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$toString (aggregation)![](/docs/v5.2/assets/link.svg)
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Definition![](/docs/v5.2/assets/link.svg)
$toString
New in version 4.0.
Converts a value to a string. If the value cannot be converted to a string,
$toString
errors. If the value is null or missing,$toString
returns null.$toString
has the following syntax:{ $toString: <expression> } The
$toString
takes any valid expression.The
$toString
is a shorthand for the following$convert
expression:{ $convert: { input: <expression>, to: "string" } } Tip
See also:
Behavior![](/docs/v5.2/assets/link.svg)
The following table lists the input types that can be converted to a string:
Input Type | Behavior |
---|---|
Boolean | Returns the boolean value as a string. |
Double | Returns the double value as a string. |
Decimal | Returns the decimal value as a string. |
Integer | Returns the integer value as a string. |
Long | Returns the long value as a string. |
ObjectId | Returns the ObjectId value as a hexadecimal string.. |
String | No-op. Returns the string value. |
Date | Returns the date as a string. |
The following table lists some conversion to string examples:
Example | Results |
---|---|
{$toString: true} | "true" |
{$toString: false} | "false" |
{$toString: 2.5} | "2.5" |
{$toString: NumberInt(2)} | "2" |
{$toString: NumberLong(1000)} | "1000" |
{$toString: ObjectId("5ab9c3da31c2ab715d421285")} | "5ab9c3da31c2ab715d421285" |
{$toString: ISODate("2018-03-27T16:58:51.538Z")} | "2018-03-27T16:58:51.538Z" |
Example![](/docs/v5.2/assets/link.svg)
Create a collection orders
with the following documents:
db.orders.insertMany( [ { _id: 1, item: "apple", qty: 5, zipcode: 93445 }, { _id: 2, item: "almonds", qty: 2, zipcode: "12345-0030" }, { _id: 3, item: "peaches", qty: 5, zipcode: 12345 }, ] )
The following aggregation operation on the orders
collection
converts the zipcode
to string before sorting by the string value:
// Define stage to add convertedZipCode field with the converted zipcode value zipConversionStage = { $addFields: { convertedZipCode: { $toString: "$zipcode" } } }; // Define stage to sort documents by the converted zipcode sortStage = { $sort: { "convertedZipCode": 1 } }; db.orders.aggregate( [ zipConversionStage, sortStage ] )
The operation returns the following documents:
{ _id: 3, item: 'peaches', qty: 5, zipcode: 12345, convertedZipCode: '12345' }, { _id: 2, item: 'almonds', qty: 2, zipcode: '12345-0030', convertedZipCode: '12345-0030' }, { _id: 1, item: 'apple', qty: 5, zipcode: 93445, convertedZipCode: '93445' }
Note
If the conversion operation encounters an error, the aggregation
operation stops and throws an error. To override this behavior, use
$convert
instead.