Mongodb aggregate arguments to $lookup must be strings

Question

        db.absences.insert([
           { \"_id\" : 1, \"student\" : \"Ann Aardvark\", sickdays: [ new Date (\"2018-05-01\"),new Date (\"2018-08-23\") ] },
                  


        

Answer 1

Because you are trying to use the $lookup features (syntax) from MongoDB v3.6 on MongoDB v3.4

The MongoDB v3.4 $lookup syntax:

{
   $lookup:
     {
       from: ,
       localField: ,
       foreignField: ,
       as: 

     }
}

The MongoDB v3.6 $lookup syntax:

{
   $lookup:
     {
       from: ,
       let: { : , …, :  },
       pipeline: [  ],
       as: 

     }
}

https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/