Ruby on Rails

Robert Walker wrote in post #978350:
> Robert Walker wrote in post #978348:
>> Here's one way that could be accomplished:
>>
>> The jobs table
>> +----+------------+------------+-----+
>> | id | creator_id | checker_id | ... |
>> | 1 | 3 | 7 | ... |
>> | 2 | 1 | 4 | ... |
>> +----+------------+------------+-----+
>
> Also note that this technique does not conform to the First Normal Form
> (1NF) of database design.

How do you figure that? It looks well normalized to me. creator_id and
checker_id aren't really a repeating group.

> An alternative normalized approach would
> involve associating Job and Worker though a many-to-many association and
> tagging the worker with a role in the join table.
>
> the job_workers join table
> +----+--------+-----------+-------------+
> | id | job_id | worker_id | role |
> | 1 | 1 | 3 | creator |
> | 2 | 1 | 7 | checker |
> | 3 | 2 | 1 | creator |
> | 4 | 2 | 4 | checker |
> +----+--------+-----------+-------------+

This is actually less normalized in the sense that you're repeating the
role name. But that's a quibble. :)

However, whether or not it's more normalized, I do agree that the latter
approach is the more flexible.

>
> Job < AR
> has_many :job_workers
> has_many :workers, :through => :job_workers
> end
>
> JobWorker < AR
> belongs_to :job
> belongs_to :worker
> end

Don't call it JobWorker! Join models should have descriptive names.
How about Assignment?

>
> Worker < AR
> has_many :job_workers
> has_many :jobs, :through => :job_workers
> end
>
> job_1 = Job.find(1)
> job_2 = Job.find(2)
>
> puts job_1.job_workers.each { |jw| puts "#{jw.worker_id }
> :#{jw.worker_role}" }
> => 3 : creator
> => 7 : checker
>
> puts job_2.job_workers.each { |jw| puts "#{jw.worker_id} :
> #{jw.worker_role}" }
> => 1 : creator
> => 4 : checker

Best,
-- 
Marnen Laibow-Koser
http://www.marnen.org
marnen@marnen.org

Sent from my iPhone

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