MongoDB - Return all regex matches from an Array

Question

I have a mongoDB document that contains a list of email address. I'd like to use a regEx expression to return an array of matching email address in the single document. I don't need to find all matches in the Collection. I'm assuming I need to use aggregation but I can't get it to work correctly. Any advice?

{
    "_id": {
        "$oid": "621fbc842ff7d84973d537e7"
    },
    "name": "Test",
    "emailAddresses": ["[email protected]", "[email protected]", "[email protected]", "[email protected]"],
    "_class": "com.email.models.Group"
}

Search for "ema", would return:

{
    "emailAddresses": ["[email protected]", "[email protected]", "[email protected]" ]
}

Answer 1

Something like this:

 db.collection.aggregate([
  {
   $addFields: {
     emailAddresses: {
      $filter: {
       input: "$emailAddresses",
       cond: {
        "$regexMatch": {
          input: "$$this",
          regex: "ema"
        }
       }
      }
     }
    }
   }
 ])

Explained:

Define addFields aggregation stage with $filter to replace the original emailAddresses array , in the input for the filter provide the emailAddresses array and condition for the filter add regex expression by which the array elements will be filtered.

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