[SERVER-41922] Explain on $lookup ("let and pipeline" form) throws Created: 25/Jun/19  Updated: 07/Apr/23  Resolved: 28/Jun/19

Status: Closed
Project: Core Server
Component/s: Aggregation Framework
Affects Version/s: 4.0.10
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Segey Gladskikh Assignee: Eric Sedor
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Operating System: ALL
Steps To Reproduce:

db.getCollection("threads").explain().aggregate("'$lookup': { 'from': 'posts', 'let':

{ 'postsIds': '$Posts' }

, 'pipeline': [ { '$match': { '$expr':

{ '$in': [ '$_id' '$$postsIds' ] }

} } ], 'as': 'LastPosts' }")

Participants:

 Description   

I try to get plan of my aggregation including complex lookup to figure out could it utilize index of joined collection or not.

End even with simplified example (in selfdescribing repro) I get error "Expected 'pipeline' to be BSON docs (or equivalent), but got []interface {} instead."



 Comments   
Comment by Eric Sedor [ 28/Jun/19 ]

This looks to be because the argument to aggregate is a string instead of an array.

The SERVER project is for bugs and feature suggestions for the MongoDB server. As this ticket does not appear to a bug, I will now close it. If you need further assistance troubleshooting, I encourage you to ask our community by posting on the mongodb-user group or on Stack Overflow with the mongodb tag.

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