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I am trying to return "O" when the value of the field size.value is true and "N" when it's false . I am going for the $cond but so far it only return "O" because if I only put the path $size.value as a condition. Then the condition will be consider true if the field exist.

I tried to put an $eq on the value of $size.value but it's returning an error

db.getCollection('collectionA').aggregate(
         $project:
             "Object":
               { $cond: { if: {"$size.value"{$eq:"true"}}, then: "O", else: "N" } },
Do we've any solution with this method or should I move and go with switch or any other method ?
Update : The value of the field '$size.value' is not a type boolean but a type String with 2 values possible 'true' and 'false'
So I am looking to check if the value of the field '$size.value' is a String equal to 'true' or 'false'
Please try below :
If you wanted to check value of field size.value is equal to true (this query would usually return 'N' on documents where size.value field doesn't exist or value of it doesn't match with true, Basically there is syntax error in your query) :
db.getCollection('yourCollectionName').aggregate(
            $project:
                'Object':
                    { $cond: [{ $eq: ['$size.value', true] }, 'O', 'N'] }
Else if you wanted to check field size.value exists, then this (As $exist doesn't work with $cond we need to do this) :
db.getCollection('yourCollectionName').aggregate(
            $project:
                'Object':
                    { $cond: [{ $ne: [{ $ifNull: ['$size.value', 'N'] }, 'N'] }, 'O', 'N'] }
                Thx for your answer, I am in the first case. I want to check the value of '$size.value' and not his existence. But I just realized that the value of '$size.value' is not a boolean but a string with two value 'true' and 'false'  I will update the question
– Bruno SENELLART
                Dec 11, 2019 at 8:36
                @BrunoSENELLART : then you just need to replace boolean true with “true” which would make it a string match on that field, rest everything should be the same..
– whoami - fakeFaceTrueSoul
                Dec 11, 2019 at 15:35
        
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