polymorphic association issue with presetted "source_type"

[fl00r]

When I preset in my has_many association it's type (as a condition option) It will be rewriten if I save it in scope with root object, while if I save it separetly it will save it right.

class Foo < ActiveRecord::Base
  has_many :bars, as: :source, conditions: { source_type: "CustomType" }
end

class Bar < ActiveRecord::Base
  belongs_to :source, polymorphic: true
end

foo = Foo.new
bar = foo.bars.build
foo.bars << bar
bar.source_type
#=> "CustomType"
bar.save
bar.source_type
#=> still "CustomType"
foo.save
foo.bars.first.source_type
#=> "Foo"

[pixeltrix]

The Bar instance that foo.bars.first returns is not the same as the one in the bar variable. If you look at the SQL generated by foo.bars.first it adds the association conditions and the polymorphic conditions as well:

SELECT "bars".* FROM "bars" WHERE "bars"."source_id" = 1 AND "bars"."source_type" = 'Foo' AND "bars"."source_type" = 'CustomType' 

I can't see how that association would ever return anything other than an empty array. This is on Rails 3.2, if by chance you are using a older version that doesn't have the commit 9c023cc (i.e 3.0) then one of the conditions overwrites the other - I can't remember which.

Perhaps the bug you're trying to demonstrate got lost in translation to abstract code?

[fl00r]

Yeap, one line is missed foo.bars << bar.

It is actually not a bug. It is looks like a hack. If conventionally polymorphic associations MUST always store class name in *_type field so we need at least warn about it if someone tryies to rewrite this field. Or protect this field from straight changing.

Or. If we want to give the ability of rewriting this field, so we shouldn't rewrite it while saving parent object. I mean if we have already set field with some default value, save process shouldn't rewrite with class name, and if the field is blank, so it must write class name there.

What I mean. In first case when we protect our *_type:

foo = Foo.new
bar = foo.bars.build
bar.source_type
#=> "Foo", not "CustomType"! And warning 'You are trying to set protected polymorphic field blah blah blah. Rejected'

In second case

foo = Foo.new
bar = foo.bars.build
foo.bars << bar
foo.save
foo.bars.first.source_type
#=> "CustomType"

I think it should be protected from setting it in conditions option or elsewhere. Because it looks like how polymorphic associations works. And it will work like bar.source properly in any case :) because if we can rewrite *_type field it won't work without some additional class mapping magick

[ahawkins]

@fl00r is this closed then? Seems you've pretty much answered your own question. I think you may have just ran into an edge in polymorphic associations.