Extracting a portion of a model to a separate file

G’day,

I have a project that relies heavily on pluginaweeks “state_machine”
gem. While I would have liked to post this to a state_machine forum,

  1. I couldn’t find one and 2. this is probably a generic ruby concept
    that I just can’t piece together on my own - so asking here may be
    more appropriate (but still less appropriate than a straight ruby
    forum… maybe).

I have a ton of models that each have fairly complex state machines.
state_machine defines them with blocks directly in your model class
like so:

state_machine :initial => :created do
state :created

event :review do
transition any => :reviewing
end
end

My state_machine blocks however are very large and clutter up my
model.rb files…

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

Whatever it’s called. It’s preferable (for maintainability, etc) for
my models to look something like

class Thing < ActiveRecord::Base
#validations
#callbacks
#etc

line_of_code_that_loads_external_state_file_here
#maybe eval somehow
#maybe make a module that gets “mixed in”… i really dont know the
right approach
end

Any help would be appreciated.

  • FJM

[email protected] wrote:

G’day,

I have a project that relies heavily on pluginaweeks “state_machine”
gem. While I would have liked to post this to a state_machine forum,

  1. I couldn’t find one and 2. this is probably a generic ruby concept
    that I just can’t piece together on my own - so asking here may be
    more appropriate (but still less appropriate than a straight ruby
    forum… maybe).

I have a ton of models that each have fairly complex state machines.
state_machine defines them with blocks directly in your model class
like so:

state_machine :initial => :created do
state :created

event :review do
transition any => :reviewing
end
end

My state_machine blocks however are very large and clutter up my
model.rb files…

IMHO, they don’t clutter your models; they are part of your models.
I tend to think you want the state_machine blocks in the model files so
that you can review your state machine behaviors right along with your
methods and everything else. So I’m not sure that it’s such a great
idea to do what you’re asking.

However, it’s not that hard. Read on for ideas!

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

Whatever it’s called. It’s preferable (for maintainability, etc)

Why would this help maintainability? It seems to me that it would be
more maintainable to keep it all together as outlined above?

for
my models to look something like

class Thing < ActiveRecord::Base
#validations
#callbacks
#etc

line_of_code_that_loads_external_state_file_here
#maybe eval somehow
#maybe make a module that gets “mixed in”… i really dont know the
right approach
end

Well, you could take several approaches here. You could reopen the
class in a separate file…

app/models/thing.rb

class Thing < ActiveRecord::Base

validations

methods

require ‘thing_states’
end

lib/thing_states.rb

class Thing < ActiveRecord::Base
state_machine stuff
end

…you could store the state machine configuration in a YAML file or
something and read it with YAML.load or whatever that function is…you
could write a wrapper function for state_machine with a shorter
syntax…

But again, I think that this is probably not a great idea. If your
state machine definitions are part of your model functionality, they
should probably be in the same model file with everything else. If your
state machines are just “clutter”, then they probably shouldn’t be in
your code at all. (Note all the "probably"s here – I could well be
wrong.)

Any help would be appreciated.

  • FJM

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

[email protected] wrote:

On Jun 25, 9:58�am, Marnen Laibow-Koser [email protected] wrote:

I have a ton of models that each have fairly complex state machines.

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

Whatever it’s called. It’s preferable (for maintainability, etc)

Why would this help maintainability? �It seems to me that it would be
more maintainable to keep it all together as outlined above?

Maintainability was probably not the best word. Readability? Looking
for a better abstraction? I dunno. Having a model with only 300 lines
of code with 80 of those for a state machine – looks ugly. There has
to be a more readable abstraction.

Then I’d recommend finding a more readable abstraction that keeps it all
in the same place. Moving your state machine code to a separate file
essentially means that an important piece of your model functionality is
invisible when you most need to see it.

Now that I see how it works, I’m thinking something like:

instance_eval(File.read(“states.rb”), “states.rb”)

I think you’ve got the instance_eval syntax wrong here, but why on earth
would you use instance_eval instead of require or include?

There are legitimate uses for eval and instance_eval in Ruby, but they
are few and far between – enough so that their use should IMHO be
considered a code smell. If you think you need eval or instance_eval,
stop and think – there’s almost always a better way.

[…]

I see your point about keeping it together but there comes a point
where an abstraction becomes necessary…

What are you trying to abstract? Moving to a separate file is not, in
itself, abstraction. If an abstraction is what’s wanted here, let’s
find one instead of shuffling the same code around between files.

I may not be at that exact
point yet, but I see it over the horizon and want to work it out now.

Nothing wrong with speculating about future directions; just beware of
premature optimization.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

Marnen Laibow-Koser wrote:

[email protected] wrote:

On Jun 25, 9:58�am, Marnen Laibow-Koser [email protected] wrote:

I have a ton of models that each have fairly complex state machines.

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

Whatever it’s called. It’s preferable (for maintainability, etc)

Why would this help maintainability? �It seems to me that it would be
more maintainable to keep it all together as outlined above?

Maintainability was probably not the best word. Readability? Looking
for a better abstraction? I dunno. Having a model with only 300 lines
of code with 80 of those for a state machine – looks ugly. There has
to be a more readable abstraction.

Then I’d recommend finding a more readable abstraction that keeps it all
in the same place. Moving your state machine code to a separate file
essentially means that an important piece of your model functionality is
invisible when you most need to see it.

Now that I see how it works, I’m thinking something like:

instance_eval(File.read(“states.rb”), “states.rb”)

I think you’ve got the instance_eval syntax wrong here, but why on earth
would you use instance_eval instead of require or include?

Because neither require nor include do what I need them to do. Require
runs another file but if that other file relies on functions defined on
the requiring class, it can’t access them… can it? And include takes
all the methods in the included file and adds them to the including
class. Except the state definitions aren’t method definitions. They are
class functions that accept blocks which need to be run in the context
of the calling class. (Please forgive me if my terminology isn’t
entirely accurate. I’m still asking why class_eval and instance_eval
were named they way they were.)

There are legitimate uses for eval and instance_eval in Ruby, but they
are few and far between – enough so that their use should IMHO be
considered a code smell. If you think you need eval or instance_eval,
stop and think – there’s almost always a better way.

[…]

I see your point about keeping it together but there comes a point
where an abstraction becomes necessary…

What are you trying to abstract? Moving to a separate file is not, in
itself, abstraction. If an abstraction is what’s wanted here, let’s
find one instead of shuffling the same code around between files.

Yeah, this is more of a “code shuffling” today. Eventually I’d like to
encapsulate state definitions into a reusable chunk of code so that
multiple models can rely on the same definitions without the brittleness
that comes with repeating them. A wrapper around instance_eval lets me
reuse state_machines if I so desire without having to duplicate their
code.

I may not be at that exact
point yet, but I see it over the horizon and want to work it out now.

Nothing wrong with speculating about future directions; just beware of
premature optimization.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

Frank Mattia wrote:
[…]

Now that I see how it works, I’m thinking something like:

instance_eval(File.read(“states.rb”), “states.rb”)

I think you’ve got the instance_eval syntax wrong here, but why on earth
would you use instance_eval instead of require or include?

Because neither require nor include do what I need them to do. Require
runs another file but if that other file relies on functions defined on
the requiring class, it can’t access them… can it?

Sure. Just reopen the requiring class. This is exactly what I was
doing in my example in http://www.ruby-forum.com/topic/212124#921467 ;
you may want to review it.

And include takes
all the methods in the included file and adds them to the including
class. Except the state definitions aren’t method definitions. They are
class functions that accept blocks which need to be run in the context
of the calling class.

Good point. You’ll probably need extend instead of include, and you may
need the included and/or extended hooks. But this is definitely
possible.

[…]

What are you trying to abstract? Moving to a separate file is not, in
itself, abstraction. If an abstraction is what’s wanted here, let’s
find one instead of shuffling the same code around between files.

Yeah, this is more of a “code shuffling” today. Eventually I’d like to
encapsulate state definitions into a reusable chunk of code so that
multiple models can rely on the same definitions without the brittleness
that comes with repeating them.

Then do it right and put it into a module (or use inheritance).

A wrapper around instance_eval lets me
reuse state_machines if I so desire without having to duplicate their
code.

Nope! instance_eval just introduces brittleness. Learn about Ruby’s
module system and use that instead.

You almost never need to evaluate arbitrary literal code in Ruby, which
means you almost never need *eval. Metaprogramming is an amazing thing.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

Gentlemen thanks for having this conversation. Was pulling my hair out
trying to get state_machine to work with a mixin. I need to define
state_machines behaviors unique to each client while keeping a single
code base. I ended up using opening up the class like Maren suggested.

class OnDemandWorkorderWorkflow < Workflow

belongs_to :workorder

attr_accessible :type, :state, :workorder_id

require
“#{Rails.root}/lib/clients/#{CUSTOMER}/workflows/#{FILE_REFERENCE}_on_demand_workorder_workflow”

end

required file looks like this:

class OnDemandWorkorderWorkflow < Workflow

state_machine :state, :initial => :new do

# lots of events and transitions

end

On Jun 25, 9:58 am, Marnen Laibow-Koser [email protected] wrote:

I have a ton of models that each have fairly complex state machines.

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

Whatever it’s called. It’s preferable (for maintainability, etc)

Why would this help maintainability? It seems to me that it would be
more maintainable to keep it all together as outlined above?

Maintainability was probably not the best word. Readability? Looking
for a better abstraction? I dunno. Having a model with only 300 lines
of code with 80 of those for a state machine – looks ugly. There has
to be a more readable abstraction.

Now that I see how it works, I’m thinking something like:

instance_eval(File.read(“states.rb”), “states.rb”)

#maybe make a module that gets “mixed in”… i really dont know the
end

But again, I think that this is probably not a great idea. If your
state machine definitions are part of your model functionality, they
should probably be in the same model file with everything else. If your
state machines are just “clutter”, then they probably shouldn’t be in
your code at all. (Note all the "probably"s here – I could well be
wrong.)

They are definitely not “clutter” I just meant that they clutter up
an otherwise readable file. I think making some sort of wrapper for
instance_eval that figures out the model name then instance evals it
from say… app/models/states/order_states.rb or somesuch.

I see your point about keeping it together but there comes a point
where an abstraction becomes necessary… I may not be at that exact
point yet, but I see it over the horizon and want to work it out now.

On Friday, 25 June 2010 01:12:47 UTC-4, [email protected] wrote:

I have a ton of models that each have fairly complex state machines.

My state_machine blocks however are very large and clutter up my
model.rb files…

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

One mechanism that can be helpful that hasn’t been mentioned -
ActiveSupport::Concern. See here for more detail:

http://www.fakingfantastic.com/2010/09/20/concerning-yourself-with-active-support-concern/

–Matt J.

Matt J. wrote in post #1080951:

On Friday, 25 June 2010 01:12:47 UTC-4, [email protected] wrote:

I have a ton of models that each have fairly complex state machines.

My state_machine blocks however are very large and clutter up my
model.rb files…

What I want to do is extract out all of the state machine code to
another file that I can then “include” in my model. I know include is
the wrong terminology in ruby… maybe I want to modularize them?

One mechanism that can be helpful that hasn’t been mentioned -
ActiveSupport::Concern. See here for more detail:

Funny, as soon as I came back to check the update I said to myself
“knowing what I know now, I would have probably used a concern”. I
second your suggestion.

http://www.fakingfantastic.com/2010/09/20/concerning-yourself-with-active-support-concern/

–Matt J.

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