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To deconstruct an array in MongoDB, we can use the $unwind operator.

Let's suppose we have a collection named "students" with the following documents:

{
  "_id": 1,
  "name": "John",
  "grades": [81, 73, 92]
}
{
  "_id": 2,
  "name": "Mary",
  "grades": [87, 78, 95]
}

If we want to deconstruct the grades array of each document, we can use the following query:

db.students.aggregate([
  { $unwind: "$grades" }
])

The result will be:

{ "_id": 1, "name": "John", "grades": 81 }
{ "_id": 1, "name": "John", "grades": 73 }
{ "_id": 1, "name": "John", "grades": 92 }
{ "_id": 2, "name": "Mary", "grades": 87 }
{ "_id": 2, "name": "Mary", "grades": 78 }
{ "_id": 2, "name": "Mary", "grades": 95 }

The $unwind operator creates a new document for each element in the array, with the same values for all fields except for the field being unwound (grades in this case). This allows us to perform aggregation operations on the individual elements of the array.