MongoDB Array Count: $size Operator Guide

In MongoDB, you can use the aggregate pipeline operator $size to count the number of elements in an array. Here is a simple example: let’s say we have a collection called products that includes an array field named tags.

db.products.aggregate([
  {
    $project: {
      numberOfTags: { $size: "$tags" }
    }
  }
])

The above code will return a result set with a new field called numberOfTags, which contains the length of the tags array in each document.