MongoDB — Array Operators

Element in Array

db.users.find({ hobbies: "reading" })

All Elements

db.users.find({ hobbies: { $all: ["reading", "gaming"] } })

Array Size

db.users.find({ hobbies: { $size: 2 } })

Element Match

db.users.find({
  scores: { $elemMatch: { subject: "math", score: { $gte: 90 } } }
})

Array Index

db.users.find({ "hobbies.0": "reading" })  // First element

Push to Array

db.users.updateOne(
  { name: "John" },
  { $push: { hobbies: "new hobby" } }
)

Pull from Array

db.users.updateOne(
  { name: "John" },
  { $pull: { hobbies: "old hobby" } }
)

Add to Set

db.users.updateOne(
  { name: "John" },
  { $addToSet: { hobbies: "unique hobby" } }
)

Mini Practice

1. Query array elements
2. Use $all operator
3. Use $elemMatch
4. Modify arrays

Up Next

Continue with Update Operators — update operators.