For Google Drive apps that need to keep track of changes to items in Drive, the Changes collection provides an efficient way to detect changes. The collection works by providing the current state of each item, if and only if the item has changed since a given point in time.
Google Drive keeps a change log for each user and shared drive. Each has their own record of changes to items that are of interest to them.
To track changes for all items visible to a user, both the user change log and the change logs for all shared drives the user is a member of need to be replayed.
Enable change entries
A change entry represents the state of the file or shared drive at a given point in time. A change does not provide a delta between revisions. Applications that need to know which properties have changed should persist the previously known state of the item and compare.
Since changes represent the current state of an item, individual change entries may be invalidated and replaced with a newer change entry for the corresponding item.
Change entries for items no longer available to a user are marked as
in the change entry. Only the ID of the item is available in the change entry.
Track shared drives
Each shared drive has it's own change log. Even though a user may be a member of a shared drive, certain changes are only reflected in the shared drive change log and never in the user’s change log. If a file belongs to a shared drive, even if the file still appeared on the user’s change log at some point in the past, replaying the user’s change log alone won't correctly update the file's status. Instead you must replay the shared drive’s change log to capture all changes.
What is included in a user's change log
A user’s change log includes changes to shared drives they're a member of as well as changes to files in the user's corpus. For more information about corpora, see Changes and revisions overview.
These shared drive changes appear on the user’s change log:
- The user becomes a member of a shared drive.
- The user is no longer a member of a shared drive.
- There is a directly relevant change to a shared drive in which the user is a
member, for example:
- The user’s access level on that shared drive changed.
- The shared drive is renamed.
When a user becomes a member of a shared drive, a single change event for the shared drive appears in the user's change log. This implies access to all items in the shared drive. The user does not receive changes for items contained inside the shared drive when they become a member.
Members of a shared drive may see change events for items in a shared drive based on their usage. However, applications should not rely on these events when the user is a member of the shared drive. Instead, use the shared drive's change log to track changes.
If a non-member is granted file access to individual items in a shared drive, changes to those items are tracked in the user's change log. This is the same as non-shared Drive items that are shared directly with users.
Changes that appear on a shared drive change log
If a user is a member of a shared drive, they can access that shared drive's change log which contains:
- Any changes to the shared drive itself, such as addition or removal of a member
- Direct changes to the items contained in the shared drive.
Syncing permissions and capabilities
Permission changes to shared drive or items inside a shared drive are only reflected on the item itself. While all direct or indirect children of that item will inherit this change there will not be a separate entry in the change log for each of those items. Clients must either propagate the new capabilities or refetch each item if a parent has changed in order to fully reconstruct the changes.