Merge branch '290-fix-bug-where-single-select-field-without-options-can-t-be-converted-to-a-text-field' into 'develop'

Draft: Resolve "Fix bug where single select field without options can't be converted to a text field"

Closes #290

See merge request bramw/baserow!158

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

@@ -802,6 +802,11 @@ class SingleSelectFieldType(FieldType):
                 variables[variable_name] = option.value
                 values_mapping.append(f"('{int(option.id)}', %({variable_name})s)")
 
+            # If there are no values we don't need to convert the value to a string
+            # since all values will be converted to null.
+            if len(values_mapping) == 0:
+                return None
+
             sql = f"""
                 p_in = (SELECT value FROM (
                     VALUES {','.join(values_mapping)}
@@ -829,7 +834,7 @@ class SingleSelectFieldType(FieldType):
                     f"(lower(%({variable_name})s), '{int(option.id)}')"
                 )
 
-            # If there is no values we don't need to convert the value since all
+            # If there are no values we don't need to convert the value since all
             # values should be converted to null.
             if len(values_mapping) == 0:
                 return None

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

@@ -58,6 +58,10 @@ def test_single_select_field_type(data_fixture):
     field_handler.delete_field(user=user, field=field)
     assert SelectOption.objects.all().count() == 0
 
+    field = field_handler.create_field(user=user, table=table,
+                                       type_name='single_select', select_options=[])
+    field_handler.update_field(user=user, field=field, new_type_name='text')
+
 
 @pytest.mark.django_db
 def test_single_select_field_type_rows(data_fixture, django_assert_num_queries):

changelog.md

@@ -8,6 +8,8 @@
 * Fixed the "Ignored attempt to cancel a touchmove" error.
 * Refactored the has_user everywhere such that the raise_error argument is used when
   possible.
+* Fixed bug where a single select field without options could not be converted to a
+  another field.
 
 ## Released (2021-02-04)