I have the same issue. Lacie Mac OS Extended (Journaled)
Updated to Yosimite, Updated iPhoto
My iPhoto Library resides on my Lacie External Hard drive.
When I attempted to open iPhoto, I was given a message that the database needed to be updated or something like that. I accepted.
Photos were all moved to Old Masters. At this time, when I attempted to open iPhoto, it appeared completely empty (Masters folder was empty)
I ran "repair database" as suggested by photosb189 above. I waited patiently while iPhoto imported about 60,000 images into iPhoto from Old Masters (where they still reside). The process completed (although "finishing import" took a very long time... like overnight), however all of the quicktime files were rejected (over 1,000 of them). All of the photos were just imported in one big chunk with all of their previous organization lost. No years, no albums... just a big pile of 60,000 photos with my quicktimes rejected.
I'm a computer programmer myself. Can anyone point me to any documentation that might aid me in understanding why this occurred? or how iPhoto organizes things? I have a complete backup of everything (blu-ray discs & google drive). I'd love to see if I can find a way to get my iPhoto experience restored, or at least learn how I should have tried to solve this differently. I could still restore the old iPhoto package contents, but that should just bring me right back to square one.