[v9.4.x] Prometheus: Table format throwing error on empty result (#63062)

Prometheus: Table format throwing error on empty result (#63053)

* fix bug in prometheus table view which is throwing error when a query returns no results

(cherry picked from commit 79b750a4b2)

Co-authored-by: Galen Kistler <109082771+gtk-grafana@users.noreply.github.com>

public/app/plugins/datasource/prometheus/result_transformer.test.ts

@@ -721,6 +721,47 @@ describe('Prometheus Result Transformer', () => {
       expect(tableDf.fields[2].values.get(0)).toBe('value2');
       expect(tableDf.fields[3].name).toBe('Value');
     });
+
+    // Queries do not always return results
+    it('transforms dataFrame and empty dataFrame mock responses to table dataFrames', () => {
+      const value1 = 'value1';
+      const value2 = 'value2';
+
+      const dataframes = [
+        new MutableDataFrame({
+          refId: 'A',
+          fields: [
+            { name: 'time', type: FieldType.time, values: [6, 5, 4] },
+            {
+              name: 'value',
+              type: FieldType.number,
+              values: [6, 5, 4],
+              labels: { label1: value1, label2: value2 },
+            },
+          ],
+        }),
+        new MutableDataFrame({
+          refId: 'B',
+          fields: [],
+        }),
+      ];
+
+      const transformedTableDataFrames = transformDFToTable(dataframes);
+      // Expect the first query to still return valid results
+      expect(transformedTableDataFrames[0].fields.length).toBe(4);
+      expect(transformedTableDataFrames[0].fields[0].name).toBe('Time');
+      expect(transformedTableDataFrames[0].fields[1].name).toBe('label1');
+      expect(transformedTableDataFrames[0].fields[1].values.get(0)).toBe(value1);
+      expect(transformedTableDataFrames[0].fields[2].name).toBe('label2');
+      expect(transformedTableDataFrames[0].fields[2].values.get(0)).toBe(value2);
+      expect(transformedTableDataFrames[0].fields[3].name).toBe('Value #A');
+
+      // Expect the invalid/empty results not to throw an error and to return empty arrays
+      expect(transformedTableDataFrames[1].fields[1].labels).toBe(undefined);
+      expect(transformedTableDataFrames[1].fields[1].name).toBe('Value #B');
+      expect(transformedTableDataFrames[1].fields[1].values.toArray()).toEqual([]);
+      expect(transformedTableDataFrames[1].fields[0].values.toArray()).toEqual([]);
+    });
   });
 
   describe('transform', () => {

public/app/plugins/datasource/prometheus/result_transformer.ts

@@ -196,7 +196,7 @@ export function transformDFToTable(dfs: DataFrame[]): DataFrame[] {
     // Fill labelsFields with labels from dataFrames
     dataFramesByRefId[refId].forEach((df) => {
       const frameValueField = df.fields[1];
-      const promLabels = frameValueField.labels ?? {};
+      const promLabels = frameValueField?.labels ?? {};
 
       Object.keys(promLabels)
         .sort()
@@ -216,8 +216,10 @@ export function transformDFToTable(dfs: DataFrame[]): DataFrame[] {
 
     // Fill valueField, timeField and labelFields with values
     dataFramesByRefId[refId].forEach((df) => {
-      df.fields[0].values.toArray().forEach((value) => timeField.values.add(value));
-      df.fields[1].values.toArray().forEach((value) => {
+      const timeFields = df.fields[0]?.values ?? new ArrayVector();
+      const dataFields = df.fields[1]?.values ?? new ArrayVector();
+      timeFields.toArray().forEach((value) => timeField.values.add(value));
+      dataFields.toArray().forEach((value) => {
         valueField.values.add(parseSampleValue(value));
         const labelsForField = df.fields[1].labels ?? {};
         labelFields.forEach((field) => field.values.add(getLabelValue(labelsForField, field.name)));