mongo db aggregate match conditional filteration

Question

say I have 3 models:

1- Project..., target_countries

2- Freelancer..., country

3- Country...

now we have search project page where freelancer can apply for projects/ jobs than match their locations. we have 2 conditions:

1- if project owner has targeted certain countries then we check freelancer location against target_locations...

2- if no target_locations set by the owner then we skip this filter so everyone can see the project.

I need to use aggregate (not find)

here is what I have tried but no luck code sample

sample input: freelancerCountryID= 61c9d2753be49339489583b8

output: main MongoError: unknown top level operator: $cond. If you have a field name that starts with a '$' symbol, consider using $getField or $setField.

Answer 1

after digging I found the solution with the right syntax

use $expr on top of $cond since we are in a $match statment

$match:{
$expr:{
    $cond: {
        if: { 
            $and:[ {$eq: [ '$countryFilterIsActive', "ACTIVE" ]}, {$isArray:'$target_locations'} ]
        },

        then: { $in: [mongoose.Types.ObjectId(freelancerLocationID),'$target_locations'] },
        
        else: {}
    } 
}

}