wenbian / sharedb-mongo

MongoDB database adapter for ShareDB

sharedb-mongo

MongoDB database adapter for sharedb. This driver can be used both as a snapshot store and oplog.

Snapshots are stored where you'd expect (the named collection with _id=id). In addition, operations are stored in o_COLLECTION. For example, if you have a users collection, the operations are stored in o_users.

JSON document snapshots in sharedb-mongo are unwrapped so you can use mongo queries directly against JSON documents. (They just have some extra fields in the form of _v and _type). It is safe to query documents directly with the MongoDB driver or command line. Any read only mongo features, including find, aggregate, and map reduce are safe to perform concurrent with ShareDB.

However, you must always use ShareDB to edit documents. Never use the MongoDB driver or command line to directly modify any documents that ShareDB might create or edit. ShareDB must be used to properly persist operations together with snapshots.

Usage

sharedb-mongo wraps native mongodb, and it supports the same configuration options.

There are two ways to instantiate a sharedb-mongo wrapper:

1. The simplest way is to invoke the module and pass in your mongo DB arguments as arguments to the module function. For example:

const db = require('sharedb-mongo')('mongodb://localhost:27017/test');
const backend = new ShareDB({db});

2. If you'd like to reuse a mongo db connection or handle mongo driver instantiation yourself, you can pass in a function that calls back with a mongo instance.

const mongodb = require('mongodb');
const db = require('sharedb-mongo')({mongo: function(callback) {
  mongodb.connect('mongodb://localhost:27017/test', callback);
}});
const backend = new ShareDB({db});

Queries

In ShareDB, queries are represented as single JavaScript objects. But Mongo exposes methods on collections and cursors such as mapReduce, sort or count. These are encoded into ShareDBMongo's query object format through special $-prefixed keys that are interpreted and stripped out of the query before being passed into Mongo's find method.

Here are some examples:

MongoDB query code	ShareDBMongo query object
coll.find({x: 1, y: {$ne: 2}})	{x: 1, y: {$ne: 2}}
coll.find({$or: [{x: 1}, {y: 1}])	{$or: [{x: 1}, {y: 1}]}}
coll.mapReduce({map: ..., reduce: ...})	{$mapReduce: {map: ..., reduce: ...}
coll.find({x: 1}).sort({y: -1})	{x: 1, $sort: {y: -1}}
coll.find().limit(5).count({applySkipLimit: true})	{x: 1, $limit: 5, $count: {applySkipLimit: true}}

Most of Mongo 3.2's collection and cursor methods are supported. Methods calls map to query properties whose key is the method name prefixed by $ and value is the argument passed to the method. $readPref is an exception -- it takes an object with mode and tagSet fields which map to the two arguments passed into the readPref method.

For a full list of supported collection and cursor methods, see collectionOperationsMap, cursorTransformsMap and cursorOperationsMap in index.js

Error codes

Mongo errors are passed back directly. Additional error codes:

4100 -- Bad request - DB

• 4101 -- Invalid op version
• 4102 -- Invalid collection name
• 4103 -- $where queries disabled
• 4104 -- $mapReduce queries disabled
• 4105 -- $aggregate queries disabled
• 4106 -- $query property deprecated in queries
• 4107 -- Malformed query operator
• 4108 -- Only one collection operation allowed
• 4109 -- Only one cursor operation allowed
• 4110 -- Cursor methods can't run after collection method

5100 -- Internal error - DB

• 5101 -- Already closed
• 5102 -- Snapshot missing last operation field
• 5103 -- Missing ops from requested version
• 5104 -- Failed to parse query

MIT License

Copyright (c) 2015 by Joseph Gentle and Nate Smith

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.