Add allocation variety change history UI

backend/apps/plans/serializers.py

@@ -35,6 +35,8 @@ class PlanSerializer(serializers.ModelSerializer):
     crop_name = serializers.ReadOnlyField(source='crop.name')
     variety_name = serializers.ReadOnlyField(source='variety.name')
     field_name = serializers.ReadOnlyField(source='field.name')
+    variety_change_count = serializers.SerializerMethodField()
+    latest_variety_change = serializers.SerializerMethodField()
 
     class Meta:
         model = Plan
@@ -52,6 +54,32 @@ class PlanSerializer(serializers.ModelSerializer):
             notes=validated_data.get('notes', NO_CHANGE),
         )
 
+    def get_variety_change_count(self, obj):
+        prefetched = getattr(obj, '_prefetched_objects_cache', {})
+        changes = prefetched.get('variety_changes')
+        if changes is not None:
+            return len(changes)
+        return obj.variety_changes.count()
+
+    def get_latest_variety_change(self, obj):
+        prefetched = getattr(obj, '_prefetched_objects_cache', {})
+        changes = prefetched.get('variety_changes')
+        if changes is not None:
+            latest = changes[0] if changes else None
+        else:
+            latest = obj.variety_changes.select_related('old_variety', 'new_variety').first()
+        if latest is None:
+            return None
+        return {
+            'id': latest.id,
+            'changed_at': latest.changed_at,
+            'old_variety_id': latest.old_variety_id,
+            'old_variety_name': latest.old_variety.name if latest.old_variety else None,
+            'new_variety_id': latest.new_variety_id,
+            'new_variety_name': latest.new_variety.name if latest.new_variety else None,
+            'fertilizer_moved_entry_count': latest.fertilizer_moved_entry_count,
+        }
+
 
 class RiceTransplantEntrySerializer(serializers.ModelSerializer):
     field_name = serializers.CharField(source='field.name', read_only=True)

backend/apps/plans/views.py

@@ -25,11 +25,15 @@ class VarietyViewSet(viewsets.ModelViewSet):
 
 
 class PlanViewSet(viewsets.ModelViewSet):
-    queryset = Plan.objects.all()
+    queryset = Plan.objects.select_related('crop', 'variety', 'field').prefetch_related(
+        'variety_changes',
+        'variety_changes__old_variety',
+        'variety_changes__new_variety',
+    )
     serializer_class = PlanSerializer
 
     def get_queryset(self):
-        queryset = Plan.objects.all()
+        queryset = self.queryset
         year = self.request.query_params.get('year')
         if year:
             queryset = queryset.filter(year=year)

frontend/src/app/allocation/page.tsx

@@ -4,7 +4,7 @@ import { useState, useEffect, useMemo } from 'react';
 import { api } from '@/lib/api';
 import { Field, Crop, Plan } from '@/types';
 import Navbar from '@/components/Navbar';
-import { Menu, X, BarChart3, ChevronRight, ChevronDown, ArrowUp, ArrowDown, Copy, Settings, Trash2, CheckSquare, Search } from 'lucide-react';
+import { Menu, X, BarChart3, ChevronRight, ChevronDown, ArrowUp, ArrowDown, Copy, Settings, Trash2, CheckSquare, Search, History } from 'lucide-react';
 
 interface SummaryItem {
   cropId: number;
@@ -48,6 +48,13 @@ export default function AllocationPage() {
   const [searchText, setSearchText] = useState('');
   const [filterCropId, setFilterCropId] = useState<number | 0>(0);
   const [filterUnassigned, setFilterUnassigned] = useState(false);
+  const [toast, setToast] = useState<{ type: 'success' | 'error'; message: string } | null>(null);
+
+  useEffect(() => {
+    if (!toast) return;
+    const timer = window.setTimeout(() => setToast(null), 4000);
+    return () => window.clearTimeout(timer);
+  }, [toast]);
 
   useEffect(() => {
     localStorage.setItem('allocationYear', String(year));
@@ -233,17 +240,46 @@ export default function AllocationPage() {
     const existingPlan = getPlanForField(fieldId);
 
     if (!existingPlan || !existingPlan.crop) return;
+    if ((existingPlan.variety || null) === variety) return;
+
+    const nextVarietyName =
+      variety === null
+        ? '（品種未選択）'
+        : getVarietiesForCrop(existingPlan.crop).find((item) => item.id === variety)?.name || '不明';
+    const currentVarietyName = existingPlan.variety_name || '（品種未選択）';
+
+    const shouldProceed = confirm(
+      [
+        `品種を「${currentVarietyName}」から「${nextVarietyName}」へ変更します。`,
+        '施肥計画・田植え計画の関連エントリが自動で移動する場合があります。',
+        '実行しますか？',
+      ].join('\n')
+    );
+    if (!shouldProceed) return;
 
     setSaving(fieldId);
 
     try {
-      await api.patch(`/plans/${existingPlan.id}/`, {
+      const res = await api.patch(`/plans/${existingPlan.id}/`, {
         variety,
         notes: existingPlan.notes,
       });
+      const updatedPlan: Plan = res.data;
+      const movedCount = updatedPlan.latest_variety_change?.fertilizer_moved_entry_count ?? 0;
+      setToast({
+        type: 'success',
+        message:
+          movedCount > 0
+            ? `品種を変更し、施肥計画 ${movedCount} 件を移動しました。`
+            : '品種を変更しました。関連する施肥計画の移動はありませんでした。',
+      });
       await fetchData(true);
     } catch (error) {
       console.error('Failed to save variety:', error);
+      setToast({
+        type: 'error',
+        message: '品種変更に失敗しました。',
+      });
     } finally {
       setSaving(null);
     }
@@ -563,6 +599,17 @@ export default function AllocationPage() {
         {/* メインコンテンツ */}
         <div className="flex-1 min-w-0 p-4 lg:p-0">
           <div className="max-w-7xl mx-auto">
+            {toast && (
+              <div
+                className={`mb-4 rounded-md border px-4 py-3 text-sm ${
+                  toast.type === 'success'
+                    ? 'border-green-300 bg-green-50 text-green-800'
+                    : 'border-red-300 bg-red-50 text-red-800'
+                }`}
+              >
+                {toast.message}
+              </div>
+            )}
             <div className="mb-6 flex flex-col sm:flex-row sm:items-center justify-between gap-4">
               <h1 className="text-2xl font-bold text-gray-900">
                 作付け計画 <span className="text-green-700">{year}年度</span>
@@ -887,6 +934,7 @@ export default function AllocationPage() {
                                     </button>
                                   </div>
                                 ) : (
+                                  <div className="flex items-center gap-2">
                                     <select
                                       value={selectedVarietyId || ''}
                                       onChange={(e) => {
@@ -908,6 +956,21 @@ export default function AllocationPage() {
                                       ))}
                                       {selectedCropId > 0 && <option value="__add__">+ 新しい品種を追加...</option>}
                                     </select>
+                                    {plan?.latest_variety_change && (
+                                      <div
+                                        className="inline-flex items-center gap-1 rounded-full border border-amber-300 bg-amber-50 px-2 py-1 text-xs text-amber-800"
+                                        title={[
+                                          `変更日時: ${new Date(plan.latest_variety_change.changed_at).toLocaleString('ja-JP')}`,
+                                          `変更前: ${plan.latest_variety_change.old_variety_name || '未設定'}`,
+                                          `変更後: ${plan.latest_variety_change.new_variety_name || '未設定'}`,
+                                          `施肥移動件数: ${plan.latest_variety_change.fertilizer_moved_entry_count}`,
+                                        ].join('\n')}
+                                      >
+                                        <History className="h-3 w-3" />
+                                        変更履歴あり
+                                      </div>
+                                    )}
+                                  </div>
                                 )}
                               </td>
                               <td className="px-6 py-4">

frontend/src/types/index.ts

@@ -57,6 +57,16 @@ export interface Plan {
   variety: number;
   variety_name: string;
   notes: string | null;
+  variety_change_count?: number;
+  latest_variety_change?: {
+    id: number;
+    changed_at: string;
+    old_variety_id: number | null;
+    old_variety_name: string | null;
+    new_variety_id: number | null;
+    new_variety_name: string | null;
+    fertilizer_moved_entry_count: number;
+  } | null;
 }
 
 export interface Fertilizer {