Support LowCardinality type modifier

clickhouse_sqlalchemy/drivers/base.py

@@ -42,7 +42,8 @@
     'Enum8': types.Enum8,
     'Enum16': types.Enum16,
     '_array': types.Array,
-    '_nullable': types.Nullable
+    '_nullable': types.Nullable,
+    '_lowcardinality': types.LowCardinality,
 }
 
 
@@ -427,6 +428,10 @@ def visit_nullable(self, type_, **kw):
         nested_type = type_api.to_instance(type_.nested_type)
         return 'Nullable(%s)' % self.process(nested_type, **kw)
 
+    def visit_lowcardinality(self, type_, **kw):
+        nested_type = type_api.to_instance(type_.nested_type)
+        return "LowCardinality(%s)" % self.process(nested_type, **kw)
+
     def visit_int8(self, type_, **kw):
         return 'Int8'
 
@@ -582,6 +587,11 @@ def _get_column_type(self, name, spec):
             coltype = self.ischema_names['_nullable']
             return coltype(self._get_column_type(name, inner))
 
+        elif spec.startswith('LowCardinality'):
+            inner = spec[15:-1]
+            coltype = self.ischema_names['_lowcardinality']
+            return coltype(self._get_column_type(name, inner))
+
         elif spec.startswith('Enum'):
             pos = spec.find('(')
             type = spec[:pos]

clickhouse_sqlalchemy/types.py

@@ -51,6 +51,14 @@ class UUID(String):
     __visit_name__ = 'uuid'
 
 
+class LowCardinality(types.TypeEngine):
+    __visit_name__ = 'lowcardinality'
+
+    def __init__(self, nested_type):
+        self.nested_type = nested_type
+        super(LowCardinality, self).__init__()
+
+
 class Int8(Int):
     __visit_name__ = 'int8'
 

tests/test_reflection.py

@@ -49,6 +49,12 @@ def test_nullable(self):
         self.assertIsInstance(coltype, types.Nullable)
         self.assertEqual(coltype.nested_type, types.Int32)
 
+    def test_lowcardinality(self):
+        coltype = self._type_round_trip(types.LowCardinality(types.String))[0]
+
+        self.assertIsInstance(coltype, types.LowCardinality)
+        self.assertEqual(coltype.nested_type, types.String)
+
     def test_enum8(self):
         enum_options = {'three': 3, "quoted' ": 9, 'comma, ': 14}
         coltype = self._type_round_trip(