Adding extra variable to a class, how to access it?

[koloa]

somple question here but pretty confusing on my side. i have a model
towns that is mapped to my towns table. can i add an extra variable to
the class and access it in my view? basicall what i am trying to do is
return a list of towns, and next to each town, display a total number of
what i have in each town.

ive tried both attr_reader and @total but no avail.

here is my view

<% for county in @counties %>

<%= county.name %>

<% for town in county.towns %>

<%= town.name %>

<%= town.total %>

<% end %>

my town model:

class Town < ActiveRecord::Base
belongs_to :county
attr_reader :total
@total

def self.get_list
@total = 100
find(:all)
end
end

[koloa]

never mind, i figured it out. i realized you can access instance
variable directly, you need a ‘get’ method.

[koloa]

or attr_accessor :variable

Ross

[koloa]

Ross R. wrote:

or attr_accessor :variable

Ross

Strangely enough, this does not work for me. I tried:

class Page < ActiveRecord::Base
belongs_to :author
attr_accessor :typus
end

and was not able to access somepage.typus in my view. However, this
worked:

class Page < ActiveRecord::Base
belongs_to :author
def typus=(typus_value)
write_attribute(:typus, typus_value)
end

def typus
read_attribute(:typus)
end
end

Why is it that attr_accessor does not work for an AR-based class?

Thanks,
Jan

[koloa]

In addition to my recent message:

I can use somepage.typus (reading/writing) in the controller, but not
read it in the view when using attr_accessor.

Jan E. wrote:

Ross R. wrote:

or attr_accessor :variable

Ross

Strangely enough, this does not work for me. I tried:

class Page < ActiveRecord::Base
belongs_to :author
attr_accessor :typus
end

and was not able to access somepage.typus in my view. However, this
worked:

class Page < ActiveRecord::Base
belongs_to :author
def typus=(typus_value)
write_attribute(:typus, typus_value)
end

def typus
read_attribute(:typus)
end
end

Why is it that attr_accessor does not work for an AR-based class?

Thanks,
Jan

[koloa]

Jan E. schrieb:

end
def typus
read_attribute(:typus)
end
end

Why is it that attr_accessor does not work for an AR-based class?

Thanks,
Jan

Hi Jan,

did you try to access a persistent or a non-persistent attribute?

What do you get when you @page.typus in your view, I guess nil unless
you’ve done something like @page.typus = ‘something’ before…

Regards
Florian

[koloa]

Hi Jan

@children.each do |child|
  child.author = nil if child.author == page.author
  child.typus = (child.visible_children != nil) ? 'Node' : 'Page'
end

In this case I’d drop

child.typus = (child.visible_children != nil) ? ‘Node’ : ‘Page’

and def typus in the model itself:

def typus
visible_children ? ‘Node’ : ‘Page’
end

What’s your code in the view? I can’t understand why accessor shouldn’t
work…

Regards Florian

[koloa]

Florian Aßmann wrote:

Jan E. schrieb:

end
def typus
read_attribute(:typus)
end
end

Why is it that attr_accessor does not work for an AR-based class?

Thanks,
Jan

Hi Jan,

did you try to access a persistent or a non-persistent attribute?

What do you get when you @page.typus in your view, I guess nil unless
you’ve done something like @page.typus = ‘something’ before…

Regards
Florian

Hi Florian,

it’s a non-persistent attribute, calculated on the fly based on another
attribute (it’s actually a string to be used as a CSS classname).

@page.typus won’t work, because I use the instance variable @children to
store a list of Page objects (which in turn have the typus attribute):

This is what happens in the controller:

@children = Page.find(:all, :conditions => “mother_id = #{page.id}”,
:order => “position asc, title asc”)
@children.each do |child|
child.author = nil if child.author == page.author
child.typus = (child.visible_children != nil) ? ‘Node’ : ‘Page’
end

This does set @typus for each child page correctly (I inspected the
children), but I cannot access the instance variable (like child.typus)
when doing only “attr_accessor :typus” in the model.

Thanks,
Jan

[koloa]

I’m very curious about this one. For me, declaring accessors, has always
worked in my whole rails code…

The objects in children in your view are really instances of Page? Did
you make a child.inspect in vour view or child.methods.sort or maybe
even child.instance_variable_get(:@typus)?

I use inspect and methods(+grep) very often at frontend debugging…

Regards
Florian

[koloa]

Florian Aßmann wrote:

Hi Jan

@children.each do |child|
  child.author = nil if child.author == page.author
  child.typus = (child.visible_children != nil) ? 'Node' : 'Page'
end

In this case I’d drop

child.typus = (child.visible_children != nil) ? ‘Node’ : ‘Page’

and def typus in the model itself:

def typus
visible_children ? ‘Node’ : ‘Page’
end

What’s your code in the view? I can’t understand why accessor shouldn’t
work…

Thanks for the suggestion, that’s definitely an improvement (and it
works fine).

The view simply has:

<% @children.each do |child| %>

<%= child.title %>

To summarize:

• your suggestion (a simple method for each Page instance) works
• The AR-specific getter/setter methods using
  write_attribute/read_attribute work
• The generic attr_accessor method to create an attribute does not work
  (Error: undefined method)

Thanks again,
Jan

[koloa]

Florian Aßmann wrote:

I’m very curious about this one. For me, declaring accessors, has always
worked in my whole rails code…

The objects in children in your view are really instances of Page? Did
you make a child.inspect in vour view or child.methods.sort or maybe
even child.instance_variable_get(:@typus)?

I use inspect and methods(+grep) very often at frontend debugging…

Regards
Florian

Ok, here’s a simplified version of my setup (the model lists the three
variants of implementing an attribute, of which variant 1) does not
work):

Model:

class Page < ActiveRecord::Base
belongs_to :author

1)

attr_accessor :typus

2)

def typus=(typus_value)

write_attribute(:typus, typus_value)

end

def typus

read_attribute(:typus)

end

3)

def typus

visible_children ? ‘Knoten’ : ‘Seite’

end

end

The controller needs to iterate over each child for variants 2) and 3)

Controller:

class PagesController < ApplicationController

def index
page = Page.find(:first, :conditions => “id = #{params[‘id’]}”)
@title = page.title
@content = page.content
@children = Page.find(:all, :conditions => “mother_id = #{page.id}”,
:order => “position asc, title asc”)

      # @children.each { |child| child.typus = 

child.visible_children ? ‘Knoten’ : ‘Seite’ }
end

end

The view simply uses child.typus for each element of @children:

View:

<%= @title %>

<%= @content %>

<% @children.each do |child| %>

<%= child.title %>

<% end %>

Cheers,
Jan