I want to restrict the list of objects provided when editing a data item with a one to one relationship to another object, who's parent has a one to many relationship to an object also with a one to one relationship with the original object....
Customer has many Jobs
Customer has many Sites
Job has one Customer
Job has one Site (this should be restricted to only those under Customer)
Thanks martimiz - I re-read my question and realised that I didn't really explain my problem fully.
I have extended ModelAdmin so that I can manage my customer Objects through the admin interface (actually I have inherited a half finished project that uses SilverStripe, and this is the first time I have used it, so when I say I, i mean the project i'm working on!).
When editing a job, I want to ensure that the list of available Sites (in the built in drop-down list) is restricted to only the Sites of the Customer that the Job is for, if that makes sense!