在MongoDB中使用split后如何对字段进行排序?

Question

我在MongoDB中使用聚合和拆分来标记字符串字段，并且工作正常。但是我想对字段进行排序，由于某种原因，聚合排序根本不起作用。

db.coll.aggregate( { $project: { split: {$split: ["$FIELD_NAME", " "] } } } )

它给了我以下输出：

{ "_id" : 112, "split" : [ "TOKEN", "EXCH" ] }
{ "_id" : 122, "split" : [ "TOKEN", "EXCH" ] }
{ "_id" : 332, "split" : [ "TOKN", "EXCH" ] }
{ "_id" : 444, "split" : [ "ABC", "IND", "INS" ] }

但是当我尝试对拆分字段进行排序时，它会给我一个错误。

db.table_a.aggregate( { $project: { split: {$split: ["$FIELD_NAME", " "] } } }, {$sort: {"split": -1}} )
2019-10-16T14:11:22.528-0500 E QUERY    [js] Error: command failed: {
"ok" : 0,
"errmsg" : "$split requires an expression that evaluates to a string as a first argument, found: int",
"code" : 40085,
"codeName" : "Location40085"
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:18:14
_assertCommandWorked@src/mongo/shell/assert.js:534:17
assert.commandWorked@src/mongo/shell/assert.js:618:16
DB.prototype._runAggregate@src/mongo/shell/db.js:260:9
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1062:12

我尝试了不同的排序方式，但它没有按预期工作。有人可以帮忙吗？

Answer 1

您可以展开拆分，按_id排序并再次分组，将排序后的拆分推送到数组中。

db.coll.aggregate([ 
{ $project: { split: {$split: ["$FIELD_NAME", " "] } } }, 
{$unwind: "$split"}, 
{$sort: {split: -1}}, 
{$group: {_id: "$_id", sorted_split: {$push: "$split"}}} 
])