Undefined method `build' for nil:NilClass

mac · March 3, 2010, 7:22pm

hello,
m following railcast
http://media.railscasts.com/videos/073_complex_forms_part_1.mov

but i am getting error: undefined method `build’ for nil:NilClass

can you please help

though m using belongs_to and has_one relationship rather then
“has_many” is this the problem ???

if you want i can provide more details

thank you

mac · March 3, 2010, 10:50pm

On 3 March 2010 18:21, mac [email protected] wrote:

hello,
m following railcast http://media.railscasts.com/videos/073_complex_forms_part_1.mov

but i am getting error: undefined method `build’ for nil:NilClass

If you look on the line in your code where the error occurs you will
likely find that you are using something.build. The error is
indicating the your ‘something’ is nil.

If you cannot see why it is nil it might be worth your while looking
at the rails guide on debugging at http://guides.rubyonrails.org.
This shows various methods of debugging your code. For example you
can use ruby-debug to break into your code and inspect your data to
see what the problem is.

Colin

mac · March 4, 2010, 1:20pm

hello colin,
thanks for your reply,
i know what that error means… but my problem is why this is comming
& how can i achieve my solution.

more details:

content_master model:

class ContentMaster < ActiveRecord::Base
has_one :Metadata
end

metadata model:

class Metadata < ActiveRecord::Base
belongs_to :ContentMaster, :class_name => ‘ContentMaster’
end

new action in controller

def new
@content_master = ContentMaster.new
@metadata = @content_master.Metadata.build

respond_to do |format|
  format.html # new.html.erb
  format.xml  { render :xml => @content_master }
end

end

oops same error
undefined method `build’ for nil:NilClass

i hope now my problem is more clear

looking forward for help

thank you

mac · March 4, 2010, 6:08pm

On 4 March 2010 12:19, mac [email protected] wrote:

hello colin,
thanks for your reply,
i know what that error means… but my problem is why this is comming
& how can i achieve my solution.

Did you try my suggestion to use ruby-debug?

more details:

content_master model:

class ContentMaster < ActiveRecord::Base
has_one :Metadata

That should be :metadata not :Metadata

end

metadata model:

class Metadata < ActiveRecord::Base
belongs_to :ContentMaster, :class_name => ‘ContentMaster’

That should be :content_master and then the class name will not be
needed

end

new action in controller

def new
@content_master = ContentMaster.new
@metadata = @content_master.Metadata.build

Should be metadata again.

i hope now my problem is more clear

It might be worth your while having a look at the ActiveRecord
Associations guide aswell as the debugging one. That will explain how
to use associations.

Colin

mac · March 4, 2010, 6:32pm

thank you again for your reply

Did you try my suggestion to use ruby-debug?
i havent did that yet will do it as soon as possible and will report
you back

def new
@content_master = ContentMaster.new
@metadata = @content_master.Metadata.build

Should be metadata again.

though m beginner in Ruby as well as rails but i have read on some
blog that rails just convert every simple simple and underscore words
to camelCase( where required ) so it hardly matters how you write it,
they are just conventions. Though i know it is good practise to
follow conventions but i dont think it makes any error.

will do ruby debug ( for now i even dont now how to do this ) , and
will post back about result or if i found something fruitful their

thank you

mac · March 5, 2010, 1:46pm

I would very strongly suggest following the conventions, it will make
your life much easier. Also I think that in this case it may at least
in part be the cause of the problem. Consider the line
@metadata = @content_master.Metadata.build
What is Metadata here? In the model you have declared
class Metadata < ActiveRecord::Base
so Metadata is a class. But in the code you are using it as if it
were a member of the ContentMaster class, which it is not, whereas
metadata is (or at least could be, dependent on the table schema).
I suggest that you make the changes I have proposed and try it.

i have tried all the conventions you told but it does no change in
error ( hard luck ).
I suppose their is lots and lots of chaos about rails conventions &
defaults.

problem still remains unsolved !!!

thank you

mac · March 4, 2010, 9:30pm

On 4 March 2010 17:31, mac [email protected] wrote:

end
3) new action in controller
to camelCase( where required ) so it hardly matters how you write it,
they are just conventions. Though i know it is good practise to
follow conventions but i dont think it makes any error.

I would very strongly suggest following the conventions, it will make
your life much easier. Also I think that in this case it may at least
in part be the cause of the problem. Consider the line
@metadata = @content_master.Metadata.build
What is Metadata here? In the model you have declared
class Metadata < ActiveRecord::Base
so Metadata is a class. But in the code you are using it as if it
were a member of the ContentMaster class, which it is not, whereas
metadata is (or at least could be, dependent on the table schema).
I suggest that you make the changes I have proposed and try it.

Colin

mac · March 5, 2010, 2:13pm

Post the new/modified code and we can have a look.

content_master model

class ContentMaster < ActiveRecord::Base
has_one :metadata
end

metadata model:

class Metadata < ActiveRecord::Base
belongs_to :content_master
end

def new
@content_master = ContentMaster.new
@metadata = @content_master.metadata.build

respond_to do |format|
format.html # new.html.erb
format.xml { render :xml => @content_master }
end
end
still same error
undefined method `build’ for nil:NilClass

thank you

mac · March 5, 2010, 2:19pm

hello,
i found this through google

"The create and build methods are only available for has_one/
belongs_to if an association already exist. It will not work when it’s
nil. "

http://dev.rubyonrails.org/ticket/535

though this is really a old post i dont know that it is solved or
not.

thank you

mac · March 5, 2010, 1:49pm

On 5 March 2010 12:45, mac [email protected] wrote:

I suppose their is lots and lots of chaos about rails conventions &
defaults.

Not really…

problem still remains unsolved !!!

Post the new/modified code and we can have a look.

mac · March 5, 2010, 2:40pm

On 5 March 2010 13:18, mac [email protected] wrote:

"The create and build methods are only available for has_one/
belongs_to if an association already exist. It will not work when it’s
nil. "

For a has_one, it seems you can user “build_”. So for your
case:

@metadata = @content_master.build_metadata

…might do the job.

mac · March 5, 2010, 2:27pm

not.

Well, doing their suggestion works.

def new
@content_master = ContentMaster.new
@content_master.metadata = Metadata.new

respond_to do |format|
format.html # new.html.erb
format.xml { render :xml => @content_master }
end
end

Then just use @content_master.metadata in your new.html.erb or reassign
it
to @metadata, e.g.:

@metadata = @content_master.metadata = Metadata.new

The association is set up when you assign it to @content_master.metadata
so
you don’t need to call build from the nil object.

Cheers,

Andy

mac · March 5, 2010, 2:48pm

On 5 March 2010 13:26, Andy J. [email protected] wrote:

def new
@content_master = ContentMaster.new
@content_master.metadata = Metadata.new
respond_to do |format|
format.html # new.html.erb
format.xml { render :xml => @content_master }
end
end

I like to leave this to the model where possible - if I have to have
an associated object (or if I don’t want to do loads of guards like
“@content_master.metadata.attribute unless
@content_master.metadata.nil?”) I build/create the associated object
after initialise.

#content_master model
def after_initialize
metadata ||= Metadata.new
end

… it can cause problems in some cases, but can solve some in others!

(a bit of advice gleaned from the “Refactoring: Ruby Edition” book)

mac · March 5, 2010, 4:29pm

thank you @Andy
thank you @Michael

both method work in action new but comming back to problem as i was
following
http://media.railscasts.com/videos/073_complex_forms_part_1.mov

i need to create a virtual function in a model

i tried various combination (for * ) but failed

model:

class ContentMaster < ActiveRecord::Base

has_one :metadata

def meta_attribute=(meta_attribute)
*metadata = metadata.build(meta_attribute)
end

end

i tried new and build_ but they were not working ?? how
to accomplish same in model

mac · March 5, 2010, 4:29pm

thank you @Andy
thank you @Michael

both method work in action new but comming back to problem as i was
following
http://media.railscasts.com/videos/073_complex_forms_part_1.mov

i need to create a virtual function in a model

i tried various combination (for * ) but failed

model:

class ContentMaster < ActiveRecord::Base

has_one :metadata

def meta_attribute=(meta_attribute)
*metadata = metadata.build(meta_attribute)
end

end

i tried new and build_ but they were not working ?? how
to accomplish same in model

mac · March 5, 2010, 7:21pm

On Fri, Mar 5, 2010 at 8:12 AM, mac [email protected] wrote:

def new
@content_master = ContentMaster.new
@metadata = @content_master.metadata.build

  @metadata = @content_master.build_metadata

–
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

mac · March 5, 2010, 7:31pm

thank you for your reply @RickDeNatale

but solution u provided has allready been suggested.

my problem is now with defination of virtual function according to
“has_one” relation

thank you anyway
mac