$toBool (aggregation)
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Definition
$toBoolNew in version 4.0.
Converts a value to a boolean.
$toBoolhas the following syntax:{ $toBool: <expression> } The
$toBooltakes any valid expression.The
$toBoolis a shorthand for the following$convertexpression:{ $convert: { input: <expression>, to: "bool" } } Tip
See also:
Behavior
The following table lists the input types that can be converted to a boolean:
Input Type | Behavior |
|---|---|
Boolean | No-op. Returns the boolean value. |
Double | Returns true if not zero. Return false if zero. |
Decimal | Returns true if not zero. Return false if zero. |
Integer | Returns true if not zero. Return false if zero. |
Long | Returns true if not zero. Return false if zero. |
ObjectId | Returns true. |
String | Returns true. |
Date | Returns true. |
The following table lists some conversion to boolean examples:
Example | Results |
|---|---|
{$toBool: false} | false |
{$toBool: 1.99999} | true |
{$toBool: NumberDecimal("5")} | true |
{$toBool: NumberDecimal("0")} | false |
{$toBool: 100} | true |
{$toBool: ISODate("2018-03-26T04:38:28.044Z")} | true |
{$toBool: "false"} | true |
{$toBool: ""} | true |
{$toBool: null} | null |
Example
Create a collection orders with the following documents:
db.orders.insertMany( [ { _id: 1, item: "apple", qty: 5, shipped: true }, { _id: 2, item: "pie", qty: 10, shipped: 0 }, { _id: 3, item: "ice cream", shipped: 1 }, { _id: 4, item: "almonds", qty: 2, shipped: "true" }, { _id: 5, item: "pecans", shipped: "false" }, // Note: All strings convert to true { _id: 6, item: "nougat", shipped: "" } // Note: All strings convert to true ] )
The following aggregation operation on the orders collection
converts the shipped to a boolean value before finding the
unshipped orders:
// Define stage to add convertedShippedFlag field with the converted shipped value // Because all strings convert to true, include specific handling for "false" and "" shippedConversionStage = { $addFields: { convertedShippedFlag: { $switch: { branches: [ { case: { $eq: [ "$shipped", "false" ] }, then: false } , { case: { $eq: [ "$shipped", "" ] }, then: false } ], default: { $toBool: "$shipped" } } } } }; // Define stage to filter documents and pass only the unshipped orders unshippedMatchStage = { $match: { "convertedShippedFlag": false } }; db.orders.aggregate( [ shippedConversionStage, unshippedMatchStage ] )
The operation returns the following document:
{ "_id" : 2, "item" : "pie", "qty" : 10, "shipped" : 0, "convertedShippedFlag" : false } { "_id" : 5, "item" : "pecans", "shipped" : "false", "convertedShippedFlag" : false } { "_id" : 6, "item" : "nougat", "shipped" : "", "convertedShippedFlag" : false }
Note
If the conversion operation encounters an error, the aggregation
operation stops and throws an error. To override this behavior, use
$convert instead.