Querying Arrays

Rahul's skills is ['Node.js', 'MongoDB'] — an array of scalars. Three different questions: contains this value, equals this exact array, this index.

db.users.find({ skills: "MongoDB" })

{ name: "Rahul", skills: ["Node.js", "MongoDB"] }

db.users.find({ skills: ["Node.js", "MongoDB"] })
// misses if skills is ["MongoDB", "Node.js"] or has a third element

db.users.find({ "skills.0": "Node.js" })

{ skills: "MongoDB" } is contains. { skills: ["Node.js", "MongoDB"] } is equals. $in on an array field means 'the array shares at least one value with this list' — { skills: { $in: ["Redis", "MongoDB"] } } still matches Rahul. $size matches length: { skills: { $size: 2 } }.