Datasource: Fixes changing default data source causes inconsistency between panel data source and query data source (#46167)

* Datasource: Fixes changing default data source causes inconsistency between panel data source and query data source

* Fix unit tests

public/app/features/dashboard/state/DashboardMigrator.test.ts

@@ -17,6 +17,13 @@ const dataSources = {
   prom: mockDataSource({
     name: 'prom',
     type: 'prometheus',
+    isDefault: true,
+  }),
+  notDefault: mockDataSource({
+    name: 'prom-not-default',
+    uid: 'prom-not-default-uid',
+    type: 'prometheus',
+    isDefault: false,
   }),
   [MIXED_DATASOURCE_NAME]: mockDataSource({
     name: MIXED_DATASOURCE_NAME,
@@ -1840,6 +1847,33 @@ describe('DashboardModel', () => {
     });
   });
 
+  describe('when fixing query and panel data source refs out of sync due to default data source change', () => {
+    let model: DashboardModel;
+
+    beforeEach(() => {
+      model = new DashboardModel({
+        templating: {
+          list: [],
+        },
+        panels: [
+          {
+            id: 2,
+            datasource: null,
+            targets: [
+              {
+                datasource: 'prom-not-default',
+              },
+            ],
+          },
+        ],
+      });
+    });
+
+    it('should not update panel datasource to that of query level ds', () => {
+      expect(model.panels[0].datasource?.uid).toEqual('prom-not-default-uid');
+    });
+  });
+
   describe('when migrating time series axis visibility', () => {
     test('preserves x axis visibility', () => {
       const model = new DashboardModel({

public/app/features/dashboard/state/DashboardMigrator.ts

@@ -67,6 +67,40 @@ export class DashboardMigrator {
     this.dashboard = dashboardModel;
   }
 
+  /**
+   * When changing default datasource which is stored as null Grafana get's into a mixed state where queries have
+   * data source uid & type set that is different from the now new default
+   */
+  syncQueryDataSources() {
+    const dataSourceSrv = getDataSourceSrv();
+    // This only happens in some unit tests that does not set a DataSourceSrv
+    if (!dataSourceSrv) {
+      return;
+    }
+
+    const defaultDS = getDataSourceSrv().getInstanceSettings(null);
+    // if default ds is mixed then skip this
+    if (!defaultDS || defaultDS.meta.mixed) {
+      return;
+    }
+
+    for (const panel of this.dashboard.panels) {
+      // only interested in panels that use default (null) data source
+      if (panel.datasource) {
+        continue;
+      }
+
+      for (const target of panel.targets) {
+        // If query level data source is different from panel
+        if (target.datasource && target.datasource.uid !== defaultDS?.uid) {
+          // set panel level data source to data source on the query as this is more likely the correct one
+          // But impossible to say, and this changes the behavior of of what default means ahead of the big change to default
+          panel.datasource = target.datasource;
+        }
+      }
+    }
+  }
+
   updateSchema(old: any) {
     let i, j, k, n;
     const oldVersion = this.dashboard.schemaVersion;

public/app/features/dashboard/state/DashboardModel.ts

@@ -1071,6 +1071,7 @@ export class DashboardModel implements TimeModel {
   private updateSchema(old: any) {
     const migrator = new DashboardMigrator(this);
     migrator.updateSchema(old);
+    migrator.syncQueryDataSources();
   }
 
   resetOriginalTime() {