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db.collection.aggregate([{$match:{"conversations":{$elemMatch:{"page":"1000",}}}},{$lookup:{from:"messages",let:{comment_date:ISODate("2019-12-13T13:56:06.225+00:00"),},pipeline:[{$match:{$expr:{$and:[{$eq:["$$comment_date","$messages.date.0"]}]}}}],as:"messages"}},{$group:{_id:0,res:{"$addToSet":"$fullName"}}}])