using a variable name with a column name in rails model - ruby-on-rails

Question

I've a piece of code in my product model where I assign values to columns by fetching from s3. The column names includes a counter "i" as well -
The 3 sample column names are -
pic1_file_name
pic2_file_name
pic3_file_name
The problematic code is -
prod = Product.find(id)
i=1
s3 = AWS::S3.new
bucket=s3.buckets['bucket_name']
bucket.objects.each do |obj|
prod.("pic"+"#{i}".to_s+"_file_name")=obj.key[45..1]
# the above line give a syntax error, unexpected '=', expecting end-of-input
prod.("pic"+"#{i}".to_s+"_file_name").to_sym = obj.key[45..-1]
# The above line gives an error undefined method `call' for #<Product:0x7773f18>
prod.send("pic"+"#{i}".to_s+"_file_name")=obj.key[45..-1]
# The above gives syntax error, unexpected '=', expecting end-of-input
i+=1
end
prod.save
Could you please advise as to how should I structure my column name with a variable so that I can assign a value to it without having to type 15 separate columns every time.
Any pointers will be appreciated.
Thanks in advance!

Answer 1

You almost got the last one right. You see, when doing
obj.pic1_file_name = 'foo'
you're actually calling method pic1_file_name=, not pic1_file_name. That line is equivalent to this:
obj.pic1_file_name=('foo')
With that in mind, your last line becomes
prod.send("pic#{i}_file_name=", obj.key[45..-1])

Answer 2

You can use the send method to call a method from a string:
prod.send("pic#{i}_file_name") # to read
prod.send("pic#{i}_file_name=", obj.key[45..-1]) # to assign