Automatically add complementary fields to union

#210

shared/models.py

@@ -429,10 +429,19 @@ class ArticlesMixin(models.Model):
         district_meta_fields = DistrictArticlePage._meta.fields
         uniweb_meta_fields = UniwebArticlePage._meta.fields
 
+        # dictionary of class types of fields, assumes that a field cannot have a different type in each web
+        fields_dict = reduce(
+            lambda class_dict, field: self.merge_dict(
+                class_dict, {f"union_{field.column}": field}
+            ),
+            [*main_meta_fields, *district_meta_fields, *uniweb_meta_fields],
+            {},
+        )
+
         fields_reducer = (
             lambda assigned, field: assigned
             if field.column == "shared_from_id" or field.column == "shared_type"
-            else assigned | {f"union_{field.column}": F(field.column)}
+            else self.merge_dict(assigned, {f"union_{field.column}": F(field.column)})
         )
         setup_fields_order = lambda orderBy, orderFrom: reduce(
             lambda orderTo, field: self.merge_dict(orderTo, {field: orderFrom[field]}),
@@ -440,34 +449,69 @@ class ArticlesMixin(models.Model):
             {},
         )
 
-        main_fields = reduce(fields_reducer, main_meta_fields, {}) | {
+        district_only_fields = reduce(fields_reducer, district_meta_fields, {})
+        uniweb_only_fields = reduce(fields_reducer, uniweb_meta_fields, {})
+        main_only_fields = reduce(fields_reducer, main_meta_fields, {})
+
+        key_fields_default_values = {
             "union_thumb_image_id": F("search_image_id"),
+            "union_article_type": Value(2, models.PositiveSmallIntegerField()),
         }
 
+        create_complementary_field = lambda key: (
+            key_fields_default_values[key]
+            if key in key_fields_default_values
+            else (
+                # any type will suffice in the foreign key
+                Value(
+                    None,
+                    models.ForeignKey(
+                        DistrictArticlePage, blank=True, on_delete=models.SET_NULL
+                    ),
+                )
+                if isinstance(fields_dict[key], models.ForeignKey)
+                else Value(None, fields_dict[key].__class__())
+            )
+        )
+
+        reduce_complementary_fields = lambda complementary, item, notIn: (
+            self.merge_dict(
+                complementary, {item[0]: create_complementary_field(item[0])}
+            )
+            if item[0] not in notIn
+            else complementary
+        )
+
+        create_complementary_fields = lambda notIn, fromFields: reduce(
+            lambda complementary, item: reduce_complementary_fields(
+                complementary, item, dict(notIn)
+            ),
+            reduce(
+                lambda sources, source: sources + list(source.items()), fromFields, []
+            ),
+            {},
+        )
+
+        district_complementary_fields = create_complementary_fields(
+            district_only_fields, [uniweb_only_fields, main_only_fields]
+        )
+        uniweb_complementary_fields = create_complementary_fields(
+            uniweb_only_fields, [district_only_fields, main_only_fields]
+        )
+        main_complementary_fields = create_complementary_fields(
+            main_only_fields, [uniweb_only_fields, district_only_fields]
+        )
+
+        main_fields = main_only_fields | main_complementary_fields
+
         district_fields = setup_fields_order(
             main_fields,
-            reduce(fields_reducer, district_meta_fields, {})
-            | {
-                "union_region": Value(None, models.CharField()),
-                "union_article_type": Value(2, models.PositiveSmallIntegerField()),
-            },
+            district_only_fields | district_complementary_fields,
         )
 
         uniweb_fields = setup_fields_order(
             main_fields,
-            reduce(fields_reducer, uniweb_meta_fields, {})
-            | {
-                "union_author_page_id": Value(
-                    None,
-                    output_field=models.ForeignKey(
-                        DistrictArticlePage, blank=True, on_delete=models.SET_NULL
-                    ),
-                ),
-                "union_region": Value(None, models.CharField()),
-                "union_article_type": Value(2, models.PositiveSmallIntegerField()),
-                "union_is_black": Value(False, models.BooleanField()),
-                "union_thumb_image_id": F("search_image_id"),
-            },
+            uniweb_only_fields | uniweb_complementary_fields,
         )
 
         district_article_query: models.QuerySet = DistrictArticlePage.objects