Info

When I try to run the aggregation below, which has a nesting of $facet -> $lookup -> $facet -> $lookup, I get the error message "$lookup is not allowed to be used within a $facet stage". This message is wrong, since $lookup is indeed allowed in a $facet stage and works fine. The problem with the pipeline is that it has a $facet inside a $facet, which is not allowed. This is the pipeline that results in the wrong error message: db.data.aggregate([ { "$facet" : { "result" : [ { "$match" : { "ref1" : { "$exists" : true }}}, { "$lookup" : { "from" : "data", "localField" : "ref1", "foreignField" : "_id", "pipeline" : [ { "$facet" : { "result" : [ { "$match" : { "ref2" : { "$exists" : true }}}, { "$lookup" : { "from" : "data", "localField" : "ref2", "foreignField" : "_id", "as" : "ref2" }}]}}], "as" : "ref1" }}]}}]) On the other hand, for a pipeline with a $facet immediately nested within another $facet, the message is correct. This pipeline: db.data.aggregate([{"$facet" : { "x" : [ {"$facet" : { "y" : [] }}]}}]) results in the correct message "$facet is not allowed to be used within a $facet stage" The problem is the same in both 6.0.6 and 7.0.0.

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xgen-internal-githook commented on Wed, 3 Apr 2024 08:42:35 +0000: Author: {'name': 'mivanova3', 'email': '68105381+mivanova3@users.noreply.github.com', 'username': 'mivanova3'} Message: SERVER-80456 Fix error message when using $facet inside $facet (#19690) GitOrigin-RevId: f90797eedfbc172948063d8210f4b70a093248ee Branch: master https://github.com/mongodb/mongo/commit/84cd21794e55ad2521bc58711f9204ceda8eafb5

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