Finished Release v1.2.0

CHANGELOG.md

@@ -1,6 +1,11 @@
 Change Log
 ==========
 
+v1.2.0
+------
+- Add support for per-field compression codecs (rbelio, Chocorean)
+- Add support for low cardinality fields (rbelio)
+
 v1.1.0
 ------
 - Add PREWHERE support to querysets (M1hacka)

docs/class_reference.md

@@ -10,7 +10,7 @@ infi.clickhouse_orm.database
 Database instances connect to a specific ClickHouse database for running queries,
 inserting data and other operations.
 
-#### Database(db_name, db_url="http://localhost:8123/", username=None, password=None, readonly=False, autocreate=True, timeout=60, verify_ssl_cert=True)
+#### Database(db_name, db_url="http://localhost:8123/", username=None, password=None, readonly=False, autocreate=True, timeout=60, verify_ssl_cert=True, log_statements=False)
 
 
 Initializes a database instance. Unless it's readonly, the database will be
@@ -24,6 +24,7 @@ created on the ClickHouse server if it does not already exist.
 - `autocreate`: automatically create the database if it does not exist (unless in readonly mode).
 - `timeout`: the connection timeout in seconds.
 - `verify_ssl_cert`: whether to verify the server's certificate when connecting via HTTPS.
+- `log_statements`: when True, all database statements are logged.
 
 
 #### add_setting(name, value)
@@ -510,7 +511,7 @@ infi.clickhouse_orm.fields
 
 Extends Field
 
-#### ArrayField(inner_field, default=None, alias=None, materialized=None, readonly=None)
+#### ArrayField(inner_field, default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### BaseEnumField
@@ -520,7 +521,7 @@ Extends Field
 
 Abstract base class for all enum-type fields.
 
-#### BaseEnumField(enum_cls, default=None, alias=None, materialized=None, readonly=None)
+#### BaseEnumField(enum_cls, default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### BaseFloatField
@@ -530,7 +531,7 @@ Extends Field
 
 Abstract base class for all float-type fields.
 
-#### BaseFloatField(default=None, alias=None, materialized=None, readonly=None)
+#### BaseFloatField(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### BaseIntField
@@ -540,21 +541,21 @@ Extends Field
 
 Abstract base class for all integer-type fields.
 
-#### BaseIntField(default=None, alias=None, materialized=None, readonly=None)
+#### BaseIntField(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### DateField
 
 Extends Field
 
-#### DateField(default=None, alias=None, materialized=None, readonly=None)
+#### DateField(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### DateTimeField
 
 Extends Field
 
-#### DateTimeField(default=None, alias=None, materialized=None, readonly=None)
+#### DateTimeField(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Decimal128Field
@@ -592,14 +593,14 @@ Base class for all decimal fields. Can also be used directly.
 
 Extends BaseEnumField
 
-#### Enum16Field(enum_cls, default=None, alias=None, materialized=None, readonly=None)
+#### Enum16Field(enum_cls, default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Enum8Field
 
 Extends BaseEnumField
 
-#### Enum8Field(enum_cls, default=None, alias=None, materialized=None, readonly=None)
+#### Enum8Field(enum_cls, default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Field
@@ -607,7 +608,7 @@ Extends BaseEnumField
 
 Abstract base class for all field types.
 
-#### Field(default=None, alias=None, materialized=None, readonly=None)
+#### Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### FixedStringField
@@ -621,91 +622,98 @@ Extends StringField
 
 Extends BaseFloatField
 
-#### Float32Field(default=None, alias=None, materialized=None, readonly=None)
+#### Float32Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Float64Field
 
 Extends BaseFloatField
 
-#### Float64Field(default=None, alias=None, materialized=None, readonly=None)
+#### Float64Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Int16Field
 
 Extends BaseIntField
 
-#### Int16Field(default=None, alias=None, materialized=None, readonly=None)
+#### Int16Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Int32Field
 
 Extends BaseIntField
 
-#### Int32Field(default=None, alias=None, materialized=None, readonly=None)
+#### Int32Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Int64Field
 
 Extends BaseIntField
 
-#### Int64Field(default=None, alias=None, materialized=None, readonly=None)
+#### Int64Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### Int8Field
 
 Extends BaseIntField
 
-#### Int8Field(default=None, alias=None, materialized=None, readonly=None)
+#### Int8Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
+
+
+### LowCardinalityField
+
+Extends Field
+
+#### LowCardinalityField(inner_field, default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### NullableField
 
 Extends Field
 
-#### NullableField(inner_field, default=None, alias=None, materialized=None, extra_null_values=None)
+#### NullableField(inner_field, default=None, alias=None, materialized=None, extra_null_values=None, codec=None)
 
 
 ### StringField
 
 Extends Field
 
-#### StringField(default=None, alias=None, materialized=None, readonly=None)
+#### StringField(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### UInt16Field
 
 Extends BaseIntField
 
-#### UInt16Field(default=None, alias=None, materialized=None, readonly=None)
+#### UInt16Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### UInt32Field
 
 Extends BaseIntField
 
-#### UInt32Field(default=None, alias=None, materialized=None, readonly=None)
+#### UInt32Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### UInt64Field
 
 Extends BaseIntField
 
-#### UInt64Field(default=None, alias=None, materialized=None, readonly=None)
+#### UInt64Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### UInt8Field
 
 Extends BaseIntField
 
-#### UInt8Field(default=None, alias=None, materialized=None, readonly=None)
+#### UInt8Field(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 ### UUIDField
 
 Extends Field
 
-#### UUIDField(default=None, alias=None, materialized=None, readonly=None)
+#### UUIDField(default=None, alias=None, materialized=None, readonly=None, codec=None)
 
 
 infi.clickhouse_orm.engines

docs/field_types.md

@@ -121,8 +121,7 @@ db.select('SELECT * FROM $db.event', model_class=Event)
 
 Working with nullable fields
 ----------------------------
-From [some time](https://github.com/yandex/ClickHouse/pull/70) ClickHouse provides a NULL value support.
+[ClickHouse provides a NULL value support](https://clickhouse.yandex/docs/en/data_types/nullable).
-Also see some information [here](https://github.com/yandex/ClickHouse/blob/master/dbms/tests/queries/0_stateless/00395_nullable.sql).
 
 Wrapping another field in a `NullableField` makes it possible to assign `None` to that field. For example:
 
@@ -148,6 +147,79 @@ to `None`.
 
 NOTE: `ArrayField` of `NullableField` is not supported. Also `EnumField` cannot be nullable.
 
+NOTE: Using `Nullable` almost always negatively affects performance, keep this in mind when designing your databases.
+
+Working with field compression codecs
+-------------------------------------
+Besides default data compression, defined in server settings, per-field specification is also available.
+
+Supported compression algorithms:
+
+| Codec                | Argument                                   | Comment
+| -------------------- | -------------------------------------------| ----------------------------------------------------
+| NONE                 | None                                       | No compression.
+| LZ4                  | None                                       | LZ4 compression.
+| LZ4HC(`level`)       | Possible `level` range: [3, 12].           | Default value: 9. Greater values stands for better compression and higher CPU usage. Recommended value range: [4,9].
+| ZSTD(`level`)        | Possible `level`range: [1, 22].            | Default value: 1. Greater values stands for better compression and higher CPU usage. Levels >= 20, should be used with caution, as they require more memory.
+| Delta(`delta_bytes`) | Possible `delta_bytes` range: 1, 2, 4 , 8. | Default value for `delta_bytes` is `sizeof(type)` if it is equal to 1, 2,4 or 8 and equals to 1 otherwise.
+
+Codecs can be combined in a pipeline. Default table codec is not included into pipeline (if it should be applied to a field, you have to specify it explicitly in pipeline).
+
+Recommended usage for codecs:
+- Usually, values for particular metric, stored in path does not differ significantly from point to point. Using delta-encoding allows to reduce disk space usage significantly.
+- DateTime works great with pipeline of Delta, ZSTD and the column size can be compressed to 2-3% of its original size (given a smooth datetime data)
+- Numeric types usually enjoy best compression rates with ZSTD
+- String types enjoy good compression rates with LZ4HC
+
+Usage:
+```python
+class Stats(models.Model):
+
+    id                  = fields.UInt64Field(codec='ZSTD(10)')
+    timestamp           = fields.DateTimeField(codec='Delta,ZSTD')
+    timestamp_date      = fields.DateField(codec='Delta(4),ZSTD(22)')
+    metadata_id         = fields.Int64Field(codec='LZ4')
+    status              = fields.StringField(codec='LZ4HC(10)')
+    calculation         = fields.NullableField(fields.Float32Field(), codec='ZSTD')
+    alerts              = fields.ArrayField(fields.FixedStringField(length=15), codec='Delta(2),LZ4HC')
+
+    engine = MergeTree('timestamp_date', ('id', 'timestamp'))
+
+```
+
+Note: This feature is supported on ClickHouse version 19.1.16 and above. Codec arguments will be ignored by the ORM for older versions of ClickHouse.
+
+Working with LowCardinality fields
+----------------------------------
+Starting with version 19.0 ClickHouse offers a new type of field to improve the performance of queries
+and compaction of columns for low entropy data.
+
+[More specifically](https://github.com/yandex/ClickHouse/issues/4074) LowCardinality data type builds dictionaries automatically. It can use multiple different dictionaries if necessarily.
+If the number of distinct values is pretty large, the dictionaries become local, several different dictionaries will be used for different ranges of data. For example, if you have too many distinct values in total, but only less than about a million values each day - then the queries by day will be processed efficiently, and queries for larger ranges will be processed rather efficiently.
+
+LowCardinality works independently of (generic) fields compression.
+LowCardinality fields are subsequently compressed as usual.
+The compression ratios of LowCardinality fields for text data may be significantly better than without LowCardinality.
+
+LowCardinality will give performance boost, in the form of processing speed, if the number of distinct values is less than a few millions. This is because data is processed in dictionary encoded form.
+
+You can find further information about LowCardinality in [this presentation](https://github.com/yandex/clickhouse-presentations/blob/master/meetup19/string_optimization.pdf).
+
+Usage example:
+```python
+class LowCardinalityModel(models.Model):
+    date       = fields.DateField()
+    int32      = fields.LowCardinalityField(fields.Int32Field())
+    float32    = fields.LowCardinalityField(fields.Float32Field())
+    string     = fields.LowCardinalityField(fields.StringField())
+    nullable   = fields.LowCardinalityField(fields.NullableField(fields.StringField()))
+    array      = fields.ArrayField(fields.LowCardinalityField(fields.UInt64Field()))
+
+    engine = MergeTree('date', ('date',))
+```
+
+Note: `LowCardinality` field with an inner array field is not supported. Use an `ArrayField` with a `LowCardinality` inner field as seen in the example.
+
 Creating custom field types
 ---------------------------
 Sometimes it is convenient to use data types that are supported in Python, but have no corresponding column type in ClickHouse. In these cases it is possible to define a custom field class that knows how to convert the Pythonic object to a suitable representation in the database, and vice versa.

docs/toc.md

@@ -36,6 +36,8 @@
       * [Working with array fields](field_types.md#working-with-array-fields)
       * [Working with materialized and alias fields](field_types.md#working-with-materialized-and-alias-fields)
       * [Working with nullable fields](field_types.md#working-with-nullable-fields)
+      * [Working with field compression codecs](field_types.md#working-with-field-compression-codecs)
+      * [Working with LowCardinality fields](field_types.md#working-with-lowcardinality-fields)
       * [Creating custom field types](field_types.md#creating-custom-field-types)
 
    * [Table Engines](table_engines.md#table-engines)
@@ -86,6 +88,7 @@
          * [Int32Field](class_reference.md#int32field)
          * [Int64Field](class_reference.md#int64field)
          * [Int8Field](class_reference.md#int8field)
+         * [LowCardinalityField](class_reference.md#lowcardinalityfield)
          * [NullableField](class_reference.md#nullablefield)
          * [StringField](class_reference.md#stringfield)
          * [UInt16Field](class_reference.md#uint16field)

src/infi/clickhouse_orm/database.py

@@ -120,6 +120,10 @@ class Database(object):
         self.server_version = self._get_server_version()
         # Versions 1.1.53981 and below don't have timezone function
         self.server_timezone = self._get_server_timezone() if self.server_version > (1, 1, 53981) else pytz.utc
+        # Versions 19.1.16 and above support codec compression
+        self.has_codec_support = self.server_version >= (19, 1, 16)
+        # Version 19.0 and above support LowCardinality
+        self.has_low_cardinality_support = self.server_version >= (19, 0)
 
     def create_database(self):
         '''

src/infi/clickhouse_orm/engines.py

@@ -40,7 +40,7 @@ class MergeTree(Engine):
         assert date_col is None or isinstance(date_col, six.string_types), 'date_col must be string if present'
         assert partition_key is None or type(partition_key) in (list, tuple),\
             'partition_key must be tuple or list if present'
-        assert (replica_table_path is None) == (replica_name == None), \
+        assert (replica_table_path is None) == (replica_name is None), \
             'both replica_table_path and replica_name must be specified'
 
         # These values conflict with each other (old and new syntax of table engines.

src/infi/clickhouse_orm/fields.py

@@ -3,13 +3,13 @@ from six import string_types, text_type, binary_type, integer_types
 import datetime
 import iso8601
 import pytz
-import time
 from calendar import timegm
 from decimal import Decimal, localcontext
 from uuid import UUID
-
+from logging import getLogger
 from .utils import escape, parse_array, comma_join
 
+logger = getLogger('clickhouse_orm')
 
 class Field(object):
     '''
@@ -19,14 +19,16 @@ class Field(object):
     class_default = 0
     db_type = None
 
-    def __init__(self, default=None, alias=None, materialized=None, readonly=None):
+    def __init__(self, default=None, alias=None, materialized=None, readonly=None, codec=None):
         assert (None, None) in {(default, alias), (alias, materialized), (default, materialized)}, \
             "Only one of default, alias and materialized parameters can be given"
         assert alias is None or isinstance(alias, string_types) and alias != "",\
-            "Alias field must be string field name, if given"
+            "Alias field must be a string, if given"
-        assert materialized is None or isinstance(materialized, string_types) and alias != "",\
+        assert materialized is None or isinstance(materialized, string_types) and materialized != "",\
             "Materialized field must be string, if given"
         assert readonly is None or type(readonly) is bool, "readonly parameter must be bool if given"
+        assert codec is None or isinstance(codec, string_types) and codec != "", \
+            "Codec field must be string, if given"
 
         self.creation_counter = Field.creation_counter
         Field.creation_counter += 1
@@ -34,6 +36,7 @@ class Field(object):
         self.alias = alias
         self.materialized = materialized
         self.readonly = bool(self.alias or self.materialized or readonly)
+        self.codec = codec
 
     def to_python(self, value, timezone_in_use):
         '''
@@ -64,22 +67,30 @@ class Field(object):
         '''
         return escape(value, quote)
 
-    def get_sql(self, with_default_expression=True):
+    def get_sql(self, with_default_expression=True, db=None):
         '''
         Returns an SQL expression describing the field (e.g. for CREATE TABLE).
         :param with_default_expression: If True, adds default value to sql.
             It doesn't affect fields with alias and materialized values.
+        :param db: Database, used for checking supported features.
         '''
+        sql = self.db_type
         if with_default_expression:
-            if self.alias:
+            sql += self._extra_params(db)
-                return '%s ALIAS %s' % (self.db_type, self.alias)
+        return sql
-            elif self.materialized:
+
-                return '%s MATERIALIZED %s' % (self.db_type, self.materialized)
+    def _extra_params(self, db):
-            else:
+        sql = ''
-                default = self.to_db_string(self.default)
+        if self.alias:
-                return '%s DEFAULT %s' % (self.db_type, default)
+            sql += ' ALIAS %s' % self.alias
-        else:
+        elif self.materialized:
-            return self.db_type
+            sql += ' MATERIALIZED %s' % self.materialized
+        elif self.default:
+            default = self.to_db_string(self.default)
+            sql += ' DEFAULT %s' % default
+        if self.codec and db and db.has_codec_support:
+            sql += ' CODEC(%s)' % self.codec
+        return sql
 
     def isinstance(self, types):
         """
@@ -361,11 +372,11 @@ class BaseEnumField(Field):
     Abstract base class for all enum-type fields.
     '''
 
-    def __init__(self, enum_cls, default=None, alias=None, materialized=None, readonly=None):
+    def __init__(self, enum_cls, default=None, alias=None, materialized=None, readonly=None, codec=None):
         self.enum_cls = enum_cls
         if default is None:
             default = list(enum_cls)[0]
-        super(BaseEnumField, self).__init__(default, alias, materialized, readonly)
+        super(BaseEnumField, self).__init__(default, alias, materialized, readonly, codec)
 
     def to_python(self, value, timezone_in_use):
         if isinstance(value, self.enum_cls):
@@ -384,12 +395,14 @@ class BaseEnumField(Field):
     def to_db_string(self, value, quote=True):
         return escape(value.name, quote)
 
-    def get_sql(self, with_default_expression=True):
+    def get_sql(self, with_default_expression=True, db=None):
         values = ['%s = %d' % (escape(item.name), item.value) for item in self.enum_cls]
         sql = '%s(%s)' % (self.db_type, ' ,'.join(values))
         if with_default_expression:
             default = self.to_db_string(self.default)
             sql = '%s DEFAULT %s' % (sql, default)
+            if self.codec and db and db.has_codec_support:
+                sql+= ' CODEC(%s)' % self.codec
         return sql
 
     @classmethod
@@ -399,10 +412,7 @@ class BaseEnumField(Field):
         this method returns a matching enum field.
         '''
         import re
-        try:
+        from enum import Enum
-            Enum # exists in Python 3.4+
-        except NameError:
-            from enum import Enum # use the enum34 library instead
         members = {}
         for match in re.finditer("'(\w+)' = (\d+)", db_type):
             members[match.group(1)] = int(match.group(2))
@@ -425,11 +435,11 @@ class ArrayField(Field):
 
     class_default = []
 
-    def __init__(self, inner_field, default=None, alias=None, materialized=None, readonly=None):
+    def __init__(self, inner_field, default=None, alias=None, materialized=None, readonly=None, codec=None):
         assert isinstance(inner_field, Field), "The first argument of ArrayField must be a Field instance"
         assert not isinstance(inner_field, ArrayField), "Multidimensional array fields are not supported by the ORM"
         self.inner_field = inner_field
-        super(ArrayField, self).__init__(default, alias, materialized, readonly)
+        super(ArrayField, self).__init__(default, alias, materialized, readonly, codec)
 
     def to_python(self, value, timezone_in_use):
         if isinstance(value, text_type):
@@ -448,9 +458,11 @@ class ArrayField(Field):
         array = [self.inner_field.to_db_string(v, quote=True) for v in value]
         return '[' + comma_join(array) + ']'
 
-    def get_sql(self, with_default_expression=True):
+    def get_sql(self, with_default_expression=True, db=None):
-        from .utils import escape
+        sql = 'Array(%s)' % self.inner_field.get_sql(with_default_expression=False, db=db)
-        return 'Array(%s)' % self.inner_field.get_sql(with_default_expression=False)
+        if with_default_expression and self.codec and db and db.has_codec_support:
+            sql+= ' CODEC(%s)' % self.codec
+        return sql
 
 
 class UUIDField(Field):
@@ -481,12 +493,12 @@ class NullableField(Field):
     class_default = None
 
     def __init__(self, inner_field, default=None, alias=None, materialized=None,
-                 extra_null_values=None):
+                 extra_null_values=None, codec=None):
         self.inner_field = inner_field
         self._null_values = [None]
         if extra_null_values:
             self._null_values.extend(extra_null_values)
-        super(NullableField, self).__init__(default, alias, materialized, readonly=None)
+        super(NullableField, self).__init__(default, alias, materialized, readonly=None, codec=codec)
 
     def to_python(self, value, timezone_in_use):
         if value == '\\N' or value in self._null_values:
@@ -501,14 +513,38 @@ class NullableField(Field):
             return '\\N'
         return self.inner_field.to_db_string(value, quote=quote)
 
-    def get_sql(self, with_default_expression=True):
+    def get_sql(self, with_default_expression=True, db=None):
-        s = 'Nullable(%s)' % self.inner_field.get_sql(with_default_expression=False)
+        sql = 'Nullable(%s)' % self.inner_field.get_sql(with_default_expression=False, db=db)
         if with_default_expression:
-            if self.alias:
+            sql += self._extra_params(db)
-                s = '%s ALIAS %s' % (s, self.alias)
+        return sql
-            elif self.materialized:
+
-                s = '%s MATERIALIZED %s' % (s, self.materialized)
+
-            elif self.default:
+class LowCardinalityField(Field):
-                default = self.to_db_string(self.default)
+
-                s = '%s DEFAULT %s' % (s, default)
+    def __init__(self, inner_field, default=None, alias=None, materialized=None, readonly=None, codec=None):
-        return s
+        assert isinstance(inner_field, Field), "The first argument of LowCardinalityField must be a Field instance. Not: {}".format(inner_field)
+        assert not isinstance(inner_field, LowCardinalityField), "LowCardinality inner fields are not supported by the ORM"
+        assert not isinstance(inner_field, ArrayField), "Array field inside LowCardinality are not supported by the ORM. Use Array(LowCardinality) instead"
+        self.inner_field = inner_field
+        self.class_default = self.inner_field.class_default
+        super(LowCardinalityField, self).__init__(default, alias, materialized, readonly, codec)
+
+    def to_python(self, value, timezone_in_use):
+        return self.inner_field.to_python(value, timezone_in_use)
+
+    def validate(self, value):
+        self.inner_field.validate(value)
+
+    def to_db_string(self, value, quote=True):
+        return self.inner_field.to_db_string(value, quote=quote)
+
+    def get_sql(self, with_default_expression=True, db=None):
+        if db and db.has_low_cardinality_support:
+            sql = 'LowCardinality(%s)' % self.inner_field.get_sql(with_default_expression=False)
+        else:
+            sql = self.inner_field.get_sql(with_default_expression=False)
+            logger.warning('LowCardinalityField not supported on clickhouse-server version < 19.0 using {} as fallback'.format(self.inner_field.__class__.__name__))
+        if with_default_expression:
+            sql += self._extra_params(db)
+        return sql

src/infi/clickhouse_orm/migrations.py

@@ -79,7 +79,7 @@ class AlterTable(Operation):
             if name not in table_fields:
                 logger.info('        Add column %s', name)
                 assert prev_name, 'Cannot add a column to the beginning of the table'
-                cmd = 'ADD COLUMN %s %s' % (name, field.get_sql())
+                cmd = 'ADD COLUMN %s %s' % (name, field.get_sql(db=database))
                 if is_regular_field:
                     cmd += ' AFTER %s' % prev_name
                 self._alter_table(database, cmd)
@@ -93,7 +93,7 @@ class AlterTable(Operation):
         # The order of class attributes can be changed any time, so we can't count on it
         # Secondly, MATERIALIZED and ALIAS fields are always at the end of the DESC, so we can't expect them to save
         # attribute position. Watch https://github.com/Infinidat/infi.clickhouse_orm/issues/47
-        model_fields = {name: field.get_sql(with_default_expression=False)
+        model_fields = {name: field.get_sql(with_default_expression=False, db=database)
                         for name, field in iteritems(self.model_class.fields())}
         for field_name, field_sql in self._get_table_fields(database):
             # All fields must have been created and dropped by this moment

src/infi/clickhouse_orm/models.py

@@ -190,7 +190,7 @@ class Model(with_metaclass(ModelBase)):
         parts = ['CREATE TABLE IF NOT EXISTS `%s`.`%s` (' % (db.db_name, cls.table_name())]
         cols = []
         for name, field in iteritems(cls.fields()):
-            cols.append('    %s %s' % (name, field.get_sql()))
+            cols.append('    %s %s' % (name, field.get_sql(db=db)))
         parts.append(',\n'.join(cols))
         parts.append(')')
         parts.append('ENGINE = ' + cls.engine.create_table_sql(db))
@@ -316,7 +316,7 @@ class MergeModel(Model):
         cols = []
         for name, field in iteritems(cls.fields()):
             if name != '_table':
-                cols.append('    %s %s' % (name, field.get_sql()))
+                cols.append('    %s %s' % (name, field.get_sql(db=db)))
         parts.append(',\n'.join(cols))
         parts.append(')')
         parts.append('ENGINE = ' + cls.engine.create_table_sql(db))

tests/sample_migrations/0015.py

@@ -0,0 +1,7 @@
+from infi.clickhouse_orm import migrations
+from ..test_migrations import *
+
+operations = [
+    migrations.AlterTable(Model4_compressed),
+    migrations.AlterTable(Model2LowCardinality)
+]

tests/test_compressed_fields.py

@@ -0,0 +1,123 @@
+from __future__ import unicode_literals
+import unittest
+import datetime
+import pytz
+
+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 *
+from infi.clickhouse_orm.utils import parse_tsv
+
+
+class CompressedFieldsTestCase(unittest.TestCase):
+
+    def setUp(self):
+        self.database = Database('test-db', log_statements=True)
+        self.database.create_table(CompressedModel)
+
+    def tearDown(self):
+        self.database.drop_database()
+
+    def test_defaults(self):
+        # Check that all fields have their explicit or implicit defaults
+        instance = CompressedModel()
+        self.database.insert([instance])
+        self.assertEqual(instance.date_field, datetime.date(1970, 1, 1))
+        self.assertEqual(instance.datetime_field, datetime.datetime(1970, 1, 1, tzinfo=pytz.utc))
+        self.assertEqual(instance.string_field, 'dozo')
+        self.assertEqual(instance.int64_field, 42)
+        self.assertEqual(instance.float_field, 0)
+        self.assertEqual(instance.nullable_field, None)
+        self.assertEqual(instance.array_field, [])
+
+    def test_assignment(self):
+        # Check that all fields are assigned during construction
+        kwargs = dict(
+            uint64_field=217,
+            date_field=datetime.date(1973, 12, 6),
+            datetime_field=datetime.datetime(2000, 5, 24, 10, 22, tzinfo=pytz.utc),
+            string_field='aloha',
+            int64_field=-50,
+            float_field=3.14,
+            nullable_field=-2.718281,
+            array_field=['123456789123456','','a']
+        )
+        instance = CompressedModel(**kwargs)
+        self.database.insert([instance])
+        for name, value in kwargs.items():
+            self.assertEqual(kwargs[name], getattr(instance, name))
+
+    def test_string_conversion(self):
+        # Check field conversion from string during construction
+        instance = CompressedModel(date_field='1973-12-06', int64_field='100', float_field='7', nullable_field=None, array_field='[a,b,c]')
+        self.assertEqual(instance.date_field, datetime.date(1973, 12, 6))
+        self.assertEqual(instance.int64_field, 100)
+        self.assertEqual(instance.float_field, 7)
+        self.assertEqual(instance.nullable_field, None)
+        self.assertEqual(instance.array_field, ['a', 'b', 'c'])
+        # Check field conversion from string during assignment
+        instance.int64_field = '99'
+        self.assertEqual(instance.int64_field, 99)
+
+    def test_to_dict(self):
+        instance = CompressedModel(date_field='1973-12-06', int64_field='100', float_field='7', array_field='[a,b,c]')
+        self.assertDictEqual(instance.to_dict(), {
+            "date_field": datetime.date(1973, 12, 6),
+            "int64_field": 100,
+            "float_field": 7.0,
+            "datetime_field": datetime.datetime(1970, 1, 1, 0, 0, 0, tzinfo=pytz.utc),
+            "alias_field": 0.0,
+            'string_field': 'dozo',
+            'nullable_field': None,
+            'uint64_field': 0,
+            'array_field': ['a','b','c']
+        })
+        self.assertDictEqual(instance.to_dict(include_readonly=False), {
+            "date_field": datetime.date(1973, 12, 6),
+            "int64_field": 100,
+            "float_field": 7.0,
+            "datetime_field": datetime.datetime(1970, 1, 1, 0, 0, 0, tzinfo=pytz.utc),
+            'string_field': 'dozo',
+            'nullable_field': None,
+            'uint64_field': 0,
+            'array_field': ['a', 'b', 'c']
+        })
+        self.assertDictEqual(
+            instance.to_dict(include_readonly=False, field_names=('int64_field', 'alias_field', 'datetime_field')), {
+                "int64_field": 100,
+                "datetime_field": datetime.datetime(1970, 1, 1, 0, 0, 0, tzinfo=pytz.utc)
+            })
+
+    # This test will fail on clickhouse version < 19.1.16, use skip test
+    def test_confirm_compression_codec(self):
+        instance = CompressedModel(date_field='1973-12-06', int64_field='100', float_field='7', array_field='[a,b,c]')
+        self.database.insert([instance])
+        r = self.database.raw("select name, compression_codec from system.columns where table = '{}' and database='{}' FORMAT TabSeparatedWithNamesAndTypes".format(instance.table_name(), self.database.db_name))
+        lines = r.splitlines()
+        field_names = parse_tsv(lines[0])
+        field_types = parse_tsv(lines[1])
+        data = [tuple(parse_tsv(line)) for line in lines[2:]]
+        self.assertListEqual(data, [('uint64_field', 'CODEC(ZSTD(10))'),
+                                    ('datetime_field', 'CODEC(Delta(4), ZSTD(1))'),
+                                    ('date_field', 'CODEC(Delta(4), ZSTD(22))'),
+                                    ('int64_field', 'CODEC(LZ4)'),
+                                    ('string_field', 'CODEC(LZ4HC(10))'),
+                                    ('nullable_field', 'CODEC(ZSTD(1))'),
+                                    ('array_field', 'CODEC(Delta(2), LZ4HC(0))'),
+                                    ('float_field', 'CODEC(NONE)'),
+                                    ('alias_field', 'CODEC(ZSTD(4))')])
+
+
+class CompressedModel(Model):
+    uint64_field        = UInt64Field(codec='ZSTD(10)')
+    datetime_field      = DateTimeField(codec='Delta,ZSTD')
+    date_field          = DateField(codec='Delta(4),ZSTD(22)')
+    int64_field         = Int64Field(default=42, codec='LZ4')
+    string_field        = StringField(default='dozo', codec='LZ4HC(10)')
+    nullable_field      = NullableField(Float32Field(), codec='ZSTD')
+    array_field         = ArrayField(FixedStringField(length=15), codec='Delta(2),LZ4HC')
+    float_field         = Float32Field(codec='NONE')
+    alias_field         = Float32Field(alias='float_field', codec='ZSTD(4)')
+
+    engine = MergeTree('datetime_field', ('uint64_field', 'datetime_field'))

tests/test_enum_fields.py

@@ -6,10 +6,7 @@ from infi.clickhouse_orm.models import Model
 from infi.clickhouse_orm.fields import *
 from infi.clickhouse_orm.engines import *
 
-try:
+from enum import Enum
-    Enum # exists in Python 3.4+
-except NameError:
-    from enum import Enum # use the enum34 library instead
 
 
 class EnumFieldsTest(unittest.TestCase):

tests/test_migrations.py

@@ -7,14 +7,11 @@ from infi.clickhouse_orm.fields import *
 from infi.clickhouse_orm.engines import *
 from infi.clickhouse_orm.migrations import MigrationHistory
 
+from enum import Enum
 # Add tests to path so that migrations will be importable
 import sys, os
 sys.path.append(os.path.dirname(__file__))
 
-try:
-    Enum # exists in Python 3.4+
-except NameError:
-    from enum import Enum # use the enum34 library instead
 
 import logging
 logging.basicConfig(level=logging.DEBUG, format='%(message)s')
@@ -97,6 +94,17 @@ class MigrationsTestCase(unittest.TestCase):
         self.assertTrue(self.tableExists(AliasModel1))
         self.assertEqual(self.getTableFields(AliasModel1),
                           [('date', 'Date'), ('int_field', 'Int8'), ('date_alias', 'Date'), ('int_field_plus_one', 'Int8')])
+        self.database.migrate('tests.sample_migrations', 15)
+        self.assertTrue(self.tableExists(Model4_compressed))
+        if self.database.has_low_cardinality_support:
+            self.assertEqual(self.getTableFields(Model2LowCardinality),
+                             [('date', 'Date'), ('f1', 'LowCardinality(Int32)'), ('f3', 'LowCardinality(Float32)'),
+                              ('f2', 'LowCardinality(String)'), ('f4', 'LowCardinality(Nullable(String))'), ('f5', 'Array(LowCardinality(UInt64))')])
+        else:
+            logging.warning('No support for low cardinality')
+            self.assertEqual(self.getTableFields(Model2),
+                             [('date', 'Date'), ('f1', 'Int32'), ('f3', 'Float32'), ('f2', 'String'), ('f4', 'Nullable(String)'),
+                              ('f5', 'Array(UInt64)')])
 
 
 # Several different models with the same table name, to simulate a table that changes over time
@@ -258,3 +266,31 @@ class Model4Buffer_changed(BufferModel, Model4_changed):
     @classmethod
     def table_name(cls):
         return 'model4buffer'
+
+
+class Model4_compressed(Model):
+
+    date = DateField()
+    f3 = DateTimeField(codec='Delta,ZSTD(10)')
+    f2 = StringField(codec='LZ4HC')
+
+    engine = MergeTree('date', ('date',))
+
+    @classmethod
+    def table_name(cls):
+        return 'model4'
+
+
+class Model2LowCardinality(Model):
+    date = DateField()
+    f1 = LowCardinalityField(Int32Field())
+    f3 = LowCardinalityField(Float32Field())
+    f2 = LowCardinalityField(StringField())
+    f4 = LowCardinalityField(NullableField(StringField()))
+    f5 = ArrayField(LowCardinalityField(UInt64Field()))
+
+    engine = MergeTree('date', ('date',))
+
+    @classmethod
+    def table_name(cls):
+        return 'mig'

tests/test_querysets.py

@@ -7,11 +7,7 @@ from infi.clickhouse_orm.query import Q
 from .base_test_with_data import *
 import logging
 from datetime import date, datetime
-
+from enum import Enum
-try:
-    Enum # exists in Python 3.4+
-except NameError:
-    from enum import Enum  # use the enum34 library instead
 
 
 class QuerySetTestCase(TestCaseWithData):
@@ -227,7 +223,7 @@ class QuerySetTestCase(TestCaseWithData):
         qs = Person.objects_in(self.database).order_by('first_name', 'last_name')
         # Try different page sizes
         for page_size in (1, 2, 7, 10, 30, 100, 150):
-            # Iterate over pages and collect all intances
+            # Iterate over pages and collect all instances
             page_num = 1
             instances = set()
             while True: