I have a list of documents in a MongoDB with the following structure:
{
'name': 'A',
'friends': ['B', 'C']
},
{
'name': 'B',
'friends': ['A']
},
{
'name': 'C',
'friends': ['A']
},
{
'name': 'D',
'friends': []
},
{
'name': 'E',
'friends': ['C']
}
I want to recursively find the total group of friends of a given Person, e.g.
Friends of A
: ['B', 'C', 'E']
Is this possible using the aggregation framework?
You can do $graphLookup
if you are using mongo 3.4+, it is to do hierarchical join on the self collection
db.frnds.aggregate([
{$match : {'name': 'A'}},
{
$graphLookup: {
from: "frnds",
startWith: "$name",
connectFromField: "name",
connectToField: "friends",
as: "friends"
}
},
{$addFields : { friends : {$setUnion : [{$filter : {input : "$friends.name", as : "friend" , cond : {$ne : ["$name", "$$friend"]}}}] }}}
])
collection
> db.frnds.find()
{ "_id" : ObjectId("5a7e694580aae386f73cf0f5"), "name" : "A", "friends" : [ "B", "C" ] }
{ "_id" : ObjectId("5a7e694580aae386f73cf0f6"), "name" : "B", "friends" : [ "A" ] }
{ "_id" : ObjectId("5a7e694580aae386f73cf0f7"), "name" : "C", "friends" : [ "A" ] }
{ "_id" : ObjectId("5a7e694580aae386f73cf0f8"), "name" : "D", "friends" : [ ] }
{ "_id" : ObjectId("5a7e694580aae386f73cf0f9"), "name" : "E", "friends" : [ "C" ] }
result
{ "_id" : ObjectId("5a7e694580aae386f73cf0f5"), "name" : "A", "friends" : [ "B", "C", "E" ] }