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Tuesday, November 2, 2010

Rails, Factory_girl and Bioinformatics - a gotcha

I've been using factory girl as a replacement for Fixtures in a new Rails application. It has been working well but I just stumbled across a BIG gotcha for my application.

I work on bioinformatics applications with DNA and Protein sequences and having a model with a column called 'sequence' is a natural choice.

The problem is that Factory Girl allows you to create objects in which a specific field is given a sequential id. For example 'user_1', 'user_2', etc. You set that up in your Factory definition like this:
Factory.define :mymodel do |f|
f.sequence(:name) {|n| "name_#{n}" }
When you have a model with a field called sequence you would define that like this:
Factory.define :mymodel do |f|
f.sequence(:name) {|n| "name_#{n}" }
f.sequence 'acgtacgtacgt'
You see the problem... Running a test with this in it brings up an error message like this:
  1) Error:
test: A Sequence instance should be valid. (SequenceTest):
NoMethodError: undefined method `call' for nil:NilClass
/Users/jones/.rvm/gems/ruby-1.9.2-p0/gems/activesupport-3.0.1/lib/active_support/whiny_nil.rb:48:in `method_missing'
The same problem will arise if you have a column called 'association'.

This is a bad design choice to mix up field names and methods. A better choice would have been to use a 'verb' such as f.generate_sequence(:name), which is much less likely to be used as a column name.

I can't see a way around this other than changing the name of the column in my model, which I am very reluctant to do.
Machinist is an alternative to Factory Girl, so that might be a solution - or hacking the factory_girl gem to change the name of the methods...

UPDATE: Factory Girl will allow alternate syntaxes - see the "Alternate Syntaxes" section. Not sure if its the best path for me but might get me over the immediate hurdle.

UPDATE 2: Just tried Machinist and that solves the first problem... however it fails if you have a column called 'alias' in a blueprint - the trick here is to precede the column name with 'self', i.e. 'self/alias' works.



Unknown said...
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Practical Social Skills said...

Looks like error occurred since DNA sequences share the sequence naming convention in factory_girl, how about renaming to dna_sequence instead to resolve it?

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