[#88,backend][s]: add __type__ attribute to all backends to identify them and provide a more robust and generic way to load backends from a string identifier such as that __type__ field.

* Also remove recline.Model.backends registry as can be replaced with this more generic solution.
* This refactoring is necessitated by our need to serialize backend info for save/reload of a dataset and explorer state in #88.

src/backend/base.js

@@ -17,10 +17,20 @@ this.recline.Backend = this.recline.Backend || {};
   // ## recline.Backend.Base
   //
   // Base class for backends providing a template and convenience functions.
-  // You do not have to inherit from this class but even when not it does provide guidance on the functions you must implement.
+  // You do not have to inherit from this class but even when not it does
+  // provide guidance on the functions you must implement.
   //
   // Note also that while this (and other Backends) are implemented as Backbone models this is just a convenience.
   my.Base = Backbone.Model.extend({
+    // ### __type__
+    //
+    // 'type' of this backend. This should be either the class path for this
+    // object as a string (e.g. recline.Backend.Memory) or for Backends within
+    // recline.Backend module it may be their class name.
+    //
+    // This value is used as an identifier for this backend when initializing
+    // backends (see recline.Model.Dataset.initialize).
+    __type__: 'base',
 
     // ### sync
     //

src/backend/dataproxy.js

@@ -17,6 +17,7 @@ this.recline.Backend = this.recline.Backend || {};
   //
   // Note that this is a **read-only** backend.
   my.DataProxy = my.Base.extend({
+    __type__: 'dataproxy',
     defaults: {
       dataproxy_url: 'http://jsonpdataproxy.appspot.com'
     },
@@ -71,7 +72,5 @@ this.recline.Backend = this.recline.Backend || {};
       return dfd.promise();
     }
   });
-  recline.Model.backends['dataproxy'] = new my.DataProxy();
-
 
 }(jQuery, this.recline.Backend));

src/backend/elasticsearch.js

@@ -20,6 +20,7 @@ this.recline.Backend = this.recline.Backend || {};
   //
   // <pre>http://localhost:9200/twitter/tweet</pre>
   my.ElasticSearch = my.Base.extend({
+    __type__: 'elasticsearch',
     _getESUrl: function(dataset) {
       var out = dataset.get('elasticsearch_url');
       if (out) return out;
@@ -115,7 +116,6 @@ this.recline.Backend = this.recline.Backend || {};
       return dfd.promise();
     }
   });
-  recline.Model.backends['elasticsearch'] = new my.ElasticSearch();
 
 }(jQuery, this.recline.Backend));
 

src/backend/gdocs.js

@@ -17,6 +17,7 @@ this.recline.Backend = this.recline.Backend || {};
   // );
   // </pre>
   my.GDoc = my.Base.extend({
+    __type__: 'gdoc',
     getUrl: function(dataset) {
       var url = dataset.get('url');
       if (url.indexOf('feeds/list') != -1) {
@@ -134,7 +135,6 @@ this.recline.Backend = this.recline.Backend || {};
       return results;
     }
   });
-  recline.Model.backends['gdocs'] = new my.GDoc();
 
 }(jQuery, this.recline.Backend));
 

src/backend/memory.js

@@ -20,7 +20,7 @@ this.recline.Backend = this.recline.Backend || {};
     if (!metadata.id) {
       metadata.id = String(Math.floor(Math.random() * 100000000) + 1);
     }
-    var backend = recline.Model.backends['memory'];
+    var backend = new recline.Backend.Memory();
     var datasetInfo = {
       documents: data,
       metadata: metadata
@@ -35,7 +35,7 @@ this.recline.Backend = this.recline.Backend || {};
       }
     }
     backend.addDataset(datasetInfo);
-    var dataset = new recline.Model.Dataset({id: metadata.id}, 'memory');
+    var dataset = new recline.Model.Dataset({id: metadata.id}, backend);
     dataset.fetch();
     return dataset;
   };
@@ -70,6 +70,7 @@ this.recline.Backend = this.recline.Backend || {};
   //  etc ...
   //  </pre>
   my.Memory = my.Base.extend({
+    __type__: 'memory',
     initialize: function() {
       this.datasets = {};
     },
@@ -209,6 +210,5 @@ this.recline.Backend = this.recline.Backend || {};
       return facetResults;
     }
   });
-  recline.Model.backends['memory'] = new my.Memory();
 
 }(jQuery, this.recline.Backend));

src/model.js

@@ -18,7 +18,7 @@ this.recline.Model = this.recline.Model || {};
 //
 // @property {number} docCount: total number of documents in this dataset
 //
-// @property {Backend} backend: the Backend (instance) for this Dataset
+// @property {Backend} backend: the Backend (instance) for this Dataset.
 //
 // @property {Query} queryState: `Query` object which stores current
 // queryState. queryState may be edited by other components (e.g. a query
@@ -28,14 +28,24 @@ this.recline.Model = this.recline.Model || {};
 // Facets.
 my.Dataset = Backbone.Model.extend({
   __type__: 'Dataset',
+
   // ### initialize
   // 
   // Sets up instance properties (see above)
+  //
+  // @param {Object} model: standard set of model attributes passed to Backbone models
+  //
+  // @param {Object or String} backend: Backend instance (see
+  // `recline.Backend.Base`) or a string specifying that instance. The
+  // string specifying may be a full class path e.g.
+  // 'recline.Backend.ElasticSearch' or a simple name e.g.
+  // 'elasticsearch' or 'ElasticSearch' (in this case must be a Backend in
+  // recline.Backend module)
   initialize: function(model, backend) {
     _.bindAll(this, 'query');
     this.backend = backend;
-    if (backend && backend.constructor == String) {
-      this.backend = my.backends[backend];
+    if (typeof(backend) === 'string') {
+      this.backend = this._backendFromString(backend);
     }
     this.fields = new my.FieldList();
     this.currentDocuments = new my.DocumentList();
@@ -99,6 +109,35 @@ my.Dataset = Backbone.Model.extend({
     data.docCount = this.docCount;
     data.fields = this.fields.toJSON();
     return data;
+  },
+
+  // ### _backendFromString(backendString)
+  //
+  // See backend argument to initialize for details
+  _backendFromString: function(backendString) {
+    var parts = backendString.split('.');
+    // walk through the specified path xxx.yyy.zzz to get the final object which should be backend class
+    var current = window;
+    for(ii=0;ii<parts.length;ii++) {
+      if (!current) {
+        break;
+      }
+      current = current[parts[ii]];
+    }
+    if (current) {
+      return new current();
+    }
+
+    // alternatively we just had a simple string
+    var backend = null;
+    if (recline && recline.Backend) {
+      _.each(_.keys(recline.Backend), function(name) {
+        if (name.toLowerCase() === backendString.toLowerCase()) {
+          backend = new recline.Backend[name]();
+        }
+      });
+    }
+    return backend;
   }
 });