Bad Value needs an array in mongoDB

Question

I am trying to use $in inside $match condition of aggregate. I have SegmentList as literal array and Segment as a literal value. I am trying to match with $in condition as in query below.

db.collection.aggregate([
{'$match': {
    'MaterialNumber': '867522'
}}, 
 {'$project':{
    'SegmentList': {'$literal':['A']},
           'Segment':{'$literal':'A'},
           'value':{'$literal':'B'},
       }
   },
       {'$match': {
    'Segment':{'$in':'$SegmentList'}
 }
 }

])

But I am getting an error.

assert: command failed: {
"ok" : 0,
"errmsg" : "bad query: BadValue: $in needs an array",
"code" : 16810
} : aggregate failed

I am not not able to understand what is problem

s7vr · Accepted Answer · 2018-02-08 13:28:45Z

1

Not sure what you are intending to acheive here as all you are doing comparing if 'A' is in array with element 'A' which is always true.

$match in its regular form only takes a value not field reference.

No need to use $literal you can directly pass [].

You can use one of the following query based on mongo version.

3.4 & below:

{'$match': {'Segment':{'$in':['A']}}

3.6 ( not needed for your use case )

{'$match': {'$expr':{'$in':['$Segment', ['A']]}}}

answered Feb 8, 2018 at 13:28

s7vr

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