$type (aggregation)
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Definition
$typeReturns a string that specifies the BSON type of the argument.
$typehas the following operator expression syntax:{ $type: <expression> } The argument can be any valid expression.
Tip
See also:
$isNumber- checks if the argument is a number.$type (Query)- filters fields based on BSON type.
Behavior
$type
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".
If the argument is a field that is missing in the input document,
$type returns the string "missing".
The following table shows the $type output for several
common types of expressions:
Example | Results |
|---|---|
{ $type: "a" } | "string" |
{ $type: /a/ } | "regex" |
{ $type: 1 } | "double" |
{ $type: NumberLong(627) } | "long" |
{ $type: { x: 1 } } | "object" |
{ $type: [ [ 1, 2, 3 ] ] } | "array" |
Note
In the case of a literal array such as [ 1, 2, 3 ],
enclose the expression in an outer set
of array brackets to prevent MongoDB from parsing
[ 1, 2, 3 ] as an
argument list
with three arguments (1, 2, 3). Wrapping the array
[ 1, 2, 3 ] in a $literal expression
achieves the same result.
See operator expression syntax forms for more information.
Available Types
Type | Number | Alias | Notes |
|---|---|---|---|
Double | 1 | "double" | |
String | 2 | "string" | |
Object | 3 | "object" | |
Array | 4 | "array" | |
Binary data | 5 | "binData" | |
Undefined | 6 | "undefined" | Deprecated. |
ObjectId | 7 | "objectId" | |
Boolean | 8 | "bool" | |
Date | 9 | "date" | |
Null | 10 | "null" | |
Regular Expression | 11 | "regex" | |
DBPointer | 12 | "dbPointer" | Deprecated. |
JavaScript | 13 | "javascript" | |
Symbol | 14 | "symbol" | Deprecated. |
32-bit integer | 16 | "int" | |
Timestamp | 17 | "timestamp" | |
64-bit integer | 18 | "long" | |
Decimal128 | 19 | "decimal" | |
Min key | -1 | "minKey" | |
Max key | 127 | "maxKey" |
If the argument is a field that is missing in the input document,
$type returns the string "missing".
Example
This example uses a collection named coll with
the following documents:
{ _id: 0, a : 8 } { _id: 1, a : [ 41.63, 88.19 ] } { _id: 2, a : { a : "apple", b : "banana", c: "carrot" } } { _id: 3, a : "caribou" } { _id: 4, a : NumberLong(71) } { _id: 5 }
The following aggregation operation uses the $type
operator to display the type of field a for all documents
as part of the $project stage.
db.coll.aggregate([{ $project: { a : { $type: "$a" } } }])
The operation returns the following:
{ _id: 0, "a" : "double" } { _id: 1, "a" : "array" } { _id: 2, "a" : "object" } { _id: 3, "a" : "string" } { _id: 4, "a" : "long" } { _id: 5, "a" : "missing" }