feat: add global ticket capacity for conferences

conference.example.toml

@@ -6,6 +6,7 @@ timezone = "America/New_York"
 venue = "David L. Lawrence Convention Center, Pittsburgh PA"
 pretalx_event_slug = "pycon-us-2027"
 website_url = "https://us.pycon.org/2027/"
+total_capacity = 2500
 
 [[conference.sections]]
 name = "Tutorials"

src/django_program/conference/admin.py

@@ -106,7 +106,7 @@ class ConferenceAdmin(admin.ModelAdmin):
         (
             None,
             {
-                "fields": ("name", "slug", "venue", "address", "website_url"),
+                "fields": ("name", "slug", "venue", "address", "website_url", "total_capacity"),
             },
         ),
         (

src/django_program/conference/management/commands/bootstrap_conference.py

@@ -41,6 +41,7 @@
     "venue": "venue",
     "website_url": "website_url",
     "pretalx_event_slug": "pretalx_event_slug",
+    "total_capacity": "total_capacity",
 }
 
 _SECTION_FIELD_MAP: dict[str, str] = {

src/django_program/conference/migrations/0004_add_total_capacity.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.2.11 on 2026-02-14 03:10
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("program_conference", "0003_conference_address"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="conference",
+            name="total_capacity",
+            field=models.PositiveIntegerField(
+                default=0, help_text="Maximum total tickets across all types. 0 means unlimited."
+            ),
+        ),
+    ]

src/django_program/conference/models.py

@@ -26,6 +26,11 @@ class Conference(models.Model):
     stripe_publishable_key = EncryptedCharField(max_length=200, blank=True, null=True, default=None)
     stripe_webhook_secret = EncryptedCharField(max_length=200, blank=True, null=True, default=None)
 
+    total_capacity = models.PositiveIntegerField(
+        default=0,
+        help_text="Maximum total tickets across all types. 0 means unlimited.",
+    )
+
     is_active = models.BooleanField(default=True)
 
     created_at = models.DateTimeField(auto_now_add=True)

src/django_program/manage/forms.py

@@ -80,6 +80,7 @@ class Meta:
             "address",
             "website_url",
             "pretalx_event_slug",
+            "total_capacity",
             "is_active",
         ]
         widgets = {

src/django_program/manage/templates/django_program/manage/conference_edit.html

@@ -136,6 +136,18 @@ <h1>Conference Settings</h1>
       </div>
     </div>
 
+    <div class="fieldset">
+      <div class="fieldset-legend">Capacity</div>
+      <div class="form-row">
+        <div class="form-group">
+          <label for="{{ form.total_capacity.id_for_label }}">{{ form.total_capacity.label }}</label>
+          {{ form.total_capacity }}
+          {% if form.total_capacity.help_text %}<span class="helptext">{{ form.total_capacity.help_text }}</span>{% endif %}
+          {% for error in form.total_capacity.errors %}<ul class="errorlist"><li>{{ error }}</li></ul>{% endfor %}
+        </div>
+      </div>
+    </div>
+
     <div class="fieldset">
       <div class="fieldset-legend">Integrations &amp; Status</div>
       <div class="form-row--tail">

src/django_program/manage/templates/django_program/manage/ticket_type_list.html

@@ -12,6 +12,11 @@ <h1>Ticket Types</h1>
 {% endblock %}
 
 {% block content %}
+{% if global_capacity %}
+<div class="capacity-banner" style="padding:0.75rem 1rem;margin-bottom:1rem;border-radius:var(--radius-sm);background:var(--color-bg-alt);border:1px solid var(--color-border-light);">
+  <strong>{{ global_sold }} / {{ global_capacity }}</strong> tickets sold (venue capacity)
+</div>
+{% endif %}
 {% if ticket_types %}
 <table class="data-table">
   <thead>

src/django_program/manage/views.py

@@ -54,6 +54,7 @@
 from django_program.pretalx.sync import PretalxSyncService
 from django_program.programs.models import Activity, ActivitySignup, Receipt, TravelGrant, TravelGrantMessage
 from django_program.registration.models import AddOn, Order, Payment, TicketType, Voucher
+from django_program.registration.services.capacity import get_global_sold_count
 from django_program.settings import get_config
 from django_program.sponsors.models import Sponsor, SponsorLevel
 from django_program.sponsors.profiles.resolver import resolve_sponsor_profile
@@ -2410,9 +2411,12 @@ class TicketTypeListView(ManagePermissionMixin, ListView):
     paginate_by = 50
 
     def get_context_data(self, **kwargs: object) -> dict[str, object]:
-        """Add ``active_nav`` to the template context."""
+        """Add ``active_nav`` and global capacity info to the template context."""
         context = super().get_context_data(**kwargs)
         context["active_nav"] = "ticket-types"
+        if self.conference.total_capacity > 0:
+            context["global_capacity"] = self.conference.total_capacity
+            context["global_sold"] = get_global_sold_count(self.conference)
         return context
 
     def get_queryset(self) -> QuerySet[TicketType]:

src/django_program/registration/services/capacity.py

@@ -0,0 +1,94 @@
+"""Global ticket capacity enforcement for conferences.
+
+Provides functions to count, check, and validate total ticket sales against
+a conference-level capacity limit. Add-ons are excluded from the global count
+because they do not consume venue seats.
+"""
+
+from django.core.exceptions import ValidationError
+from django.db import models
+from django.utils import timezone
+
+from django_program.conference.models import Conference
+from django_program.registration.models import Order, OrderLineItem
+
+
+def get_global_sold_count(conference: object) -> int:
+    """Return the total number of tickets sold across all ticket types.
+
+    Counts OrderLineItem quantities for ticket-type items (not add-ons) in
+    orders that are PAID, PARTIALLY_REFUNDED, or PENDING with an active
+    inventory hold.
+
+    Uses ``addon__isnull=True`` rather than ``ticket_type__isnull=False`` so
+    that line items whose ticket type was deleted (SET_NULL) are still counted
+    toward the sold total, preventing oversells.
+
+    Args:
+        conference: The conference to count sales for.
+
+    Returns:
+        The total number of tickets sold.
+    """
+    now = timezone.now()
+    return (
+        OrderLineItem.objects.filter(
+            order__conference=conference,
+            addon__isnull=True,
+        )
+        .filter(
+            models.Q(order__status__in=[Order.Status.PAID, Order.Status.PARTIALLY_REFUNDED])
+            | models.Q(order__status=Order.Status.PENDING, order__hold_expires_at__gt=now),
+        )
+        .aggregate(total=models.Sum("quantity"))["total"]
+        or 0
+    )
+
+
+def get_global_remaining(conference: object) -> int | None:
+    """Return the number of tickets still available under the global cap.
+
+    Args:
+        conference: The conference to check capacity for.
+
+    Returns:
+        The remaining ticket count, or ``None`` if the conference has no
+        global capacity limit (``total_capacity == 0``).
+    """
+    if conference.total_capacity == 0:
+        return None
+    sold = get_global_sold_count(conference)
+    return conference.total_capacity - sold
+
+
+def validate_global_capacity(conference: object, desired_total: int) -> None:
+    """Raise ``ValidationError`` if ``desired_total`` would exceed global capacity.
+
+    Acquires a row-level lock on the conference via ``select_for_update()`` to
+    prevent race conditions when multiple concurrent requests validate capacity
+    at the same time. The caller **must** already be inside a
+    ``transaction.atomic`` block.
+
+    The early-return check for unlimited conferences happens **after** the lock
+    is acquired so that a stale in-memory instance cannot bypass enforcement.
+
+    Args:
+        conference: The conference to validate against.
+        desired_total: The total number of ticket items in the cart
+            (across all ticket types, excluding add-ons).
+
+    Raises:
+        ValidationError: If the desired total exceeds the conference's
+            ``total_capacity``.
+    """
+    locked = Conference.objects.select_for_update().get(pk=conference.pk)
+    if locked.total_capacity == 0:
+        return
+    sold = get_global_sold_count(locked)
+    remaining = locked.total_capacity - sold
+    if desired_total > remaining:
+        if remaining <= 0:
+            raise ValidationError(f"This conference is sold out (venue capacity: {locked.total_capacity}).")
+        raise ValidationError(
+            f"Only {remaining} tickets remaining for this conference (venue capacity: {locked.total_capacity})."
+        )

src/django_program/registration/services/cart.py

@@ -22,6 +22,7 @@
     TicketType,
     Voucher,
 )
+from django_program.registration.services.capacity import validate_global_capacity
 from django_program.settings import get_config
 
 
@@ -131,6 +132,11 @@ def add_ticket(cart: Cart, ticket_type: TicketType, qty: int = 1) -> CartItem:
         existing_in_orders=existing_in_orders,
     )
 
+    validate_global_capacity(
+        cart.conference,
+        _get_cart_total_ticket_qty(cart) + qty,
+    )
+
     if ticket_type.requires_voucher:
         voucher = cart.voucher
         if voucher is None or not voucher.unlocks_hidden_tickets:
@@ -666,6 +672,9 @@ def _validate_ticket_quantity(cart: Cart, ticket_type: TicketType, new_qty: int)
             f"{ticket_type.limit_per_user} for '{ticket_type.name}'."
         )
 
+    other_ticket_qty = _get_cart_total_ticket_qty(cart, exclude_ticket_type=ticket_type)
+    validate_global_capacity(cart.conference, other_ticket_qty + new_qty)
+
 
 def _validate_addon_quantity(addon: AddOn, new_qty: int) -> None:
     """Validate remaining stock for a new add-on quantity."""
@@ -708,6 +717,24 @@ def _cascade_remove_orphaned_addons(cart: Cart, removing_ticket_type_id: int) ->
             addon_item.delete()
 
 
+def _get_cart_total_ticket_qty(cart: Cart, *, exclude_ticket_type: TicketType | None = None) -> int:
+    """Return the total ticket quantity in the cart (excluding add-ons).
+
+    Args:
+        cart: The cart to sum ticket items from.
+        exclude_ticket_type: Optionally exclude items of this ticket type
+            from the sum (used by ``update_quantity`` to compute the total
+            of *other* tickets before adding the new quantity).
+
+    Returns:
+        The total number of ticket items in the cart.
+    """
+    qs = cart.items.filter(ticket_type__isnull=False)
+    if exclude_ticket_type is not None:
+        qs = qs.exclude(ticket_type=exclude_ticket_type)
+    return qs.aggregate(total=models.Sum("quantity"))["total"] or 0
+
+
 def _item_is_voucher_applicable(
     item: CartItem,
     applicable_ticket_ids: set[int] | None,

src/django_program/registration/services/checkout.py

@@ -22,6 +22,7 @@
     Payment,
     Voucher,
 )
+from django_program.registration.services.capacity import validate_global_capacity
 from django_program.registration.services.cart import get_summary_from_items
 from django_program.registration.signals import order_paid
 from django_program.settings import get_config
@@ -100,7 +101,7 @@ def checkout(
         if not items:
             raise ValidationError("Cannot check out an empty cart.")
 
-        _revalidate_stock(items)
+        _revalidate_stock(items, cart.conference)
 
         summary = get_summary_from_items(cart, items)
 
@@ -339,9 +340,13 @@ def _increment_voucher_usage(*, voucher: Voucher | None, now: object) -> None:
         raise ValidationError(f"Voucher code '{voucher.code}' is no longer valid.")
 
 
-def _revalidate_stock(items: list[object]) -> None:
+def _revalidate_stock(items: list[object], conference: object) -> None:
     """Re-validate stock availability for all cart items at checkout time.
 
+    Args:
+        items: Pre-fetched cart items to validate.
+        conference: The conference these items belong to.
+
     Raises:
         ValidationError: If any item has insufficient stock or missing prerequisites.
     """
@@ -353,6 +358,28 @@ def _revalidate_stock(items: list[object]) -> None:
         elif item.addon is not None:
             _revalidate_addon_stock(item, now, ticket_type_ids)
 
+    _revalidate_global_capacity(items, conference)
+
+
+def _revalidate_global_capacity(items: list[object], conference: object) -> None:
+    """Validate that checkout ticket quantities fit within the global cap.
+
+    Sums ticket quantities from the cart items and validates against the
+    conference's ``total_capacity``.
+
+    Args:
+        items: Pre-fetched cart items from the checkout flow.
+        conference: The conference to validate capacity against.
+
+    Raises:
+        ValidationError: If the total tickets would exceed the global cap.
+    """
+    ticket_items = [item for item in items if item.ticket_type_id is not None]
+    if not ticket_items:
+        return
+    total_qty = sum(item.quantity for item in ticket_items)
+    validate_global_capacity(conference, total_qty)
+
 
 def _revalidate_ticket_stock(item: object) -> None:
     """Validate a ticket type is still available with sufficient stock."""

tests/test_conference/test_bootstrap_command.py

@@ -448,3 +448,50 @@ def test_bootstrap_deferred_keys_prints_notice(tmp_path):
 
     assert "Skipping 'sponsor_levels'" in output
     assert "sponsors app" in output
+
+
+@pytest.mark.django_db
+def test_bootstrap_sets_total_capacity(tmp_path):
+    config_path = _write_config(
+        tmp_path / "capacity.toml",
+        """[conference]
+name = "PyCon Capacity Test"
+start = 2027-05-01
+end = 2027-05-03
+timezone = "UTC"
+total_capacity = 1000
+
+[[conference.sections]]
+name = "Talks"
+start = 2027-05-02
+end = 2027-05-02
+""",
+    )
+
+    call_command("bootstrap_conference", config=config_path)
+
+    conference = Conference.objects.get(slug="pycon-capacity-test")
+    assert conference.total_capacity == 1000
+
+
+@pytest.mark.django_db
+def test_bootstrap_without_total_capacity_defaults_to_zero(tmp_path):
+    config_path = _write_config(
+        tmp_path / "no_capacity.toml",
+        """[conference]
+name = "PyCon No Cap"
+start = 2027-05-01
+end = 2027-05-03
+timezone = "UTC"
+
+[[conference.sections]]
+name = "Talks"
+start = 2027-05-02
+end = 2027-05-02
+""",
+    )
+
+    call_command("bootstrap_conference", config=config_path)
+
+    conference = Conference.objects.get(slug="pycon-no-cap")
+    assert conference.total_capacity == 0

tests/test_manage/test_forms.py

@@ -63,6 +63,7 @@ def test_meta_fields(self):
             "address",
             "website_url",
             "pretalx_event_slug",
+            "total_capacity",
             "is_active",
         ]
         assert list(form.fields.keys()) == expected
@@ -74,6 +75,7 @@ def test_valid_data(self):
                 "start_date": "2027-05-01",
                 "end_date": "2027-05-03",
                 "timezone": "UTC",
+                "total_capacity": 0,
                 "is_active": True,
             }
         )