aggregation framework - Recursive search on a collection in MongoDB -


i have list of documents in mongodb tree structure, model tree structures parent references pattern used. want single aggregation query returns ancestor list(till root), given 'name' property.

structure:

{   '_id': '1',   'name': 'a',   'parent': '', }, {   '_id': '2',   'name': 'b',   'parent': 'a', }, {   '_id': '3',   'name': 'c',   'parent': 'b', }, {   '_id': '4',   'name': 'd',   'parent': 'c', }

aggregation result:(given, name = 'd')

{   '_id': '4',   'name': 'd',   'ancestors': [{name:'c'}, {name:'b'}, {name:'a'}] }

note: can't change document structure now. cause many problems. saw many solutions suggest use model tree structures array of ancestors. cannot use now. there way achieve above pattern using single aggregation query? thank you

starting mongodb 3.4, can aggregation framework.

the first , important stage in our pipeline $graphlookup stage. $graphlookup allows recursively match on "parent" , "name" field. result, ancestors of each "name".

the next stage in pipeline $match stage select "name" interested in.

the final stage $addfields or $project stage apply expression "ancestors" array using $map array operator.

of course $reversearray operator reverse our array in order expected result. 

db.collection.aggregate(     [          { "$graphlookup": {              "from": "collection",              "startwith": "$parent",              "connectfromfield": "parent",              "connecttofield": "name",              "as": "ancestors"         }},          { "$match": { "name": "d" } },          { "$addfields": {              "ancestors": {                  "$reversearray": {                      "$map": {                          "input": "$ancestors",                          "as": "t",                          "in": { "name": "$$t.name" }                     }                  }              }         }}     ] )

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