Use pipeline $count, add test

packages/mongodb/src/adapter.ts

@@ -214,6 +214,7 @@ export class MongoDbAdapter<
       const aggregateParams = {
         ...params,
         paginate: false,
+        pipeline: [...params.pipeline, { $count: 'total' }],
         query: {
           ...params.query,
           $select: [this.id],
@@ -222,8 +223,8 @@ export class MongoDbAdapter<
           $limit: undefined
         }
       }
-      const result = await this.aggregateRaw(aggregateParams).then((result) => result.toArray())
-      return result.length
+      const [result] = await this.aggregateRaw(aggregateParams).then((result) => result.toArray())
+      return result.total
     }
 
     const model = await this.getModel(params)

packages/mongodb/test/index.test.ts

@@ -83,11 +83,6 @@ const testSuite = adapterTests([
   'params.adapter + multi'
 ])
 
-const defaultPaginate = {
-  default: 10,
-  max: 50
-}
-
 describe('Feathers MongoDB Service', () => {
   const personSchema = {
     $id: 'Person',
@@ -573,12 +568,19 @@ describe('Feathers MongoDB Service', () => {
     it('can count documents with aggregation', async () => {
       const service = app.service('people')
       const paginateBefore = service.options.paginate
-      service.options.paginate = defaultPaginate
-      const query = { age: { $gte: 25 } }
-      const findResult = await app.service('people').find({ query })
-      const aggregationResult = await app.service('people').find({ query, pipeline: [] })
 
-      assert.deepStrictEqual(findResult.total, aggregationResult.total)
+      const test = async (paginate: any) => {
+        service.options.paginate = paginate
+        const query = { age: { $gte: 25 } }
+        const findResult = await app.service('people').find({ query })
+        const aggregationResult = await app.service('people').find({ query, pipeline: [] })
+        assert.deepStrictEqual(findResult.total, aggregationResult.total)
+      }
+
+      await test({ default: 10, max: 50 })
+      // There are 2 people with age >= 25.
+      // Test that aggregation works when results are less than default
+      await test({ default: 1, max: 50 })
 
       service.options.paginate = paginateBefore
     })