Variables

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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 1mo ago
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