mongoose — Array variable in query

Question

I'm trying to write a mongoose query that allows me to find a document with a populated array, where the name of the array is stored in a variable. I've tried various syntaxes, using [square brackets], etc, and I've searched but can't find anything that works.

var arrayName = req.params.abbreviation + "Films";
console.log(arrayName); //documentaryFilms

FilmModel.findOne({
  $and: [
    { incomplete: false },
    { [arrayName].[0]: { $exists: true } }
...

Does anyone know how this can be achieved? Thank you

Tobias S. · Accepted Answer · 2022-04-05 12:10:08Z

1

Use the $size operator to get the length of the array.

FilmModel.aggregate(
[
     {
       $addFields: {
        "size_of_array": {
          $size: "$abcFilms"
        }
       }
     }
     { 
       $match: { "size_of_array": { $gt: 0 } } 
     }
])

If you want to filter based on an element with index n in an array take a look at $arrayElemAt operator.

edited Apr 5, 2022 at 12:10

answered Apr 5, 2022 at 11:30

Tobias S.

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2 Comments

Joseph Over a year ago

That doesn't seem to be working for me (I also tried $gt: 0), it just gives "Network Error at createError" As for the $arrayElemAt suggestion, I tried the following, but it didn't work either: { [arrayName]: { $arrayElemAt: [ [0], { $exists: true } ] } }

Tobias S. Over a year ago

I updated my answer. $size doesn't work with $gt or any comparisons for some reason. We have to use an aggregate then.

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