Elements Operator

1. $exists

// Find products whose field contains price
shop> db.products.find({price: {$exists: true}})

// Find prodcuts whose field contains price and price is greater than 1250
shop> db.products.find({price: {$exists: true}, price: {$gt:1250}})

1. $type

// Find products whose isFeatured type is boolean
shop> db.products.find({isFeatured: {$type: 'bool'}})
// Find products whose price is number
shop> db.products.find({price: {$type: 'number'}})

1. $size

// Find comments which has 4 comments in the array
shop> db.comments.find({'comments': {$size: 4}})
[
  {
    _id: 1,
    title: 'Introduction to MongoDB',
    content: 'MongoDB is a popular NoSQL database...',
    author: 'John Doe',
    comments: [
      { user: 'Alice', text: 'Great article!' },
      { user: 'Bob', text: 'Thanks for sharing.' },
      { user: 'Eva', text: 'Its beatifull!' },
      { user: 'jessy' }
    ],
    metadata: { views: 1000, likes: 50 }
  }
]