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$toLong (aggregation)![](/zh-cn/docs/v4.4/assets/link.svg)
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Definition![](/zh-cn/docs/v4.4/assets/link.svg)
$toLong
Converts a value to a long. If the value cannot be converted to a long,
$toLong
errors. If the value is null or missing,$toLong
returns null.$toLong
has the following syntax:{ $toLong: <expression> } The
$toLong
takes any valid expression.The
$toLong
is a shorthand for the following$convert
expression:{ $convert: { input: <expression>, to: "long" } } Tip
See also:
Behavior![](/zh-cn/docs/v4.4/assets/link.svg)
The following table lists the input types that can be converted to a decimal:
The following table lists the input types that can be converted to a long:
Input Type | Behavior |
---|---|
Boolean | Returns NumberLong(0) for false .Returns NumberLong(1) for true . |
Double | Returns truncated value. The truncated double value must fall within the minimum and maximum value for a long. You cannot convert a double value whose truncated value is less than the minimum long value or is greater than the maximum long value. |
Decimal | Returns truncated value. The truncated decimal value must fall within the minimum and maximum value for a long. You cannot convert a decimal value whose truncated value is less than the minimum long value or is greater than the maximum long value. |
Integer | Returns the int value as a long. |
Long | No-op. Returns the long value. |
String | Returns the numerical value of the string. The string value must be of a base 10 long (e.g.
You cannot convert a string value of a float or decimal or
non-base 10 number (e.g. |
Date | Converts the Date into the number of milliseconds since the
epoch. |
The following table lists some conversion to long examples:
Example | Results |
---|---|
{ $toLong: true } | NumberLong("1") |
{ $toLong: false } | NumberLong("0") |
{ $toLong: 1.99999 } | NumberLong("1") |
{ $toLong: NumberDecimal("5.5000") } | NumberLong("5") |
{ $toLong: NumberDecimal("9223372036854775808.0") } | Error |
{ $toLong: NumberInt(8) } | NumberLong(8) |
{ $toLong: ISODate("2018-03-26T04:38:28.044Z") } | NumberLong("1522039108044") |
{ $toLong: "-2" } | NumberLong("-2") |
{ $toLong: "2.5" } | Error |
{ $toLong: null } | null |
Example![](/zh-cn/docs/v4.4/assets/link.svg)
Create a collection orders
with the following documents:
db.orders.insert( [ { _id: 1, item: "apple", qty: NumberInt(5) }, { _id: 2, item: "pie", qty: "100" }, { _id: 3, item: "ice cream", qty: NumberLong(500) }, { _id: 4, item: "almonds", qty: "50" }, ] )
The following aggregation operation on the orders
collection
converts the qty
to long before sorting by the value:
// Define stage to add convertedQty field with converted qty value qtyConversionStage = { $addFields: { convertedQty: { $toLong: "$qty" } } }; // Define stage to sort documents by the converted qty values sortStage = { $sort: { "convertedQty": -1 } }; db.orders.aggregate( [ qtyConversionStage, sortStage ])
The operation returns the following documents:
{ "_id" : 1, "item" : "apple", "qty" : 5, "convertedQty" : NumberLong(5) } { "_id" : 2, "item" : "pie", "qty" : "100", "convertedQty" : NumberLong(100) } { "_id" : 3, "item" : "ice cream", "qty" : NumberLong(500), "convertedQty" : NumberLong(500) } { "_id" : 4, "item" : "almonds", "qty" : "50", "convertedQty" : NumberLong(50) }
Note
If the conversion operation encounters an error, the aggregation
operation stops and throws an error. To override this behavior, use
$convert
instead.