perf(contracts): optimize ContractAdmin queries on add and change views

- Avoid loading all database ContractPost instances when adding a new contract
- Use select_related('contract') on ContractPost to prevent N+1 queries in __str__
- Only include ContractOperationTemplatePostInline on saved contracts
- Add prefetch_related('teams') for CompanyMember in pause reason assignments
- Optimize ContractAdmin changelist queryset with select_related and prefetch_related

loko/contracts/admin.py

@@ -75,6 +75,11 @@ def _get_pause_reason_inline():
         verbose_name = "Réassignation automatique sur pause"
         verbose_name_plural = "Réassignations automatiques sur pause"
 
+        def formfield_for_foreignkey(self, db_field, request, **kwargs):
+            if db_field.name == "assigned_member":
+                kwargs["queryset"] = CompanyMember.objects.prefetch_related('teams').order_by('name')
+            return super().formfield_for_foreignkey(db_field, request, **kwargs)
+
     return ContractPauseReasonAssignmentInline
 
 
@@ -106,15 +111,21 @@ def _get_operation_template_posts_inline():
             if db_field.name == "contract_post":
                 contract_id = request.resolver_match.kwargs.get('object_id') if request.resolver_match else None
                 if contract_id:
-                    kwargs["queryset"] = ContractPost.objects.filter(contract_id=contract_id).order_by('order_number')
+                    kwargs["queryset"] = ContractPost.objects.filter(
+                        contract_id=contract_id
+                    ).select_related('contract').order_by('order_number')
+                else:
+                    kwargs["queryset"] = ContractPost.objects.none()
             elif db_field.name == "operation_template":
                 contract_id = request.resolver_match.kwargs.get('object_id') if request.resolver_match else None
                 if contract_id:
-                    contract = Contract.objects.filter(pk=contract_id).first()
+                    contract = Contract.objects.prefetch_related('thematics').filter(pk=contract_id).first()
                     if contract and contract.thematics.exists():
                         kwargs["queryset"] = OperationTemplate.objects.filter(
                             Q(thematic__in=contract.thematics.all()) | Q(thematic__isnull=True)
                         ).distinct().order_by('name')
+                else:
+                    kwargs["queryset"] = OperationTemplate.objects.none()
             return super().formfield_for_foreignkey(db_field, request, **kwargs)
 
     return ContractOperationTemplatePostInline
@@ -131,8 +142,14 @@ class ContractAdmin(admin.ModelAdmin):
     list_filter = ('is_blocked', 'is_active', 'municipalities', 'thematics', 'uses_occupations', 'occupations_required', 'uses_intervention_manager', 'allow_team_members_edit', 'auto_assign_control_team', 'send_daily_summary')
     filter_horizontal = ('thematics', 'municipalities')
 
+    def get_queryset(self, request):
+        return super().get_queryset(request).select_related('company', 'executive_officer').prefetch_related('municipalities', 'thematics')
+
     def get_inlines(self, request, obj=None):
-        return [_get_pause_reason_inline(), _get_symptom_autoclose_inline(), _get_operation_template_posts_inline()] + list(super().get_inlines(request, obj))
+        inlines = [_get_pause_reason_inline(), _get_symptom_autoclose_inline()]
+        if obj:
+            inlines.append(_get_operation_template_posts_inline())
+        return inlines + list(super().get_inlines(request, obj))
 
     fieldsets = (
         (None, {