tenge

Tenge

Thin convenience layer on top of mongojs for MongoDB operations in Node.js

General behavior tends to stay close to "native" MongoDB interface libraries like mongojs or mongoskin. The "batteries" include:

• before- and after-operation hooks
• user- and url-friendly ID generation (by default with shortid)
• customizable query transformers for complex query shortcuts

Example

Before using Tenge, it should be provided a connection string URI to MongoDB. The connection string should follow the format described in the mongo connection string docs. Normally it will be done on the early configuration stage of the app. If you try to instantiate Tenge without calling connect() first, you'll get an error.

var Tenge = require('tenge')

//simple usage for local db
Tenge.connect({uri: 'mydb'})

// the db is on a remote server (the port default to mongo)
Tenge.connect({uri: 'example.com/mydb'})

//providing credentials
Tenge.connect({uri: 'username:[e-mail]/mydb'})

Tenge is supposed to be inherited every time an interface to a new collection is desired. So let's suppose we have a collection containing a list of articles. In a simplest case a model layer for it can look like:

//in a primitive case it'll work even like this
var articleModel = new Tenge({collection: 'articles'})

In a more advanced scenario it'll have a dedicated module:

module.exports = ArticleModel

function ArticleModel() {
    Tenge.call(this, {collection: 'articles'})
    // some functionality extension happens here...
}
require('util').inherits(ArticleModel, Tenge)

Not uncommon is the situation when an application-wide model class inherits from Tenge and registers app-specific customizations (like hooks and auto-generated fields), and then each collection interface inherits from this app's BaseModel.

API

Public API of Tenge is wrapped around mongojs Database and Collection objects. If you consider provided interface insufficient, you can opt for using raw objects with methods _db(), _collection(), and _findCursor() call.

Tenge methods in general receive an object with params and a callback as a second argument.

articleModel.find({sort: {date: 1}, limit: 10}, function(err, docs) {
    //check err and work with docs
})

Callback always has the standard Node.js signature:

function callback(err, data)

Initialization

Tenge.connect(params)

The static call to be made before instantiating any model.

Params:

• params.uri: URI describing connection to the database, according to the format described in mongo connection string docs
• [params.authMechanism]: authentication to MongoDB server, can be 'MongoCR' (default), or 'ScramSHA1' (the default auth mechanism for MongoDB 3).

Example:

var Tenge = require('tenge')
Tenge.connect({uri: 'username:[e-mail]/mydb'})

Tenge(params)

Constructor for model instances. Can be inherited or just used as is.

Params:

• params.collection: collection name to work with

See also: _collection()

Tenge._db()

Accessor for the underlying mongojs database object. Before using, call Tenge.connect().

_collection(cb) and collection initialization

Asynchronous accessor to the underlying mongojs collection object. Upon the first access to the collection via this method, the collection initialization will happen.

Default behavior is to ensure the custom id field of the collection is indexed uniquely and hook the insert operation to automatically generate the id field for each document that doesn't have it.

Important: no custom IDs are generated upon upsert event. If this behavior is desirable, please consider using an after-upsert hook in a similar fashion as the before-insert one is used for this purpose.

To override default behavior, see _initCollection() implementation.

Here is an example how to utilize this method to make Tenge automatically create non-existent collections upon the first access (error handling is omitted for brevity):

MyModel.prototype._initCollection = function(colname, cb) {
    var self = this;
    var super = Tenge.prototype._initCollection.bind(this, colname, cb);

    Tenge._db().getCollectionNames(function(err, collections) {
        if (collections.indexOf(modelOpts.collection) > -1) {
            super();
        } else {
            Tenge._db().createCollection(colname, function(err) {
                super();
            });
        }
    });
}

Events

The majority of CRUD operations described below supports before- and/or after-hooks allowing the model layer to maintain cross-collection integrity in a decoupled manner.

Please note that this mechanism has limited capabilities in complex environments (for example, several application instances are running concurrently) and was meant to be used mainly on the model level.

Events are described by the action name (often same as the CRUD method), like 'insert', 'remove', 'upsert' etc. Handlers are asynchronous functions with a signature function(params, next), chained via the next callback accepting an error. The handler chain execution will be stopped after the first error passed to the next().

For params format, see the doc for corresponding CRUD action.

before(action, handler)

Registering a before-hook for the actions like 'insert', 'remove'. All handlers will receive the same params object and are welcome to modify it in place.

Any error ocurred inside the hook will abort the whole operation and the hook chain.

Example implementation of providing custom IDs upon insert:

model.before('insert', function(params, next) {
    _.each(params.docs, function(doc) {
        doc.id = doc.id || self.makeID();
    });
    next();
});

Note that there is no before-update hook. This is done intentionally for the reason that in multi-instance app the naïve straight-forward implementation will lead to dangerous data integrity threats.

after(action, handler)

Registering an after-hook for the actions like 'insert', 'update', 'upsert', 'remove'.

Important: Any error ocurred inside the hook will not roll back the whole operation, it will just abort the hook chain.

CRUD

insert(params, cb)

An insert operation accepting a single document of arbitrary structure or an array of such documents.

Params:

• [params.doc | params.docs]: both params are optional but any of them should be set.

Hooks:

• before insert: will receive a params.docs with documents to be inserted. Documents can be modified in-place;
• after insert: will receive a params.docs array of inserted documents, with ids assigned.

Returns an array of inserted documents via the callback.

Example:

model.insert({docs: [
    {artist: 'marley'}, {artist: 'hendrix'}, {artist: 'santana'}
]}, function(err, docs) {
    _.each(docs, function(doc) {
        expect(doc).to.have.property('_id');
        expect(doc).to.have.property('id');
    });
    expect(_.uniq(_.pluck(docs, 'id'))).to.have.length(docs.length);
});

find(params, cb)

A simple find operation. Works as a wrapper around the mongojs cursor operation. Below the generic find arguments are described, which are also applicable to other find-alike mehods.

Params:

• [params.query]: a mongo query object
• [params.fields]: specification of fields ('projection') to return
• [params.sort]: cursor specification of sorting to match the query
• [params.limit]: cursor limit spec; a falsy value is treated as no limit
• [params.skip]: cursor skip spec

Returns a result of toArray() call on the mongo cursor via callback.

findOne(params, cb)

Returns the first doc of the resultset matched by all passed params. Params spec is same as of find().

count(params, cb)

Returns the total number of documents matching the query

Params:

• [params.query]: a mongo query object

size(params, cb)

Returns the number of documents matching the query after applying skip, and limit conditions.

Params:

• [params.query]: a mongo query object
• [params.limit]: cursor limit spec; a falsy value is treated as no limit
• [params.skip]: cursor skip spec

remove(params, cb)

Removes documents matching the query filters.

Params:

• [params.query]: a mongo query object
• [params.fields]: specification of fields ('projection') to return
• [params.sort]: cursor specification of sorting to match the query
• [params.limit]: cursor limit spec; a falsy value is treated as no limit
• [params.skip]: cursor skip spec

Hooks:

• before remove: will get all objects to be removed via params.docs
• after remove: will get objects removed via params.docs

Returns docs removed (with filtered out fields according to the params.fields spec).

updateOne(params, cb)

An update operation for a single document (implemented via findAndModify()).

If no document was found for update:

• if params.upsert was set, a new document will be upserted (important: no custom ID will be generated in this case); please refer also to mongo docs about upsert and unique indexing;
• if params.upsert was not set, it will be treated as an error. If this behavior is not desirable, use updateAll().

Params:

• params.query: a mongo query object
• params.(update|remove): mongo update object
• [params.fields]: specification of fields to return
• [params.sort]: cursor specification of sorting to match the query
• [params.upsert]: a truthy value means that the upsert bahavior is desired

Hooks:

• after update: will get object updated via params.docs array
• after upsert: will get object upserted via params.docs array

Returns an updated/upserted document via callback. To differentiate between handling of upserted and updated documents, use 'after-' hooks.

updateAll(params, cb)

An update operation for multiple documents.

If no documents match the query criteria, it won't be treated as an error:

• if params.upsert was set, the new document will be upserted (important: no custom ID will be generated in this case);
• if params.upsert was not set, the call just returns an empty array as a result. No hooks will be triggered.

Params:

• params.query: a mongo query object
• params.update: mongo update object
• [params.fields]: specification of fields to return
• [params.sort]: cursor specification of sorting to match the query
• [params.upsert]: a truthy value means that the upsert bahavior is desired

Hooks:

• after update: will get objects updated via params.docs array
• after upsert: will get objects upserted via params.docs array

Returns an array of documents updated/upserted via callback. To differentiate between handling of upserted and updated documents, use 'after-' hooks.

_queryTransformers and params.query.$$

There is a special case in params.query which is not compliant to mongo query object format and will be processed by Tenge before passing it to mongo. This is the params.query.$$ field in a query object.

If this field is present, for each key in this $$ object, a corresponding transformer function will be called which will return an object merged into the params.query.

Right now the following transformers are supported:

• $$.id --> {id: val}
• $$.ids --> {id: {$in: val}}
• $$._id --> {_id: OID(val)}
• $$._ids --> {_id: {$in: val.map(OID)}}

Example:

// Tenge has these transformers among the default ones:
Tenge.prototype._queryTransformers = {
    id: function(val) {
        return {id: val};
    },
    ids: function(val) {
        return {id: {$in: val}};
    }
};

// using in find operation:
model.find({query: {$$: {ids: ["NkXtJhvB", "V1GQFknvH"]}}}, callback);

Utilities

makeOID([id])

A convenience method to genereta a new OID or convert id string into the mongo ObjectId if argument string is provided.

makeID()

Generates an url-friendly id (with shortid).

Older versions of MongoDB

As per mongojs doc, for MongoDB 2.4 or older, index creation and deletion is not supported. As this is a feature necessary for custom IDs generation, Tenge won't work out-of the box in this case. Please consider either to submit a PR to mongojs, or implement a workaround like this:

module.exports = BaseModel

function BaseModel() {
    Tenge.apply(this, arguments)
}
require('util').inherits(BaseModel, Tenge)

BaseModel.prototype._initCollection = function(colname, cb) {
    var self = this;
    var col = self._db().collection(colname);

    //assuming that collection already exists and a unique index
    // over `id` field is created
    self.before('insert', function(params, next) {
        _.each(params.docs, function(doc) {
            doc.id = doc.id || self.makeID();
        });
        next();
    });

    cb(null, col);
};

TODO

• customizible error reporting + mongojs + mongodb errors
• bulk operations (attention to upserts in update and findAndModify)
• db.on('error), db.on('ready') support