Detailed steps to reproduce the problem?

Example provided in Mongo documentation does not work. 

Link below:

https://www.mongodb.com/docs/v7.0/reference/operator/aggregation/lookup/#std-label-lookup-multiple-joins

Steps to reproduce::

try:
  db.orders.insert_many( [
    { "_id" : 1, "item" : "almonds", "price" : 12, "ordered" : 2 },
    { "_id" : 2, "item" : "pecans", "price" : 20, "ordered" : 1 },
    { "_id" : 3, "item" : "cookies", "price" : 10, "ordered" : 60 }
  ] )

  db.warehouses.insert_many( [
    { "_id" : 1, "stock_item" : "almonds", "warehouse": "A", "instock" : 120 },
    { "_id" : 2, "stock_item" : "pecans", "warehouse": "A", "instock" : 80 },
    { "_id" : 3, "stock_item" : "almonds", "warehouse": "B", "instock" : 60 },
    { "_id" : 4, "stock_item" : "cookies", "warehouse": "B", "instock" : 40 },
    { "_id" : 5, "stock_item" : "cookies", "warehouse": "A", "instock" : 80 }
  ] )
except BaseException as e:
  print(e)

print(list(db.orders.aggregate( [
   {
      "$lookup":
         

{            "from": "warehouses",            "let": \{ "order_item": "$item", "order_qty": "$ordered" }

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

{ "$and":                        [                          \{ "$eq": [ "$stock_item",  "$$order_item" ] }

,
                         { "$gte": [ "$instock", "$$order_qty" ] }
                       ]
                    }
                 }
              },
              { "$project":

{ "stock_item": 0, "_id": 0 }

}
           ],
           "as": "stockdata"
         }
    }

] )))

As you will see, stockdata field will be empty.

The exact Python version used, with patch level:

3.11.4 (main, Jun  7 2023, 10:13:09) [GCC 12.2.0]      

The exact version of PyMongo used, with patch level:

4.6.0.dev0

True

The operating system and version (e.g. Windows 7, OSX 10.8, ...)

Linux b314816f84cf 6.2.0-25-generic #25-Ubuntu SMP PREEMPT_DYNAMIC Fri Jun 16

17:05:07 UTC 2023 x86_64 GNU/Linux  

 

Web framework or asynchronous network library used, if any, with version (e.g. Django 1.7, mod_wsgi 4.3.0, gevent 1.0.1, Tornado 4.0.2, ...)