$cond (aggregation)
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Definition
Compatibility
You can use $cond
for deployments hosted in the following
environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
Syntax
The $cond
expression has one of two syntaxes:
{ $cond: { if: <boolean-expression>, then: <true-case>, else: <false-case> } }
Or:
{ $cond: [ <boolean-expression>, <true-case>, <false-case> ] }
$cond
requires all three arguments (if-then-else
)
for either syntax.
If the <boolean-expression>
evaluates to true
, then
$cond
evaluates and returns the value of the
<true-case>
expression. Otherwise, $cond
evaluates
and returns the value of the <false-case>
expression.
The arguments can be any valid expression. For more information on expressions, see Expression Operators.
Example
The following example use a inventory
collection with the following
documents:
{ "_id" : 1, "item" : "abc1", qty: 300 } { "_id" : 2, "item" : "abc2", qty: 200 } { "_id" : 3, "item" : "xyz1", qty: 250 }
The following aggregation operation uses the $cond
expression to set the discount
value to 30
if qty
value is
greater than or equal to 250 and to 20
if qty
value is less
than 250
:
db.inventory.aggregate( [ { $project: { item: 1, discount: { $cond: { if: { $gte: [ "$qty", 250 ] }, then: 30, else: 20 } } } } ] )
The operation returns the following results:
{ "_id" : 1, "item" : "abc1", "discount" : 30 } { "_id" : 2, "item" : "abc2", "discount" : 20 } { "_id" : 3, "item" : "xyz1", "discount" : 30 }
The following operation uses the array syntax of the
$cond
expression and returns the same results:
db.inventory.aggregate( [ { $project: { item: 1, discount: { $cond: [ { $gte: [ "$qty", 250 ] }, 30, 20 ] } } } ] )