$type (aggregation)
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Definition
$type-
New in version 3.4.
Returns 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.
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. |
| JavaScript (with scope) | 15 | “javascriptWithScope” | |
| 32-bit integer | 16 | “int” | |
| Timestamp | 17 | “timestamp” | |
| 64-bit integer | 18 | “long” | |
| Decimal128 | 19 | “decimal” | New in version 3.4. |
| 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" }