add single stage support instead

Author: gagik

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

@@ -390,19 +390,18 @@ describe('Database', function () {
         serviceProviderCursor = stubInterface<ServiceProviderAggCursor>();
       });
 
-      it('throws if the given argument is not an array', async function () {
-        let caughtError: MongoshInvalidInputError | undefined;
-        // eslint-disable-next-line @typescript-eslint/no-unsafe-argument
-        await database.aggregate({} as any).catch((err) => {
-          caughtError = err;
-        });
-        expect(caughtError?.message).contains(
-          'Aggregate pipeline argument must be an array'
+      it('calls serviceProvider.aggregateDb with pipleline and options', 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 pipleline and options', async function () {
-        await database.aggregate([{ $piplelineStage: {} }], { options: true });
+      it('supports a single aggregation stage', async function () {
+        await database.aggregate({ $piplelineStage: {} }, { options: true });
 
         expect(serviceProvider.aggregateDb).to.have.been.calledWith(
           database._name,

packages/shell-api/src/database.ts

@@ -412,6 +412,14 @@ export default class Database extends ShellApiWithMongoClass {
     return await this._runAdminCommand(cmd, {});
   }
 
+  async aggregate(
+    singleStage: Document,
+    options?: Document
+  ): Promise<AggregationCursor>;
+  async aggregate(
+    pipeline: Document[],
+    options?: Document
+  ): Promise<AggregationCursor>;
   /**
    * Run an aggregation against the db.
    *
@@ -423,14 +431,18 @@ 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');
 
     if (!Array.isArray(pipeline)) {