Variables

Aggregation expressions can use both user-defined and system variables.
Variables can hold any BSON type data. To access the value of the variable, prefix the variable name with double dollar signs ();i.e."); i.e. ");i.e."
".
For example:
Variable
Access via $
Brief Description
close
$$CLOSE
returns the absolute value of a number
context
$$CONTEXT
returns a numeric value between 0 and π radians for x between -1 and 1
cursor
$$CURSOR
returns the inverse hyperbolic cosine of a number
date
$$DATE
N/A
env
$$ENV
N/A
now
$$NOW
A variable that returns the current datetime value
random
$$RANDOM
returns a floating-point, pseudo-random number in the range 0 to less than 1
remove
$$REMOVE
A variable which evaluates to the missing value
request
$$REQUEST
N/A
root
$$ROOT
References the root currently being processed in the aggregation pipeline stage
script
$$SCRIPT
N/A
var
$$VAR
N/A

Accumulators

Conditionals

Last modified 1yr ago

Variable	Access via $	Brief Description
close	`$$CLOSE`	returns the absolute value of a number
context	`$$CONTEXT`	returns a numeric value between 0 and π radians for x between -1 and 1
cursor	`$$CURSOR`	returns the inverse hyperbolic cosine of a number
date	`$$DATE`	N/A
env	`$$ENV`	N/A
now	`$$NOW`	A variable that returns the current datetime value
random	`$$RANDOM`	returns a floating-point, pseudo-random number in the range 0 to less than 1
remove	`$$REMOVE`	A variable which evaluates to the missing value
request	`$$REQUEST`	N/A
root	`$$ROOT`	References the root currently being processed in the aggregation pipeline stage
script	`$$SCRIPT`	N/A
var	`$$VAR`	N/A