CODEWITHSUNDEEP
mongodbaggregation-framework
LienM
LienM

Reputation: 145

Unrecognized pipeline stage name: '$concat'

I am using:

db.version()

3.2.3

version()

3.2.0-17-gde480c0

db.getCollection('events').aggregate([
    { $concat: [ "$element", " - ", "$Eventtype" ] }
])

gives me the following error:

"assert: command failed: {
    "ok" : 0,
    "errmsg" : "Unrecognized pipeline stage name: '$concat'",
    "code" : 16436
} : aggregate failed
_getErrorWithCode@src/mongo/shell/utils.js:23:13
doassert@src/mongo/shell/assert.js:13:14
assert.commandWorked@src/mongo/shell/assert.js:266:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1215:5
@(shell):1:1"

What am I doing wrong here?

Upvotes: 1

Views: 8077

Answers (1)

dyouberg
dyouberg

Reputation: 2332

You're using $concat as a pipeline stage in the aggregation pipeline.

See here for a list of the stages.

$concat is used as a string modifier to concatenate the results.

See here for examples.

They tend to use $concat in a $project pipeline stage in the examples to combine two values of a document into one.

For instance:

{ $project: { itemDescription: { $concat: [ "$item", " - ", "$description" ] } } }

in your case it might look something like...

{ $project: { event: { $concat: [ "$element", " - ", "$Eventtype" ] } } }

Upvotes: 2

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