Has many through with an extra field

Rails
1

Hello,

I’m trying to solve a common task with many to many relationships.

Here are my class definitions:

class User < ActiveRecord::Base
has_many :questionnaires
has_many :forms, :through => :questionnaires
end

class Form < ActiveRecord::Base
has_many :questionnaires
has_many :users, :through => :questionnaires
end

class Questionnaire < ActiveRecord::Base
belongs_to :user
belongs_to :form
end

My problem is to include an extra date field named active_at to User
new/edit form.

When creating a user I need to check forms (via checkboxes) which it
belongs to. I know it can be done by creating checkboxes with name like
‘user[form_ids][]’. But I also need to enter a date field for each of
checked relations which will be stored in the questionnaire join model.

Any help is very appreciated
Bodo

2

On Wed, Feb 15, 2012 at 10:13 AM, Bodo K. [email protected]
wrote:

My problem is to include an extra date field named active_at to User
new/edit form.

When creating a user I need to check forms (via checkboxes) which it
belongs to. I know it can be done by creating checkboxes with name like
‘user[form_ids][]’. But I also need to enter a date field for each of
checked relations which will be stored in the questionnaire join model.

Any help is very appreciated

We recently had a long (and confusing) discussion about this

https://groups.google.com/forum/#!topic/rubyonrails-talk/W-FTZNPNUeE/discussion

Looking back at it, I would suggest take it step-by-step.

Try first to understand how to get it to work on the model level, write
unit tests for
that and only after that, build your new/edit view code that will
generate
the params
hash that will fill in the values.

There is a good chance you will need to do some “manual” tweaking to
completely build up the datastructure from the params hash. I mean a
simple user = create(params[:user]) may require you defining some
additional setter methods.

Maybe, the core is that you will need to override the

form_ids=(id,id,…)

method on the User model (start with

rails c

User.new.methods.grep(/form_ids=/)

to see if it is defined.

Assuming you use Rails 3.2.x you could start playing with
(UNTESTED code, probably not optimal, just a hint):

class Questionnaire < ActiveRecord::Base
belongs_to :user, :inverse_of => :users
belongs_to :form, :inverse_of => :forms # important for the save after
build !

google this line: "The last line ought to save the through record (a

Taggable). This will only work if the :inverse_of is set:"
end

class User < ActiveRecord::Base
has_many :questionnaires
has_many :forms, :through => :questionnaires

def form_ids=(form_id_array)
super # will pass the argument to higher-up function and build the
associated forms
self.forms.each do |form|
# I presume this will be populated by now
qs = form.questionnaires
qs = qs.select{|q| q.user == self} # filter only those that are
this
user
raise “BOOOM” if qs.size > 1 # there can be only 1 (check it to
be
sure)
q = qs.first
q.active_at Time.now
end
end
end

Then check the result manually and with tests.

Then save the user and check if all is still correct.

Once you can set the active_at to Time.now, a next phase can start to
set it to actual values, that are gotten from the form (probably need
to make a non-standard input format that may be an array of hashes
with in each entry the form_id and the date for that form_id ??).

I hope this helps, but I keep finding this non-trivial …

If I overlook the obvious, standard solution, I would be glad to be
corrected.

Peter

3

Thanks.

I forgot to mention that one solution is discussed on

When I try this approach I got an error message from inside the original
routine below:

Couldn’t find Questionnaire without an ID

(In my case Product is User, Category is Form and Categorization is
Questionnaire.)

def initialized_categorizations # this is the key method
[].tap do |o|
Category.all.each do |category|
if c = categorizations.find { |c| c.category_id == category.id }
o << c.tap { |c| c.enable ||= true }
else
o << Categorization.new(category: category)
end
end
end
end
…

My question is what the error line tries to do in detail.

Anyway, I’m surprised that for this common problem there is still no
reasonable solution available.

Regards
Bodo

4

On Wed, Feb 15, 2012 at 11:55 AM, Bodo K. [email protected]
wrote:

Couldn’t find Questionnaire without an ID
o << Categorization.new(category: category)
end
end
end
end
…

My question is what the error line tries to do in detail.

In that case, could you then send your particular implementation
and the stack trace that you got.

A wild guess is that there is a problem where looking for
an ID (that is only generated when saving to the database;
but at this time your questionaire object is still in the making
in memory and does not have an id yet).

That is why I used the “select” code in my proposal (checks
in the array in memory using the belongs_to result == self)
and not find (which would look for an entry in db, but we have
not saved yet at that point).

HTH,

Peter