Properly fix duplicate course instances

* Add script to merge existing course instances
* Have client only send one course instance creation
* Have server return existing course instance if one for the given classroom/course exists
* Remove bandaid code from ClassroomView

app/views/courses/ClassroomView.coffee

@@ -53,11 +53,6 @@ module.exports = class ClassroomView extends RootView
     @sessions = new CocoCollection([], { model: LevelSession })
 
   onCourseInstancesSync: ->
-    # clear duplicates with lodash magic
-    groups = _.groupBy @courseInstances.models, (ci) -> ci.get('courseID')
-    @courseInstances.reset(_.map(_.values(groups), _.first))
-    # TODO: Make having multiple course instances for a classroom/course pair impossible in the db
-    
     @sessions = new CocoCollection([], { model: LevelSession })
     for courseInstance in @courseInstances.models
       sessions = new CocoCollection([], { url: "/db/course_instance/#{courseInstance.id}/level_sessions", model: LevelSession })
@@ -205,7 +200,9 @@ module.exports = class ClassroomView extends RootView
 
     if courseInstance.isNew()
       # adding the first student to this course, so generate the course instance for it
-      courseInstance.save(null, {validate: false})
+      if not courseInstance.saving
+        courseInstance.save(null, {validate: false})
+        courseInstance.saving = true
       courseInstance.once 'sync', onCourseInstanceCreated
     else
       onCourseInstanceCreated()

scripts/mongodb/migrations/2016-02-05-remove-dup-course-instances.js

@@ -0,0 +1,53 @@
+
+var currentClassroom = null;
+var courseInstances = {};
+var count = 0;
+load('node_modules/lodash/lodash.js');
+
+function toStrings(array) {
+    return _.sortBy(_.map(array, function(item) { return item.valueOf(); }));
+}
+
+function mergeMembers(members1, members2) {
+    var members1 = members1 || [];
+    var members2 = members2 || [];
+    var members = members1.concat(members2);
+    if(!members.length) 
+        return [];
+    print('concat:');
+    print('\t', members1.length, JSON.stringify(toStrings(members1)));
+    print('\t', members2.length, JSON.stringify(toStrings(members2)));
+    print('\t', members.length, JSON.stringify(toStrings(members)));
+    members = _.uniq(members, false, function(member) { return member.valueOf() });
+    print('\t', members.length, JSON.stringify(toStrings(members)));
+    return members;
+}
+
+var count = 0;
+
+db.course.instances.find({classroomID: {$exists: true}}).sort({classroomID: 1}).forEach(function(courseInstance) {
+    count += 1;
+    if(count % 100 === 0) { print('count', count); }
+    if (!currentClassroom || !courseInstance.classroomID.equals(currentClassroom)) {
+        currentClassroom = courseInstance.classroomID;
+        courseInstances = {};
+    }
+    if (courseInstances[courseInstance.courseID]) {
+        var keeper = courseInstances[courseInstance.courseID];
+        if (!keeper.classroomID.equals(courseInstance.classroomID)) {
+            throw new Error('This should not happen.');
+            return;
+        }
+        print('duplicate...', count, 'in classroom', courseInstance.classroomID, keeper.members.length, courseInstance.members.length);
+        print(JSON.stringify(courseInstance, null, '\t'));
+        print(JSON.stringify(keeper, null, '\t'));
+        keeper.members = mergeMembers(keeper.members, courseInstance.members);
+        print('new members', keeper.members.length);
+        print('save', db.course.instances.save(keeper));
+        print('remove', db.course.instances.remove({_id:courseInstance._id}), true);
+        print('keeper id', keeper._id)
+    }
+    else {
+        courseInstances[courseInstance.courseID] = courseInstance;
+    }
+});

server/courses/course_instance_handler.coffee

@@ -133,7 +133,14 @@ CourseInstanceHandler = class CourseInstanceHandler extends Handler
       Course.findById req.body.courseID, (err, course) =>
         return @sendDatabaseError(res, err) if err
         return @sendNotFoundError(res, 'Course not found') unless course
-        super(req, res)
+        q = { 
+          courseID: mongoose.Types.ObjectId(req.body.courseID)
+          classroomID: mongoose.Types.ObjectId(req.body.classroomID)
+        }
+        CourseInstance.findOne(q).exec (err, doc) =>
+          return @sendDatabaseError(res, err) if err
+          return @sendSuccess(res, @formatEntity(req, doc)) if doc
+          super(req, res)
 
   makeNewInstance: (req) ->
     doc = new CourseInstance({

spec/server/functional/course_instance.spec.coffee

@@ -23,6 +23,25 @@ describe 'POST /db/course_instance', ->
       expect(res.statusCode).toBe(200)
       expect(body.classroomID).toBeDefined()
       done()
+      
+  it 'returns the same CourseInstance if you POST twice', (done) ->
+    test = @
+    url = getURL('/db/course_instance')
+    data = {
+      name: 'Some Name'
+      courseID: test.course.id
+      classroomID: test.classroom.id
+    }
+    request.post {uri: url, json: data}, (err, res, body) ->
+      expect(res.statusCode).toBe(200)
+      expect(body.classroomID).toBeDefined()
+      firstID = body._id
+      request.post {uri: url, json: data}, (err, res, body) ->
+        expect(res.statusCode).toBe(200)
+        expect(body.classroomID).toBeDefined()
+        secondID = body._id
+        expect(firstID).toBe(secondID)
+        done()
 
   it 'returns 404 if the Course does not exist', (done) ->
     test = @