fix: 修复点单商品在多店铺间跳动

扫码绑店参数只消费一次，避免 Tab 返回反复换绑；一人多条脏绑定取最新并在换绑时清理，hqsp 稳定取当前店。

Co-authored-by: Cursor <cursoragent@cursor.com>

shop/services/__init__.py

@@ -0,0 +1 @@
+# shop.services

shop/services/shop_binding.py

@@ -0,0 +1,95 @@
+"""用户店铺绑定：一人只能绑定一家店（业务约定）。"""
+from django.db import transaction
+from django.db.models import F
+
+from shop.models import Dianpu, YonghuDianpuBangding
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def get_latest_binding_qs(yonghu):
+    """同一用户可能历史残留多条绑定，一律取最近更新的一条。"""
+    return (
+        YonghuDianpuBangding.objects
+        .filter(yonghu=yonghu)
+        .select_related('dianpu')
+        .order_by('-UpdateTime', '-id')
+    )
+
+
+def get_user_shop_binding(yonghu):
+    """读取当前生效绑定（最新一条）。"""
+    return get_latest_binding_qs(yonghu).first()
+
+
+def _delete_extra_bindings(yonghu, keep_id=None):
+    """
+    删除同一用户多余绑定行，并扣减对应店铺绑定数。
+    keep_id: 保留的绑定主键；None 表示全部删除。
+    """
+    qs = YonghuDianpuBangding.objects.select_for_update().filter(yonghu=yonghu)
+    if keep_id is not None:
+        qs = qs.exclude(pk=keep_id)
+    extras = list(qs.select_related('dianpu'))
+    for row in extras:
+        try:
+            dianpu = row.dianpu
+            dianpu.bangding_yonghushu = F('bangding_yonghushu') - 1
+            dianpu.save(update_fields=['bangding_yonghushu'])
+        except Exception:
+            logger.warning('扣减多余绑定店铺人数失败 binding=%s', row.pk, exc_info=True)
+        row.delete()
+    return len(extras)
+
+
+@transaction.atomic
+def set_user_shop_binding(yonghu, dianpu):
+    """
+    将用户唯一绑定到 dianpu；清理多余行。
+    返回 (changed: bool, msg: str)
+    """
+    yonghu_locked = type(yonghu).objects.select_for_update().get(pk=yonghu.pk)
+    dianpu_locked = Dianpu.objects.select_for_update().get(pk=dianpu.pk)
+
+    if dianpu_locked.zhuangtai != 1:
+        return False, '店铺已被封禁，无法绑定'
+
+    rows = list(
+        YonghuDianpuBangding.objects.select_for_update()
+        .filter(yonghu=yonghu_locked)
+        .select_related('dianpu')
+        .order_by('-UpdateTime', '-id')
+    )
+
+    if rows:
+        primary = rows[0]
+        if primary.dianpu_id == dianpu_locked.id:
+            # 已是目标店：清掉多余行即可
+            _delete_extra_bindings(yonghu_locked, keep_id=primary.pk)
+            return False, '已绑定该店铺'
+
+        old = primary.dianpu
+        old.bangding_yonghushu = F('bangding_yonghushu') - 1
+        old.save(update_fields=['bangding_yonghushu'])
+
+        primary.dianpu = dianpu_locked
+        primary.save(update_fields=['dianpu', 'UpdateTime'])
+        _delete_extra_bindings(yonghu_locked, keep_id=primary.pk)
+    else:
+        primary = YonghuDianpuBangding.query.create(yonghu=yonghu_locked, dianpu=dianpu_locked)
+
+    dianpu_locked.bangding_yonghushu = F('bangding_yonghushu') + 1
+    dianpu_locked.save(update_fields=['bangding_yonghushu'])
+    return True, '绑定成功'
+
+
+@transaction.atomic
+def clear_user_shop_binding(yonghu):
+    """解除用户全部店铺绑定。返回被解除的主店铺 id 或 None。"""
+    yonghu_locked = type(yonghu).objects.select_for_update().get(pk=yonghu.pk)
+    primary = get_latest_binding_qs(yonghu_locked).first()
+    old_id = primary.dianpu_id if primary else None
+    _delete_extra_bindings(yonghu_locked, keep_id=None)
+    return old_id