$isArray (aggregation)
On this page
This version of the documentation is archived and no longer supported. View the current documentation to learn how to upgrade your version of MongoDB server.
Definition
$isArrayNew in version 3.2.
Determines if the operand is an array. Returns a boolean.
$isArrayhas the following syntax:{ $isArray: [ <expression> ] }
Behavior
The <expression> can be any valid expression. For more information on expressions, see
Expressions.
Example | Results |
|---|---|
{ $isArray: [ "hello" ] } | false |
{ $isArray: [ [ "hello", "world" ] ] } | true |
Example
A collection named warehouses contains the following documents:
{ "_id" : 1, instock: [ "chocolate" ], ordered: [ "butter", "apples" ] } { "_id" : 2, instock: [ "apples", "pudding", "pie" ] } { "_id" : 3, instock: [ "pears", "pecans"], ordered: [ "cherries" ] } { "_id" : 4, instock: [ "ice cream" ], ordered: [ ] }
The following example checks if the instock and the ordered
fields are arrays before concatenating the two:
db.warehouses.aggregate([ { $project: { items: { $cond: { if: { $and: [ { $isArray: "$instock" }, { $isArray: "$ordered" } ] }, then: { $concatArrays: [ "$instock", "$ordered" ] }, else: "One or more fields is not an array." } } } } ])
{ "_id" : 1, "items" : [ "chocolate", "butter", "apples" ] } { "_id" : 2, "items" : "One or more fields is not an array." } { "_id" : 3, "items" : [ "pears", "pecans", "cherries" ] } { "_id" : 4, "items" : [ "ice cream" ] }