Support LowCardinality columns in ad-hoc queries

CHANGELOG.md

@@ -1,6 +1,10 @@
 Change Log
 ==========
 
+Unreleased
+----------
+- Support LowCardinality columns in ad-hoc queries
+
 v1.2.0
 ------
 - Add support for per-field compression codecs (rbelio, Chocorean)

src/infi/clickhouse_orm/models.py

@@ -88,6 +88,10 @@ class ModelBase(type):
         if db_type.startswith('Nullable'):
             inner_field = cls.create_ad_hoc_field(db_type[9 : -1])
             return orm_fields.NullableField(inner_field)
+        # LowCardinality
+        if db_type.startswith('LowCardinality'):
+            inner_field = cls.create_ad_hoc_field(db_type[15 : -1])
+            return orm_fields.LowCardinalityField(inner_field)
         # Simple fields
         name = db_type + 'Field'
         if not hasattr(orm_fields, name):

tests/base_test_with_data.py

@@ -35,7 +35,7 @@ class TestCaseWithData(unittest.TestCase):
 class Person(Model):
 
     first_name = StringField()
-    last_name = StringField()
+    last_name = LowCardinalityField(StringField())
     birthday = DateField()
     height = Float32Field()
     passport = NullableField(UInt32Field())

tests/test_database.py

@@ -209,3 +209,12 @@ class DatabaseTestCase(TestCaseWithData):
         # Remove the setting and see that now it works
         self.database.add_setting('max_columns_to_read', None)
         list(self.database.select('SELECT * from system.tables'))
+
+    def test_create_ad_hoc_field(self):
+        # Tests that create_ad_hoc_field works for all column types in the database
+        from infi.clickhouse_orm.models import ModelBase
+        query = "SELECT DISTINCT type FROM system.columns"
+        for row in self.database.select(query):
+            if row.type in ('IPv4', 'IPv6'):
+                continue # unsupported yet
+            ModelBase.create_ad_hoc_field(row.type)