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$isArray (aggregation)
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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" ] }