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MongoDB Driver for Lua

lua-mongo is a binding to the MongoDB C Driver for Lua.

  • Unified API for MongoDB commands, CRUD operations and GridFS in the MongoDB C Driver.

  • Support for custom data transformation handlers when converting to/from BSON documents.

  • Transparent conversion from Lua/JSON to BSON for convenience.

  • Automatic conversion of Lua numbers to/from BSON Int32, Int64 and Double types depending on their capacity without precision loss (when Lua allows it). Manual conversion is also available.


  • lua >= 5.1 (or luajit)
  • libmongoc >= 1.9

Building and installing with LuaRocks

To build and install, run:

luarocks make

To install the latest release using luarocks.org, run:

luarocks install lua-mongo

Building and installing with CMake

To build and install, run:

cmake .
make install

To build against a specific Lua version, set the USE_LUA_VERSION variable. For example:

cmake -D USE_LUA_VERSION=5.1 .

or for LuaJIT:

cmake -D USE_LUA_VERSION=jit .

To build in a separate directory, replace . with a path to the source.

To check your build, run:

make test

A local MongoDB server at mongodb:// will be used for testing by default. Test settings can be configured in test/test.lua.

Getting started

Preparing the playground:

local mongo = require 'mongo'
local client = mongo.Client 'mongodb://'
local collection = client:getCollection('lua-mongo-test', 'test')
collection:drop() -- Clear collection

-- Common variables
local id = mongo.ObjectID()
local query1 = mongo.BSON '{ "age" : { "$gt" : 25 } }'
local query2 = mongo.BSON { _id = id }

Basic features and operations:

-- Store document
collection:insert { _id = id, name = 'John Smith', age = 50 }

-- Fetch document
local document = collection:findOne(query1):value()

-- Iterate in a for-loop
for document in collection:find(query1):iterator() do

-- Implicit Lua/JSON to BSON conversion where BSON is required
collection:insert { integer = 123 }
collection:insert '{ "string" : "abc" }'

-- Use options in queries
print(collection:count({}, { skip = 1, limit = 2 }))

-- Access to BSON where needed
local bson = collection:findOne(query1)
print(bson) -- BSON is converted to JSON using tostring()

-- Explicit BSON to Lua conversion
local value = bson:value()

-- Transparently include BSON documents in other documents
collection:update(query2, { age = 60, backup = bson }) -- Update document
collection:remove(query2) -- Remove document

Bulk write operations can be used to execute multiple insert, update, replace and remove operations together. Executing write operations in batches reduces the number of network round trips increasing write throughput.

local bulk = collection:createBulkOperation()

-- Multiple insertions
bulk:insert { a = 1 }
bulk:insert { b = 2 }
bulk:insert { c = 3 }

-- Multiple modifications
bulk:replaceOne({ a = 1 }, { b = 1 })
bulk:updateMany('{}', '{ "$inc" : { "b" : 2 } }')
bulk:removeOne { c = 3 }

-- Execute all the queued operations

The use of __toBSON metamethods and BSON handlers gives full control over how Lua values are represented in BSON documents and vice versa. In particular, this API facilitates support for Lua classes (tables with metatables) on their way to and/or from MongoDB.

local TestClass = {} -- Class metatable

local function TestObject(id, name) -- Constructor
    local object = {
        id = id,
        name = name,
    return setmetatable(object, TestClass)

function TestClass:__tostring() -- Method
    return tostring(self.id) .. ' --> ' .. self.name

function TestClass:__toBSON() -- Called when object is serialized into BSON
    return {
        _id = self.id,
        binary = mongo.Binary(self.name), -- Store 'name' as BSON Binary for example

-- A root '__toBSON' metamethod may return a table or BSON document.
-- A nested '__toBSON' metamethod may return a value, BSON type or BSON document.

-- BSON handler
local function handler(document)
    local id = document._id
    local name = document.binary:unpack() -- Restore 'name' from BSON Binary
    return TestObject(id, name)

-- Anything callable can serve as a BSON handler. For instance, it can be a table or userdata
-- with a '__call' metamethod.

-- Note that the same handler will be called for each nested document. Thus, the handler should
-- be able to differentiate documents based on some internal criteria.

local object = TestObject(id, 'John Smith')

-- Explicit BSON <-> Lua conversion
local bson = mongo.BSON(object)
local object = bson:value(handler)

-- Store object

-- Restore object
local object = collection:findOne(query2):value(handler)

-- Iterate objects in a for-loop
for object in collection:find(query2):iterator(handler) do

Check out the API Reference for more information.

See also the MongoDB Manual for detailed information about MongoDB commands and CRUD operations.