MongoDB Aggregation Framework: Unary Operator

💚 Unary operator:

A unary operator is an operator that performs the operation on a single field or value within a document during the aggregation pipeline. It performs its operation only in a single field not performs its operator for the entire group.

** Unary operators are usually used in the $project stage. 

** In the group stage, the unary operator can be used only in conjunction with the accumulator.

$type: Returns the BSON data type of a field. For example, you can use $type it to filter documents based on the data type of a specific field.

$size: Returns the number of elements in an array field. This can be useful when working with arrays to perform operations based on the array size.

$exists: Checks if a field exists in a document. This is useful for filtering documents that contain or do not contain a specific field.

$not: Negates the boolean value of a given expression. It's used to perform logical negation on a condition.

$type:

db.persons.aggregate([

{$project: {name: 1, 

    nameType: {$type: "$name"}, 

    ageType: {$type: "$age"}, 

    tagsType: {$type: "$tags"}, 

    companyType: {$type: "$company"}}}

])

Output:

{ 

    "_id" : ObjectId("64dca7221921e7b46b5ad811"), 

    "name" : "Aurelia Gonzales", 

    "nameType" : "string", 

    "ageType" : "int", 

    "tagsType" : "array", 

    "companyType" : "object"

}