(core) Return RecordSet instead of list from property access when possible, to allow further property access

Summary: While `$ref.other_ref` returns a reference (Record) allowing chaining more properties like `$ref.other_ref.foo`, reflists (RecordSet) did not allow this, e.g. `$reflist.other_ref` returned a plain list of records, preventing chaining more dot notation. Discussed here: https://grist.slack.com/archives/CDHABLZJT/p1648845745765839

Test Plan: Added a Python unit test. Formulas like `$reflist.other_ref` were already very common though, and getting the functionality code slightly wrong leads to a flood of test failures.

Reviewers: jarek

Reviewed By: jarek

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3354

sandbox/grist/table.py

@@ -598,8 +598,8 @@ class Table(object):
 
   # Called when record.foo is accessed
   def _get_col_value(self, col_id, row_id, relation):
-    [value] = self._get_col_subset(col_id, [row_id], relation)
-    return value
+    [value] = self._get_col_subset_raw(col_id, [row_id], relation)
+    return records.adjust_record(relation, value)
 
   def _attribute_error(self, col_id, relation):
     self._engine._use_node(self._new_columns_node, relation)
@@ -607,8 +607,28 @@ class Table(object):
 
   # Called when record_set.foo is accessed
   def _get_col_subset(self, col_id, row_ids, relation):
+    values = self._get_col_subset_raw(col_id, row_ids, relation)
+
+    # When all the values are the same type of Record (i.e. all references to the same table)
+    # combine them into a single RecordSet for that table instead of a list
+    # so that more attribute accesses can be chained,
+    # e.g. record_set.foo.bar where `foo` is a Reference column.
+    value_types = list(set(map(type, values)))
+    if len(value_types) == 1 and issubclass(value_types[0], records.Record):
+      return records.RecordSet(
+        values[0]._table,
+        # This is different from row_ids: these are the row IDs referenced by these Records,
+        # whereas row_ids are where the values were being stored.
+        [val._row_id for val in values],
+        relation.compose(values[0]._source_relation),
+      )
+    else:
+      return [records.adjust_record(relation, value) for value in values]
+
+  # Internal helper to optimise _get_col_value
+  # so that it doesn't make a singleton RecordSet just to immediately unpack it
+  def _get_col_subset_raw(self, col_id, row_ids, relation):
     col = self.all_columns[col_id]
     # creates a dependency and brings formula columns up-to-date.
     self._engine._use_node(col.node, relation, row_ids)
-    # TODO: when column is a reference, support property access in return value
-    return [records.adjust_record(relation, col.get_cell_value(row_id)) for row_id in row_ids]
+    return [col.get_cell_value(row_id) for row_id in row_ids]

sandbox/grist/test_recordlist.py

@@ -1,5 +1,7 @@
 import testutil
 import test_engine
+from objtypes import RecordSetStub
+
 
 class TestRecordList(test_engine.EngineTestCase):
   col = testutil.col_schema_row
@@ -83,3 +85,18 @@ class TestRecordList(test_engine.EngineTestCase):
       [1, "Mammals",  [1, 3],     [1, 3],   True],
       [2, "Reptilia", [2, 4],     [2, 4],   True],
     ])
+
+  def test_attribute_chain(self):
+    self.load_sample(self.sample)
+    self.add_column('Class', 'Names', type='Any', isFormula=True,
+        formula="$Creatures.Class.Name")
+    self.add_column('Class', 'Creatures2', type='Any', isFormula=True,
+        formula="$Creatures.Class.Creatures")
+
+    mammals = RecordSetStub("Creatures", [1, 3])
+    reptiles = RecordSetStub("Creatures", [2, 4])
+    self.assertTableData("Class", data=[
+      ["id", "Name",     "Creatures", "Names",                  "Creatures2"],
+      [1,    "Mammals",  [1, 3],      ["Mammals", "Mammals"],   [mammals, mammals]],
+      [2,    "Reptilia", [2, 4],      ["Reptilia", "Reptilia"], [reptiles, reptiles]],
+    ])