How to extract matching strings from array and create new array

Question

I need to extract strings that contain the word 'DREAMS' from 'STYLE.' and create a new array with it.

MongoDB Documents:

[
  {
    name: "STYLE",
    params: ['DREAMS-FEEDING', 'DREAMS-PARI', 'SOFT']
  }, 
  {
    name: "BRAND",
    params: ['DREAMS', 'FEATHERLINE']
  }
]

The result should be:

['DREAMS-FEEDING', 'DREAMS-PARI']

Answer 1

You can apply the $regex operator to the params array. In the projection, with $filter and $regexMatch operators to filter the element(s) in the array.

db.collection.find({
  name: "STYLE",
  params: {
    $regex: "DREAMS"
  }
},
{
  name: 1,
  params: {
    $filter: {
      input: "$params",
      cond: {
        $regexMatch: {
          input: "$$this",
          regex: "DREAMS"
        }
      }
    }
  }
})

Demo @ Mongo Playground