MongoDB -- Setting a conditional statement in .find()

Question

for aggregate, $cond can be used to form an if-statement. I'm wonder if there's a similar function for .find()

When I tried using $cond in find(), I get

"unknown top level operator: $cond"

I'm trying to do the following (in pseudo code):

if condition is True:
    set filter for find to thing_1
else:
    set filter for find to thing_2

this whole thing becomes a string and is stored in a database. I'm trying to follow suit and form that one string only. Unless I can use an OR somehow — JChao
– JChao, Commented Mar 29, 2017 at 22:06

jhughes · Accepted Answer · 2018-10-17 16:38:30Z

1

If you are on Mongo 3.6 or greater, you could try using the $expr operator. Which would then allow you to use $cond.

$expr Allows the use of aggregation expressions within the query language.

Their example can be found here

db.supplies.find( {
    $expr: {
       $lt:[ {
          $cond: {
             if: { $gte: ["$qty", 100] },
             then: { $divide: ["$price", 2] },
             else: { $divide: ["$price", 4] }
           }
       },
       5 ] }
} )

answered Oct 17, 2018 at 16:38

jhughes

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1 Comment

nickt Over a year ago

Thanks. Would I be able to use this through the mongodb compass app?

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