AggregationCursor will not emit errors like QueryCursor when errors thrown in pre hook.

[jsas]

Prerequisites

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

Mongoose version

8.10.0

Node.js version

20.15

MongoDB server version

5

Typescript version (if applicable)

No response

Description

Using Model.aggregate.cursor() will not emit errors like QueryCursor when errors thrown in pre hook.

schema.pre('aggregate', function(next) {
  if (!this.options.allowed) {  
    throw new Error(`hey, that's nacho cheese!`)
  }
  next()
})

// -----------

// this would throw
const res = await Model.aggregate([{ $limit: 1 }], { allowed: false }).exec()
return res

// this will continue and stream results
const cursor = Model.aggregate([{ $limit: 1 }], { allowed: false }).cursor()
const aahsss = []
for await(const it of cursor) {
   aahsss.push(it)
}

QueryCursor seems to have this implemented. Is this by design, because aggregations aren't "ORMey"?

Steps to Reproduce

• create a schema with a pre('aggregate') hook that throws an error
• use Model.aggregate([{$limit: 1 }]).cursor()
• see a document rather that an error thrown or emitted

Expected Behavior

expect aggregation cursor to emit an error from a failed pre('aggregate') hook

[jsas]

i have a workaround for now, setting an error on the Aggregate instance before throwing but our plugins need to be aware of it, obv.

    // https://github.com/Automattic/mongoose/issues/15279
    options = { ...options, error: null }
    const agg = it.aggregate(pipeline, options)
    const cursor = agg.cursor()
    if (agg.options.error) {
      throw agg.options.error
    }
    return new ReadableStreamCursor(cursor)

and in a plugin

  #preAggregation = (requireContext) => {
    return function(next) {
      this.getContext = () => $get(this, 'context')
      const context = rInstance(this?.options?.context, Context)
      if (context) {
        $set(this, 'context', context)
      } else if (rBool(this.options?.requireContext, requireContext)) {
        // throwing in pre-aggregate skips the next plugin but swallows the error
        // set an error on the agg for the caller to examine, and clear the pipeline
        // in case they don't. 
        // @todo https://github.com/Automattic/mongoose/issues/15279
        const fault = new Error('context expected')
        const pipeline = this.pipeline()
        pipeline.splice(0, pipeline.length, { $match: { _id: null } })
        this.options.error = fault
        throw fault
      }
      next()
    }
  }

[vkarpov15]

This is a bug, fix will be in v8.11.1