Weird foreign key constraint failure in transaction

Rails
1

I have an ActiveRecord transaction that works some times and fails some
times. I’ve narrowed it down to where the failure depends on the
inclusion of an empty method from a library object. By ‘empty’, I mean
I’ve removed all code from the method, so the problem is related to
making the method call (i.e. it’s not in my code). Here’s some pseudo
code.

def myMethod
ClassA.transaction do
# saving class B obj succeeds when this next method is commented
out,
# but it fails with ‘update violates foreign key constraint’ when
this method is called
MyLibraryClass.donothing
@objectOfClassA.save!
@objectOfClassB.refToA = objectOfClassA.id
@objectOfClassB.save!
end
end

It behaves as if the second save cannot see the object created in the
first save, even though they both happen within the transaction.

Why would the inclusion of the unrelated, empty method ‘donothing’ have
such an effect?

2

On 30 Apr 2008, at 19:45, Seth Tager wrote:

ClassA.transaction do

saving class B obj succeeds when this next method is commented

out,

but it fails with ‘update violates foreign key constraint’ when

this method is called
MyLibraryClass.donothing
@objectOfClassA.save!
@objectOfClassB.refToA = objectOfClassA.id
I assume this should read @objectOfClassB.refToA = @objectOfClassA.id
such an effect?
Because saying MyLibraryClass means const_missing is hit, triggering
the load of my_library_class.rb which contains something funny? (if
true then just putting
MyLibraryClass in your method (ie call no method on it at all) will
also trigger the error you are seeing).

Fred

3

Frederick C. wrote:

On 30 Apr 2008, at 19:45, Seth Tager wrote:

ClassA.transaction do

saving class B obj succeeds when this next method is commented

out,

but it fails with ‘update violates foreign key constraint’ when

this method is called
MyLibraryClass.donothing
@objectOfClassA.save!
@objectOfClassB.refToA = objectOfClassA.id
I assume this should read @objectOfClassB.refToA = @objectOfClassA.id

yes, that’s how it should have read.

such an effect?
Because saying MyLibraryClass means const_missing is hit, triggering
the load of my_library_class.rb which contains something funny? (if
true then just putting
MyLibraryClass in your method (ie call no method on it at all) will
also trigger the error you are seeing).

You’re correct. The error is triggered even with no method call. But
even weirder, I moved the MyLibraryClass statement outside of the
transaction entirely and it still triggered the error.

However, your message helped:
you got me wondering what was in the library class and I found that
another developer had added this:
require File.dirname(FILE) + ‘/…/config/environment’

and that turns out to be causing a problem. I can’t explain why that
would cause the observed behavior, but at least it’s fixed. Thanks.