Why not [] as ActiveRecord::Base class method?

Rails
1

Here’s a little method

module ActiveRecord
class Base
def self.
find(id)
end
end
end

So you can write

MyModel[12]

as an equivalent to

MyModle.find(12)

Just a little sugar, nothing else really. Is anyone aware of why that
would be ill-advised? It seems to work with my extremely limited
testing.

It’s non-orthogonal with respect to association proxies, so maybe that’s
bad:

MyModel[12] is the same as MyModel.find(12)

but

MyModel.friends[12] is not the same as MyModel.friends.find(12)

2

jamis buck has suggested the same thing:
http://weblog.jamisbuck.org/2007/4/4/activerecord-base-find-shortcut

3

My instinct is to say, “yes, but what happens when record #5 is
deleted?” There are two problems at play:

  1. The use of incrementing integers for primary keys (bad, btw, we
    need guids much of the time) misleads us into thinking of the table as
    an array indexed by the primary keys. It is not. It is a collection
    indexed by the primary keys.
  2. The use of the [] operator with integer operands likewise
    intuitively directs to an array. But in ruby, a[5] might be the sixth
    element of an array, or the value of a hash for the key 5.

Since these classes are mapped to tables, and tables are certainly
collections of rows, then the use of the [] operator is sensible.

HOWEVER…

You are not the sole maintainer of this code. Sooner or later,
someone else is going to maintain it. You are changing a base
behavior of the system. Be sure to leave markers.

Is MyModel.friends.find even well defined?

4

Student wrote:

My instinct is to say, “yes, but what happens when record #5 is
deleted?”

Presumably, MyModel[5] would then simply find nothing.

There are two problems at play:

  1. The use of incrementing integers for primary keys (bad, btw, we
    need guids much of the time)

Why?

misleads us into thinking of the table as
an array indexed by the primary keys. It is not. It is a collection
indexed by the primary keys.

True, but so what? The distinction is somewhat irrelevant for the
current question.

[…]

You are not the sole maintainer of this code. Sooner or later,
someone else is going to maintain it. You are changing a base
behavior of the system.
[…]

I think it’s more correct to say that he’s adding a behavior to the
system – after all, .find should still work.

Best,

Marnen Laibow-Koser
[email protected]