Querying Documents

Querying allows you to retrieve documents using filters, sorting, pagination and projection. low-json-db supports a rich set of MongoDB-style operators.

find() – Multiple Documents

// All documents
const all = users.find().toArray();

// With a filter
const adults = users.find({ age: { $gte: 18 } }).toArray();

// Multiple conditions (AND)
const result = users.find({
  city: 'Lagos',
  age: { $gt: 30 }
}).toArray();

findOne() – Single Document

const alice = users.findOne({ name: 'Alice' });
// returns the document or null

When the query is a simple equality on an indexed field, findOne uses the index for extremely fast lookup.

Query Builder Methods

find() returns a QueryBuilder that supports chaining:

const page = users
  .find({ age: { $gte: 25 } })
  .sort({ name: 1 })
  .skip(0)
  .limit(10)
  .project({ name: 1, age: 1, city: 1 })
  .toArray();

Available methods

Method	Description
`limit(n)`	Limit number of results
`skip(n)`	Skip the first n results (pagination)
`sort({ field: 1 \| -1 })`	Sort ascending (1) or descending (-1)
`project({ field: 1 })`	Include only selected fields
`toArray()`	Execute and return all matching documents
`first()`	Return only the first matching document
`count()`	Return the number of matching documents

Supported Query Operators

Operator	Meaning	Example
`$eq`	Equal	`{ age: { $eq: 30 } }`
`$ne`	Not equal	`{ status: { $ne: 'banned' } }`
`$gt / $gte`	Greater than / equal	`{ age: { $gte: 18 } }`
`$lt / $lte`	Less than / equal	`{ price: { $lt: 100 } }`
`$in`	Value is in array	`{ city: { $in: ['Lagos', 'Abuja'] } }`
`$nin`	Value is not in array	`{ role: { $nin: ['guest'] } }`
`$exists`	Field exists	`{ email: { $exists: true } }`
`$regex`	Regular expression	`{ name: { $regex: '^A', $options: 'i' } }`
`$or / $and / $nor`	Logical operators	`{ $or: [{ age: 20 }, { city: 'Lagos' }] }`

Nested Fields

// Documents that look like: { profile: { city: 'Lagos' } }
users.find({ 'profile.city': 'Lagos' }).toArray();

Next: Learn how to update documents.