Added check for duplicate email and username

common/djangoapps/user_api/api/account.py

 """Python API for user accounts.
 
+
 Account information includes a student's username, password, and email
 address, but does NOT include user profile information (i.e., demographic
 information and preferences).
 
 """
 from django.db import transaction, IntegrityError
+from django.db.models import Q
 from django.core.validators import validate_email, validate_slug, ValidationError
 from user_api.models import User, UserProfile, Registration, PendingEmailChange
 from user_api.helpers import intercept_errors
@@ -138,6 +140,34 @@ def create_account(username, password, email):
     return registration.activation_key
 
 
+def check_account_exists(username=None, email=None):
+    """Check whether an account with a particular username or email already exists.
+
+    Keyword Arguments:
+        username (unicode)
+        email (unicode)
+
+    Returns:
+        list of conflicting fields
+
+    Example Usage:
+        >>> account_api.check_account_exists(username="bob")
+        []
+        >>> account_api.check_account_exists(username="ted", email="ted@example.com")
+        ["email", "username"]
+
+    """
+    conflicts = []
+
+    if email is not None and User.objects.filter(email=email).exists():
+        conflicts.append("email")
+
+    if username is not None and User.objects.filter(username=username).exists():
+        conflicts.append("username")
+
+    return conflicts
+
+
 @intercept_errors(AccountInternalError, ignore_errors=[AccountRequestError])
 def account_info(username):
     """Retrieve information about a user's account.

common/djangoapps/user_api/tests/test_views.py

@@ -1037,7 +1037,6 @@ class RegistrationViewTest(ApiTestCase):
         response = self.client.post(self.url, data)
         self.assertHttpBadRequest(response)
 
-
     @override_settings(REGISTRATION_EXTRA_FIELDS={"country": "required"})
     @ddt.data("email", "name", "username", "password", "country")
     def test_register_missing_required_field(self, missing_field):
@@ -1055,21 +1054,65 @@ class RegistrationViewTest(ApiTestCase):
         response = self.client.post(self.url, data)
         self.assertHttpBadRequest(response)
 
-    def test_register_already_authenticated(self):
-        data = {
+    def test_register_duplicate_email(self):
+        # Register the first user
+        response = self.client.post(self.url, {
             "email": self.EMAIL,
             "name": self.NAME,
             "username": self.USERNAME,
             "password": self.PASSWORD,
-        }
+        })
+        self.assertHttpOK(response)
 
-        # Register once, which will also log us in
-        response = self.client.post(self.url, data)
+        # Try to create a second user with the same email address
+        response = self.client.post(self.url, {
+            "email": self.EMAIL,
+            "name": "Someone Else",
+            "username": "someone_else",
+            "password": self.PASSWORD,
+        })
+        self.assertEqual(response.status_code, 409)
+        self.assertEqual(response.content, json.dumps(["email"]))
+
+    def test_register_duplicate_username(self):
+        # Register the first user
+        response = self.client.post(self.url, {
+            "email": self.EMAIL,
+            "name": self.NAME,
+            "username": self.USERNAME,
+            "password": self.PASSWORD,
+        })
         self.assertHttpOK(response)
 
-        # Try to register again
-        response = self.client.post(self.url, data)
-        self.assertHttpBadRequest(response)
+        # Try to create a second user with the same username
+        response = self.client.post(self.url, {
+            "email": "someone+else@example.com",
+            "name": "Someone Else",
+            "username": self.USERNAME,
+            "password": self.PASSWORD,
+        })
+        self.assertEqual(response.status_code, 409)
+        self.assertEqual(response.content, json.dumps(["username"]))
+
+    def test_register_duplicate_username_and_email(self):
+        # Register the first user
+        response = self.client.post(self.url, {
+            "email": self.EMAIL,
+            "name": self.NAME,
+            "username": self.USERNAME,
+            "password": self.PASSWORD,
+        })
+        self.assertHttpOK(response)
+
+        # Try to create a second user with the same username
+        response = self.client.post(self.url, {
+            "email": self.EMAIL,
+            "name": "Someone Else",
+            "username": self.USERNAME,
+            "password": self.PASSWORD,
+        })
+        self.assertEqual(response.status_code, 409)
+        self.assertEqual(response.content, json.dumps(["email", "username"]))
 
     def _assert_reg_field(self, extra_fields_setting, expected_field):
         """Retrieve the registration form description from the server and

common/djangoapps/user_api/views.py

 """HTTP end-points for the User API. """
+import json
 
 from django.conf import settings
 from django.contrib.auth.models import User
@@ -177,6 +178,7 @@ class RegistrationView(APIView):
         return HttpResponse(form_desc.to_json(), content_type="application/json")
 
     @method_decorator(ensure_csrf_cookie)
+    @method_decorator(require_post_params(DEFAULT_FIELDS))
     def post(self, request):
         """Create the user's account.
 
@@ -198,6 +200,18 @@ class RegistrationView(APIView):
         request.POST["honor_code"] = "true"
         request.POST["terms_of_service"] = "true"
 
+        # Handle duplicate username/email
+        conflicts = account_api.check_account_exists(
+            username=request.POST.get('username'),
+            email=request.POST.get('email')
+        )
+        if conflicts:
+            return HttpResponse(
+                status=409,
+                content=json.dumps(conflicts),
+                content_type="application/json"
+            )
+
         # For the initial implementation, shim the existing login view
         # from the student Django app.
         from student.views import create_account