can not push object id in array of object using mongo object code example

Example 1: mongodb add multiple element to array

db.students.update(
   { name: "joe" },
   { $push: { scores: { $each: [ 90, 92, 85 ] } } }
)

Example 2: mongodb add to array if not exists

db.tags.update(
    {name: 'sport'},
    {$addToSet: { videoIDs: "34f54e34c" } }
);