app: implement `connector()` and `connectors`

Allow browserified applications to explicitly register connectors
to use in data-sources via `app.connector(name, exportsFromRequire)`.

Include built-in connectors like `Memory` and `Remote` in the registry.

Modify `dataSourcesFromConfig()` to resolve the connector via
`app.connectors` first and only then fall back to auto-require
the connector module.

lib/application.js

@@ -196,9 +196,30 @@ app.models = function () {
 app.dataSource = function (name, config) {
   this.dataSources[name] =
   this.dataSources[classify(name)] =
-  this.dataSources[camelize(name)] = dataSourcesFromConfig(config);
+  this.dataSources[camelize(name)] =
+    dataSourcesFromConfig(config, this.connectors);
 }
 
+/**
+ * Register a connector.
+ *
+ * When a new data-source is being added via `app.dataSource`, the connector
+ * name is looked up in the registered connectors first.
+ *
+ * Connectors are required to be explicitly registered only for applications
+ * using browserify, because browserify does not support dynamic require,
+ * which is used by LoopBack to automatically load the connector module.
+ *
+ * @param {String} name Name of the connector, e.g. 'mysql'.
+ * @param {Object} connector Connector object as returned
+ *   by `require('loopback-connector-{name}')`.
+ */
+app.connector = function(name, connector) {
+  this.connectors[name] =
+  this.connectors[classify(name)] =
+  this.connectors[camelize(name)] = connector;
+};
+
 /**
  * Get all remote objects.
  * @returns {Object} [Remote objects](http://apidocs.strongloop.com/strong-remoting/#remoteobjectsoptions).
@@ -523,17 +544,22 @@ function camelize(str) {
   return stringUtils.camelize(str);
 }
 
-function dataSourcesFromConfig(config) {
+function dataSourcesFromConfig(config, connectorRegistry) {
   var connectorPath;
 
   assert(typeof config === 'object', 
     'cannont create data source without config object');
 
   if(typeof config.connector === 'string') {
-    connectorPath = path.join(__dirname, 'connectors', config.connector+'.js');
+    var name = config.connector;
+    if (connectorRegistry[name]) {
+      config.connector = connectorRegistry[name];
+    } else {
+      connectorPath = path.join(__dirname, 'connectors', name + '.js');
 
-    if(fs.existsSync(connectorPath)) {
-      config.connector = require(connectorPath);
+      if (fs.existsSync(connectorPath)) {
+        config.connector = require(connectorPath);
+      }
     }
   }
 

lib/loopback.js

@@ -79,6 +79,15 @@ function createApplication() {
   // Create a new instance of datasources registry per each app instance
   app.datasources = app.dataSources = {};
 
+  // Create a new instance of connector registry per each app instance
+  app.connectors = {};
+
+  // Register built-in connectors. It's important to keep this code
+  // hand-written, so that all require() calls are static
+  // and thus browserify can process them (include connectors in the bundle)
+  app.connector('memory', loopback.Memory);
+  app.connector('remote', loopback.Remote);
+
   return app;
 }
 

test/app.test.js

@@ -128,6 +128,14 @@ describe('app', function() {
     });
   });
 
+  describe('app.dataSource', function() {
+    it('looks up the connector in `app.connectors`', function() {
+      app.connector('custom', loopback.Memory);
+      app.dataSource('custom', { connector: 'custom' });
+      expect(app.dataSources.custom.name).to.equal(loopback.Memory.name);
+    });
+  });
+
   describe('app.boot([options])', function () {
     beforeEach(function () {
       app.boot({
@@ -502,4 +510,39 @@ describe('app', function() {
         });
     });
   });
+
+  describe('app.connectors', function() {
+    it('is unique per app instance', function() {
+      app.connectors.foo = 'bar';
+      var anotherApp = loopback();
+      expect(anotherApp.connectors.foo).to.equal(undefined);
+    });
+
+    it('includes Remote connector', function() {
+      expect(app.connectors.remote).to.equal(loopback.Remote);
+    });
+
+    it('includes Memory connector', function() {
+      expect(app.connectors.memory).to.equal(loopback.Memory);
+    });
+  });
+
+  describe('app.connector', function() {
+     // any connector will do
+    it('adds the connector to the registry', function() {
+      app.connector('foo-bar', loopback.Memory);
+      expect(app.connectors['foo-bar']).to.equal(loopback.Memory);
+    });
+
+    it('adds a classified alias', function() {
+      app.connector('foo-bar', loopback.Memory);
+      expect(app.connectors.FooBar).to.equal(loopback.Memory);
+    });
+
+    it('adds a camelized alias', function() {
+      app.connector('FOO-BAR', loopback.Memory);
+      console.log(app.connectors);
+      expect(app.connectors.FOOBAR).to.equal(loopback.Memory);
+    });
+  });
 });