ActiveRecord: Can't change the value of self

I have a system where uploads are stored in a database with a filename
based on the MD5 hash of the file contents. Following the logic of this,
I assigned upload_file_name to be a unique index in my migration.

What I want to do is, whenever a user tries to upload a file whose md5
hash already exists in the database, just redirect to that other record
rather than making a copy (which actually just throw an error because
upload_file_name is a unique index)

So I put in my model:

self = other_upload if other_upload =
Upload.find_by_upload_file_name(self[:upload_file_name])

which ActiveRecord doesn’t let me do saying “Can’t change the value of
self”

Ideas?

On 19 February 2011 06:54, Shea B. [email protected] wrote:

self = other_upload if other_upload =
Upload.find_by_upload_file_name(self[:upload_file_name])

which ActiveRecord doesn’t let me do saying “Can’t change the value of
self”

That is not an ActiveRecord issue it is a basic Ruby issue. Once you
are inside an instance method I do not think there is any way of
suddenly deciding you want to be in the method of a different object.
You could put something like the above code in a method of the model
that, rather than setting self, returns either itself or the
alternative, then call that method from the controller.

Colin

thanks for the help.

On 19 February 2011 09:12, Colin L. [email protected] wrote:

suddenly deciding you want to be in the method of a different object.
+1
The functionality you’re interested in should be called from the
controller.

pseudo-Ruby

upload = Upload.new(params[:upload])
if Upload.find_by_file_name(upload.file_name)
upload = Upload.find_by_file_name(upload.file_name)
end

You can’t change “self” to “be” a different instance, but you can
overwrite a variable containing one instance, with another instance.

I guess I just have to do it in the controller – I just wish there was
some way I could put it into the model that way I never have to worry
about it in
my “skinny controller”.

I assume you’re replying to my post… but because you cut everything,
I don’t know for sure…

On 19 February 2011 17:36, Shea B. [email protected] wrote:

I know I have to do it in the controller is just wish there was some way
I could put it into the model that way I never have to worry about it in
my “skinny controller”.

find_or_initialize_by_?

Although, if you’re doing some fudging with MD5 hashes, you may not be
able to use the dynamic methods…

upload.rb

def self.find_or_initialize_by_params(params)
upload = Upload.new(params)
return Upload.find_by_upload_file_name(upload.upload_file_name) ||
upload
end

#controller
upload = Upload.find_or_initialize_by_params(params)

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