Fix DatatypeMismatch on bulk insert for tables with formula fields (baserow#4993)

Author: dimmur-brw

backend/src/baserow/contrib/database/fields/fields.py

@@ -223,6 +223,9 @@ def __class__(self):
         # expression field.
         return self.expression_field.__class__
 
+    def get_placeholder(self, value, compiler, connection):
+        return "%s"
+
     def get_transform(self, name):
         # When a model field of this type is pickled and stored in the Baserow model
         # cache, the lookups on the class setup in the __init__ are not persisted.

backend/tests/baserow/contrib/database/rows/test_rows_handler.py

@@ -16,6 +16,7 @@
     extract_user_field_names_from_params,
     get_include_exclude_fields,
 )
+from baserow.contrib.database.fields.handler import FieldHandler
 from baserow.contrib.database.fields.models import SelectOption
 from baserow.contrib.database.rows.exceptions import RowDoesNotExist
 from baserow.contrib.database.rows.handler import RowHandler
@@ -1082,6 +1083,42 @@ def test_import_rows_with_read_only_field(
     assert len(rows) == 0
 
 
+@pytest.mark.django_db
+def test_import_rows_with_broken_lookup_field(data_fixture):
+    user = data_fixture.create_user()
+    table = data_fixture.create_database_table(user=user)
+    table2 = data_fixture.create_database_table(user=user, database=table.database)
+    data_fixture.create_text_field(name="primary", table=table, primary=True)
+    target_field = data_fixture.create_text_field(
+        name="target", table=table2, primary=True
+    )
+
+    linkrowfield = FieldHandler().create_field(
+        user, table, "link_row", name="link", link_row_table=table2
+    )
+    FieldHandler().create_field(
+        user,
+        table,
+        "lookup",
+        name="lookup",
+        through_field_id=linkrowfield.id,
+        target_field_id=target_field.id,
+    )
+
+    FieldHandler().update_field(user, linkrowfield.specific, new_type_name="text")
+
+    handler = RowHandler()
+    rows, report = handler.import_rows(
+        user=user,
+        table=table,
+        data=[["row1", ""], ["row2", ""]],
+        send_realtime_update=False,
+    )
+
+    assert len(rows) == 2
+    assert report == {}
+
+
 @pytest.mark.django_db
 @patch("baserow.contrib.database.rows.signals.rows_updated.send")
 @patch("baserow.contrib.database.rows.signals.before_rows_update.send")

changelog/entries/unreleased/bug/4992_fix_datatypemismatch_on_bulk_insert_for_tables_with_formula_.json

@@ -0,0 +1,9 @@
+{
+    "type": "bug",
+    "message": "Fix DatatypeMismatch on bulk insert for tables with formula fields",
+    "issue_origin": "github",
+    "issue_number": 4992,
+    "domain": "database",
+    "bullet_points": [],
+    "created_at": "2026-03-17"
+}