$expr with $regexMatch doesn't work when the pattern is inside an array

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Based in this example, I'm using $expr and $regexMatch to implement "reverse regex" queries in MongoDB. For instance this example works

However, this only seems to work when the regex is in a first level field in the MongoDB document. In the case the regex is within an element in an array (as in this other example I get errors like this:

query failed: (Location51105) Executor error during find command :: caused by :: $regexMatch needs 'regex' to be of type string or regex

Is there any way of supporting this case?

mongodb regex
1 Answers

The regex allows only string input, You can use $map operator to loop the array elements and check the condition,

  • $map to iterate loop of patterns.pattern array and check $regexMatch condition, it will return boolean value
  • $anyElementTrue to check if any element is true then it will true
db.collection.find({
  "$expr": {
    "$anyElementTrue": {
      "$map": {
        "input": "$patterns.pattern",
        "in": {
          "$regexMatch": {
            "input": "Room1",
            "regex": "$$this",
            "options": "i"
          }
        }
      }
    }
  }
})

Playground

user_89871280
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