Add a query cancelling example (#42)

* Add a query cancelling example

* Update examples/cancel_operation.js

Co-authored-by: Jesse <jwhitehouse@airpost.net>

Co-authored-by: Jesse <jwhitehouse@airpost.net>

Author: kravets-levko

examples/cancel_operation.js

@@ -0,0 +1,70 @@
+const { DBSQLClient } = require('../');
+
+const client = new DBSQLClient();
+
+const host = '****.databricks.com';
+const path = '/sql/1.0/endpoints/****';
+const token = 'dapi********************************';
+
+async function getQueryResult(operation) {
+  const utils = DBSQLClient.utils;
+
+  await utils.waitUntilReady(operation, false, () => {});
+  console.log('Fetching data...');
+  await utils.fetchAll(operation);
+  await operation.close();
+
+  return utils.getResult(operation).getValue();
+}
+
+async function cancelQuery(operation) {
+  return new Promise((resolve, reject) => {
+    operation
+      .cancel()
+      .then((status) => {
+        if (status.success()) {
+          resolve();
+        } else {
+          reject(new Error(status.getInfo().join('\n')));
+        }
+      })
+      .catch(reject);
+  });
+}
+
+client
+  .connect({ host, path, token })
+  .then(async (client) => {
+    const session = await client.openSession();
+
+    // Execute long-running query
+    console.log('Running query...');
+    const queryOperation = await session.executeStatement(
+      `
+        SELECT id 
+        FROM RANGE(100000000)
+        ORDER BY RANDOM() + 2 asc
+      `,
+      { runAsync: true },
+    );
+    getQueryResult(queryOperation)
+      .then((result) => console.log(`Query returned ${result.length} row(s)`))
+      .catch((error) => console.log(`Failed to load data: ${error.message}`));
+
+    // Cancel query
+    cancelQuery(queryOperation)
+      .then(() => console.log('Query cancelled'))
+      .catch((error) => console.log(`Failed to cancel query: ${error.message}`));
+
+    // Expected output in console:
+    //
+    // > node examples/cancel_operation.js                                                                                                                                  Node 16.13.1
+    // Running query...
+    // Query cancelled
+    // Failed to load data: The operation was canceled by a client
+
+    await session.close();
+  })
+  .catch((error) => {
+    console.log(error);
+  });