3
考慮下面的數據庫的集合:求和蒙戈子文檔字段
> db.collection.find()
{ "_id" : 1, "results" : { "record" : { "price" : 100 } } }
{ "_id" : 2, "results" : { "record" : { "price" : 200 } } }
{ "_id" : 3, "results" : { "record" : { "price" : 300 } } }
如何我可以使用聚合(或映射簡化),以獲得各results.record.price
字段的總和?
> db.collection.aggregate({$group : { _id:"", "results.record.price" : {$sum : "$results.record.price"}}}, {$project:{_id: 0, "results.record.price" : "$results.record.price"}})
Error: Printing Stack Trace
at printStackTrace (src/mongo/shell/utils.js:37:15)
at DBCollection.aggregate (src/mongo/shell/collection.js:897:9)
at (shell):1:15
Mon Oct 28 20:15:24.065 aggregate failed: {
"errmsg" : "exception: the group aggregate field name 'results.record.price' cannot be used because $group's field names cannot contain '
.'",
"code" : 16414,
"ok" : 0
} at src/mongo/shell/collection.js:898
'_id:「」'是什麼意思?感謝您的幫助 –
@kevin'_id'是組標識符。在那種情況下,由於它是不變的,空字符串,每個處理的記錄將被合併成一個組,由該空字符串標識。你可以使用其他常量,比如'null',''a「'等等。 – Rafa
你能否檢查一下 - http://stackoverflow.com/questions/19664748/summing-mongo-sub-document-array –