$toBool (aggregation)

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Definition
Behavior
Example

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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" } }

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.insert( [
   { _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.

Back

$tanh (aggregation)

$toDate (aggregation)