
The operation `#eeeeee minus 30` is deprecated and will be an error in future versions.
Consider using Sass's color functions instead.
http://sass-lang.com/documentation/Sass/Script/Functions.html#other_color_functions

DEPRECATION WARNING on line 128 of gems/erd-0.6.0/app/assets/stylesheets/erd/erd.css.scss:
The operation `#fffebe minus 6` is deprecated and will be an error in future versions.
Consider using Sass's color functions instead.
http://sass-lang.com/documentation/Sass/Script/Functions.html#other_color_functions

DEPRECATION WARNING on line 375 of gems/erd-0.6.0/app/assets/stylesheets/erd/erd.css.scss:
The operation `#444444 plus 50` is deprecated and will be an error in future versions.
Consider using Sass's color functions instead.
http://sass-lang.com/documentation/Sass/Script/Functions.html#other_color_functions

DEPRECATION WARNING on line 400 of gems/erd-0.6.0/app/assets/stylesheets/erd/erd.css.scss:
The operation `#444444 minus 10` is deprecated and will be an error in future versions.
Consider using Sass's color functions instead.
http://sass-lang.com/documentation/Sass/Script/Functions.html#other_color_functions

DEPRECATION WARNING on line 422 of gems/erd-0.6.0/app/assets/stylesheets/erd/erd.css.scss:
The operation `white minus 6` is deprecated and will be an error in future versions.
Consider using Sass's color functions instead.
http://sass-lang.com/documentation/Sass/Script/Functions.html#other_color_functions

DEPRECATION WARNING on line 490 of gems/erd-0.6.0/app/assets/stylesheets/erd/erd.css.scss:
The operation `white minus 20` is deprecated and will be an error in future versions.
Consider using Sass's color functions instead.
http://sass-lang.com/documentation/Sass/Script/Functions.html#other_color_functions

Platform:
OS: Mac OS X
Ruby: 1.9.3
Rails: 3.0.5
Graphviz: 2.30.1

Got error:
undefined methodisolate_namespace' for Erd::Engine:Class`

Not sure if this gem is still begin actively developed but I received this error on hitting localhost:3000/erd.

Running Mavericks, Ruby 2.1, Rails 4.1beta, latest Grahpviz from Homebrew.

Saving diagram failed! Graphviz produced errors. Verify it has support for filetype=plain, or use filetype=dot. Original error: 2014-01-31 09:24:41.027 dot[37149:d07] CoreText performance note: Client called CTFontCreateWithName() using name "Arial Italic" and got font with PostScript name "Arial-ItalicMT". For best performance, only use PostScript names when calling this API.

With rails-3.2.12 and erd-0.3.0, rails cannot bootstrap in RAILS_ENV=test.

For example, rails c test causes an error below:

erd-0.3.0/app/controllers/erd/models_controller.rb:6: syntax error, unexpected '<', expecting keyword_end (SyntaxError)
      <%= render :partial => 'erd/erd/model', :object => model -%>

# Gemfile
group :development, :test do
  gem 'erd'
end

But, with rails 4.0.0, it works fine.

Can I export erd diagram as pdf?
Thanks

ArgumentError in Erd::ErdController#index
comparison of NilClass with 0 failed
Extracted source (around line #140):

      }.compact
      max_model_x = models.map {|m| m[:x].to_f + m[:width].to_f }.max
      erd_width = [[(BigDecimal(svg_width) * 72).round, max_model_x].min + 150, 1024].max
      max_model_y = models.map {|m| m[:y].to_f + m[:height].to_f }.max
      erd_height = [[(BigDecimal(svg_height) * 72).round, max_model_y].min + 150, 768].max
      # edge tail head n x1 y1 .. xn yn [label xl yl] style color

Some companies will only use gems with a certain license.
The canonical and easy way to check is via the gemspec
via e.g.

spec.license = 'MIT'
# or
spec.licenses = ['MIT', 'GPL-2']

Bundler now generates gems with a default 'MIT' license. There is even a License Finder
to help companies ensure all gems they use meet their licensing needs. This tool depends on license information being available in the gemspec.
Including a license in your gemspec is a good practice, in any case.

If you need help choosing a license, github has created a license picker tool

How did I find you?

I'm using a script to collect stats on gems, originally looking for download data, but decided to collect licenses too,
and make issues for gemspecs not specifying a license as a public service :)
So far it's going pretty well.
I've written a blog post about it

Just began testing with the below fixes, so no guarantees.

1. Asset names passed to helpers should not include the "/assets/" prefix.
   The error points to app/views/erd/erd/erd.html.erb. I can generate the pdf diagram ok by running 'erd' from the Rails-Root folder. This code pattern has now been made breaking** in Rails 4.2, and affects many files within the gem's install folder. The first to fail was /erd-0.4.0/app/views/erd/erd/_model.html.erb.

My fix was to run the following (adjust to your gem install path):
find .../.rvm/gems/ruby-2.2.1/gems/erd-0.4.0/app/views/erd/erd/ -type f -exec sed -i 's#/assets/erd/#/erd/#g' {} +
find .../.rvm/gems/ruby-2.2.1/gems/erd-0.4.0/app/assets/javascripts/erd/ -type f -exec sed -i 's#/assets/erd/#/erd/#g' {} +
find .../.rvm/gems/ruby-2.2.1/gems/erd-0.4.0/app/assets/stylesheets/erd/ -type f -exec sed -i 's#/assets/erd/#/erd/#g' {} +
find .../.rvm/gems/ruby-2.2.1/gems/erd-0.4.0/vendor/assets/stylesheets/ -type f -exec sed -i 's#/assets/erd/#/erd/#g' {} +

2. 'Asset filtered out and will not be served:' error.
   This can be fixed by putting the following in /config/initializers/assets
   Rails.application.config.assets.precompile += %w( erd/* )

BTW - great gem, and thank you for creating something that should have been built into Rails since at least version 1.1 - I had this core Gui-functionality at my fingertips 20+ years ago in other environments. Cheers!

** I am not sure why the Rails team thinks it is so imperative to break working, readable code - disregarding thousands of hours of others' lives and making Rails coders look slow and buggy in so doing. Backwards compatibility for reasonable, 5 year periods, would reflect app-lifespans. Maybe they can create their own "Fedorails" to "play" on, and let the rest of us serve our clients?

[2012-05-01 09:46:34.636] FATAL NoMethodError (undefined method name' for nil:NilClass): rails-erd (0.4.5) lib/rails_erd/domain.rb:102:inblock (2 levels) in relationships_mapping'
rails-erd (0.4.5) lib/rails_erd/domain.rb:100:in each' rails-erd (0.4.5) lib/rails_erd/domain.rb:100:inblock in relationships_mapping'
rails-erd (0.4.5) lib/rails_erd/domain.rb:99:in tap' rails-erd (0.4.5) lib/rails_erd/domain.rb:99:inrelationships_mapping'
rails-erd (0.4.5) lib/rails_erd/domain.rb:77:in relationships_by_entity_name' rails-erd (0.4.5) lib/rails_erd/domain/attribute.rb:58:inforeign_key?'
rails-erd (0.4.5) lib/rails_erd/domain/attribute.rb:40:in content?' rails-erd (0.4.5) lib/rails_erd/diagram.rb:178:inblock (2 levels) in filtered_attributes'
rails-erd (0.4.5) lib/rails_erd/diagram.rb:178:in each' rails-erd (0.4.5) lib/rails_erd/diagram.rb:178:innone?'
rails-erd (0.4.5) lib/rails_erd/diagram.rb:178:in block in filtered_attributes' rails-erd (0.4.5) lib/rails_erd/diagram.rb:175:inreject'
rails-erd (0.4.5) lib/rails_erd/diagram.rb:175:in filtered_attributes' rails-erd (0.4.5) lib/rails_erd/diagram.rb:129:inblock in generate'
rails-erd (0.4.5) lib/rails_erd/diagram.rb:128:in each' rails-erd (0.4.5) lib/rails_erd/diagram.rb:128:ingenerate'
rails-erd (0.4.5) lib/rails_erd/diagram.rb:119:in create' rails-erd (0.4.5) lib/rails_erd/diagram.rb:74:increate'
erd (0.1.1) app/controllers/erd/erd_controller.rb:14:in index' actionpack (3.2.3) lib/action_controller/metal/implicit_render.rb:4:insend_action'
actionpack (3.2.3) lib/abstract_controller/base.rb:167:in process_action' actionpack (3.2.3) lib/action_controller/metal/rendering.rb:10:inprocess_action'
actionpack (3.2.3) lib/abstract_controller/callbacks.rb:18:in block in process_action' activesupport (3.2.3) lib/active_support/callbacks.rb:458:in_run__4443814287318799090__process_action__2694220428115231325__callbacks'
activesupport (3.2.3) lib/active_support/callbacks.rb:405:in __run_callback' activesupport (3.2.3) lib/active_support/callbacks.rb:385:in_run_process_action_callbacks'
activesupport (3.2.3) lib/active_support/callbacks.rb:81:in run_callbacks' actionpack (3.2.3) lib/abstract_controller/callbacks.rb:17:inprocess_action'
actionpack (3.2.3) lib/action_controller/metal/rescue.rb:29:in process_action' actionpack (3.2.3) lib/action_controller/metal/instrumentation.rb:30:inblock in process_action'
activesupport (3.2.3) lib/active_support/notifications.rb:123:in block in instrument' activesupport (3.2.3) lib/active_support/notifications/instrumenter.rb:20:ininstrument'
activesupport (3.2.3) lib/active_support/notifications.rb:123:in instrument' actionpack (3.2.3) lib/action_controller/metal/instrumentation.rb:29:inprocess_action'
actionpack (3.2.3) lib/action_controller/metal/params_wrapper.rb:205:in process_action' activerecord (3.2.3) lib/active_record/railties/controller_runtime.rb:18:inprocess_action'
actionpack (3.2.3) lib/abstract_controller/base.rb:121:in process' actionpack (3.2.3) lib/abstract_controller/rendering.rb:45:inprocess'
actionpack (3.2.3) lib/action_controller/metal.rb:203:in dispatch' actionpack (3.2.3) lib/action_controller/metal/rack_delegation.rb:14:indispatch'
actionpack (3.2.3) lib/action_controller/metal.rb:246:in block in action' actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:73:incall'
actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:73:in dispatch' actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:36:incall'
journey (1.0.3) lib/journey/router.rb:68:in block in call' journey (1.0.3) lib/journey/router.rb:56:ineach'
journey (1.0.3) lib/journey/router.rb:56:in call' actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:600:incall'
railties (3.2.3) lib/rails/engine.rb:479:in call' railties (3.2.3) lib/rails/railtie/configurable.rb:30:inmethod_missing'
journey (1.0.3) lib/journey/router.rb:68:in block in call' journey (1.0.3) lib/journey/router.rb:56:ineach'
journey (1.0.3) lib/journey/router.rb:56:in call' actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:600:incall'
actionpack (3.2.3) lib/action_dispatch/middleware/best_standards_support.rb:17:in call' rack (1.4.1) lib/rack/etag.rb:23:incall'
rack (1.4.1) lib/rack/conditionalget.rb:25:in call' actionpack (3.2.3) lib/action_dispatch/middleware/head.rb:14:incall'
actionpack (3.2.3) lib/action_dispatch/middleware/params_parser.rb:21:in call' actionpack (3.2.3) lib/action_dispatch/middleware/flash.rb:242:incall'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in context' rack (1.4.1) lib/rack/session/abstract/id.rb:200:incall'
actionpack (3.2.3) lib/action_dispatch/middleware/cookies.rb:338:in call' activerecord (3.2.3) lib/active_record/query_cache.rb:64:incall'
activerecord (3.2.3) lib/active_record/connection_adapters/abstract/connection_pool.rb:467:in call' actionpack (3.2.3) lib/action_dispatch/middleware/callbacks.rb:28:inblock in call'
activesupport (3.2.3) lib/active_support/callbacks.rb:405:in _run__4376859758047906647__call__2221242394031032558__callbacks' activesupport (3.2.3) lib/active_support/callbacks.rb:405:in__run_callback'
activesupport (3.2.3) lib/active_support/callbacks.rb:385:in _run_call_callbacks' activesupport (3.2.3) lib/active_support/callbacks.rb:81:inrun_callbacks'
actionpack (3.2.3) lib/action_dispatch/middleware/callbacks.rb:27:in call' actionpack (3.2.3) lib/action_dispatch/middleware/reloader.rb:65:incall'
actionpack (3.2.3) lib/action_dispatch/middleware/remote_ip.rb:31:in call' actionpack (3.2.3) lib/action_dispatch/middleware/debug_exceptions.rb:16:incall'
actionpack (3.2.3) lib/action_dispatch/middleware/show_exceptions.rb:56:in call' railties (3.2.3) lib/rails/rack/logger.rb:26:incall_app'
railties (3.2.3) lib/rails/rack/logger.rb:16:in call' actionpack (3.2.3) lib/action_dispatch/middleware/request_id.rb:22:incall'
rack (1.4.1) lib/rack/methodoverride.rb:21:in call' rack (1.4.1) lib/rack/runtime.rb:17:incall'
activesupport (3.2.3) lib/active_support/cache/strategy/local_cache.rb:72:in call' rack (1.4.1) lib/rack/lock.rb:15:incall'
actionpack (3.2.3) lib/action_dispatch/middleware/static.rb:62:in call' railties (3.2.3) lib/rails/engine.rb:479:incall'
railties (3.2.3) lib/rails/application.rb:220:in call' rack (1.4.1) lib/rack/content_length.rb:14:incall'
railties (3.2.3) lib/rails/rack/log_tailer.rb:14:in call' rack (1.4.1) lib/rack/handler/webrick.rb:59:inservice'
/Users/aabolts/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in service' /Users/aabolts/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:inrun'
/Users/aabolts/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

class << self
       def status
         migrated_versions = ActiveRecord::Base.connection.select_values("SELECT version FROM #{ActiveRecord::Migrator.schema_migrations_table_name}").map {\|v\| '%.3d' % v}
         migrations = []
         ActiveRecord::Migrator.migrations_paths.each do \|path\|
           Dir.foreach(Rails.root.join(path)) do \|file\|
--

vendor/bundle/ruby/2.5.0/gems/erd-0.4.0/lib/erd/migrator.rb:9:in status' vendor/bundle/ruby/2.5.0/gems/erd-0.4.0/app/controllers/erd/erd_controller.rb:19:in index'