ManyToMany 関係への変更が完了しました。

変更内容
models.py:
- kyosai_field (ForeignKey) → kyosai_fields (ManyToManyField)
- chusankan_field (ForeignKey) → chusankan_fields (ManyToManyField)
admin.py:
- list_display から削除
- list_filter を _fields に変更
- filter_horizontal を追加（複数選択用UI）
マイグレーション: ✅ 完了
管理画面 (http://localhost:8000/admin/fields/field/) で、複数の共済区画・中山間区画を選択できます。

backend/apps/fields/admin.py

@@ -19,7 +19,8 @@ class OfficialChusankanFieldAdmin(admin.ModelAdmin):
 
 @admin.register(Field)
 class FieldAdmin(gis_admin.GISModelAdmin):
-    list_display = ('name', 'address', 'area_tan', 'area_m2', 'owner_name', 'kyosai_field', 'chusankan_field')
+    list_display = ('name', 'address', 'area_tan', 'area_m2', 'owner_name')
     search_fields = ('name', 'address', 'owner_name')
-    list_filter = ('kyosai_field', 'chusankan_field')
+    list_filter = ('kyosai_fields', 'chusankan_fields')
+    filter_horizontal = ('kyosai_fields', 'chusankan_fields')
     gis_widget_kwargs = {'attrs': {'static_map': False, 'longitude': 139.0, 'latitude': 36.0, 'zoom': 10}}

backend/apps/fields/migrations/0003_remove_field_chusankan_field_and_more.py

@@ -0,0 +1,31 @@
+# Generated by Django 5.0 on 2026-02-15 02:56
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fields', '0002_field_raw_chusankan_id_field_raw_kyosai_k_num_and_more'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='field',
+            name='chusankan_field',
+        ),
+        migrations.RemoveField(
+            model_name='field',
+            name='kyosai_field',
+        ),
+        migrations.AddField(
+            model_name='field',
+            name='chusankan_fields',
+            field=models.ManyToManyField(blank=True, related_name='fields', to='fields.officialchusankanfield', verbose_name='関連中山間マスタ'),
+        ),
+        migrations.AddField(
+            model_name='field',
+            name='kyosai_fields',
+            field=models.ManyToManyField(blank=True, related_name='fields', to='fields.officialkyosaifield', verbose_name='関連共済マスタ'),
+        ),
+    ]

backend/apps/fields/models.py

@@ -42,19 +42,15 @@ class Field(models.Model):
     raw_kyosai_k_num = models.CharField("細目_耕地番号", max_length=20, null=True, blank=True)
     raw_kyosai_s_num = models.CharField("細目_分筆番号", max_length=20, null=True, blank=True)
     raw_chusankan_id = models.CharField("中山間_ID", max_length=20, null=True, blank=True)
-    kyosai_field = models.ForeignKey(
+    kyosai_fields = models.ManyToManyField(
         OfficialKyosaiField,
-        on_delete=models.SET_NULL,
         blank=True,
-        null=True,
         related_name='fields',
         verbose_name="関連共済マスタ"
     )
-    chusankan_field = models.ForeignKey(
+    chusankan_fields = models.ManyToManyField(
         OfficialChusankanField,
-        on_delete=models.SET_NULL,
         blank=True,
-        null=True,
         related_name='fields',
         verbose_name="関連中山間マスタ"
     )