Merge pull request #12 from sergei-maertens/issue/10-readonly-fields

Support read only private media fields

Author: sergei-maertens

privates/admin.py

@@ -142,3 +142,31 @@ def get_urls(self):
             )
 
         return extra + default
+
+    def get_object(self, request, object_id, from_field=None):
+        """
+        Override to replace the readonly private media file field accessors.
+
+        See issue #10 - injecting the private media (admin specific) URLs for readonly
+        fields is not possible since all the form field machinery gets bypassed, and
+        a bunch of helpers/utilities that are private Django API are used to render a
+        form, fieldsets, field lines and ultimately the field. This call chain ends up
+        in ``django.db.models.fields.file.FieldFile.url``. We cannot blindly always
+        return the admin URL at the model level, since these URLs should not be exposed
+        to non-admin users.
+
+        So, in the admin context we instead taint the model instance so that our custom
+        ``FieldFile`` class/attr_class can introspect this and conditionally build up
+        the correct URL.
+        """
+        obj = super().get_object(request, object_id, from_field=from_field)  # type: ignore
+
+        readonly_fields = self.get_readonly_fields(request, obj=obj)  # type: ignore
+        obj._private_media_readonly_fields = [
+            field
+            for field in self.get_private_media_fields()
+            if field in readonly_fields
+        ]
+        obj._private_media_model_admin = self
+
+        return obj

privates/fields.py

@@ -1,8 +1,40 @@
-from django.db.models import FileField, ImageField
+from __future__ import annotations
+
+from django.db.models import FileField, ImageField, Model
+from django.db.models.fields.files import FieldFile, ImageFieldFile
+from django.urls import reverse
 
 from .storages import private_media_storage
 
 
+class PrivateMediaFieldFileMixin:
+    instance: Model
+
+    @property
+    def url(self) -> str:
+        django_url = super().url  # type: ignore
+
+        readonly_fields = getattr(self.instance, "_private_media_readonly_fields", None)
+        model_admin = getattr(self.instance, "_private_media_model_admin", None)
+        if not readonly_fields or not model_admin:
+            return django_url
+
+        field_name = self.field.name  # type: ignore
+        if field_name not in readonly_fields:
+            return django_url
+
+        url_name = f"admin:{model_admin._get_private_media_view_name(field_name)}"
+        return reverse(url_name, kwargs={"pk": self.instance.pk})
+
+
+class PrivateMediaFieldFile(PrivateMediaFieldFileMixin, FieldFile):
+    pass
+
+
+class PrivateMediaImageFieldFile(PrivateMediaFieldFileMixin, ImageFieldFile):
+    pass
+
+
 class PrivateMediaFieldMixin:
     """
     Enable a private media storage for file-based model fields.
@@ -25,8 +57,12 @@ class PrivateMediaFileField(PrivateMediaFieldMixin, FileField):
     A generic private media file field.
     """
 
+    attr_class = PrivateMediaFieldFile
+
 
 class PrivateMediaImageField(PrivateMediaFieldMixin, ImageField):
     """
     A private media image field.
     """
+
+    attr_class = PrivateMediaImageFieldFile

privates/storages.py

@@ -12,6 +12,9 @@ class PrivateMediaFileSystemStorage(FileSystemStorage):
     * ``settings.PRIVATE_MEDIA_URL`` is the internal URL used for files.
     """
 
+    _location: str | None
+    _base_url: str | None
+
     def _clear_cached_properties(self, setting, **kwargs):
         super()._clear_cached_properties(setting, **kwargs)
         if setting == "PRIVATE_MEDIA_ROOT":

testapp/admin.py

@@ -2,7 +2,7 @@
 
 from privates.admin import PrivateMediaMixin
 
-from .models import File, File2, File3
+from .models import File, File2, File3, File4
 
 
 @admin.register(File)
@@ -20,3 +20,8 @@ class FileAdmin2(FileAdmin):
 @admin.register(File3)
 class File3Admin(PrivateMediaMixin, admin.ModelAdmin):
     pass
+
+
+@admin.register(File4)
+class File4Admin(PrivateMediaMixin, admin.ModelAdmin):
+    readonly_fields = ("file",)

testapp/migrations/0004_file3_file4.py

@@ -0,0 +1,33 @@
+# Generated by Django 5.1.6 on 2025-02-26 12:29
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("testapp", "0003_file2"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="File3",
+            fields=[],
+            options={
+                "proxy": True,
+                "indexes": [],
+                "constraints": [],
+            },
+            bases=("testapp.file",),
+        ),
+        migrations.CreateModel(
+            name="File4",
+            fields=[],
+            options={
+                "proxy": True,
+                "indexes": [],
+                "constraints": [],
+            },
+            bases=("testapp.file",),
+        ),
+    ]

testapp/models.py

@@ -18,3 +18,8 @@ class Meta:
 class File3(File):
     class Meta:
         proxy = True
+
+
+class File4(File):
+    class Meta:
+        proxy = True

testapp/settings.py

@@ -1,5 +1,7 @@
 import os
 
+DEBUG = True
+
 USE_TZ = True
 
 BASE_DIR = os.path.abspath(os.path.dirname(__file__))
@@ -19,6 +21,7 @@
     "django.contrib.contenttypes",
     "django.contrib.auth",
     "django.contrib.messages",
+    "django.contrib.staticfiles",
     "django.contrib.sessions",
     "django.contrib.admin",
     "privates",
@@ -51,6 +54,8 @@
     },
 ]
 
+STATIC_URL = "static/"
+
 PRIVATE_MEDIA_ROOT = os.path.join(BASE_DIR, "private_media")
 PRIVATE_MEDIA_URL = "/protected/"
 

tests/test_admin.py

@@ -47,6 +47,7 @@ def test_admin_widget_url_empty_initial(admin_client):
 def test_admin_widget_url_inmemoryfile(admin_client):
     url = reverse("admin:testapp_file_add")
     response = admin_client.post(url, {"file": BytesIO(b"")}, follow=True)
+    assert response.status_code == 200
 
 
 @pytest.mark.django_db
@@ -75,3 +76,19 @@ def test_admin_no_download_field(admin_client, private_file):
     display_value = img.text.strip()
 
     assert display_value == _("Currently: %s") % private_file.image.name
+
+
+@pytest.mark.django_db
+def test_admin_readonly_field(admin_client, private_file):
+    """
+    Assert that readonly files have the correct download URL.
+    """
+    url = reverse("admin:testapp_file4_change", args=(private_file.pk,))
+    change_page = admin_client.get(url)
+    assert change_page.status_code == 200
+    html = change_page.content.decode("utf-8")
+    doc = pq(html)
+    download_link = doc.find(".readonly a").eq(0)
+    assert download_link.attr("href") == reverse(
+        "admin:testapp_file4_file", args=(private_file.pk,)
+    )

tests/test_modelfield.py

@@ -1,5 +1,7 @@
 from django.conf import settings
 
+import pytest
+
 from privates.storages import PrivateMediaStorage
 from testapp.models import File
 
@@ -8,3 +10,13 @@ def test_private_media_file_field():
     file = File()
     assert isinstance(file.file.storage, PrivateMediaStorage)
     assert file.file.storage.base_location == settings.PRIVATE_MEDIA_ROOT
+
+
+@pytest.mark.django_db
+def test_url_property(private_file):
+    # outside if the admin, the URL property must use django's default behaviour
+    url = private_file.file.url
+
+    assert url.startswith("/protected/")
+    assert "dummy" in url
+    assert url.endswith(".txt")