I want to update an object or push an object to an array in one query? For e.g if the document is

{list: [{a: 1}]}

I want to add a new object

{b: 2}

to list if this object doesn't exists in the list otherwise I want to update it.

db.temp.update({
  list: {
    $exists: true
  }
},
{
  $set: { 
    "list.$[elem].a1": 10, 
  },
  $pushIfNoMatch: {
    list: {b: 2}
  }
}, 
{
  arrayFilters: [{
    "elem.a": {
      $ne: 1 
    }
  }], 
  
  multi: true,
  upsert: true
})

Since condition in arrayFilter will return false, $pushIfNoMatch operator will work and the new state of document will be

{list: [{a: 1}, {b: 2}]}

if we change the condition to $eq: 1, the $set operator will work and new state will be

{list: [{a: 1, a1: 10}]}