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Type:
Bug
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Resolution: Duplicate
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: Aggregation Framework
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None
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Fully Compatible
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ALL
It seems not possible to access a specific array element in the $group stage. For instance, let's say my documents have 2 arrays, I want to unwind the first array and group by the campaign_id and day pair. I also want to access a certain array element for some reason, but I can not.
mongos> db.test.find()
{ "_id" : ObjectId("548608660094d27682c03666"), "campaign_id" : 1, "channel1" : [ { "day" : 0, "delivered" : 10 }, { "day" : 1, "delivered" : 1 } ], "channel2" : [ { "day" : 0, "delivered" : 5 }, { "day" : 1, "delivered" : 6 } ] }
{ "_id" : ObjectId("548608a20094d27682c03667"), "campaign_id" : 2, "channel1" : [ { "day" : 0, "delivered" : 1 }, { "day" : 1, "delivered" : 1 } ], "channel2" : [ { "day" : 0, "delivered" : 5 }, { "day" : 1, "delivered" : 5 } ], "channel3" : [ { "day" : 0, "delivered" : 11 }, { "day" : 1, "delivered" : 1 } ] }
mongos> db.test.aggregate({$unwind : "$channel1"},{$group : {_id : {campaign_id : "$campaign_id", day : "$channel1.day"}, xxx: {$first : "$channel2"} }})
{ "_id" : { "campaign_id" : 2, "day" : 1 }, "xxx" : [ { "day" : 0, "delivered" : 5 }, { "day" : 1, "delivered" : 5 } ] }
{ "_id" : { "campaign_id" : 1, "day" : 1 }, "xxx" : [ { "day" : 0, "delivered" : 5 }, { "day" : 1, "delivered" : 6 } ] }
{ "_id" : { "campaign_id" : 2, "day" : 0 }, "xxx" : [ { "day" : 0, "delivered" : 5 }, { "day" : 1, "delivered" : 5 } ] }
{ "_id" : { "campaign_id" : 1, "day" : 0 }, "xxx" : [ { "day" : 0, "delivered" : 5 }, { "day" : 1, "delivered" : 6 } ] }
mongos> db.test.aggregate({$unwind : "$channel1"},{$group : {_id : {campaign_id : "$campaign_id", day : "$channel1.day"}, xxx: {$first : "$channel2.0.day"} }})
{ "_id" : { "campaign_id" : 2, "day" : 1 }, "xxx" : [ ] }
{ "_id" : { "campaign_id" : 1, "day" : 1 }, "xxx" : [ ] }
{ "_id" : { "campaign_id" : 2, "day" : 0 }, "xxx" : [ ] }
{ "_id" : { "campaign_id" : 1, "day" : 0 }, "xxx" : [ ] }
mongos> db.test.aggregate({$unwind : "$channel1"},{$group : {_id : {campaign_id : "$campaign_id", day : "$channel1.day"}, xxx: {$first : "$channel2.0"} }})
{ "_id" : { "campaign_id" : 2, "day" : 1 }, "xxx" : [ ] }
{ "_id" : { "campaign_id" : 1, "day" : 1 }, "xxx" : [ ] }
{ "_id" : { "campaign_id" : 2, "day" : 0 }, "xxx" : [ ] }
{ "_id" : { "campaign_id" : 1, "day" : 0 }, "xxx" : [ ] }
mongos> db.test.aggregate({$unwind : "$channel1"},{$group : {_id : {campaign_id : "$campaign_id", day : "$channel1.day"}, xxx: {$first : "$channel2[0]"} }})
{ "_id" : { "campaign_id" : 2, "day" : 1 }, "xxx" : null }
{ "_id" : { "campaign_id" : 1, "day" : 1 }, "xxx" : null }
{ "_id" : { "campaign_id" : 2, "day" : 0 }, "xxx" : null }
{ "_id" : { "campaign_id" : 1, "day" : 0 }, "xxx" : null }
- duplicates
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SERVER-4589 aggregation: need an array indexing operator
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- Closed
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