Capacity Management

[!NOTE] Capacity behavior below is implemented in app/api/register/route.ts and app/api/events/[slug]/capacity/route.ts.

Real-time capacity tracking

EventSlot tracks occupancy using Event fields:

• capacity: organiser-defined maximum confirmed slots
• confirmedCount: current confirmed registrations
• waitlistCount: current waitlist size

During registration, the API fetches a fresh event record and decides status:

if (freshEvent.capacity != null && freshEvent.confirmedCount >= freshEvent.capacity) {
  status = 'waitlist'
} else {
  status = 'confirmed'
}

What happens when capacity is reached

When confirmed slots are full:

1. New registration is saved with status waitlist
2. waitlistPosition is assigned from updated waitlistCount
3. Organiser receives waitlist growth intelligence notifications

Editing capacity mid-event

Organisers (or permitted collaborators/admin) can increase capacity using:

• PATCH /api/events/[slug]/capacity

Rules enforced:

• newCapacity must be an integer > 0
• newCapacity must be greater than current capacity
• added slots are computed and used for auto-promotion

Database-level consistency and race condition prevention

Registration writes and counter updates run inside Prisma transactions. Capacity promotion also runs inside a single transaction that:

1. Selects eligible waitlist rows in order
2. Updates their status to confirmed
3. Updates event counters atomically

This prevents partial updates across event and registration records.

Capacity check logic (implementation pattern)

const result = await prisma.$transaction(async tx => {
  const waitlistToPromote = await tx.registration.findMany({
    where: { eventId: event.id, status: 'waitlist' },
    orderBy: { waitlistPosition: 'asc' },
    take: Math.min(addedSlots, event.waitlistCount),
  })
 
  const promoted = waitlistToPromote.length
 
  await Promise.all(
    waitlistToPromote.map(item =>
      tx.registration.update({
        where: { id: item.id },
        data: { status: 'confirmed', waitlistPosition: null },
      })
    )
  )
 
  return tx.event.update({
    where: { id: event.id },
    data: {
      capacity: newCapacity,
      confirmedCount: { increment: promoted },
      waitlistCount: { increment: promoted * -1 },
    },
  })
})