For Google Drive apps that must track changes to files, the changes
collection provides an efficient
way to detect all file changes, including those shared with a user. If the file
has changed, the collection provides the current state of each file.
Get start page token
To request the page token for the current state of the account, use the changes.getStartPageToken
.
Store and use this token in your initial call to changes.list
.
To retrieve the current page token:
Java
drive/snippets/drive_v3/src/main/java/FetchStartPageToken.java
import com.google.api.client.googleapis.json.GoogleJsonResponseException ; import com.google.api.client.http.HttpRequestInitializer ; import com.google.api.client.http.javanet.NetHttpTransport ; import com.google.api.client.json.gson.GsonFactory ; import com.google.api.services.drive.Drive ; import com.google.api.services.drive.DriveScopes ; import com.google.api.services.drive.model.StartPageToken ; import com.google.auth.http.HttpCredentialsAdapter ; import com.google.auth.oauth2.GoogleCredentials ; import java.io.IOException ; import java.util.Arrays ; /* Class to demonstrate use-case of Drive's fetch start page token */ public class FetchStartPageToken { /** * Retrieve the start page token for the first time. * * @return Start page token as String. * @throws IOException if file is not found */ public static String fetchStartPageToken () throws IOException { /*Load pre-authorized user credentials from the environment. TODO(developer) - See https://developers.google.com/identity for guides on implementing OAuth2 for your application. */ GoogleCredentials credentials = GoogleCredentials . getApplicationDefault () . createScoped ( Arrays . asList ( DriveScopes . DRIVE_FILE )); HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter ( credentials ); // Build a new authorized API client service. Drive service = new Drive . Builder ( new NetHttpTransport (), GsonFactory . getDefaultInstance (), requestInitializer ) . setApplicationName ( "Drive samples" ) . build (); try { StartPageToken response = service . changes () . getStartPageToken (). execute (); System . out . println ( "Start token: " + response . getStartPageToken ()); return response . getStartPageToken (); } catch ( GoogleJsonResponseException e ) { // TODO(developer) - handle error appropriately System . err . println ( "Unable to fetch start page token: " + e . getDetails ()); throw e ; } } }
Python
drive/snippets/drive-v3/change_snippet/fetch_start_page_token.py
import google.auth from googleapiclient.discovery import build from googleapiclient.errors import HttpError def fetch_start_page_token (): """Retrieve page token for the current state of the account. Returns & prints : start page token Load pre-authorized user credentials from the environment. TODO(developer) - See https://developers.google.com/identity for guides on implementing OAuth2 for the application. """ creds , _ = google . auth . default () try : # create drive api client service = build ( "drive" , "v3" , credentials = creds ) # pylint: disable=maybe-no-member response = service . changes () . getStartPageToken () . execute () print ( f 'Start token: { response . get ( "startPageToken" ) } ' ) except HttpError as error : print ( f "An error occurred: { error } " ) response = None return response . get ( "startPageToken" ) if __name__ == "__main__" : fetch_start_page_token ()
PHP
drive/snippets/drive_v3/src/DriveFetchStartPageToken.php
< ?php use Google\Client; use Google\Service\Drive; # TODO - PHP client currently chokes on fetching start page token function fetchStartPageToken() { try { $client = new Client(); $client->useApplicationDefaultCredentials(); $client->addScope(Drive::DRIVE); $driveService = new Drive($client); $response = $driveService->changes->getStartPageToken(); printf("Start token: %s\n", $response->startPageToken); return $response->startPageToken; } catch(Exception $e) { echo "Error Message: ".$e; } }
.NET
drive/snippets/drive_v3/DriveV3Snippets/FetchStartPageToken.cs
using Google.Apis.Auth.OAuth2 ; using Google.Apis.Drive.v3 ; using Google.Apis.Services ; namespace DriveV3Snippets { // Class to demonstrate use-case of Drive's fetch start page token public class FetchStartPageToken { /// <summary> /// Retrieve the starting page token. /// </summary> /// <returns>start page token as String, null otherwise.</returns> public static string DriveFetchStartPageToken () { try { /* Load pre-authorized user credentials from the environment. TODO(developer) - See https://developers.google.com/identity for guides on implementing OAuth2 for your application. */ GoogleCredential credential = GoogleCredential . GetApplicationDefault () . CreateScoped ( DriveService . Scope . Drive ); // Create Drive API service. var service = new DriveService ( new BaseClientService . Initializer { HttpClientInitializer = credential , ApplicationName = "Drive API Snippets" }); var response = service . Changes . GetStartPageToken (). Execute (); // Prints the token value. Console . WriteLine ( "Start token: " + response . StartPageTokenValue ); return response . StartPageTokenValue ; } catch ( Exception e ) { // TODO(developer) - handle error appropriately if ( e is AggregateException ) { Console . WriteLine ( "Credential Not found" ); } else { throw ; } } return null ; } } }
Node.js
drive/snippets/drive_v3/change_snippets/fetch_start_page_token.js
/** * Retrieve page token for the current state of the account. **/ async function fetchStartPageToken () { // Get credentials and build service // TODO (developer) - Use appropriate auth mechanism for your app const { GoogleAuth } = require ( 'google-auth-library' ); const { google } = require ( 'googleapis' ); const auth = new GoogleAuth ({ scopes : 'https://www.googleapis.com/auth/drive.appdata' , }); const service = google . drive ({ version : 'v3' , auth }); try { const res = await service . changes . getStartPageToken ({}); const token = res . data . startPageToken ; console . log ( 'start token: ' , token ); return token ; } catch ( err ) { // TODO(developer) - Handle error throw err ; } }
Get changes
To retrieve the list of changes for the currently signed in user, send a GET
request to the changes
collection, as detailed in the changes.list
.
Entries in the changes
collection are in chronological order (the oldest
changes appear first). The includeRemoved
and restrictToMyDrive
query
parameters determine whether the response should include removed or shared
items.
Java
drive/snippets/drive_v3/src/main/java/FetchChanges.java
import com.google.api.client.googleapis.json.GoogleJsonResponseException ; import com.google.api.client.http.HttpRequestInitializer ; import com.google.api.client.http.javanet.NetHttpTransport ; import com.google.api.client.json.gson.GsonFactory ; import com.google.api.services.drive.Drive ; import com.google.api.services.drive.DriveScopes ; import com.google.api.services.drive.model.ChangeList ; import com.google.auth.http.HttpCredentialsAdapter ; import com.google.auth.oauth2.GoogleCredentials ; import java.io.IOException ; import java.util.Arrays ; /* Class to demonstrate use-case of Drive's fetch changes in file. */ public class FetchChanges { /** * Retrieve the list of changes for the currently authenticated user. * * @param savedStartPageToken Last saved start token for this user. * @return Saved token after last page. * @throws IOException if file is not found */ public static String fetchChanges ( String savedStartPageToken ) throws IOException { /*Load pre-authorized user credentials from the environment. TODO(developer) - See https://developers.google.com/identity for guides on implementing OAuth2 for your application.*/ GoogleCredentials credentials = GoogleCredentials . getApplicationDefault () . createScoped ( Arrays . asList ( DriveScopes . DRIVE_FILE )); HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter ( credentials ); // Build a new authorized API client service. Drive service = new Drive . Builder ( new NetHttpTransport (), GsonFactory . getDefaultInstance (), requestInitializer ) . setApplicationName ( "Drive samples" ) . build (); try { // Begin with our last saved start token for this user or the // current token from getStartPageToken() String pageToken = savedStartPageToken ; while ( pageToken != null ) { ChangeList changes = service . changes (). list ( pageToken ) . execute (); for ( com . google . api . services . drive . model . Change change : changes . getChanges ()) { // Process change System . out . println ( "Change found for file: " + change . getFileId ()); } if ( changes . getNewStartPageToken () != null ) { // Last page, save this token for the next polling interval savedStartPageToken = changes . getNewStartPageToken (); } pageToken = changes . getNextPageToken (); } return savedStartPageToken ; } catch ( GoogleJsonResponseException e ) { // TODO(developer) - handle error appropriately System . err . println ( "Unable to fetch changes: " + e . getDetails ()); throw e ; } } }
Python
drive/snippets/drive-v3/change_snippet/fetch_changes.py
import google.auth from googleapiclient.discovery import build from googleapiclient.errors import HttpError def fetch_changes ( saved_start_page_token ): """Retrieve the list of changes for the currently authenticated user. prints changed file's ID Args: saved_start_page_token : StartPageToken for the current state of the account. Returns: saved start page token. Load pre-authorized user credentials from the environment. TODO(developer) - See https://developers.google.com/identity for guides on implementing OAuth2 for the application. """ creds , _ = google . auth . default () try : # create drive api client service = build ( "drive" , "v3" , credentials = creds ) # Begin with our last saved start token for this user or the # current token from getStartPageToken() page_token = saved_start_page_token # pylint: disable=maybe-no-member while page_token is not None : response = ( service . changes () . list ( pageToken = page_token , spaces = "drive" ) . execute () ) for change in response . get ( "changes" ): # Process change print ( f 'Change found for file: { change . get ( "fileId" ) } ' ) if "newStartPageToken" in response : # Last page, save this token for the next polling interval saved_start_page_token = response . get ( "newStartPageToken" ) page_token = response . get ( "nextPageToken" ) except HttpError as error : print ( f "An error occurred: { error } " ) saved_start_page_token = None return saved_start_page_token if __name__ == "__main__" : # saved_start_page_token is the token number fetch_changes ( saved_start_page_token = 209 )
PHP
drive/snippets/drive_v3/src/DriveFetchChanges.php
< ?php use Google\Client; use Google\Service\Drive; # TODO - PHP client currently chokes on fetching start page token function fetchChanges() { try { $client = new Client(); $client->useApplicationDefaultCredentials(); $client->addScope(Drive::DRIVE); $driveService = new Drive($client); # Begin with our last saved start token for this user or the # current token from getStartPageToken() $savedStartPageToken = readLine("Enter Start Page Token: "); $pageToken = $savedStartPageToken; while ($pageToken != null) { $response = $driveService->changes->listChanges($pageToken, array( 'spaces' => 'drive' )); foreach ($response->changes as $change) { // Process change printf("Change found for file: %s", $change->fileId); } if ($response->newStartPageToken != null) { // Last page, save this token for the next polling interval $savedStartPageToken = $response->newStartPageToken; } $pageToken = $response->nextPageToken; } echo $savedStartPageToken; } catch(Exception $e) { echo "Error Message: ".$e; } } require_once 'vendor/autoload.php';
.NET
drive/snippets/drive_v3/DriveV3Snippets/FetchChanges.cs
using Google.Apis.Auth.OAuth2 ; using Google.Apis.Drive.v3 ; using Google.Apis.Services ; namespace DriveV3Snippets { // Class to demonstrate use-case of Drive's fetch changes in file. public class FetchChanges { /// <summary> /// Retrieve the list of changes for the currently authenticated user. /// prints changed file's ID /// </summary> /// <param name="savedStartPageToken">last saved start token for this user.</param> /// <returns>saved token for the current state of the account, null otherwise.</returns> public static string DriveFetchChanges ( string savedStartPageToken ) { try { /* Load pre-authorized user credentials from the environment. TODO(developer) - See https://developers.google.com/identity for guides on implementing OAuth2 for your application. */ GoogleCredential credential = GoogleCredential . GetApplicationDefault () . CreateScoped ( DriveService . Scope . Drive ); // Create Drive API service. var service = new DriveService ( new BaseClientService . Initializer { HttpClientInitializer = credential , ApplicationName = "Drive API Snippets" }); // Begin with our last saved start token for this user or the // current token from GetStartPageToken() string pageToken = savedStartPageToken ; while ( pageToken != null ) { var request = service . Changes . List ( pageToken ); request . Spaces = "drive" ; var changes = request . Execute (); foreach ( var change in changes . Changes ) { // Process change Console . WriteLine ( "Change found for file: " + change . FileId ); } if ( changes . NewStartPageToken != null ) { // Last page, save this token for the next polling interval savedStartPageToken = changes . NewStartPageToken ; } pageToken = changes . NextPageToken ; } return savedStartPageToken ; } catch ( Exception e ) { // TODO(developer) - handle error appropriately if ( e is AggregateException ) { Console . WriteLine ( "Credential Not found" ); } else { throw ; } } return null ; } } }
Node.js
drive/snippets/drive_v3/change_snippets/fetch_changes.js
/** * Retrieve the list of changes for the currently authenticated user. * @param {string} savedStartPageToken page token got after executing fetch_start_page_token.js file **/ async function fetchChanges ( savedStartPageToken ) { // Get credentials and build service // TODO (developer) - Use appropriate auth mechanism for your app const { GoogleAuth } = require ( 'google-auth-library' ); const { google } = require ( 'googleapis' ); const auth = new GoogleAuth ({ scopes : 'https://www.googleapis.com/auth/drive.readonly' , }); const service = google . drive ({ version : 'v3' , auth }); try { let pageToken = savedStartPageToken ; do { const res = await service . changes . list ({ pageToken : savedStartPageToken , fields : '*' , }); res . data . changes . forEach (( change ) = > { console . log ( 'change found for file: ' , change . fileId ); }); pageToken = res . data . newStartPageToken ; return pageToken ; } while ( pageToken ); } catch ( err ) { // TODO(developer) - Handle error throw err ; } }
The changes
collection in the response
might contain a nextPageToken
. If the nextPageToken
is listed, it can be used to gather the
next page of changes. If it's not listed, the client application should store
the newStartPageToken
in the response for future use. With the page token
stored, the client application is prepared to query again for future changes.
Receive notifications
Use the changes.watch
method to
subscribe to updates in the change log. Notifications don't contain details
about the changes. Instead, they indicate that new changes are available. To
retrieve the actual changes, poll the change feed as described in Get
changes
.
For more information, see Notifications for resource changes .
