(core) Respect sort_by in lookupOne, and allow reverse sorting

Summary:
Ensure that `lookupOne` (via `RecordSet.get_one`) pays attention to the `sort_by` parameter by picking the first of its sorted list of row IDs.

Allow specifying reverse sort order in `sort_by` by adding `"-"` before the column ID.

Suggested in https://grist.slack.com/archives/C0234CPPXPA/p1665756041063079

Test Plan: Extended Python lookup test

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3675

sandbox/grist/records.py

@@ -177,7 +177,15 @@ class RecordSet(object):
     return False
 
   def get_one(self):
-    row_id = min(self._row_ids) if self._row_ids else 0
+    if not self._row_ids:
+      # Default to the empty/sample record
+      row_id = 0
+    elif self._sort_by:
+      # Pick the first record in the sorted order
+      row_id = self._row_ids[0]
+    else:
+      # Pick the first record in the order of the underlying table, for backwards compatibility.
+      row_id = min(self._row_ids)
     return self._table.Record(row_id, self._source_relation)
 
   def _get_col(self, col_id):

sandbox/grist/table.py

@@ -505,8 +505,15 @@ class Table(object):
     lookup_map = self._get_lookup_map(col_ids)
     row_id_set, rel = lookup_map.do_lookup(key)
     if sort_by:
-      row_ids = sorted(row_id_set,
-                       key=lambda r: column.SafeSortKey(self._get_col_value(sort_by, r, rel)))
+      if not isinstance(sort_by, six.string_types):
+        raise TypeError("sort_by must be a column ID (string)")
+      reverse = sort_by.startswith("-")
+      sort_col = sort_by.lstrip("-")
+      row_ids = sorted(
+        row_id_set,
+        key=lambda r: column.SafeSortKey(self._get_col_value(sort_col, r, rel)),
+        reverse=reverse,
+      )
     else:
       row_ids = sorted(row_id_set)
     return self.RecordSet(row_ids, rel, group_by=kwargs, sort_by=sort_by)

sandbox/grist/test_lookups.py

@@ -756,7 +756,23 @@ return ",".join(str(r.id) for r in Students.lookupRecords(firstName=fn, lastName
       "SCHEMA": [
         [1, "Table1", [
           [1, "num", "Numeric", False, "", "", ""],
-          [2, "lookup", "Any", True, "Table1.lookupRecords(sort_by='num').num", "", ""],
+          [4, "is_num", "Any", True,
+           "isinstance($num, float)", "", ""],
+          [2, "lookup", "Any", True,
+           "Table1.lookupRecords(sort_by='num').num", "", ""],
+          [3, "lookup_reverse", "Any", True,
+           "Table1.lookupRecords(sort_by='-num').num", "", ""],
+          [5, "lookup_first", "Any", True,
+           "Table1.lookupOne().num", "", ""],
+          [6, "lookup_min", "Any", True,
+           "Table1.lookupOne(sort_by='num').num", "", ""],
+          [7, "lookup_min_num", "Any", True,
+           "Table1.lookupOne(is_num=True, sort_by='num').num", "", ""],
+          [8, "lookup_max", "Any", True,
+           "Table1.lookupOne(sort_by='-num').num", "", ""],
+          [9, "lookup_max_num",
+           "Any", True,
+           "Table1.lookupOne(is_num=True, sort_by='-num').num", "", ""],
         ]]
       ],
       "DATA": {
@@ -774,8 +790,18 @@ return ",".join(str(r.id) for r in Students.lookupRecords(firstName=fn, lastName
 
     self.assertTableData(
       "Table1", cols="subset", rows="subset", data=[
-        ["id", "lookup"],
-        [1, [None, 0, 1, 2, 3, 'foo']],
+        ["id",
+         "lookup",
+         "lookup_reverse",
+         "lookup_first",
+         "lookup_min", "lookup_min_num",
+         "lookup_max", "lookup_max_num"],
+        [1,
+         [None, 0, 1, 2, 3, 'foo'],
+         ['foo', 3, 2, 1, 0, None],
+         2,  # lookup_first: first record (by id)
+         None, 0,  # lookup_min[_num]
+         'foo', 3],  # lookup_max[_num]
       ])
 
   def test_conversion(self):