mongoose-dbref - Plugin support for DBRef in Mongoose

Overview

Mongoose-DBRef is an extension for Mongoose that exposes the DBRef type from the the node-mongodb-native driver as a top level type in the Mongoose ORM and provides some utilities, plugins and patches that allow DBRef instances to be dereferenced from the models.

Extension contents

The extension provides the following types:

• DBRef : this is the schema type that can be used for database references

The extension provides the following plugins:

• resolveDBRefs : used to create getter/setter methods that resolve DBRefs
• dbrefHooks : adds hooks to schema and model for DBRefs

The extension includes the following monkey-patches:

• dbref.fetch : used to resolve the dbref against a supplied connection

The extension provides the following utilities:

• fetch : fetches the object referenced by a DBRef value

Installation

npm install mongoose-dbref

Setup

To install all of the types, plugins, patches and utilities provided by the extension into a Mongoose instance:

var mongoose = require("mongoose");
   
// Create a connection to your database
var db = mongoose.createConnection("mongodb://localhost/sampledb");

// Access the mongoose-dbref module and install everything
var dbref = require("mongoose-dbref");
var utils = dbref.utils

// Install the types, plugins and monkey patches
var loaded = dbref.install(mongoose);

The loaded value returned contains 2 properties:

• loaded.types : the join types that were loaded
• loaded.plugins : the extension plugins that were loaded

If you want to control what is installed, you can either install types/plugins/patches separately (see below) or pass in a second argument to the install function.

If this second argument is a Function then it will be used as a filter when installing the types, plugins and patches. If it is an Object then the types property (either a filter Function or list of type names) is used when loading the types, the plugins property (either a filter Function or list of plugin names) is used when installing the plugins and the patches property (either a filter Function or list of patch names) is used when installing the patches.

Loading Types Only

To just install the types provided by the extension:

var mongoose = require("mongoose");

// Create a connection to your database
var db = mongoose.createConnection("mongodb://localhost/sampledb");

// Access the mongoose-dbref module
var dbref = require("mongoose-dbref");
var utils = dbref.utils

// Install the plugins
var loaded = dbref.loadTypes(mongoose);

The loaded value returned contains the types that were loaded, keyed by the name of each type loaded.

If you just want to load a specific list of types, or want to filter the types loaded then use one of the following signatures with the loadTypes() function:

• loadTypes(mongoose, 'dbref') : just loads the dbref type
• loadTypes(mongoose, function(type) { return type.slice(1,2) === 'db'; }) : loads types starting with db

Installing Plugins Only

To just install the plugins provided by the extension:

var mongoose = require("mongoose");
   
// Create a connection to your database
var db = mongoose.createConnection("mongodb://localhost/sampledb");

// Access the mongoose-dbref module
var dbref = require("mongoose-dbref");
var utils = dbref.utils

// Install the plugins
var loaded = dbref.installPlugins(mongoose);

The loaded value returned contains the plugins that were loaded, keyed by the name of each plugin loaded.

If you just want to install a specific list of plugins, or want to filter the plugins loaded then use one of the following signatures with the installPlugins() function:

• installPlugins(mongoose, 'resolveDBRefs') : just install the resolveDBRef plugin
• installPlugins(mongoose, function(plugin) { return plugin.slice(1,2) === 'db'; }) : installs plugins starting with db

Installing Patches Only

To just install the patches provided by the extension (all patches, named named patches or filtered patches):

var mongoose = require("mongoose");
   
// Create a connection to your database
var db = mongoose.createConnection("mongodb://localhost/sampledb");

// Access the mongoose-dbref module and the utilities
var dbref = require("mongoose-dbref");
var utils = dbref.utils;

// Install the monkey patches
dbref.installPatches(mongoose);

If you just want to install a specific list of patches, or want to filter the patches loaded then use one of the following signatures with the installPatches() function:

• installPatches(mongoose, 'fetch') : just install the fetch patch
• installPatches(mongoose, function(patch) { return patch.slice(1,2) === 'db'; }) : installs patch starting with db

Using the types

Once you have loaded the types, or installed the whole extension, you can begin to use them.

Type: DBRef

The DBRef type is a top-level schema type that can be used to identfied a field as holding a MongoDb database reference. You use the type as you would any other standard type.

var DBRef = mongoose.SchemaTypes.DBRef;

var LineItemSchema = new Schema({
	order: DBRef,
 	description: String,
	cost: Number
});

var OrderSchema = new Schema({
	poNumber: String,
	lineItems: [DBRef]
});

This will create two schema - OrderSchema that has a field (lineItems) which can hold multiple references, and LineItemSchema that has a field order with a single reference.

All of the standard options (required, index etc) can be applied to these fields.

Using the plugins

Once you have installed the plugins, or installed the whole extension, you can begin to use them.

Plugin: resolveDBRefs

The resolveDBRefs plugin can be used to be used to automatically install getter and setter methods for fields where a resolve option has been set.

These methods will map DBRef values to/from objects via the database connection of the owning model.

For example:

var LineItemSchema = new Schema({
	order: {type: DBRef, resolve: true},
 	description: String,
	cost: Number
});

This will create two methods:

• getOrder(callback) - this will asynchronously resolve the DBRef value in the order field

• setOrder(value) - this will cast the value (a model) to a DBRef value that is set in the order field

In addition if the cache option is set, then the object resolved from teh DBRef value will be cached in a cache property ($order for the order field) and the getter method signature will be changed to getOrder(callback, force). The additional, optional, parameter force can be used to bypass any cached value.

This plugin can be installed on the mongoose instance or on individual schema, but the "owning" mongoose instance for the schema must always be specified during the installation.

Plugin: dbrefHooks

The dbrefHooks plugin can be used to create hooks that on the model and schema instances that map to/from DBRef values.

To do this a _dbref virtual and a fetch static are installed on each schema created such that the _dbref virtual will return the DBRef for the model instance, and the fetch static will resolve a supplied DBRef and invoke a callback function appropriately.

Using the patches

Once you have installed the patches, or installed the whole extension, you can begin to use them.

Patch: dbref.fetch

This fetch monkey patch to the DBRef class can be used to resolve a DBRef value when supplied with a mongoos database connection and a callback function.

var mongoose = require("mongoose");
var db = mongoose.createConnection("mongodb://localhost/sampledb");

var utils = require("mongoose-dbref").utils;

var LineItem = db.model('LineItem');

LineItem.findById("4dee1f473abd4fbc61000001",
	function(err, doc) {
		doc.order.fetch(db, 
			function(err, doc) {
			    if (err) throw err;
				console.log("Order = " + doc);
			});
	});

In this example, the order of a specific LineItem is fetched using the database connection that was used to find the LineItem instance.

Using the utilities

Once you have installed the utilities, or installed the whole extension, you can begin to use them.

Utility: fetch

This fetch utility function can be used to resolve a given DBRef value when supplied with a mongoose database connection and a callback function.

var mongoose = require("mongoose");
var db = mongoose.createConnection("mongodb://localhost/sampledb");

var utils = require("mongoose-dbref").utils;

var LineItem = db.model('LineItem');

LineItem.findById("4dee1f473abd4fbc61000001",
	function(err, doc) {
		utils.fetch(db, doc.order,
			function(err, doc) {
			    if (err) throw err;
				console.log("Order = " + doc);
			});
	});

In this example, the order of a specific LineItem is fetched using the database connection that was used to find the LineItem instance.

Contributors

• Stuart Hudson

License

MIT License

Acknowledgements

• Brian Noguchi for the 'mongoose-types' extension that was used as a template for this extension

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Author

Stuart Hudson