Incorrect aggregation types for $group since 6.4.0

[Naeoth]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

6.4.6

Node.js version

16.15.0

MongoDB server version

5.0

Description

The type changed on the 6.4.0: f57e007#diff-46be1d2c4ab7acfb5007f7bcccbf3d2e9551597d0bd0d91cc0400a4faffb76cfR116-R118

and gives an error on a valid mongoDB aggregation query.

error TS2769: No overload matches this call.
  Overload 1 of 2, '(pipeline?: PipelineStage[], options?: AggregateOptions, callback?: Callback<T[]>): Aggregate<T[]>', gave the following error.
    Type 'string' is not assignable to type 'Record<string | number | symbol, never>'.
  Overload 2 of 2, '(pipeline: PipelineStage[], callback?: Callback<T[]>): Aggregate<T[]>', gave the following error.
    Type 'string' is not assignable to type 'Record<string | number | symbol, never>'.

50         count: { $count: "$value" },

For a group the type should be as before:

$group: { _id: any } | { [key: string]: { [op in AccumulatorOperator]?: any } }

Steps to Reproduce

Model.aggregate([
    {
      $group: {
        _id: "$createdAt",
        count: { "$count": "$value" },
      },
    },
 ])

Expected Behavior

No response

[Naeoth]

@vkarpov15

I just test on 6.5.1, but your MR doesn't fix the bug :/

The Group interface is declared like that:

    export interface Group {
      /** [`$group` reference](https://docs.mongodb.com/manual/reference/operator/aggregation/group) */
      $group: { _id: any } | { [key: string]: AccumulatorOperator }
    }

but the mongoDB documention describes:

    {
      $group:
        {
          _id: <expression>, // Group key
          <field1>: { <accumulator1> : <expression1> },
          ...
        }
     }

So mongoose should have something like:

   export interface Group {
     /** [`$group` reference](https://docs.mongodb.com/manual/reference/operator/aggregation/group) */
     $group: { _id: any } | { [key: string]: { [op in AccumulatorOperator]?: any } } }
   }

[vkarpov15]

@Naeoth I took a closer look and the typings as written are correct, and do support the syntax described in the MongoDB documentation. { [key: string]: AccumulatorOperator } is more correct because MongoDB doesn't support multiple accumulator expressions on one field. Multiple accumulators throw "The field 'field-name-here' must specify one accumulator"