find() and findOne()

MongoDB gives you two core methods for reading documents out of a collection: find() and findOne().

find()

Returns all documents that match a query object. Leave the query empty to return every document in the collection.

db.collection.find()

db.employees.find()
// returns every document in the employees collection

findOne()

Returns only the first matching document. Leave the query empty and it returns the first document it finds.

db.collection.findOne()

Query Documents

Pass a condition object as the first argument to filter results.

db.employees.findOne({ city: "Mumbai" })
// returns the first document where city is Mumbai

db.employees.find({ city: "Mumbai" })
// returns every document where city is Mumbai

Querying Nested (Embedded) Fields

Use dot notation, wrapped in quotes, to reach into an embedded document.

db.employees.find({ 'reportinmgr.mgrid': 105 })

Projection

Both find() and findOne() accept a second argument — the projection — that controls which fields come back in the result.

db.collection.find({}, { field: 1 })

db.employees.find({}, { name: 1 })
// { _id: ObjectId(...), name: 'Rahul Gupta' }

Notice _id is included by default even though it wasn't listed — MongoDB always returns _id unless you explicitly exclude it.

db.employees.find({}, { name: 1, email: 1 })
// returns _id, name and email for every document

db.employees.find({}, { _id: 0, name: 1 })
// { name: 'Rahul Gupta' }

• Use 1 to include a field.
• Use 0 to exclude a field.
• You can also exclude just one field and get everything else, e.g. { reportinmgr: 0 }.

Common Errors & Troubleshooting

• A nested-field query returns nothing — dot-notation paths like 'reportinmgr.mgrid' must be a quoted string, not reportinmgr.mgrid written bare — unquoted dots aren't valid JavaScript object key syntax.
• Projection returns _id even though you only listed other fields — _id is included by default in every projection; you must exclude it explicitly with { _id: 0, ... } if you don't want it.
• Mixing inclusion and exclusion in one projection — { name: 1, email: 0 } throws an error. You can't mix 1s and 0s in the same projection object, except for the special case of excluding just _id alongside inclusions.

Key Takeaways

• find() returns a cursor over all matches; findOne() returns a single document.
• Query nested fields with dot notation in quotes: "parent.child".
• Projection's second argument decides which fields are returned — _id is included unless you set it to 0.