> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# $toLong  (expression operator)

## Definition

Converts a value to a long. If the value cannot be converted to a long, [`$toLong`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/tolong.md#mongodb-expression-exp.-toLong) errors. If the value is null or missing, [`$toLong`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/tolong.md#mongodb-expression-exp.-toLong) returns null.

[`$toLong`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/tolong.md#mongodb-expression-exp.-toLong) has the following syntax:

```javascript
{
   $toLong: <expression>
}
```

The [`$toLong`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/tolong.md#mongodb-expression-exp.-toLong) takes any valid [expression.](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions)

The [`$toLong`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/tolong.md#mongodb-expression-exp.-toLong) is a shorthand for the following [`$convert`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/convert.md#mongodb-expression-exp.-convert) expression:

```javascript
{ $convert: { input: <expression>, to: "long" } }
```

**See also:**

[`$convert`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/convert.md#mongodb-expression-exp.-convert)

## Behavior

The following table lists the input types that can be converted to a long:

| Input Type | Behavior |
| --- | --- |
| Boolean | Returns Long(0) for  `false`.Returns Long(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. `"-5"`, `"123456"`). You cannot convert a string value of a float or decimal or non-base 10 number (e.g. `"-5.0"`, `"0x6400"`) |
| Date | Converts the Date into the number of milliseconds since the epoch. |

**See also:**

To convert strings in bases other than `10`, use [`$convert`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/convert.md#mongodb-expression-exp.-convert) with the `base` option.

The following table lists some conversion to long examples:

| Example | Results |
| --- | --- |
| `{ $toLong: true }` | Long("1") |
| `{ $toLong: false }` | Long("0") |
| `{ $toLong: 1.99999 }` | Long("1") |
| `{ $toLong: Decimal128("5.5000") }` | Long("5") |
| `{ $toLong: Decimal128("9223372036854775808.0") }` | Error |
| `{ $toLong: Int32(8) }` | Long(8) |
| `{ $toLong: ISODate("2018-03-26T04:38:28.044Z") }` | Long("1522039108044") |
| `{ $toLong: "-2" }` | Long("-2") |
| `{ $toLong: "2.5" }` | Error |
| `{ $toLong: null }` | null |

## Example

Create a collection `orders` with the following documents:

```javascript
db.orders.insertMany( [
   { _id: 1, item: "apple", qty: Int32(5) },
   { _id: 2, item: "pie", qty: "100" },
   { _id: 3, item: "ice cream", qty: Long("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:

```javascript
// 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:

```javascript
{ _id: 3, item: 'ice cream', qty: Long("500"), convertedQty: Long("500") },
{ _id: 2, item: 'pie', qty: '100', convertedQty: Long("100") },
{ _id: 4, item: 'almonds', qty: '50', convertedQty: Long("50") },
{ _id: 1, item: 'apple', qty: 5, convertedQty: Long("5") }
```

**Note:**

If the conversion operation encounters an error, the aggregation operation stops and throws an error. To override this behavior, use [`$convert`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/convert.md#mongodb-expression-exp.-convert) instead.