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How does MongoDB WiredTiger storage engine ensure data durability? |
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Answer» Recursive queries can be performed within a collection using $graphLookUp which is an aggregate pipeline stage. If a collection has a self-referencing field like the classic example of MANAGER for an employee, then a QUERY to get the entire REPORTING structure for manager “David” would look like this db.employees.aggregate( [ { $graphLookup: { from: "employees", startWith: "David", connectFromField: "manager", connectToField: "name", as: "Reporting Structure" } } ] )For the following documents in the employee collection, { "_id" : 4, "name" : " David " , "manager" : "Sarah" } { "_id" : 5, "name" : "John" , "manager" : "David" } { "_id" : 6, "name" : "Richard", "manager" : " John " } { "_id" : 7, "name" : "Stacy" , "manager" : " Richard " }Output of the above $graphLookup operation would result in the following 3 documents returned { "_id" : 5, "name" : "John" , "manager" : "David", … } { "_id" : 6, "name" : "Richard", "manager" : " John ", … } { "_id" : 7, "name" : "Stacy" , "manager" : " Richard", … }The hierarchy starts with “David” which is specified in startWith and there on the DATA for each of the members in that reporting hierarchy are fetched recursively |
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