[#17,backend][s]: add readonly attribute on backends indicating whether they are 'read-only'.

src/backend/base.js

@@ -32,6 +32,13 @@ this.recline.Backend = this.recline.Backend || {};
     // backends (see recline.Model.Dataset.initialize).
     __type__: 'base',
 
+
+    // ### readonly
+    //
+    // Class level attribute indicating that this backend is read-only (that
+    // is, cannot be written to).
+    readonly: true,
+
     // ### sync
     //
     // An implementation of Backbone.sync that will be used to override

src/backend/dataproxy.js

@@ -18,6 +18,7 @@ this.recline.Backend = this.recline.Backend || {};
   // Note that this is a **read-only** backend.
   my.DataProxy = my.Base.extend({
     __type__: 'dataproxy',
+    readonly: true,
     defaults: {
       dataproxy_url: 'http://jsonpdataproxy.appspot.com'
     },

src/backend/elasticsearch.js

@@ -21,6 +21,7 @@ this.recline.Backend = this.recline.Backend || {};
   // <pre>http://localhost:9200/twitter/tweet</pre>
   my.ElasticSearch = my.Base.extend({
     __type__: 'elasticsearch',
+    readonly: true,
     _getESUrl: function(dataset) {
       var out = dataset.get('elasticsearch_url');
       if (out) return out;

src/backend/gdocs.js

@@ -18,6 +18,7 @@ this.recline.Backend = this.recline.Backend || {};
   // </pre>
   my.GDoc = my.Base.extend({
     __type__: 'gdoc',
+    readonly: true,
     getUrl: function(dataset) {
       var url = dataset.get('url');
       if (url.indexOf('feeds/list') != -1) {

src/backend/memory.js

@@ -71,6 +71,7 @@ this.recline.Backend = this.recline.Backend || {};
   //  </pre>
   my.Memory = my.Base.extend({
     __type__: 'memory',
+    readonly: false,
     initialize: function() {
       this.datasets = {};
     },

test/backend.test.js

@@ -25,6 +25,11 @@ function makeBackendDataset() {
   return dataset;
 }
 
+test('Memory Backend: readonly', function () {
+  var backend = new recline.Backend.Memory();
+  equal(backend.readonly, false);
+});
+
 test('Memory Backend: createDataset', function () {
   var dataset = recline.Backend.createDataset(memoryData.documents, memoryData.fields, memoryData.metadata);
   equal(memoryData.metadata.id, dataset.id);
@@ -217,6 +222,8 @@ test('DataProxy Backend', function() {
   // needed only if not stubbing
   // stop();
   var backend = new recline.Backend.DataProxy();
+  ok(backend.readonly, false);
+
   var dataset = new recline.Model.Dataset({
       url: 'http://webstore.thedatahub.org/rufuspollock/gold_prices/data.csv'
     },