Avoid deleting default homepage by ID in home app migration (#13194)

Fixes #4235. It is not safe to assume that the default homepage created in wagtailcore.0002_initial_data will always have the ID 2 on all database configurations, so identify it based on slug, depth and content type instead.

CHANGELOG.txt

@@ -50,6 +50,7 @@
  * Fix: Remove ngram parser on MySQL that prevented autocomplete search from returning results (Vince Salvino)
  * Fix: Only enable ManifestStaticFilesStorage in production settings, to aid test running (M. Sumair Khokhar)
  * Fix: Update `BooleanColumn` icons so they can be distinguished without relying on color (Sage Abdullah)
+ * Fix: Do not delete default homepage by ID in home app migration (Matt Westcott)
  * Docs: Add missing tag library imports to footer template code in tutorial (Dimaco)
  * Docs: Improve documentation around securing user-uploaded files (Jake Howard)
  * Docs: Introduce search_fields in a dedicated tutorial section instead of the introduction (Matt Westcott)

docs/releases/7.1.md

@@ -65,6 +65,7 @@ The [](../reference/contrib/settings) app now allows permission over site settin
  * Remove ngram parser on MySQL that prevented autocomplete search from returning results (Vince Salvino)
  * Only enable ManifestStaticFilesStorage in production settings, to aid test running (M. Sumair Khokhar)
  * Update `BooleanColumn` icons so they can be distinguished without relying on color (Sage Abdullah)
+ * Do not delete default homepage by ID in home app migration (Matt Westcott)
 
 ### Documentation
 

wagtail/project_template/home/migrations/0002_create_homepage.py

@@ -8,9 +8,14 @@ def create_homepage(apps, schema_editor):
     Site = apps.get_model("wagtailcore.Site")
     HomePage = apps.get_model("home.HomePage")
 
-    # Delete the default homepage
-    # If migration is run multiple times, it may have already been deleted
-    Page.objects.filter(id=2).delete()
+    # Delete the default homepage (of type Page) as created by wagtailcore.0002_initial_data,
+    # if it exists
+    page_content_type = ContentType.objects.get(
+        model="page", app_label="wagtailcore"
+    )
+    Page.objects.filter(
+        content_type=page_content_type, slug="home", depth=2
+    ).delete()
 
     # Create content type for homepage model
     homepage_content_type, __ = ContentType.objects.get_or_create(