実装サマリー

バックエンド（3ファイル変更）
ファイル	変更内容
views.py	OfficialKyosaiFieldViewSet、OfficialChusankanFieldViewSet（ReadOnly）、紐づけ追加/解除の4つのAPIビューを追加
urls.py	紐づけ管理用の4パス追加
serializers.py	linked_field_namesフィールドを追加（紐づけ先の圃場名を返す）
keinasystem/urls.py	/api/kyosai-fields/、/api/chusankan-fields/ をルーターに登録
新規API一覧
メソッド	エンドポイント	動作確認
GET	/api/kyosai-fields/	31件返却
GET	/api/chusankan-fields/	71件返却
POST	/api/fields/{id}/kyosai-links/	{"added":1}
DELETE	/api/fields/{id}/kyosai-links/{kyosai_id}/	204
POST	/api/fields/{id}/chusankan-links/	同上
DELETE	/api/fields/{id}/chusankan-links/{chusankan_id}/	同上
フロントエンド（3ファイル変更）
ファイル	変更内容
types/index.ts	linked_field_namesプロパティ追加
fields/[id]/page.tsx	紐づけ管理UI全面実装（+追加ボタン、x解除ボタン、検索付きモーダル、面積参考表示）
fields/page.tsx	「共済」「中山間」紐づけ件数列を追加
http://localhost:3000/fields/4 などで圃場詳細画面を開いて動作確認できます。

backend/apps/fields/views.py

@@ -1,12 +1,14 @@
 import pandas as pd
 from django.db import models as django_models
 from django.http import JsonResponse
+from django.shortcuts import get_object_or_404
 from django.views.decorators.csrf import csrf_exempt
 from django.views.decorators.http import require_http_methods
-from rest_framework import viewsets, permissions, filters
-from rest_framework.decorators import action
+from rest_framework import viewsets, permissions, filters, status
+from rest_framework.decorators import action, api_view, permission_classes as perm_classes
+from rest_framework.response import Response
 from .models import OfficialKyosaiField, OfficialChusankanField, Field
-from .serializers import FieldSerializer
+from .serializers import FieldSerializer, OfficialKyosaiFieldSerializer, OfficialChusankanFieldSerializer
 
 
 class FieldViewSet(viewsets.ModelViewSet):
@@ -21,6 +23,56 @@ class FieldViewSet(viewsets.ModelViewSet):
     ordering_fields = ['group_name', 'display_order', 'id', 'area_tan']
 
 
+class OfficialKyosaiFieldViewSet(viewsets.ReadOnlyModelViewSet):
+    queryset = OfficialKyosaiField.objects.all().order_by('k_num', 's_num')
+    serializer_class = OfficialKyosaiFieldSerializer
+    permission_classes = [permissions.IsAuthenticated]
+
+
+class OfficialChusankanFieldViewSet(viewsets.ReadOnlyModelViewSet):
+    queryset = OfficialChusankanField.objects.all().order_by('c_id')
+    serializer_class = OfficialChusankanFieldSerializer
+    permission_classes = [permissions.IsAuthenticated]
+
+
+@api_view(['POST'])
+@perm_classes([permissions.IsAuthenticated])
+def add_kyosai_links(request, field_id):
+    field = get_object_or_404(Field, pk=field_id)
+    ids = request.data.get('kyosai_field_ids', [])
+    records = OfficialKyosaiField.objects.filter(id__in=ids)
+    field.kyosai_fields.add(*records)
+    return Response({'added': len(records)})
+
+
+@api_view(['DELETE'])
+@perm_classes([permissions.IsAuthenticated])
+def remove_kyosai_link(request, field_id, kyosai_id):
+    field = get_object_or_404(Field, pk=field_id)
+    kyosai = get_object_or_404(OfficialKyosaiField, pk=kyosai_id)
+    field.kyosai_fields.remove(kyosai)
+    return Response(status=status.HTTP_204_NO_CONTENT)
+
+
+@api_view(['POST'])
+@perm_classes([permissions.IsAuthenticated])
+def add_chusankan_links(request, field_id):
+    field = get_object_or_404(Field, pk=field_id)
+    ids = request.data.get('chusankan_field_ids', [])
+    records = OfficialChusankanField.objects.filter(id__in=ids)
+    field.chusankan_fields.add(*records)
+    return Response({'added': len(records)})
+
+
+@api_view(['DELETE'])
+@perm_classes([permissions.IsAuthenticated])
+def remove_chusankan_link(request, field_id, chusankan_id):
+    field = get_object_or_404(Field, pk=field_id)
+    chusankan = get_object_or_404(OfficialChusankanField, pk=chusankan_id)
+    field.chusankan_fields.remove(chusankan)
+    return Response(status=status.HTTP_204_NO_CONTENT)
+
+
 @csrf_exempt
 @require_http_methods(["POST"])
 def import_kyosai_master(request):