Dashboard: SchemaV2 - Fix stateless variable query with default datasource (#106850)

* Dashboard: SchemaV2 - Fix stateless variable query with default datasource

* Add warning for debugging purposes

* fix test add expected warning

public/app/features/dashboard-scene/serialization/layoutSerializers/utils.test.ts

@@ -9,12 +9,12 @@ jest.mock('@grafana/runtime', () => ({
     ...jest.requireActual('@grafana/runtime').config,
     bootData: {
       settings: {
-        defaultDatasource: 'default-ds-grafana',
+        defaultDatasource: 'default-ds-prometheus',
         datasources: {
-          'default-ds-grafana': {
-            uid: 'default-ds-uid',
-            name: 'Default DS',
-            meta: { id: 'default-ds-grafana' },
+          'default-ds-prometheus': {
+            uid: 'default-prometheus-uid',
+            name: 'Default Prometheus',
+            meta: { id: 'prometheus' },
             type: 'datasource',
           },
           prometheus: {
@@ -61,7 +61,7 @@ describe('getRuntimePanelDataSource', () => {
     });
   });
 
-  it('should infer datasource based on query kind when datasource is not specified', () => {
+  it('should prioritize default datasource when it matches the query kind', () => {
     const query: PanelQueryKind = {
       kind: 'PanelQuery',
       spec: {
@@ -78,12 +78,35 @@ describe('getRuntimePanelDataSource', () => {
     const result = getRuntimePanelDataSource(query);
 
     expect(result).toEqual({
-      uid: 'prometheus-uid',
+      uid: 'default-prometheus-uid',
       type: 'prometheus',
     });
   });
 
+  it('should fall back to first available datasource when default datasource type does not match query kind', () => {
+    const query: PanelQueryKind = {
+      kind: 'PanelQuery',
+      spec: {
+        refId: 'A',
+        hidden: false,
+        datasource: undefined,
+        query: {
+          kind: 'loki',
+          spec: {},
+        },
+      },
+    };
+
+    const result = getRuntimePanelDataSource(query);
+
+    expect(result).toEqual({
+      uid: 'loki-uid',
+      type: 'loki',
+    });
+  });
+
   it('should use default datasource when no datasource is specified and query kind does not match any available datasource', () => {
+    jest.spyOn(console, 'warn').mockImplementation();
     const query: PanelQueryKind = {
       kind: 'PanelQuery',
       spec: {
@@ -100,9 +123,13 @@ describe('getRuntimePanelDataSource', () => {
     const result = getRuntimePanelDataSource(query);
 
     expect(result).toEqual({
-      uid: 'default-ds-uid',
-      type: 'default-ds-grafana',
+      uid: 'default-prometheus-uid',
+      type: 'prometheus',
     });
+
+    expect(console.warn).toHaveBeenCalledWith(
+      'Could not find datasource for query kind unknown-type, defaulting to prometheus'
+    );
   });
 
   it('should handle the case when datasource uid is empty string', () => {
@@ -125,7 +152,7 @@ describe('getRuntimePanelDataSource', () => {
     const result = getRuntimePanelDataSource(query);
 
     expect(result).toEqual({
-      uid: 'prometheus-uid',
+      uid: 'default-prometheus-uid',
       type: 'prometheus',
     });
   });

public/app/features/dashboard-scene/serialization/layoutSerializers/utils.ts

@@ -224,14 +224,29 @@ function getDataSourceForQuery(
   const defaultDatasource = config.bootData.settings.defaultDatasource;
   const dsList = config.bootData.settings.datasources;
 
-  // Look up by query type/kind
+  // First check if the default datasource matches the query type
+  if (dsList && dsList[defaultDatasource] && dsList[defaultDatasource].meta.id === queryKind) {
+    // In the datasource list from bootData "id" is the type and the uid could be uid or the name
+    // in cases like grafana, dashboard or mixed datasource
+    return {
+      uid: dsList[defaultDatasource].uid || dsList[defaultDatasource].name,
+      type: dsList[defaultDatasource].meta.id,
+    };
+  }
+
+  // Look up by query type/kind from all available datasources
   const bestGuess = dsList && Object.values(dsList).find((ds) => ds.meta.id === queryKind);
 
   if (bestGuess) {
     return { uid: bestGuess.uid, type: bestGuess.meta.id };
   } else if (dsList && dsList[defaultDatasource]) {
+    // Fallback to default datasource even if type doesn't match
     // In the datasource list from bootData "id" is the type and the uid could be uid or the name
     // in cases like grafana, dashboard or mixed datasource
+
+    console.warn(
+      `Could not find datasource for query kind ${queryKind}, defaulting to ${dsList[defaultDatasource].meta.id}`
+    );
     return {
       uid: dsList[defaultDatasource].uid || dsList[defaultDatasource].name,
       type: dsList[defaultDatasource].meta.id,