mongodb - Combining multiple sub-documents into a new doc in mongo -

i trying query multiple sub-documents in mongodb , return single doc. think aggregation framework way go, but, can't see right.

take following docs:

{     "board_id": "1",     "hosts":       [{         "name": "bob",         "ip": "10.1.2.3"      },     {          "name": "tom",          "ip": "10.1.2.4"     }]  }  {     "board_id": "2",     "hosts":      [{         "name": "mickey",         "ip": "10.2.2.3"     },     {         "name": "mouse",         "ip": "10.2.2.4"     }] }  {      "board_id": "3",      "hosts":      [{         "name": "pavel",         "ip": "10.3.2.3"     },     {         "name": "kenrick",         "ip": "10.3.2.4"      }] } 

trying query result this:

{     "hosts":      [{         "name": "bob",         "ip": "10.1.2.3"     },     {          "name": "tom",          "ip": "10.1.2.4"     },     {          "name": "mickey",          "ip": "10.2.2.3"     },     {         "name": "mouse",         "ip": "10.2.2.4"     },      {          "name": "pavel",          "ip": "10.3.2.3"      },      {         "name": "kenrick",         "ip": "10.3.2.4"      }] } 

i've tried this:

db.collection.aggregate([ { $unwind: '$hosts' }, { $project : { name: 1, hosts: 1, _id: 0 }} ]) 

but it's not quite want.

you can aggregate. let's assume data in collection named board, please replace whatever collection name is.

db.board.aggregate([ {$unwind:"$hosts"}, {$group:{_id:null, hosts:{$addtoset:"$hosts"}}}, {$project:{_id:0, hosts:1}} ]).pretty() 

it return

    {         "hosts" : [             {                 "name" : "kenrick",                 "ip" : "10.3.2.4"             },             {                 "name" : "pavel",                 "ip" : "10.3.2.3"             },             {                 "name" : "mouse",                 "ip" : "10.2.2.4"             },             {                 "name" : "mickey",                 "ip" : "10.2.2.3"             },             {                 "name" : "tom",                 "ip" : "10.1.2.4"             },             {                 "name" : "bob",                 "ip" : "10.1.2.3"             }         ]     }