Re: Two Core Data .mom Files

FROM : Matthew Firlik
DATE : Wed Apr 04 11:03:00 2007

On Apr 2, 2007, at 8:34 AM, Richard Somers wrote:

> Create a core data document based application using the standard 
> apple template.
> The debug application bundle contains a single mom file 
> MyDocument.mom.
>
> The released application bundle contains two mom files, 
> MyDocument.mom and MyDocument-79FD2C8B.mom. These two files are 
> identical when compared with FileMerge.
>
> Why two mom files for the released bundle, why are they identical, 
> and why the weird name?



This is a result of building "Universal".

The "Debug" configuration only compiles for the native architecture, 
whereas the "Release" configuration for Xcode compiles all "source" 
files for the application for each architecture (and then lipos them 
together.)  A development-time Core Data data model (.xcdatamodel) is 
effectively considered a source file by Xcode, since it is processed 
into a .mom file by using the data model compiler.  The Xcode v2.x 
toolchain is not able to determine which source files are architecture 
agnostic -- and as a result, the data model is also compiled once for 
each architecture.

The resulting files are the same (since the architecture doesn't 
matter);  however, the Xcode build system creates the second file 
(with the extension) to ensure built files do not overwrite one 
another.  This is why you end up with two files, rather than just one.

Core Data isn't bothered by this particular circumstance:  if you 
attempt to load both models, the framework notices the collision in 
entity names -- but compares the entities and properties and finds 
them to be equal, so it just moves on (using one of the models.)  As a 
result, the second file should not affect your product (other than 
taking up space.)

This issue has been filed, and will be addressed in an upcoming Xcode 
tools release.

- matthew

= = = = =
Matthew Firlik
<email_removed>