Database Manual / Reference / Query Language / Expressions

$toBool (expression operator)

Definition

$toBool

Converts a value to a boolean.

$toBool has the following syntax:

{
   $toBool: <expression>
}

The $toBool takes any valid expression.

The $toBool is a shorthand for the following $convert expression:

{ $convert: { input: <expression>, to: "bool" } }

Tip

$convert

Behavior

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

Input Type	Behavior
Array	Returns true
Binary data	Returns true
Boolean	No-op. Returns the boolean value.
Code	Returns true
Date	Returns true
Decimal	Returns true if not zero Return false if zero
Double	Returns true if not zero Return false if zero
Integer	Returns true if not zero Return false if zero
JavaScript	Returns true
Long	Returns true if not zero Return false if zero
MaxKey	Returns true
MinKey	Returns true
Null	Returns null
Object	Returns true
ObjectId	Returns true
Regular expression	Returns true
String	Returns true
Timestamp	Returns true

To learn more about data types in MongoDB, see BSON Types.

The following table lists some conversion to boolean examples:

Example	Results
`{$toBool: false}`	false
`{$toBool: 1.99999}`	true
`{$toBool: Decimal128("5")}`	true
`{$toBool: Decimal128("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.

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