feat(bigquery): add bigquery_multi_statement_transaction sample to ru…

bigquery/transactions/bigquery_multi_statement_transaction.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# [START bigquery_multi_statement_transaction]
+import sys
+
+from google.api_core import exceptions
+from google.cloud import bigquery
+
+
+def run_multi_statement_transaction(
+    project_id: str,
+    dataset_id: str,
+    source_table_id: str,
+    target_table_id: str,
+) -> None:
+    """Executes a multi-statement SQL transaction with exception rollback handling.
+
+    Args:
+        project_id: Google Cloud project ID (for example, 'example-project').
+        dataset_id: BigQuery dataset ID containing the tables
+            (for example, 'example_dataset').
+        source_table_id: Source staging table ID to merge and clear
+            (for example, 'example_new_arrivals').
+        target_table_id: Target inventory table ID to update atomically
+            (for example, 'example_inventory').
+    """
+    client = bigquery.Client(project=project_id)
+    source_ref = f"{project_id}.{dataset_id}.{source_table_id}"
+    target_ref = f"{project_id}.{dataset_id}.{target_table_id}"
+    # BigQuery scopes a multi-statement transaction to a single script query job, spawning child
+    # jobs for each statement and rolling back uncommitted changes on error.
+    sql = f"""
+        BEGIN
+          BEGIN TRANSACTION;
+          MERGE `{target_ref}` AS inv
+          USING `{source_ref}` AS src
+          ON inv.product = src.product
+          WHEN MATCHED THEN
+            UPDATE SET quantity = inv.quantity + src.quantity
+          WHEN NOT MATCHED THEN
+            INSERT (product, quantity) VALUES (src.product, src.quantity);
+          DELETE FROM `{source_ref}` WHERE TRUE;
+          COMMIT TRANSACTION;
+        EXCEPTION WHEN ERROR THEN
+          ROLLBACK TRANSACTION;
+          RAISE USING MESSAGE = @@error.message;
+        END;
+        SELECT
+          COUNT(*) AS inventory_rows
+        FROM `{target_ref}`;
+    """
+
+    try:
+        print(f"Running multi-statement transaction into: {target_ref}")
+        query_job = client.query(sql)
+        rows = list(query_job.result())
+    except exceptions.NotFound as err:
+        print(
+            f"error: tables '{source_table_id}' or '{target_table_id}' not found in dataset "
+            f"'{dataset_id}' for project '{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+    except exceptions.GoogleAPICallError as err:
+        print(
+            f"error: multi-statement transaction failed on '{source_table_id}' and "
+            f"'{target_table_id}' in dataset '{dataset_id}' for project '{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+
+    inventory_rows = rows[0].inventory_rows if rows else 0
+    print(f"Resource ID: {target_ref}")
+    print(f"Child Jobs: {query_job.num_child_jobs}")
+    print(f"Inventory Rows: {inventory_rows}")
+    print(f"Job ID: {query_job.job_id}")
+    print(f"Source Table: {source_ref}")
+    print("Transaction State: COMMITTED")
+
+
+# [END bigquery_multi_statement_transaction]

bigquery/transactions/bigquery_multi_statement_transaction_test.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest import mock
+
+import bigquery_multi_statement_transaction
+from google.api_core import exceptions
+import pytest
+
+
+def test_run_multi_statement_transaction_success(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    with mock.patch("google.cloud.bigquery.Client") as mock_client_cls:
+        mock_client = mock_client_cls.return_value
+        mock_job = mock.MagicMock()
+        mock_job.job_id = "example-job-123"
+        mock_job.num_child_jobs = 3
+        mock_row = mock.MagicMock()
+        mock_row.inventory_rows = 3
+        mock_job.result.return_value = [mock_row]
+        mock_client.query.return_value = mock_job
+
+        bigquery_multi_statement_transaction.run_multi_statement_transaction(
+            project_id="example-project",
+            dataset_id="example_dataset",
+            source_table_id="example_new_arrivals",
+            target_table_id="example_inventory",
+        )
+
+        mock_client.query.assert_called_once()
+        captured = capsys.readouterr()
+        assert (
+            "Resource ID: example-project.example_dataset.example_inventory"
+            in captured.out
+        )
+        assert "Child Jobs: 3" in captured.out
+        assert "Inventory Rows: 3" in captured.out
+        assert "Transaction State: COMMITTED" in captured.out
+
+
+def test_run_multi_statement_transaction_not_found(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    with mock.patch("google.cloud.bigquery.Client") as mock_client_cls:
+        mock_client = mock_client_cls.return_value
+        mock_client.query.side_effect = exceptions.NotFound("Table not found")
+
+        bigquery_multi_statement_transaction.run_multi_statement_transaction(
+            project_id="example-project",
+            dataset_id="example_dataset",
+            source_table_id="example_new_arrivals",
+            target_table_id="example_inventory",
+        )
+
+        captured = capsys.readouterr()
+        assert "error:" in captured.err
+        assert "example_inventory" in captured.err

bigquery/transactions/noxfile_config.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+TEST_CONFIG_OVERRIDE = {
+    # You can opt out from the test for specific Python versions.
+    "ignored_versions": ["2.7", "3.7", "3.8", "3.9", "3.10", "3.11"],
+    # Enforce type hints on new samples.
+    "enforce_type_hints": True,
+    "gcloud_project_env": "GOOGLE_CLOUD_PROJECT",
+    "pip_version_override": None,
+    "envs": {},
+}

bigquery/transactions/requirements-test.txt

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+pytest==9.0.3; python_version >= "3.10"

bigquery/transactions/requirements.txt

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+google-cloud-bigquery==3.47.0