March 2019
Intermediate to advanced
394 pages
11h 4m
English
Content preview from Mastering MongoDB 4.x - Second Edition
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Conditional expressions
Expressions can be used to output different data to the next stage in our pipeline based on Boolean truth tests:
$cond
The $cond phrase will evaluate an expression of the format if...then...else, and depending on the result of the if statement, it will return the value of the then statement or else branches. The input can be either three named parameters or three expressions in an ordered list:
$ifNull
The $ifNull phrase will evaluate an expression and return the first expression if it is not null or the second expression if the first expression is null. Null can be either a missing field or a field with an undefined value:
$switch
Similar to a programming language's switch statement, $switch will execute a specified ...
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