JoinDataFrames: Keep field name if possible

packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts

@@ -1,5 +1,6 @@
 import { toDataFrame } from '../../dataframe/processDataFrame';
-import { FieldType } from '../../types/dataFrame';
+import { getFieldDisplayName } from '../../field';
+import { DataFrame, FieldType } from '../../types/dataFrame';
 import { mockTransformationsRegistry } from '../../utils/tests/mockTransformationsRegistry';
 
 import { calculateFieldTransformer } from './calculateField';
@@ -266,6 +267,64 @@ describe('align frames', () => {
     `);
   });
 
+  it('maintains naming convention after join', () => {
+    const series1 = toDataFrame({
+      name: 'Muta',
+      fields: [
+        { name: 'Time', type: FieldType.time, values: [1000, 2000] },
+        { name: 'Value', type: FieldType.number, values: [1, 100] },
+      ],
+    });
+    expect(getFieldDisplayNames([series1])).toMatchInlineSnapshot(`
+      [
+        "Time",
+        "Muta",
+      ]
+    `);
+    expect(getFieldNames([series1])).toMatchInlineSnapshot(`
+      [
+        "Time",
+        "Value",
+      ]
+    `);
+
+    const series2 = toDataFrame({
+      name: 'Muta',
+      fields: [
+        { name: 'Time', type: FieldType.time, values: [1000] },
+        { name: 'Value', type: FieldType.number, values: [150] },
+      ],
+    });
+    expect(getFieldDisplayNames([series2])).toMatchInlineSnapshot(`
+      [
+        "Time",
+        "Muta",
+      ]
+    `);
+    expect(getFieldNames([series2])).toMatchInlineSnapshot(`
+      [
+        "Time",
+        "Value",
+      ]
+    `);
+
+    const out = joinDataFrames({ frames: [series1, series2] })!;
+    expect(getFieldDisplayNames([out])).toMatchInlineSnapshot(`
+      [
+        "Time",
+        "Muta 1",
+        "Muta 2",
+      ]
+    `);
+    expect(getFieldNames([out])).toMatchInlineSnapshot(`
+      [
+        "Time",
+        "Muta",
+        "Muta",
+      ]
+    `);
+  });
+
   it('supports duplicate times', () => {
     //----------
     // NOTE!!!
@@ -357,3 +416,11 @@ describe('align frames', () => {
     });
   });
 });
+
+function getFieldDisplayNames(data: DataFrame[]): string[] {
+  return data.flatMap((frame) => frame.fields.map((f) => getFieldDisplayName(f, frame, data)));
+}
+
+function getFieldNames(data: DataFrame[]): string[] {
+  return data.flatMap((frame) => frame.fields.map((f) => f.name));
+}

packages/grafana-data/src/transformations/transformers/joinDataFrames.ts

@@ -1,7 +1,7 @@
 import intersect from 'fast_array_intersect';
 
 import { getTimeField, sortDataFrame } from '../../dataframe';
-import { DataFrame, Field, FieldMatcher, FieldType } from '../../types';
+import { DataFrame, Field, FieldMatcher, FieldType, TIME_SERIES_VALUE_FIELD_NAME } from '../../types';
 import { fieldMatchers } from '../matchers';
 import { FieldMatcherID } from '../matchers/ids';
 
@@ -180,12 +180,18 @@ export function joinDataFrames(options: JoinOptions): DataFrame | undefined {
         nullModesFrame.push(spanNulls === true ? NULL_REMOVE : spanNulls === -1 ? NULL_RETAIN : NULL_EXPAND);
 
         let labels = field.labels ?? {};
+        let name = field.name;
         if (frame.name) {
-          labels = { ...labels, name: frame.name };
+          if (field.name === TIME_SERIES_VALUE_FIELD_NAME) {
+            name = frame.name;
+          } else {
+            labels = { ...labels, name: frame.name };
+          }
         }
 
         fields.push({
           ...field,
+          name,
           labels, // add the name label from frame
         });
       }