Added Datastore error sample.

datastore/error.js

@@ -0,0 +1,55 @@
+// Copyright 2016, Google, Inc.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+'use strict';
+
+var gcloud = require('gcloud');
+
+var dataset = gcloud.datastore.dataset({
+  projectId: process.env.GCLOUD_PROJECT
+});
+
+// [START error]
+function runQuery(cb) {
+  var query = dataset.createQuery(['foo']).start('badrequest');
+
+  dataset.runQuery(query, function (err, entities) {
+    // Check for an error
+    if (err) {
+      console.log(err.errors); // [...]
+      console.log(err.code); // 400
+      console.log(err.message); // "Bad Request"
+      console.log(err.response); // {...}
+
+      // Process error
+
+      // For example, treat permission error like no entities were found
+      if (err.code === 403) {
+        return cb(null, []);
+      }
+
+      // Forward the error to the caller
+      return cb(err);
+    }
+
+    // We're good
+    return cb(null, entities);
+  });
+}
+// [END error]
+
+exports.runQuery = runQuery;
+
+if (module === require.main) {
+  runQuery(function () {});
+}

datastore/package.json

@@ -9,6 +9,7 @@
     "node": ">=0.10.x"
   },
   "scripts": {
+    "error": "node error.js",
     "tasks": "node tasks.js"
   },
   "dependencies": {

test/datastore/error.test.js

@@ -0,0 +1,31 @@
+// Copyright 2015-2016, Google, Inc.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+'use strict';
+
+var error = require('../../datastore/error.js');
+var assert = require('assert');
+
+describe('datastore/error', function () {
+  it('should have an error', function (done) {
+    error.runQuery(function (err) {
+      try {
+        assert.ok(err);
+        assert.equal(err.code, 400);
+        done();
+      } catch (err) {
+        done(err);
+      }
+    });
+  });
+});