fix(articles): Orphaned User reference throws server error

Adds an additional check for the existence of a populated user
reference, when determining if the current user has immediate access to
the requested article.

Without this fix, the server will throw an error if the requested
article doesn't have a populated user field.

Modified the article & articles list view's to check if the article has
a populated user. If not, then it will display "Deleted User" in place
of the missing user reference.

Added a server-side test that ensures we can get a single article if
the article.user field is referencing a deleted user.

Fixes meanjs#1082

modules/articles/client/views/list-articles.client.view.html

@@ -8,7 +8,8 @@ <h1>Articles</h1>
         Posted on
         <span ng-bind="article.created | date:'mediumDate'"></span>
         by
-        <span ng-bind="article.user.displayName"></span>
+        <span ng-if="article.user" ng-bind="article.user.displayName"></span>
+        <span ng-if="!article.user">Deleted User</span>
       </small>
       <h4 class="list-group-item-heading" ng-bind="article.title"></h4>
       <p class="list-group-item-text" ng-bind="article.content"></p>

modules/articles/client/views/view-article.client.view.html

@@ -15,7 +15,8 @@ <h1 ng-bind="article.title"></h1>
       Posted on
       <span ng-bind="article.created | date:'mediumDate'"></span>
       by
-      <span ng-bind="article.user.displayName"></span>
+      <span ng-if="article.user" ng-bind="article.user.displayName"></span>
+      <span ng-if="!article.user">Deleted User</span>
     </em>
   </small>
   <p class="lead" ng-bind="article.content"></p>

modules/articles/server/policies/articles.server.policy.js

@@ -49,7 +49,7 @@ exports.isAllowed = function (req, res, next) {
   var roles = (req.user) ? req.user.roles : ['guest'];
 
   // If an article is being processed and the current user created it then allow any manipulation
-  if (req.article && req.user && req.article.user.id === req.user.id) {
+  if (req.article && req.user && req.article.user && req.article.user.id === req.user.id) {
     return next();
   }
 

modules/articles/tests/server/article.server.routes.tests.js

@@ -313,6 +313,93 @@ describe('Article CRUD tests', function () {
     });
   });
 
+  it('should be able to get a single article that has an orphaned user reference', function (done) {
+    // Create orphan user creds
+    var _creds = {
+      username: 'orphan',
+      password: 'M3@n.jsI$Aw3$0m3'
+    };
+
+    // Create orphan user
+    var _orphan = new User({
+      firstName: 'Full',
+      lastName: 'Name',
+      displayName: 'Full Name',
+      email: 'orphan@test.com',
+      username: _creds.username,
+      password: _creds.password,
+      provider: 'local'
+    });
+
+    _orphan.save(function (err, orphan) {
+      // Handle save error
+      if (err) {
+        return done(err);
+      }
+
+      agent.post('/api/auth/signin')
+        .send(_creds)
+        .expect(200)
+        .end(function (signinErr, signinRes) {
+          // Handle signin error
+          if (signinErr) {
+            return done(signinErr);
+          }
+
+          // Get the userId
+          var orphanId = orphan._id;
+
+          // Save a new article
+          agent.post('/api/articles')
+            .send(article)
+            .expect(200)
+            .end(function (articleSaveErr, articleSaveRes) {
+              // Handle article save error
+              if (articleSaveErr) {
+                return done(articleSaveErr);
+              }
+
+              // Set assertions on new article
+              (articleSaveRes.body.title).should.equal(article.title);
+              should.exist(articleSaveRes.body.user);
+              should.equal(articleSaveRes.body.user._id, orphanId);
+
+              // force the article to have an orphaned user reference
+              orphan.remove(function () {
+                // now signin with valid user
+                agent.post('/api/auth/signin')
+                  .send(credentials)
+                  .expect(200)
+                  .end(function (err, res) {
+                    // Handle signin error
+                    if (err) {
+                      return done(err);
+                    }
+
+                    // Get the article
+                    agent.get('/api/articles/' + articleSaveRes.body._id)
+                      .expect(200)
+                      .end(function (articleInfoErr, articleInfoRes) {
+                        // Handle article error
+                        if (articleInfoErr) {
+                          return done(articleInfoErr);
+                        }
+
+                        // Set assertions
+                        (articleInfoRes.body._id).should.equal(articleSaveRes.body._id);
+                        (articleInfoRes.body.title).should.equal(article.title);
+                        should.equal(articleInfoRes.body.user, undefined);
+
+                        // Call the assertion callback
+                        done();
+                      });
+                  });
+              });
+            });
+        });
+    });
+  });
+
   afterEach(function (done) {
     User.remove().exec(function () {
       Article.remove().exec(done);