P: Add SDK support for moving photos between folders in the catalog

One possible way of moving a photo to another folder (which only became possible starting with LR 14.3):

1. Save the photo’s metadata to disk using the long-undocumented photo:saveMetadata().  It’s been present for many, many years.

2. Use catalog:getTargetPhoto() and :getTargetPhotos() to save the current selection and then set the selection to the photos to be moved.

3. Use LrSelection.removeFromCatalog() to remove the selected photos from the catalog.

4. Use LrFileUtils.move() to move the photos, along with any .xmp and .acr sidecars, to the target folder.

5. Use catalog:addPhoto() to import the photos into the catalog from their new location.

Note that the SDK is riddled with race conditions and undocumented asynchrony. Here is the utility function many of my plugins use to safely save a photo’s metadata to disk:

--[[----------------------------------------------------------------------------
public string path, string err
saveMetadata (LrPhoto photo)

Initiates a Metadata > Save Metadata To File for the photo and waits for up
to 10 seconds for it complete.  Ignores videos and virtual copies.

Returns in "path" the file to which the metadata was saved (a .xmp for
raws, nil for videos and virtual copies, the photo file itself otherwise).

If a photo can't be saved, returns an error message in "err".

Starting in LR 15, photo:saveMetadata() can return before saving to disk.
This might have occurred many years previously, not sure, but it didn't
occur in LR 14.
------------------------------------------------------------------------------]]

function Util.saveMetadata (photo) 
    local fileFormat = photo:getRawMetadata ("fileFormat")
    local isVirtualCopy = photo:getRawMetadata ("isVirtualCopy") 
    if fileFormat == "VIDEO" or isVirtualCopy then return nil, nil end 

    local function returnErr (err)
        local msg = Util.logError ("Couldn't save metadata to file: %s\n%s",
            photo.path, err)
        return photo.path, msg
        end

        --[[ Sometimes photo:saveMetadata() fails with an obscure
        error, perhaps because of a race inside LR. Retrying 
        for up to 10 seconds seems to reduce the occurrences. ]]
    local startTime = currentTime ()
    for i = 1, math.huge do 
        local success, err = LrTasks.pcall (photo.saveMetadata, photo)
        if success then 
            if i > 1 then 
                Debug.logn ("Util.saveMetadata:", i, 
                    "tries needed for successful save", photo.path)
                end
            break
            end
        if i >= 10 and not success then return returnErr (err) end 
        LrTasks.sleep (1)
        end

        --[[ Starting in LR 15, photo:saveMetadata () is asynchronous.
        Wait until we observe the file's modification time changes. ]]
    local paths = fileFormat ~= "RAW" and {photo.path} or 
        {removeExtension (photo.path) .. ".xmp", 
         photo.path .. "_xmp"}

    local delay, waitTime, maxWaitTime = 0.01, 0, 5
    while true do
        if currentTime () > startTime + maxWaitTime then 
            return returnErr ("Timed out")
            end

        for _, path in ipairs (paths) do 
            local modTime = fileAttributes (path).fileModificationDate or 0
            if modTime >= startTime then 
                if waitTime > 0 then
                    Util.logError ("Util.saveMetadata wait: %g secs %s", 
                        waitTime, path)
                    end
                return path, nil 
                end
            end

        LrTasks.sleep (delay)
        waitTime = waitTime + delay
        delay = math.min (delay * 1.5, 0.2)
        end


    return path, nil
    end

Really need this - not sure why the request has been open for more than 3 years

I could really use the move feature as well.

While finally automating our complete Lightroom workflow top to bottom, I now discover there is no photo:move() and photo:delete().

I am so extremely dissappointed right now. For what reason could these functions be possible missing from the SDK?

There was a years-old feature request for this (and to delete photos from the catalog) in the old feedback forum, but apparently it didn't get copied over when Adobe transitioned to the new forum platform.