fix: remove expand_fields from conference list and add server-side pagination (#19)

Part A — Remove expand_fields from conference list:
- List view no longer inlines participants/issues (N+1 eliminated)
- Detail view (single conference) still returns expanded fields

Part B — Add opt-in server-side pagination:
- ?limit= and ?offset= params on conferences, sessions, participants, events
- Returns { results: [...], count: N } when pagination params are present
- Returns original { data: [...] } format when no params (backward compatible)
- Default limit=50, max=200, with input validation

Part C — Fix BaseModel.filter() eager materialization:
- Removed .exists() call (result was discarded)
- Removed eager for-loop that called prepare() on every row
- filter() now returns a lazy QuerySet so LIMIT/OFFSET work at DB level
- prepare() moved into serialize() to preserve App.prepare() behavior

Closes #17

Author: Boanerges1996

app/models/basemodel.py

@@ -153,19 +153,15 @@ def get_or_create(cls, *args, **kwargs):
     def filter(cls, *args, **kwargs):
         """
         Wrapper over the standard filter method that adds the is_active flag.
+        Returns a lazy QuerySet so that pagination (LIMIT/OFFSET) is applied
+        at the database level rather than in Python.
 
         :param args: the anonymous query criteria
         :param kwargs: the named (key word) query criteria
         :return the filtered QuerySet object
         """
         kwargs['is_active'] = True
-        filtered = cls.objects.filter(*args, **kwargs).order_by('created_at')
-        filtered.exists()
-
-        for obj in filtered:
-            obj.prepare()
-
-        return filtered
+        return cls.objects.filter(*args, **kwargs).order_by('created_at')
 
     def prepare(self):
         """

app/utils.py

@@ -167,6 +167,8 @@ def serialize(
     final_alias_list.update(alias_list)
 
     for obj in objs:
+        if hasattr(obj, 'prepare'):
+            obj.prepare()
         d = {}
         for field in obj._meta.get_fields():
             key = field.name
@@ -344,4 +346,31 @@ def build_conference_summary(conference):
         pass
 
 def clamp(n, smallest, largest):
-    return max(smallest, min(n, largest))
+    return max(smallest, min(n, largest))
+
+
+def paginate_and_serialize(request, queryset, default_limit=50, max_limit=200, **serialize_kwargs):
+    """
+    Adds opt-in server-side pagination to list endpoints.
+    If ?limit= or ?offset= is present, returns { results: [...], count: N }.
+    Otherwise returns the original { data: [...] } format for backward compatibility.
+    """
+    limit_param = request.GET.get('limit')
+    offset_param = request.GET.get('offset')
+
+    if limit_param is not None or offset_param is not None:
+        try:
+            limit = clamp(int(limit_param or default_limit), 1, max_limit)
+            offset = max(0, int(offset_param or 0))
+        except (ValueError, TypeError):
+            from .errors import INVALID_PARAMETERS
+            raise PMError(status=400, app_error=INVALID_PARAMETERS)
+
+        count = queryset.count()
+        page = queryset[offset:offset + limit]
+        return {
+            'results': serialize(page, **serialize_kwargs)['data'],
+            'count': count,
+        }
+    else:
+        return serialize(queryset, **serialize_kwargs)

app/views/conference_events_view.py

@@ -17,4 +17,4 @@ def get(cls, request, pk=None):
         except Conference.DoesNotExist:
             raise PMError(status=400, app_error=CONFERENCE_NOT_FOUND)
 
-        return EventView.retrieve_events(event_type=request.GET.get('type'), conference=conference)
+        return EventView.retrieve_events(request, event_type=request.GET.get('type'), conference=conference)

app/views/conference_view.py

@@ -4,7 +4,7 @@
 
 from ..errors import (INVALID_PARAMETERS, CONFERENCE_NOT_FOUND,
                       MISSING_PARAMETERS, PMError)
-from ..utils import JSONHttpResponse, serialize
+from ..utils import JSONHttpResponse, serialize, paginate_and_serialize
 from ..models.conference import Conference
 from .generic_view import GenericView
 
@@ -45,10 +45,7 @@ def filter(cls, request):
             raise PMError(status=400, app_error=INVALID_PARAMETERS)
 
         return JSONHttpResponse(
-            content=serialize(
-                objs=objs,
-                expand_fields=('participants', 'issues'),
-            ),
+            content=paginate_and_serialize(request, objs),
         )
 
     @classmethod

app/views/event_view.py

@@ -12,7 +12,7 @@
 from ..models.connection import Connection
 from ..models.generic_event import GenericEvent
 from ..models.participant import Participant
-from ..utils import JSONHttpResponse, serialize, validate_string, validate_positive_number
+from ..utils import JSONHttpResponse, serialize, paginate_and_serialize, validate_string, validate_positive_number
 
 
 class EventView(GenericView):
@@ -52,12 +52,12 @@ def query_events(event_type=None, conference=None, participant=None, filters=Non
             raise PMError(status=400, app_error=INVALID_PARAMETERS)
 
     @staticmethod
-    def retrieve_events(event_type=None, conference=None, participant=None, filters=None):
+    def retrieve_events(request, event_type=None, conference=None, participant=None, filters=None):
         """Used to return a JSON response of a specific event query"""
 
         objs = EventView.query_events(event_type, conference, participant, filters)
 
-        return JSONHttpResponse(content=serialize(objs))
+        return JSONHttpResponse(content=paginate_and_serialize(request, objs))
 
     @classmethod
     def get(cls, request):
@@ -97,6 +97,7 @@ def get(cls, request):
                     filters[key] = request.GET.get(rkey)
 
             return cls.retrieve_events(
+                request,
                 event_type=request.GET.get('type'),
                 conference=conference,
                 participant=participant,

app/views/participant_view.py

@@ -2,7 +2,7 @@
 
 from ..errors import (INVALID_PARAMETERS, PARTICIPANT_NOT_FOUND,
                       MISSING_PARAMETERS, PMError)
-from ..utils import JSONHttpResponse, serialize
+from ..utils import JSONHttpResponse, serialize, paginate_and_serialize
 from ..models.participant import Participant
 from .generic_view import GenericView
 
@@ -43,9 +43,7 @@ def filter(cls, request):
             raise PMError(status=400, app_error=INVALID_PARAMETERS)
 
         return JSONHttpResponse(
-            content=serialize(
-                objs=objs,
-            ),
+            content=paginate_and_serialize(request, objs),
         )
 
     @classmethod

app/views/session_view.py

@@ -11,7 +11,7 @@
 from ..models.participant import Participant
 from ..models.session import Session
 from ..utils import (JSONHttpResponse, generate_session_token, get_client_ip, get_geoip_data,
-                     serialize, validate_string, validate_meta, validate_positive_number)
+                     serialize, paginate_and_serialize, validate_string, validate_meta, validate_positive_number)
 from .generic_view import GenericView
 
 
@@ -75,8 +75,8 @@ def get(cls, request):
         if objs is not None:
             return JSONHttpResponse(
                 status=200,
-                content=serialize(
-                    objs,
+                content=paginate_and_serialize(
+                    request, objs,
                     blacklist=('constraints',),
                     expand_fields=('issues',),
                 )