Looking Southwest Off Quandary
I’m presenting at the Microsoft SharePoint Conference 2012 in Las Vegas
August 30, 2012
A Simple SharePoint 2013 App To Create Geolocation Fields and Map Views
September 18, 2012

If you are creating an App for SharePoint 2013 and plan to access BCS external data by using the REST API to query an external list, keep in mind that you must package your External Content Type in the SPAPP as well.  If you do not, you will see this error returned by your request to the REST service:

Access denied. You do not have permission to perform this action or access this resource.

And you will see this error in the ULS logs when the query attempts to execute.

System.UnauthorizedAccessException: Apps cannot use External Content Types defined in the Business Data Connectivity Shared Service Application metadata catalog. Apps should package any External Content Type definitions in a BDC model file which is packaged and deployed as part of the SharePoint App.

If you try to use the CSOM Javascript API you will get an error similar to this one:

The metadata catalog file BusinessDataMetadataCatalog/BDCMetadata.bdcm could not be found on the site http://app-cbb5c08e54bb2a.apps.powder.ski/BCSExternalDataSPApp.

Only 43 days until ski season!