When are media files re-downloaded?

Without wishing to derail this thread further, this does relate to a question I have on media and how/when they are updated.

  • If a form definition is updated do all media (CSV/image etc) also get redownloaded to device?
  • If any supporting media are updated without a form definition, update are they not updated on device?
  • I feel like I've seen reference to this elsewhere, but is there also a plan to include tilesets in media so they don't have to be sideloaded.

If media were downloaded initially and then only when updated they were redownloaded, this would be very helpful for sync speeds, I have been loading hundreds to thousands [*] of media and would like to use frequently updated CSV reference files also.

[*] in this case I didn't upload to Central, rather I sideloaded ~1gb / 6000x images over USB and upon definition update I renamed the folder version # so the latest definition had a path to the media)

Lastly, to bring it back on topic, being able to load and display and select locations/items in the placement-map appearance would be incredible!

Collect treats forms as "updated" if the form definition or the media files are different on the server than they are on the device. It won't redownload media files it's already got on the device however as it compares the hashes of local files with the hash the server returns for the media files and will skip files it already has. This optimization requires the server you're using to implement the Open Rosa spec correctly of course - Central does this, but a custom server might not. If you're using "Exactly Match Server" for form management, this should all be happening in the background.

In your use case, Collect should only redownload the updated CSV (and the form definition assuming you're changing the form version each time).

It's definitely been discussed before but it's not something the core team is currently working on.

Thanks for the confirmation, I expected something like this, but the time for a definition update is often so long I thought perhaps it was replacing everything.

I won't derail this thread any further and will ask elsewhere if needed.

@ahblake I've realized that I got my cases confused here: if the form version changes Collect doesn't check for matching hashes and simply downloads all media files into a new directory. I'd been thinking about the case where form version does not change but the media files do (a new one is added for example) - this case isn't actually possible with Central, but Collect does deal with it. We're going to work out if we can change the behaviour so that media files don't get redownloaded (for updates) without causing any problems.

Aha, that clears it up and explains why definition updates take as long as the initial form add.

I have some image heavy forms that will have frequent definition updates, not redownloading and duplicating in definition version folders would be great for update speed and device storage.

1 Like

I've split out this thread about media re-downloads because it stands on its own. @seadowg has made the update he described so that existing media files aren't re-downloaded. We should have a beta for that within the next 24 hours.


I'll test this shortly, fantastic!