I am trying to select documents using the $type operator.

Here is my collection :

{id: 1, a: [{b: "", c: ""}]},
{id: 2, a: {b: "", c: ""}}

Here is my queries :

db.collection.find( {a: { $type: "array"}} )
// It will return id: 1

db.collection.find( {a: { $type: "object"}} )
// It will return id: 2 AND id: 1

With the second query, I want to select only the object type.

https://mongoplayground.net/p/kp6UVzrUzjA
I am doing it wrong?

CodePudding user response：

Each type match with the type or with array that contains at least one member of that type. see this

Query

Test code here

db.collection.find({
  a: {
    $not: {
      $type: "array"
    },
    $type: "object"
  }
})

CodePudding user response：

You can also use an aggregation pipeline:

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $eq: [ { $type: "$a" }, "object" ]
      }
    }
  }
])

$type (aggregation)

Unlike the $type query operator, which matches array elements based on their BSON type, the $type aggregation operator does not examine array elements. Instead, when passed an array as its argument, the $type aggregation operator returns the type of the argument, i.e. "array".