CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-framework
MetalMad
MetalMad

Reputation: 446

ObjectId function invalid object id length error with $project using Mongodb 3.4.15

This is my aggregation 

db.getCollection("entities").aggregate([
    {$match : {...omissis..},
    {$project : {ancestors : 1}},  
    {$unwind: "$ancestors"}]);

The result is 

{ 
    "_id" : ObjectId("5b855ffb17285c29501dd801"), 
    "ancestors" : "5c62ef9b8521e37b80517583"
},
{ 
    "_id" : ObjectId("5b8537d3571c4f3e3c0dcf54"), 
    "ancestors" : "5c75565b3e44853a18cc9d11"
}

I want to convert the ancestors string into ObjectId. I have done a lot of tests , my last one is adding this pipeline

{$project: {
             result : {
                    "$let" : {
                              "vars" : { "id" : "$ancestors" },
                              "in" : ObjectId('$$id')
                             }
                       }
           } 
 }

Every tests I made I have the same error

Error: invalid object id: length :

The ancestors string is a valid ObjectId and I don't understand how to solve this error.

I know there are new commands with Mongodb 4.0 but this project still uses 3.4.15.

Upvotes: 0

Views: 707

Answers (1)

Mani
Mani

Reputation: 1549

I used cursor and javascript to achieve this. Please try this

db.getCollection("entities").aggregate([
    {$match : {...omissis..},
    {$project : {ancestors : 1}},  
    {$unwind: "$ancestors"}]).forEach(function(doc){
    doc.ancestors = ObjectId(doc.ancestors)
    print(doc);
    })

Upvotes: 1

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