Add support for FixedString fields

README.rst

@@ -252,6 +252,7 @@ Currently the following field types are supported:
 Class                DB Type     Pythonic Type      Comments
 ===================  ========    =================  ===================================================
 StringField          String      unicode            Encoded as UTF-8 when written to ClickHouse
+FixedStringField     String      unicode            Encoded as UTF-8 when written to ClickHouse
 DateField            Date        datetime.date      Range 1970-01-01 to 2038-01-19
 DateTimeField        DateTime    datetime.datetime  Minimal value is 1970-01-01 00:00:00; Always in UTC
 Int8Field            Int8        int                Range -128 to 127

src/infi/clickhouse_orm/fields.py

@@ -90,6 +90,24 @@ class StringField(Field):
         raise ValueError('Invalid value for %s: %r' % (self.__class__.__name__, value))
 
 
+class FixedStringField(StringField):
+
+    def __init__(self, length, default=None, alias=None, materialized=None):
+        self._length = length
+        self.db_type = 'FixedString(%d)' % length
+        super(FixedStringField, self).__init__(default, alias, materialized)
+
+    def to_python(self, value, timezone_in_use):
+        value = super(FixedStringField, self).to_python(value, timezone_in_use)
+        return value.rstrip('\0')
+
+    def validate(self, value):
+        if isinstance(value, text_type):
+            value = value.encode('UTF-8')
+        if len(value) > self._length:
+            raise ValueError('Value of %d bytes is too long for FixedStringField(%d)' % (len(value), self._length))
+
+
 class DateField(Field):
 
     min_value = datetime.date(1970, 1, 1)

src/infi/clickhouse_orm/models.py

@@ -58,6 +58,10 @@ class ModelBase(type):
         if db_type.startswith('Array'):
             inner_field = cls.create_ad_hoc_field(db_type[6 : -1])
             return orm_fields.ArrayField(inner_field)
+        # FixedString
+        if db_type.startswith('FixedString'):
+            length = int(db_type[12 : -1])
+            return orm_fields.FixedStringField(length)
         # Simple fields
         name = db_type + 'Field'
         if not hasattr(orm_fields, name):

tests/test_fixed_string_fields.py

@@ -0,0 +1,58 @@
+# -*- coding: utf-8 -*-
+
+import unittest
+
+from infi.clickhouse_orm.database import Database
+from infi.clickhouse_orm.models import Model
+from infi.clickhouse_orm.fields import *
+from infi.clickhouse_orm.engines import *
+
+
+class FixedStringFieldsTest(unittest.TestCase):
+
+    def setUp(self):
+        self.database = Database('test-db')
+        self.database.create_table(FixedStringModel)
+
+    def tearDown(self):
+        self.database.drop_database()
+
+    def _insert_sample_data(self):
+        self.database.insert([
+            FixedStringModel(date_field='2016-08-30', fstr_field=''),
+            FixedStringModel(date_field='2016-08-30'),
+            FixedStringModel(date_field='2016-08-31', fstr_field='foo'),
+            FixedStringModel(date_field='2016-08-31', fstr_field=u'לילה')
+        ])
+
+    def _assert_sample_data(self, results):
+        self.assertEquals(len(results), 4)
+        self.assertEquals(results[0].fstr_field, '')
+        self.assertEquals(results[1].fstr_field, 'ABCDEFGHIJK')
+        self.assertEquals(results[2].fstr_field, 'foo')
+        self.assertEquals(results[3].fstr_field, u'לילה')
+
+    def test_insert_and_select(self):
+        self._insert_sample_data()
+        query = 'SELECT * from $table ORDER BY date_field'
+        results = list(self.database.select(query, FixedStringModel))
+        self._assert_sample_data(results)
+        
+    def test_ad_hoc_model(self):
+        self._insert_sample_data()
+        query = 'SELECT * from $db.fixedstringmodel ORDER BY date_field'
+        results = list(self.database.select(query))
+        self._assert_sample_data(results)
+
+    def test_assignment_error(self):
+        for value in (17, 'this is too long', u'זה ארוך', None, 99.9):
+            with self.assertRaises(ValueError):
+                FixedStringModel(fstr_field=value)
+
+
+class FixedStringModel(Model):
+
+    date_field = DateField()
+    fstr_field = FixedStringField(12, default='ABCDEFGHIJK')
+
+    engine = MergeTree('date_field', ('date_field',))