Simple ActiveRecord serialise problem

[Andy Jeffries]

When I create a table with the following SQL:

# create table foos (id SERIAL, content VARCHAR(255));

And define a class as follows:

class Foo < ActiveRecord::Base
serialize :content, JSON
end

Creating a new instance of the class gives an error:

> f = Foo.new
NoMethodError: undefined method `read' for nil:NilClass
from /Users/andy/.rvm/gems/ruby-1.9.2-p290/gems/activesupport-3.1.0/lib/active_support/whiny_nil.rb:48:in `method_missing'
from /Users/andy/Code/FakePlatform/vendor/gems/Darwin/gems/json-1.4.6/lib/json/common.rb:286:in `load'
from /Users/andy/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.0/lib/active_record/base.rb:1938:in `block in set_serialized_attributes'

Does anyone have any ideas how to fix this?

It should work (it's such a simple case).

Cheers,

Andy

[Frederick Cheung]

On Oct 6, 11:02 am, Andy Jeffries <a...@andyjeffries.co.uk> wrote:
> When I create a table with the following SQL:
>
> # create table foos (id SERIAL, content VARCHAR(255));
>
> And define a class as follows:
>
> class Foo < ActiveRecord::Base
>   serialize :content, JSON
> end

the second argument to serialise is used to say that you always want
the serialised object to be of a certain class (e.g. Hash, an
application specific class etc.). I'm not sure what you meant by
passing JSON as that argument but I suspect that it isn't doing what
you think it is.

Fred

>
> Creating a new instance of the class gives an error:
>
> > f = Foo.new
>
> NoMethodError: undefined method `read' for nil:NilClass
> from /Users/andy/.rvm/gems/ruby-1.9.2-p290/gems/activesupport-3.1.0/lib/active_s upport/whiny_nil.rb:48:in `method_missing'
>  from /Users/andy/Code/FakePlatform/vendor/gems/Darwin/gems/json-1.4.6/lib/json/c ommon.rb:286:in `load'

>  from /Users/andy/.rvm/gems/ruby-1.9.2-p290/gems/activerecord-3.1.0/lib/active_re cord/base.rb:1938:in `block in set_serialized_attributes'

[Andy Jeffries]

the second argument to serialise is used to say that you always want
the serialised object to be of a certain class (e.g. Hash, an
application specific class etc.). I'm not sure what you meant by
passing JSON as that argument but I suspect that it isn't doing what
you think it is.

I was basing it on this article (as well as a stack overflow answer) that you can provide a custom serializer in Rails 3.1:

http://edgerails.info/articles/what-s-new-in-edge-rails/2011/03/09/custom-activerecord-attribute-serialization/index.html

JSON provides a dump and load method on the class so it should be acceptable as the serializer.

Is this article incorrect or my understanding of it?

Cheers,

Andy

[Andy Jeffries]

I was basing it on this article (as well as a stack overflow answer) that you can provide a custom serializer in Rails 3.1:

http://edgerails.info/articles/what-s-new-in-edge-rails/2011/03/09/custom-activerecord-attribute-serialization/index.html

JSON provides a dump and load method on the class so it should be acceptable as the serializer.

Is this article incorrect or my understanding of it?

Having just had a read of ActiveRecord::Base, I still can't see how I go wrong…

Base#serialize (line 557 of base.rb in ActiveRecord 3.1.0)

if the object supplied as the second argument responds to :load and :dump (which JSON does), then it uses that object, if not it wraps it in a YAMLColumn and sets the entry in serialized_attributes to that object.  Then in:

Base#arel_attributes_values (line 1963 of base.rb in ActiveRecord 3.1.0)

if there is an entry in serialized_attributes for a given attribute name (with a value put in to the coder variable) it calls coder.dump with the attribute value.

So, I can't understand why JSON wouldn't work as a second parameter...

Cheers,

Andy

[Tim Shaffer]

You're using the syntax of serialize properly.

The problem looks like it's in the JSON.load method not properly handling a nil value:

def load(source, proc = nil)

  if source.respond_to? :to_str

    source = source.to_str

  elsif source.respond_to? :to_io

    source = source.to_io.read

  else

    source = source.read

  end

  result = parse(source, :max_nesting => false, :allow_nan => true)

  recurse_proc(result, &proc) if proc

  result

end    

Basically it gets to the line "source = source.read" and throws up because source is nil and nil doesn't have a read method.

[Andy Jeffries]

I've also just tried upgrading JSON to 1.6.0 (as that's the version that seems to be installed if I do gem install json), same problem.

Cheers,

Andy