[enhance] access datasource information with dot notation to fix MQL

Deconstructing the dataSource caused an exception when no dataSource was set
with the query.

Accessing by dot notation with null operator fixes this issue.

Adding tests to prevent this happening again

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>

src/plugins/query_enhancements/server/utils/facet.test.ts

@@ -0,0 +1,119 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { Logger } from 'opensearch-dashboards/server';
+import { Facet, FacetProps } from './facet';
+
+describe('Facet', () => {
+  let facet: Facet;
+  let mockClient: jest.Mock;
+  let mockLogger: jest.Mocked<Logger>;
+  let mockContext: any;
+  let mockRequest: any;
+
+  beforeEach(() => {
+    mockClient = jest.fn();
+    mockLogger = ({
+      error: jest.fn(),
+    } as unknown) as jest.Mocked<Logger>;
+
+    const props: FacetProps = {
+      client: { asScoped: jest.fn().mockReturnValue({ callAsCurrentUser: mockClient }) },
+      logger: mockLogger,
+      endpoint: 'test-endpoint',
+    };
+
+    facet = new Facet(props);
+
+    mockContext = {
+      dataSource: {
+        opensearch: {
+          legacy: {
+            getClient: jest.fn().mockReturnValue({ callAPI: mockClient }),
+          },
+        },
+      },
+    };
+
+    mockRequest = {
+      body: {
+        query: {
+          query: 'test query',
+          dataset: {
+            dataSource: {
+              id: 'test-id',
+              meta: {
+                name: 'test-name',
+                sessionId: 'test-session',
+              },
+            },
+          },
+        },
+        format: 'jdbc',
+        lang: 'sql',
+      },
+    };
+  });
+
+  describe('describeQuery', () => {
+    it('should handle request with complete dataset information', async () => {
+      mockClient.mockResolvedValue({ result: 'success' });
+
+      const result = await facet.describeQuery(mockContext, mockRequest);
+
+      expect(result).toEqual({ success: true, data: { result: 'success' } });
+      expect(mockClient).toHaveBeenCalledWith('test-endpoint', {
+        body: {
+          query: 'test query',
+          datasource: 'test-name',
+          sessionId: 'test-session',
+          lang: 'sql',
+        },
+      });
+    });
+
+    it('should handle request with missing dataSource', async () => {
+      mockRequest.body.query.dataset.dataSource = undefined;
+      mockClient.mockResolvedValue({ result: 'success' });
+
+      const result = await facet.describeQuery(mockContext, mockRequest);
+
+      expect(result).toEqual({ success: true, data: { result: 'success' } });
+      expect(mockClient).toHaveBeenCalledWith('test-endpoint', {
+        body: {
+          query: 'test query',
+          lang: 'sql',
+        },
+      });
+    });
+
+    it('should handle request with missing dataset', async () => {
+      mockRequest.body.query.dataset = undefined;
+      mockClient.mockResolvedValue({ result: 'success' });
+
+      const result = await facet.describeQuery(mockContext, mockRequest);
+
+      expect(result).toEqual({ success: true, data: { result: 'success' } });
+      expect(mockClient).toHaveBeenCalledWith('test-endpoint', {
+        body: {
+          query: 'test query',
+          lang: 'sql',
+        },
+      });
+    });
+
+    it('should handle errors', async () => {
+      const error = new Error('Test error');
+      mockClient.mockRejectedValue(error);
+
+      const result = await facet.describeQuery(mockContext, mockRequest);
+
+      expect(result).toEqual({ success: false, data: error });
+      expect(mockLogger.error).toHaveBeenCalledWith(
+        'Facet fetch: test-endpoint: Error: Test error'
+      );
+    });
+  });
+});

src/plugins/query_enhancements/server/utils/facet.ts

@@ -38,8 +38,8 @@ export class Facet {
   ): Promise<FacetResponse> => {
     try {
       const query: Query = request.body.query;
-      const { dataSource } = query.dataset!;
-      const { meta } = dataSource!;
+      const dataSource = query.dataset?.dataSource;
+      const meta = dataSource?.meta;
       const { format, lang } = request.body;
       const params = {
         body: {