MongoDB provides different types of comparison expression operators that are used in the aggregation pipeline stages $cmp operator is one of them. This operator is used to perform a comparison between two values and return the following result according to the condition:
- If the first value is greater than the second value, then this operator will return 1.
- If the first value is less than the second value, then this operator will return -1.
- If both the values are equal, then this operator will return 0.
Syntax:
{ $cmp: [ <expression1>, <expression2> ] }
Examples:
In the following examples, we are working with:
Database: GeeksforGeeks
Collection: example
Document: two documents that contain the details of the shapes in the form of field-value pairs.
Using $cmp Operator:
In this example, we are comparing the value of the side field with 4 and $cmp operator return 0 which means both values are equal.
db.example.aggregate([{$match: {name: "Square"}},
... {$project: {result: {$cmp:["$side", 4]}}}])Using $cmp Operator in the Embedded Document:
In this example, we are comparing the value of the measurement.height field with the value of the measurement.width field and $cmp operator return -1 which means both values of measurement.height field is less than the value of the measurement.width field.
db.example.aggregate([{$match: {name: "Rectangle"}},
... {$project: {result:
... {$cmp:["$measurement.height", "$measurement.width"]}}}])