Details
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Type:
Bug
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Status: Open
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Priority:
Major - P3
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Resolution: Unresolved
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Affects Version/s: None
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Fix Version/s: Backlog
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Component/s: Aggregation Framework
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Labels:
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Operating System:ALL
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Sprint:Query 11 (03/14/16)
Description
My database contains the following documents:
use test;
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db.test.insert(
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{
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'name' : 'first',
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'color' : 'blue',
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'type' : 'break'
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}
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)
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db.test.insert(
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{
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'name' : 'second',
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'color' : 'red',
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//'type' : 'break'
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}
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)
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Note that the second document does not have a type field, it's missing. The aggregation pipeline produces inconsistent results sometimes showing 'type' :null in the id field, and sometimes not.
For example, the following aggregation does NOT return the missing type in the key:
db.test.aggregate([
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{
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$group : {
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'_id' : {
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'name' : '$name',
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'type' : '$type',
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'color' : '$color'
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},
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'count' : {$sum : 1}
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}
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},
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{
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$group : {
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'_id' : {
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'type' : '$_id.type',
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'color' : '$_id.color'
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},
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'count' : {$sum : 1}
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}
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}
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])
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Results in:
{ "_id" : { "type" : "break", "color" : "blue" }, "count" : 1 }
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{ "_id" : { "color" : "red" }, "count" : 1 }
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However, this aggregation, returns back a 'type' : null,
db.test.aggregate([
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{
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$group : {
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'_id' : {
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'name' : '$name',
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'type' : '$type',
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'color' : '$color'
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},
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'count' : {$sum : 1}
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}
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},
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{
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$group : {
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'_id' : {
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'type' : '$_id.type',
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//'color' : '$_id.color'
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},
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'count' : {$sum : 1}
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}
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}
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])
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Results in:
{ "_id" : { "type" : "break" }, "count" : 1 }
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{ "_id" : { "type" : null }, "count" : 1 }
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Note that the only difference was the comment out of the 'color' field in the second group.
The results should be consistent between these two queries. Either the first results should look like:
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