Fix incorrect test and clean up edge case for Vector Index

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 - Fixed copying of `TypeMap` and `TypeConfigurator`. Previously, the same global `TypeConfigurator` instance was used in all copies of a `TypeMap`. @rly [#1302](https://github.com/hdmf-dev/hdmf/pull/1302)
 - Fixed `get_data_shape` to use `Data.data.shape` instead of `Data.shape`, which may be overridden by subclasses. @rly [#1311](https://github.com/hdmf-dev/hdmf/pull/1311)
+- Fixed a broken test and refactored `VectorIndex.get`. @rly, @mavaylon1 [#1293](https://github.com/hdmf-dev/hdmf/pull/1293)
 
 ### Added
 - Added a check for a compound datatype that is not defined in the schema or spec. This is currently not supported. @mavaylon1 [#1276](https://github.com/hdmf-dev/hdmf/pull/1276)

src/hdmf/common/table.py

@@ -204,21 +204,8 @@ def get(self, arg, **kwargs):
                 indices = arg
             ret = list()
             if len(indices) > 0:
-                # Note: len(indices) == 0 for test_to_hierarchical_dataframe_empty_tables.
-                # This is an edge case test for to_hierarchical_dataframe() on empty tables.
-                # When len(indices) == 0, ret is expected to be an empty list, defined above.
-                try:
-                    data = self.target.get(slice(None),  **kwargs)
-                except IndexError:
-                    """
-                    Note: TODO: test_to_hierarchical_dataframe_indexed_dtr_on_last_level.
-                    This is the old way to get the data and not an untested feature.
-                    """
-                    for i in indices:
-                        ret.append(self.__getitem_helper(i, **kwargs))
-
-                    return ret
-
+                # Load the entire target table at once to avoid multiple I/O calls
+                data = self.target.get(slice(None),  **kwargs)
                 slices = [self.__get_slice(i) for i in indices]
                 if isinstance(data, pd.DataFrame):
                     ret = [data.iloc[s] for s in slices]

tests/unit/common/test_linkedtables.py

@@ -445,7 +445,7 @@ def test_to_hierarchical_dataframe_indexed_dtr_on_last_level(self):
         p1 = DynamicTable(name='parent_table', description='parent_table',
                           columns=[VectorData(name='p1', description='p1', data=np.arange(3)), dtr_p1, vi_dtr_p1])
         # Super-parent table
-        dtr_sp = DynamicTableRegion(name='sl1', description='sl1', data=np.arange(4), table=p1)
+        dtr_sp = DynamicTableRegion(name='sl1', description='sl1', data=np.arange(3), table=p1)
         vi_dtr_sp = VectorIndex(name='sl1_index', data=[1, 2, 3], target=dtr_sp)
         spt = DynamicTable(name='super_parent_table', description='super_parent_table',
                            columns=[VectorData(name='sp1', description='sp1', data=np.arange(3)), dtr_sp, vi_dtr_sp])