how to add object in array in mongodb code example

Example 1: mongodb push to arry in update

db.collection.update({_id:xx}, {$push:{letters : {$each:['first one'], $position:0}}})

Example 2: mongodb push to arry in update

db.collection.update({_id:xx}, {$pop:{letters : -1}})

Example 3: insert item into list mongodb

db.col.update(
    { name: 'doc', 'list.id': 2 }, 
    {$push: {'list.$.items': {id: 5, name: 'item5'}}}
)