fix(shell-api): Add support for running aggregate database with a single stage MONGOSH-1868 (#2218)

Co-authored-by: Anna Henningsen <anna.henningsen@mongodb.com>

Author: gagik

packages/shell-api/src/database.spec.ts

@@ -400,6 +400,16 @@ describe('Database', function () {
         );
       });
 
+      it('supports a single aggregation stage', async function () {
+        await database.aggregate({ $piplelineStage: {} }, { options: true });
+
+        expect(serviceProvider.aggregateDb).to.have.been.calledWith(
+          database._name,
+          [{ $piplelineStage: {} }],
+          { options: true }
+        );
+      });
+
       it('calls serviceProvider.aggregateDb with explicit batchSize', async function () {
         await database.aggregate([{ $piplelineStage: {} }], {
           options: true,

packages/shell-api/src/database.ts

@@ -423,15 +423,20 @@ export default class Database extends ShellApiWithMongoClass {
   @returnType('AggregationCursor')
   @apiVersions([1])
   async aggregate(
-    pipeline: Document[],
+    pipelineOrSingleStage: Document | Document[],
     options?: Document
   ): Promise<AggregationCursor> {
     if ('background' in (options ?? {})) {
       await this._instanceState.printWarning(
         aggregateBackgroundOptionNotSupportedHelp
       );
     }
+    const pipeline: Document[] = Array.isArray(pipelineOrSingleStage)
+      ? pipelineOrSingleStage
+      : [pipelineOrSingleStage];
+
     assertArgsDefinedType([pipeline], [true], 'Database.aggregate');
+
     this._emitDatabaseApiCall('aggregate', { options, pipeline });
 
     const { aggOptions, dbOptions, explain } = adaptAggregateOptions(options);
@@ -1429,6 +1434,7 @@ export default class Database extends ShellApiWithMongoClass {
         CommonErrors.CommandFailed
       );
     }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-type-assertion
     for (const cmdDescription of Object.values(result.commands) as Document[]) {
       if ('slaveOk' in cmdDescription) {
         cmdDescription.secondaryOk = cmdDescription.slaveOk;