DataSource: Allow data source plugins to set query default values (#49581)

* make it possible to set default query

* set default query in cloudwatch ds

* remove cloudwatch example code

* apply feedback

* Update public/app/features/explore/state/query.ts

Co-authored-by: Giordano Ricci <me@giordanoricci.com>

* Update public/app/features/query/components/QueryGroup.tsx

Co-authored-by: Giordano Ricci <me@giordanoricci.com>

* add alpha tag to method definiton

Co-authored-by: Giordano Ricci <me@giordanoricci.com>

packages/grafana-data/src/types/datasource.ts

@@ -345,6 +345,12 @@ abstract class DataSourceApi<
     | StandardVariableSupport<DataSourceApi<TQuery, TOptions>>
     | CustomVariableSupport<DataSourceApi<TQuery, TOptions>>
     | DataSourceVariableSupport<DataSourceApi<TQuery, TOptions>>;
+
+  /*
+   * Optionally, use this method to set default values for a query
+   * @alpha -- experimental
+   */
+  getDefaultQuery?(app: CoreApp): Partial<TQuery>;
 }
 
 export interface MetadataInspectorProps<

public/app/features/explore/Explore.tsx

@@ -158,8 +158,8 @@ export class Explore extends React.PureComponent<Props, ExploreState> {
   };
 
   onClickAddQueryRowButton = () => {
-    const { exploreId, queryKeys } = this.props;
+    const { exploreId, queryKeys, datasourceInstance } = this.props;
-    this.props.addQueryRow(exploreId, queryKeys.length);
+    this.props.addQueryRow(exploreId, queryKeys.length, datasourceInstance);
   };
 
   onMakeAbsoluteTime = () => {

public/app/features/explore/state/query.ts

@@ -5,6 +5,7 @@ import { mergeMap, throttleTime } from 'rxjs/operators';
 
 import {
   AbsoluteTimeRange,
+  CoreApp,
   DataQuery,
   DataQueryErrorType,
   DataQueryResponse,
@@ -213,10 +214,17 @@ export const clearCacheAction = createAction<ClearCachePayload>('explore/clearCa
 /**
  * Adds a query row after the row with the given index.
  */
-export function addQueryRow(exploreId: ExploreId, index: number): ThunkResult<void> {
+export function addQueryRow(
+  exploreId: ExploreId,
+  index: number,
+  datasource: DataSourceApi | undefined | null
+): ThunkResult<void> {
   return (dispatch, getState) => {
     const queries = getState().explore[exploreId]!.queries;
-    const query = generateEmptyQuery(queries, index);
+    const query = {
+      ...datasource?.getDefaultQuery?.(CoreApp.Explore),
+      ...generateEmptyQuery(queries, index),
+    };
 
     dispatch(addQueryRowAction({ exploreId, index, query }));
   };

public/app/features/query/components/QueryGroup.tsx

@@ -3,6 +3,7 @@ import React, { PureComponent } from 'react';
 import { Unsubscribable } from 'rxjs';
 
 import {
+  CoreApp,
   DataQuery,
   DataSourceApi,
   DataSourceInstanceSettings,
@@ -137,6 +138,7 @@ export class QueryGroup extends PureComponent<Props, State> {
     const ds = !dsSettings?.meta.mixed ? dsSettings : defaultDataSource;
 
     return {
+      ...this.state.dataSource?.getDefaultQuery?.(CoreApp.PanelEditor),
       datasource: { uid: ds?.uid, type: ds?.type },
     };
   }