For Google Drive apps that need to keep track of changes to items in Drive, theChanges collection provides an efficient way todetect changes. The collection works by providing the current state of eachitem, 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 hastheir 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 thechange 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 pointin time. A change does not provide a delta between revisions. Applicationsthat need to know which properties have changed should persist thepreviously known state of the item and compare.
Since changes represent the current state of an item, individual changeentries may be invalidated and replaced with a newer change entry forthe corresponding item.
Tombstones
Change entries for items no longer available to a user are marked as deletedin the change entry. Only the ID of the item is available in the change entry.
Each shared drive has its own change log. Even though a user may be a memberof a shared drive, certain changes are only reflected in the shared drive changelog 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 thepast, replaying the user’s change log alone won't correctly update the file'sstatus. Instead you must replay the shared drive’s change log to capture allchanges.
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 wellas 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 amember, 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 eventfor the shared drive appears in the user's change log. This impliesaccess to all items in the shared drive. The user does not receive changes foritems 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 basedon their usage. However, applications should not rely on these events when theuser is a member of the shared drive. Instead, use the shared drive's change log totrack 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 sameas non-shared Drive items that are shared directly with users.
If a user is a member of a shared drive, they can access that shared drive's changelog 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 onlyreflected on the item itself. While all direct or indirect children of thatitem will inherit this change there will not be a separate entry in the changelog for each of those items. Clients must eitherpropagate the new capabilities or refetch each item if a parent haschanged in order to fully reconstruct the changes.
