fix(events): add pagination to listEvents to prevent unbounded MongoDB queries

[anshul23102]

Related Issue

Closes #281

Problem

listEvents called eventCrud.list() with no filter, sort limit, or pagination:

const listEvents = async () => eventCrud.list();

eventCrud.list() maps to model.find({}) with no limit(). As the events collection grows, every call to GET /events fetches the full collection in one round-trip, eventually exhausting available memory and causing response timeouts.

Fix

Three coordinated changes:

1. baseService.js — add optional skip and limit to list

const list = async ({ filter = {}, populate, sort, skip, limit } = {}) => {
  let query = applyQueryOptions(model.find(filter), { populate, sort });
  if (typeof skip  === 'number') query = query.skip(skip);
  if (typeof limit === 'number') query = query.limit(limit);
  return await query;
};

Both parameters are optional (no defaults), so every other caller of eventCrud.list() or any other CRUD service is completely unaffected.

2. eventService.js — paginate listEvents

const listEvents = async ({ page = 1, limit = 20 } = {}) => {
  const safeLimit = Math.min(Math.max(1, Number(limit)), 100);
  const safePage  = Math.max(1, Number(page));
  const skip      = (safePage - 1) * safeLimit;

  const [events, total] = await Promise.all([
    eventCrud.list({ skip, limit: safeLimit }),
    eventCrud.model.countDocuments(),
  ]);

  return { events, total, page: safePage, limit: safeLimit, totalPages: Math.ceil(total / safeLimit) };
};

Promise.all fetches the page and the total count in parallel, keeping the round-trip cost to one extra query.

3. event.controller.js — forward query parameters

const result = await listEventsService({
    page: req.query.page,
    limit: req.query.limit,
});
res.json(result);

Response Shape Change

Before	After
Raw array of events	{ events, total, page, limit, totalPages }

Files Changed

File	Change
backend/services/baseService.js	Add optional skip and limit to list
backend/services/eventService.js	Replace plain eventCrud.list() with paginated implementation
backend/controllers/event.controller.js	Forward req.query.page and req.query.limit to service

Testing

• GET /events returns first 20 events with pagination metadata.
• GET /events?page=2&limit=10 returns events 11-20.
• limit=500 is clamped to 100.

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