From: Brian Candler <b.candler@...>
Date: 2009-03-12T17:50:44+09:00
Subject: Re: help with refactor and db/ar advice

ball wrote:
> 1. Is there a way to take advantage of the schema so that I don't have
> to re-write it in the load function?

puts FoodDescription.columns.inspect
puts FoodDescription.map { |c| c.name }.inspect

> 2. Is there a way I can write a generic load function (taking
> advantage of #1 if available, or not if not).

As long as the columns in the text source appear in the same order as 
the columns in the database definition you should be fine. I think this 
ordering is guaranteed by the database, otherwise you couldn't 
meaningfully do "INSERT INTO foo VALUES (x,y,z)" (without naming the 
columns) or "SELECT * FROM foo"

> 3. What is the "better" way (than ][1..-2]) to strip a string of a
> starting/ending ~

Do it all in one go. A couple of options:

records = line.split(/^/).map { |rec| rec[1..-2] }
records = line.scan(/~([^~^]*)~/)

but they won't work unless *all* your fields are ~ delimited. So this 
might work better for you:

records = line.split(/^/).map { |rec| rec.sub(/~(.*)~) { $1 } }

> 4. Should I just use an AR generated primary key, rather than the data
> sets ASCII primary key? (many of the tables in the datasets have
> composite keys, in which I will not implement, so I am curious if I
> just create all of the primary keys through AR insted).

ActiveRecord has some hard-coded assumptions about primary keys. If you 
override its assumption that the key is called "id" then it won't 
generate keys automatically for new records. If you have non-integer 
primary key then it may or may not work. It certainly doesn't handle 
composite primary keys; I saw a plugin which claimed to do this some 
time ago, but I don't know if it's been kept up to date.

So my advice with AR is: if you are working with an existing 
database/schema that you don't control then try using non-standard 
primary keys, but if you control the schema yourself, follow AR's 
assumption of an integer primary key.
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