fix: count linked array primary fields (baserow#5279)

* fix: count linked array primary fields

* address copilot feedback

Author: silvestrid

backend/src/baserow/contrib/database/formula/ast/function_defs.py

@@ -2423,10 +2423,10 @@ def type_function(
         func_call: BaserowFunctionCall[UnTyped],
         arg: BaserowExpression[BaserowFormulaValidType],
     ) -> BaserowExpression[BaserowFormulaType]:
-        if BaserowGetFileCount().can_accept_arg(arg):
+        if BaserowGetFileCount().can_accept_arg(arg) and not arg.many:
             return BaserowGetFileCount()(arg)
 
-        if isinstance(arg.expression_type, BaserowFormulaArrayType):
+        if isinstance(arg.expression_type, BaserowFormulaArrayType) and not arg.many:
             return BaserowArrayLength()(arg)
 
         return arg.expression_type.count(func_call, arg).with_valid_type(

backend/tests/baserow/contrib/database/field/test_formula_field_type.py

@@ -2340,3 +2340,116 @@ def test_count_formula_for_link_row_field_with_null_values(data_fixture):
     )
 
     assert getattr(row_a, formula_field.db_column) == 3
+
+
+@pytest.mark.django_db
+def test_count_formula_for_link_row_field_with_array_primary_field(data_fixture):
+    """
+    A links to B, and B's primary field is a lookup array through a B to C link.
+    count(field('<link field>')) must count linked B rows, not each B row's inner
+    primary lookup array length (github issue #5276)
+    """
+
+    user = data_fixture.create_user()
+
+    table_a, table_b, link_a_to_b = data_fixture.create_two_linked_tables(user=user)
+    table_b_primary = table_b.field_set.get(primary=True)
+    table_b_primary.primary = False
+    table_b_primary.save()
+
+    table_c = data_fixture.create_database_table(user=user)
+    primary_c = data_fixture.create_text_field(
+        table=table_c, name="Field C", primary=True
+    )
+    link_b_to_c = data_fixture.create_link_row_field(
+        table=table_b,
+        link_row_table=table_c,
+        name="Link C",
+    )
+    data_fixture.create_formula_field(
+        table=table_b,
+        name="Primary lookup",
+        primary=True,
+        formula=f"lookup('{link_b_to_c.name}', '{primary_c.name}')",
+    )
+    count_formula = data_fixture.create_formula_field(
+        table=table_a,
+        name="Count",
+        formula=f"count(field('{link_a_to_b.name}'))",
+    )
+
+    row_handler = RowHandler()
+    rows_c = row_handler.force_create_rows(
+        user=user,
+        table=table_c,
+        rows_values=[{primary_c.db_column: "C1"}, {primary_c.db_column: "C2"}],
+        model=table_c.get_model(),
+    ).created_rows
+    rows_b = row_handler.force_create_rows(
+        user=user,
+        table=table_b,
+        rows_values=[
+            {link_b_to_c.db_column: [rows_c[0].id]},
+            {link_b_to_c.db_column: [rows_c[1].id]},
+        ],
+        model=table_b.get_model(),
+    ).created_rows
+    row_a = row_handler.force_create_rows(
+        user=user,
+        table=table_a,
+        rows_values=[{link_a_to_b.db_column: [row.id for row in rows_b]}],
+        model=table_a.get_model(),
+    ).created_rows[0]
+
+    assert getattr(row_a, count_formula.db_column) == 2
+
+
+@pytest.mark.django_db
+def test_count_formula_for_link_row_field_with_file_primary_field(data_fixture):
+    """
+    A links to B, and B's primary field is a file field. count(field('<link field>'))
+    must count linked B rows, not each B row's primary file count.
+    """
+
+    user = data_fixture.create_user()
+
+    table_a, table_b, link_a_to_b = data_fixture.create_two_linked_tables(user=user)
+    table_b_primary = table_b.field_set.get(primary=True)
+    table_b_primary.primary = False
+    table_b_primary.save()
+
+    primary_b = data_fixture.create_file_field(
+        table=table_b, name="Files", primary=True
+    )
+    count_formula = data_fixture.create_formula_field(
+        table=table_a,
+        name="Count",
+        formula=f"count(field('{link_a_to_b.name}'))",
+    )
+
+    user_file_1 = data_fixture.create_user_file()
+    user_file_2 = data_fixture.create_user_file()
+    user_file_3 = data_fixture.create_user_file()
+    row_handler = RowHandler()
+    rows_b = row_handler.force_create_rows(
+        user=user,
+        table=table_b,
+        rows_values=[
+            {
+                primary_b.db_column: [
+                    {"name": user_file_1.name},
+                    {"name": user_file_2.name},
+                ]
+            },
+            {primary_b.db_column: [{"name": user_file_3.name}]},
+        ],
+        model=table_b.get_model(),
+    ).created_rows
+    row_a = row_handler.force_create_rows(
+        user=user,
+        table=table_a,
+        rows_values=[{link_a_to_b.db_column: [row.id for row in rows_b]}],
+        model=table_a.get_model(),
+    ).created_rows[0]
+
+    assert getattr(row_a, count_formula.db_column) == 2

changelog/entries/unreleased/bug/5276_fix_count_formula_returning_array_for_linked_array_primary_fields.json

@@ -0,0 +1,9 @@
+{
+    "type": "bug",
+    "message": "Fixed count() returning an array instead of a number for link row fields whose linked primary field is an array formula or lookup.",
+    "issue_origin": "github",
+    "issue_number": 5276,
+    "domain": "database",
+    "bullet_points": [],
+    "created_at": "2026-04-29"
+}