Merge pull request #366 from Dmitry-k42/master

Fix for issue #363: exception raises on insert to a nullable low cardinality columns

clickhouse_driver/columns/lowcardinalitycolumn.py

@@ -48,12 +48,14 @@ def write_state_prefix(self, buf):
     def _write_data(self, items, buf):
         index, keys = [], []
         key_by_index_element = {}
+        nested_is_nullable = False
 
         if self.nested_column.nullable:
             # First element represents NULL if column is nullable.
             index.append(self.nested_column.null_value)
             # Prevent null map writing. Reset nested column nullable flag.
             self.nested_column.nullable = False
+            nested_is_nullable = True
 
             for x in items:
                 if x is None:
@@ -94,7 +96,19 @@ def _write_data(self, items, buf):
         write_binary_int64(serialization_type, buf)
         write_binary_int64(len(index), buf)
 
-        self.nested_column.write_data(index, buf)
+        if nested_is_nullable:
+            # Given we reset nested column nullable flag above,
+            # we need to write null map manually. If to invoke
+            # write_data method, it will cause an exception,
+            # because `prepare_data` may not be able to handle
+            # null value correctly.
+            self.nested_column.write_items(
+                [self.nested_column.null_value], buf)
+            # Remove null map from index, because it is already written.
+            index_to_write = index[1:]
+            self.nested_column.write_data(index_to_write, buf)
+        else:
+            self.nested_column.write_data(index, buf)
         write_binary_int64(len(items), buf)
         int_column.write_items(keys, buf)
 

tests/columns/test_low_cardinality.py

@@ -65,6 +65,15 @@ def test_date(self):
             inserted = self.client.execute(query)
             self.assertEqual(inserted, data)
 
+    def test_nullable_date(self):
+        with self.create_table('a LowCardinality(Nullable(Date))'):
+            data = [(date(2023, 4, 1), ), (None, ), (date(1970, 1, 1), )]
+            self.client.execute('INSERT INTO test (a) VALUES', data)
+
+            query = 'SELECT * FROM test'
+            inserted = self.client.execute(query)
+            self.assertEqual(inserted, data)
+
     def test_float(self):
         with self.create_table('a LowCardinality(Float)'):
             data = [(float(x),) for x in range(300)]