Create a BigQuery client using a service account key file.

## Code sample

### C#


Before trying this sample, follow the C# setup instructions in the
[BigQuery quickstart using
client libraries](https://docs.cloud.google.com/bigquery/docs/quickstarts/quickstart-client-libraries).


For more information, see the
[BigQuery C# API
reference documentation](https://docs.cloud.google.com/dotnet/docs/reference/Google.Cloud.BigQuery.V2/latest).


To authenticate to BigQuery, set up Application Default Credentials.
For more information, see

[Set up authentication for client libraries](https://docs.cloud.google.com/bigquery/docs/authentication#client-libs).

    var credentials = GoogleCredential.FromFile(jsonPath);
    var client = BigQueryClient.Create(projectId, credentials);

### Java


Before trying this sample, follow the Java setup instructions in the
[BigQuery quickstart using
client libraries](https://docs.cloud.google.com/bigquery/docs/quickstarts/quickstart-client-libraries).


For more information, see the
[BigQuery Java API
reference documentation](https://docs.cloud.google.com/java/docs/reference/google-cloud-bigquery/latest/overview).


To authenticate to BigQuery, set up Application Default Credentials.
For more information, see

[Set up authentication for client libraries](https://docs.cloud.google.com/bigquery/docs/authentication#client-libs).

    public static void explicit() throws IOException {
      // TODO(developer): Replace these variables before running the sample.
      String projectId = "MY_PROJECT_ID";
      File credentialsPath = new File("path/to/your/service_account.json");

      // Load credentials from JSON key file. If you can't set the GOOGLE_APPLICATION_CREDENTIALS
      // environment variable, you can explicitly load the credentials file to construct the
      // credentials.
      GoogleCredentials credentials;
      try (FileInputStream serviceAccountStream = new FileInputStream(credentialsPath)) {
        credentials = ServiceAccountCredentials.fromStream(serviceAccountStream);
      }

      // Instantiate a client.
      BigQuery bigquery =
          BigQueryOptions.newBuilder()
              .setCredentials(credentials)
              .setProjectId(projectId)
              .build()
              .getService();

      // Use the client.
      System.out.println("Datasets:");
      for (Dataset dataset : bigquery.listDatasets().iterateAll()) {
        System.out.printf("%s%n", dataset.getDatasetId().getDataset());
      }
    }

### Python


Before trying this sample, follow the Python setup instructions in the
[BigQuery quickstart using
client libraries](https://docs.cloud.google.com/bigquery/docs/quickstarts/quickstart-client-libraries).


For more information, see the
[BigQuery Python API
reference documentation](https://docs.cloud.google.com/python/docs/reference/bigquery/latest).


To authenticate to BigQuery, set up Application Default Credentials.
For more information, see

[Set up authentication for client libraries](https://docs.cloud.google.com/bigquery/docs/authentication#client-libs).

    from google.cloud import https://docs.cloud.google.com/python/docs/reference/bigquery/latest
    from google.oauth2 import service_account

    # TODO(developer): Set key_path to the path to the service account key
    #                  file.
    # key_path = "path/to/service_account.json"

    credentials = service_account.Credentials.from_service_account_file(
        key_path,
        scopes=["https://www.googleapis.com/auth/cloud-platform"],
    )

    # Alternatively, use service_account.Credentials.from_service_account_info()
    # to set credentials directly via a json object rather than set a filepath
    # TODO(developer): Set key_json to the content of the service account key file.
    # credentials = service_account.Credentials.from_service_account_info(key_json)

    client = https://docs.cloud.google.com/python/docs/reference/bigquery/latest.https://docs.cloud.google.com/python/docs/reference/bigquery/latest/google.cloud.bigquery.client.Client.html(
        credentials=credentials,
        project=credentials.project_id,
    )

## What's next


To search and filter code samples for other Google Cloud products, see the
[Google Cloud sample browser](https://docs.cloud.google.com/docs/samples?product=bigquery).