$regex within $project mongodb aggregation

Question

I have a users collection which has a location field with type String. I want to pass a score field along the document which shows whether the document's location is similar to the text "Austin". For instance the recorded location is Austin, Texas, I want it to be matched with Austin. I thought it would be possible to use $regex for this.

I wrote this aggregation:

$project: {
  score: {
    $cond: 
      if: {
        $regex: {'$location': /Austin/}
      },
      then: 1,
      else: 0
    }
  },
  location: 1,
  firstName: 1,
  lastName: 1
}

But what I get is :

{
    "name": "MongoError",
    "errmsg": "exception: invalid operator '$regex'",
    "code": 15999,
    "ok": 0
}

$cond: {if: then: else} docs.mongodb.org/manual/reference/operator/aggregation/cond — YOU
– YOU, Commented Apr 25, 2015 at 14:32
any sample data? I can't guess what is score looks like, and how you want it. — YOU
– YOU, Commented Apr 25, 2015 at 14:46
looks like $regex does not support in $project, might need to use mapReduce to build another table. — YOU
– YOU, Commented Apr 25, 2015 at 15:27

J.F. · Accepted Answer · 2021-09-26 00:56:24Z

0

I know this is an old question but since version 4.2 you can use $regexMatch.

You can use this stage:

{
  $project: {
    score: {
      $cond: {
        if: {
          $regexMatch: {
            input: "$location",
            regex: "Austin"
          }
        },
        then: 1,
        else: 0
      }
    },
    location: 1,
    firstName: 1,
    lastName: 1
  }
}

Example here

answered Sep 26, 2021 at 0:56

J.F.

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