Querying Documents

find() and findOne() read documents back out, and a small set of query operators like $gt, $in, and $or handle everything WHERE does in SQL.

Finding everything, and finding one

JS mongosh

db.posts.find()

Output

[
  { _id: ObjectId("65f1a3104c1a2b3c4d5e6f71"), title: 'Hello, MongoDB', author: 'Priya', views: 0 },
  { _id: ObjectId("65f1a3334c1a2b3c4d5e6f72"), title: 'Indexes Explained', author: 'Sam', views: 12 },
  { _id: ObjectId("65f1a3334c1a2b3c4d5e6f73"), title: 'Schema Design 101', author: 'Priya', views: 5 }
]

A query filter — a document describing what to match — narrows that down. findOne() works the same way but only ever returns a single document:

JS mongosh

db.posts.findOne({ author: "Priya" })

Output

{ _id: ObjectId("65f1a3104c1a2b3c4d5e6f71"), title: 'Hello, MongoDB', author: 'Priya', views: 0 }

Comparison operators

Operators like $gt (greater than) and $in (matches any value in a list) go inside the filter, keyed to the field they apply to:

JS mongosh

db.posts.find({ views: { $gt: 4 } })

Output

[
  { _id: ObjectId("65f1a3334c1a2b3c4d5e6f72"), title: 'Indexes Explained', author: 'Sam', views: 12 },
  { _id: ObjectId("65f1a3334c1a2b3c4d5e6f73"), title: 'Schema Design 101', author: 'Priya', views: 5 }
]

JS mongosh

db.posts.find({ author: { $in: ["Priya", "Sam"] } })

Output

// matches all three documents — every author is either Priya or Sam

$or and projections

$or takes an array of filters and matches a document that satisfies any of them. A second argument to find() — a projection — controls which fields come back:

JS mongosh

db.posts.find(
  { $or: [{ views: 0 }, { author: "Sam" }] },
  { title: 1, _id: 0 }
)

Output

[
  { title: 'Hello, MongoDB' },
  { title: 'Indexes Explained' }
]

The $eq/null gotcha: querying { field: null } matches documents where field is explicitly set to null and documents where field doesn't exist at all — both count. If you specifically need "this field is present but null," you need { field: { $type: "null" } }, or check for presence separately with $exists.

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