chore: sample for snapshot isolation

README.md

@@ -190,6 +190,7 @@ Samples are in the [`samples/`](https://github.com/googleapis/nodejs-spanner/tre
 | Queryoptions | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/queryoptions.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/queryoptions.js,samples/README.md) |
 | Quickstart | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/quickstart.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/quickstart.js,samples/README.md) |
 | Read data with database role | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/read-data-with-database-role.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/read-data-with-database-role.js,samples/README.md) |
+| Performs a read-write transaction with isolation level option | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/repeatable-read.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/repeatable-read.js,samples/README.md) |
 | Sets a request tag for a single query | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/request-tag.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/request-tag.js,samples/README.md) |
 | Run Batch update with RPC priority | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/rpc-priority-batch-dml.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/rpc-priority-batch-dml.js,samples/README.md) |
 | Run partitioned update with RPC priority | [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/rpc-priority-partitioned-dml.js) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/rpc-priority-partitioned-dml.js,samples/README.md) |

samples/README.md

@@ -115,6 +115,7 @@ and automatic, synchronous replication for high availability.
   * [Queryoptions](#queryoptions)
   * [Quickstart](#quickstart)
   * [Read data with database role](#read-data-with-database-role)
+  * [Performs a read-write transaction with isolation level option](#performs-a-read-write-transaction-with-isolation-level-option)
   * [Sets a request tag for a single query](#sets-a-request-tag-for-a-single-query)
   * [Run Batch update with RPC priority](#run-batch-update-with-rpc-priority)
   * [Run partitioned update with RPC priority](#run-partitioned-update-with-rpc-priority)
@@ -1868,6 +1869,23 @@ __Usage:__
 
 
 
+### Performs a read-write transaction with isolation level option
+
+View the [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/repeatable-read.js).
+
+[![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/nodejs-spanner&page=editor&open_in_editor=samples/repeatable-read.js,samples/README.md)
+
+__Usage:__
+
+
+`node snapshot-isolation.js <INSTANCE_ID> <DATABASE_ID> <PROJECT_ID>`
+
+
+-----
+
+
+
+
 ### Sets a request tag for a single query
 
 View the [source code](https://github.com/googleapis/nodejs-spanner/blob/main/samples/request-tag.js).

samples/repeatable-read.js

@@ -0,0 +1,98 @@
+// Copyright 2025 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
+//
+//      http://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.
+
+// sample-metadata:
+//  title: Performs a read-write transaction with isolation level option
+//  usage: node snapshot-isolation.js <INSTANCE_ID> <DATABASE_ID> <PROJECT_ID>
+
+'use strict';
+
+function main(
+  instanceId = 'my-instance',
+  databaseId = 'my-database',
+  projectId = 'my-project-id'
+) {
+  // [START spanner_isolation_level]
+  // Imports the Google Cloud Spanner client library
+  const {Spanner, protos} = require('@google-cloud/spanner');
+  // The isolation level specified at the client-level will be applied
+  // to all RW transactions.
+  const isolationOptionsForClient = {
+    defaultTransactionOptions: {
+      isolationLevel:
+        protos.google.spanner.v1.TransactionOptions.IsolationLevel.SERIALIZABLE,
+    },
+  };
+
+  // Instantiates a client with defaultTransactionOptions
+  const spanner = new Spanner({
+    projectId: projectId,
+    defaultTransactionOptions: isolationOptionsForClient,
+  });
+
+  function runTransactionWithIsolationLevel() {
+    // Gets a reference to a Cloud Spanner instance and database
+    const instance = spanner.instance(instanceId);
+    const database = instance.database(databaseId);
+    // The isolation level specified at the request level takes precedence over the isolation level configured at the client level.
+    const isolationOptionsForTransaction = {
+      isolationLevel:
+        protos.google.spanner.v1.TransactionOptions.IsolationLevel
+          .REPEATABLE_READ,
+    };
+
+    database.runTransaction(
+      isolationOptionsForTransaction,
+      async (err, transaction) => {
+        if (err) {
+          console.error(err);
+          return;
+        }
+        try {
+          const query =
+            'SELECT AlbumTitle FROM Albums WHERE SingerId = 1 AND AlbumId = 1';
+          const results = await transaction.run(query);
+          // Gets first album's title
+          const rows = results[0].map(row => row.toJSON());
+          const albumTitle = rows[0].AlbumTitle;
+          console.log(`previous album title ${albumTitle}`);
+
+          const update =
+            "UPDATE Albums SET AlbumTitle = 'New Album Title' WHERE SingerId = 1 AND AlbumId = 1";
+          const [rowCount] = await transaction.runUpdate(update);
+          console.log(
+            `Successfully updated ${rowCount} record in Albums table.`
+          );
+          await transaction.commit();
+          console.log(
+            'Successfully executed read-write transaction with isolationLevel option.'
+          );
+        } catch (err) {
+          console.error('ERROR:', err);
+        } finally {
+          transaction.end();
+          // Close the database when finished.
+          await database.close();
+        }
+      }
+    );
+  }
+  runTransactionWithIsolationLevel();
+  // [END spanner_isolation_level]
+}
+process.on('unhandledRejection', err => {
+  console.error(err.message);
+  process.exitCode = 1;
+});
+main(...process.argv.slice(2));

samples/system-test/spanner.test.js

@@ -675,6 +675,24 @@ describe('Autogenerated Admin Clients', () => {
     );
   });
 
+  // isolation_level_option
+  it('should run read-write transaction with isolation level option set', () => {
+    const output = execSync(
+      `node snapshot-isolation.js ${INSTANCE_ID} ${DATABASE_ID} ${PROJECT_ID}`
+    );
+    console.log(output);
+    assert.match(
+      output,
+      new RegExp('Successfully updated 1 record into the Singers table.')
+    );
+    assert.match(
+      output,
+      new RegExp(
+        'Successfully executed read-write transaction with isolationLevel option.'
+      )
+    );
+  });
+
   // query with RPC priority for run command
   it('should use RPC priority from request options for run command', async () => {
     const output = execSync(