Retrieve changes

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

View on GitHub

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

View on GitHub

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

View on GitHub

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

View on GitHub

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

View on GitHub

/**
 * 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

View on GitHub

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

View on GitHub

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

View on GitHub

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

View on GitHub

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

View on GitHub

/**
 * 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.

Note: While not documented in changes.watch, the method does require a pageToken parameter similar to changes.list. This can be retrieved from changes.getStartPageToken.

For more information, see Notifications for resource changes.