Database Engines Supoort

README.md

@@ -7,9 +7,8 @@ Supports both synchronous and asynchronous ways to interact with the clickhouse
 
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 Introduction
 ============
@@ -21,3 +20,4 @@ It allows you to define model classes whose instances can be written to the data
 This and other examples can be found in the `examples` folder.
 
 To learn more please visit the [documentation](https://sswest.github.io/ch-orm/).
+

docs/class_reference.md

@@ -10,7 +10,7 @@ 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, auto_create=True, timeout=60, verify_ssl_cert=True, log_statements=False)
+#### Database(db_name, db_url="http://localhost:8123/", username=None, password=None, readonly=False, auto_create=True, timeout=60, verify_ssl_cert=True, log_statements=False, engine=Atomic())
 
 
 Initializes a database instance. Unless it's readonly, the database will be
@@ -26,6 +26,7 @@ created on the ClickHouse server if it does not already exist.
 - `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.
+- `engine`: By default, ClickHouse uses the Atomic database engine.
 
 
 #### add_setting(name, value)
@@ -180,6 +181,7 @@ created on the ClickHouse server if it does not already exist.
 - `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.
+- `engine`: By default, ClickHouse uses the Atomic database engine.
 
 
 #### add_setting(name, value)
@@ -1241,30 +1243,95 @@ Extends Field
 clickhouse_orm.engines
 ----------------------
 
-### Engine
+### DatabaseEngine
+
+### Atomic
+
+Extends DatabaseEngine
+
+
+It supports non-blocking DROP TABLE and RENAME TABLE queries and atomic EXCHANGE TABLES queries.
+Atomic database engine is used by default.
+
+### Lazy
+
+Extends DatabaseEngine
+
+
+Keeps tables in RAM only expiration_time_in_seconds seconds after last access.
+Can be used only with *Log tables.
+
+It’s optimized for storing many small *Log tables,
+for which there is a long time interval between accesses.
+
+### MySQL
+
+Extends DatabaseEngine
+
+
+Allows to connect to databases on a remote MySQL server and perform INSERT and
+SELECT queries to exchange data between ClickHouse and MySQL.
+
+The MySQL database engine translate queries to the MySQL server so you can perform operations
+such as SHOW TABLES or SHOW CREATE TABLE.
+
+### PostgreSQL
+
+Extends DatabaseEngine
+
+
+Allows to connect to databases on a remote PostgreSQL server. Supports read and write operations
+ (SELECT and INSERT queries) to exchange data between ClickHouse and PostgreSQL.
+
+Gives the real-time access to table list and table structure from
+remote PostgreSQL with the help of SHOW TABLES and DESCRIBE TABLE queries.
+
+Supports table structure modifications (ALTER TABLE ... ADD|DROP COLUMN).
+If use_table_cache parameter (see the Engine Parameters below) it set to 1,
+the table structure is cached and not checked for being modified,
+but can be updated with DETACH and ATTACH queries.
+
+### SQLite
+
+Extends DatabaseEngine
+
+
+Allows to connect to SQLite database and perform INSERT and SELECT queries to
+exchange data between ClickHouse and SQLite.
+
+#### SQLite(db_path)
+
+
+- `db_path`: Path to a file with SQLite database.
+
+
+clickhouse_orm.engines
+----------------------
+
+### TableEngine
 
 ### TinyLog
 
-Extends Engine
+Extends TableEngine
 
 ### Log
 
-Extends Engine
+Extends TableEngine
 
 ### Memory
 
-Extends Engine
+Extends TableEngine
 
 ### MergeTree
 
-Extends Engine
+Extends TableEngine
 
 #### MergeTree(date_col=None, order_by=(), sampling_expr=None, index_granularity=8192, replica_table_path=None, replica_name=None, partition_key=None, primary_key=None)
 
 
 ### Buffer
 
-Extends Engine
+Extends TableEngine
 
 
 Buffers the data to write in RAM, periodically flushing it to another table.
@@ -1276,7 +1343,7 @@ Read more [here](https://clickhouse.tech/docs/en/engines/table-engines/special/b
 
 ### Merge
 
-Extends Engine
+Extends TableEngine
 
 
 The Merge engine (not to be confused with MergeTree) does not store data itself,
@@ -1289,7 +1356,7 @@ https://clickhouse.tech/docs/en/engines/table-engines/special/merge/
 
 ### Distributed
 
-Extends Engine
+Extends TableEngine
 
 
 The Distributed engine by itself does not store data,
@@ -2208,7 +2275,7 @@ Initializer.
 #### floor(n=None)
 
 
-#### formatDateTime(format, timezone=NO_VALUE)
+#### formatDateTime(fmt, timezone=NO_VALUE)
 
 
 #### gcd(b)
@@ -3234,7 +3301,7 @@ Initializer.
 #### toStartOfTenMinutes()
 
 
-#### toStartOfWeek(mode=0)
+#### toStartOfWeek()
 
 
 #### toStartOfYear()
@@ -3602,7 +3669,8 @@ Returns: A list of SystemPart objects
 Gets active data from system.parts table
 
 - `database`: A database object to fetch data from.
-- `conditions`: WHERE clause conditions. Database and active conditions are added automatically
+- `conditions`: WHERE clause conditions.
+    Database and active conditions are added automatically
 
 Returns: A list of SystemPart objects
 

scripts/generate_ref.py

@@ -138,7 +138,8 @@ if __name__ == '__main__':
     module_doc([aio_database.AioDatabase])
     module_doc([models.Model, models.BufferModel, models.MergeModel, models.DistributedModel, models.Constraint, models.Index])
     module_doc(sorted([fields.Field] + all_subclasses(fields.Field), key=lambda x: x.__name__), False)
-    module_doc([engines.Engine] + all_subclasses(engines.Engine), False)
+    module_doc([engines.DatabaseEngine] + all_subclasses(engines.DatabaseEngine), False)
+    module_doc([engines.TableEngine] + all_subclasses(engines.TableEngine), False)
     module_doc([query.QuerySet, query.AggregateQuerySet, query.Q])
     module_doc([funcs.F])
     module_doc([system_models.SystemPart])

src/clickhouse_orm/aio/database.py

@@ -80,7 +80,10 @@ class AioDatabase(Database):
         """
         Creates the database on the ClickHouse server if it does not already exist.
         """
-        await self._send("CREATE DATABASE IF NOT EXISTS `%s`" % self.db_name)
+        await self._send(
+            "CREATE DATABASE IF NOT EXISTS `%s` ENGINE = %s"
+            % (self.db_name, self.engine.create_database_sql())
+        )
         self.db_exists = True
 
     async def drop_database(self):

src/clickhouse_orm/database.py

@@ -11,6 +11,7 @@ from typing import Optional, Generator, Union, Any
 import pytz
 import httpx
 
+from .engines import DatabaseEngine, Atomic
 from .models import ModelBase, MODEL
 from .utils import parse_tsv, import_submodules
 from .session import ctx_session_id, ctx_session_timeout
@@ -110,6 +111,7 @@ class Database:
         timeout=60,
         verify_ssl_cert=True,
         log_statements=False,
+        engine: DatabaseEngine = Atomic(),
     ):
         """
         Initializes a database instance. Unless it's readonly, the database will be
@@ -125,6 +127,7 @@ class Database:
         - `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.
+        - `engine`: By default, ClickHouse uses the Atomic database engine.
         """
         self.db_name = db_name
         self.db_url = db_url
@@ -132,6 +135,7 @@ class Database:
         self._readonly = readonly
         self.auto_create = auto_create
         self.timeout = timeout
+        self.engine = engine
         self.request_session = self._client_class(verify=verify_ssl_cert, timeout=timeout)
         if username:
             self.request_session.auth = (username, password or "")
@@ -175,7 +179,10 @@ class Database:
         """
         Creates the database on the ClickHouse server if it does not already exist.
         """
-        self._send("CREATE DATABASE IF NOT EXISTS `%s`" % self.db_name)
+        self._send(
+            "CREATE DATABASE IF NOT EXISTS `%s` ENGINE = %s"
+            % (self.db_name, self.engine.create_database_sql())
+        )
         self.db_exists = True
 
     def drop_database(self):

src/clickhouse_orm/engines.py

@@ -14,27 +14,153 @@ if TYPE_CHECKING:
 logger = logging.getLogger("clickhouse_orm")
 
 
-class Engine:
+class TableEngine:
     def create_table_sql(self, db: Database) -> str:
         raise NotImplementedError()  # pragma: no cover
 
 
-class TinyLog(Engine):
+class DatabaseEngine:
+    def create_database_sql(self) -> str:
+        raise NotImplementedError()  # pragma: no cover
+
+
+class Atomic(DatabaseEngine):
+    """
+    It supports non-blocking DROP TABLE and RENAME TABLE queries and atomic EXCHANGE TABLES queries.
+    Atomic database engine is used by default.
+    """
+
+    def create_database_sql(self) -> str:
+        return "Atomic"
+
+
+class Lazy(DatabaseEngine):
+    """
+    Keeps tables in RAM only expiration_time_in_seconds seconds after last access.
+    Can be used only with *Log tables.
+
+    It’s optimized for storing many small *Log tables,
+    for which there is a long time interval between accesses.
+    """
+
+    def __int__(self, expiration_time_in_seconds: int):
+        self.expiration_time_in_seconds = expiration_time_in_seconds
+
+    def create_database_sql(self) -> str:
+        return f"Lazy({self.expiration_time_in_seconds})"
+
+
+class MySQL(DatabaseEngine):
+    """
+    Allows to connect to databases on a remote MySQL server and perform INSERT and
+    SELECT queries to exchange data between ClickHouse and MySQL.
+
+    The MySQL database engine translate queries to the MySQL server so you can perform operations
+    such as SHOW TABLES or SHOW CREATE TABLE.
+    """
+
+    def __int__(self, host: str, port: int, database: str, user: str, password: str):
+        """
+        - `host`: MySQL server address.
+        - `port`: MySQL server port.
+        - `database`: Remote database name.
+        - `user`: MySQL user.
+        - `password`: User password.
+        """
+        self.host_port = f"{host}:{port}"
+        self.database = database
+        self.user = user
+        self.password = password
+
+    def create_database_sql(self) -> str:
+        return f"MySQL('{self.host_port}', '{self.database}', '{self.user}', '{self.password}')"
+
+
+class PostgreSQL(DatabaseEngine):
+    """
+    Allows to connect to databases on a remote PostgreSQL server. Supports read and write operations
+     (SELECT and INSERT queries) to exchange data between ClickHouse and PostgreSQL.
+
+    Gives the real-time access to table list and table structure from
+    remote PostgreSQL with the help of SHOW TABLES and DESCRIBE TABLE queries.
+
+    Supports table structure modifications (ALTER TABLE ... ADD|DROP COLUMN).
+    If use_table_cache parameter (see the Engine Parameters below) it set to 1,
+    the table structure is cached and not checked for being modified,
+    but can be updated with DETACH and ATTACH queries.
+    """
+
+    def __int__(
+        self,
+        host: str,
+        port: int,
+        database: str,
+        user: str,
+        password: str,
+        schema: str = None,
+        use_table_cache: int = None,
+    ):
+        """
+        - `host`: PostgreSQL server address.
+        - `port`: PostgreSQL server port.
+        - `database`: Remote database name.
+        - `user`: PostgreSQL user.
+        - `password`: User password.
+        - `schema`: PostgreSQL schema.
+        - `use_table_cache`: Defines if the database table structure is cached or not.
+        """
+        self.host_port = f"{host}:{port}"
+        self.database = database
+        self.user = user
+        self.password = password
+        self.schema = schema
+        self.use_table_cache = use_table_cache
+        self._params = [
+            f"'{self.password}'",
+            f"'{self.database}'",
+            f"'{self.user}'",
+            f"'{self.password}'",
+        ]
+        if self.schema is not None:
+            self._params.append(f"'{self.schema}'")
+        if self.use_table_cache is not None:
+            self._params.append(str(self.use_table_cache))
+
+    def create_database_sql(self) -> str:
+        return f"PostgreSQL({','.join(self._params)})"
+
+
+class SQLite(DatabaseEngine):
+    """
+    Allows to connect to SQLite database and perform INSERT and SELECT queries to
+    exchange data between ClickHouse and SQLite.
+    """
+    def __init__(self, db_path: str):
+        """
+        - `db_path`: Path to a file with SQLite database.
+        """
+        self.db_path = db_path
+
+    def create_database_sql(self) -> str:
+        return f"SQLite('{self.db_path}')"
+
+
+class TinyLog(TableEngine):
     def create_table_sql(self, db):
         return "TinyLog"
 
 
-class Log(Engine):
+class Log(TableEngine):
     def create_table_sql(self, db):
         return "Log"
 
 
-class Memory(Engine):
+class Memory(TableEngine):
     def create_table_sql(self, db):
         return "Memory"
 
 
-class MergeTree(Engine):
+class MergeTree(TableEngine):
     def __init__(
         self,
         date_col: Optional[str] = None,
@@ -245,7 +371,7 @@ class ReplacingMergeTree(MergeTree):
         return params
 
 
-class Buffer(Engine):
+class Buffer(TableEngine):
     """
     Buffers the data to write in RAM, periodically flushing it to another table.
     Must be used in conjuction with a `BufferModel`.
@@ -289,7 +415,7 @@ class Buffer(Engine):
         return sql
 
 
-class Merge(Engine):
+class Merge(TableEngine):
     """
     The Merge engine (not to be confused with MergeTree) does not store data itself,
     but allows reading from any number of other tables simultaneously.
@@ -305,7 +431,7 @@ class Merge(Engine):
         return "Merge(`%s`, '%s')" % (db.db_name, self.table_regex)
 
 
-class Distributed(Engine):
+class Distributed(TableEngine):
     """
     The Distributed engine by itself does not store data,
     but allows distributed query processing on multiple servers.
@@ -360,4 +486,4 @@ class Distributed(Engine):
 
 
 # Expose only relevant classes in import *
-__all__ = get_subclass_names(locals(), Engine)
+__all__ = get_subclass_names(locals(), TableEngine)

src/clickhouse_orm/funcs.py

@@ -5,6 +5,8 @@ from types import FunctionType
 from .utils import is_iterable, comma_join, NO_VALUE, arg_to_sql
 from .query import Cond, QuerySet
 
+# pylint: disable=C0103,C0116
+
 
 def binary_operator(func):
     """
@@ -179,10 +181,10 @@ class FunctionOperatorsMixin:
         return F._not(self)
 
     def isIn(self, others):
-        return F._in(self, others)
+        return F._in(self, others)  # pylint: disable=W0212
 
     def isNotIn(self, others):
-        return F._notIn(self, others)
+        return F._notIn(self, others)  # pylint: disable=W0212
 
 
 class FMeta(type):
@@ -215,7 +217,8 @@ class FMeta(type):
     @staticmethod
     def _add_func(cls, base_func, new_name, extra_args):
         """
-        Adds a new func to the cls, based on the signature of the given base_func but with a new name.
+        Adds a new func to the cls, based on the signature of the given
+        base_func but with a new name.
         """
         # Get the function's signature
         sig = signature(base_func)
@@ -247,7 +250,7 @@ class FMeta(type):
         setattr(cls, new_name, new_func)
 
 
-class F(Cond, FunctionOperatorsMixin, metaclass=FMeta):
+class F(Cond, FunctionOperatorsMixin, metaclass=FMeta):  # pylint: disable=R0904
     """
     Represents a database function call and its arguments.
     It doubles as a query condition when the function returns a boolean result.
@@ -476,7 +479,7 @@ class F(Cond, FunctionOperatorsMixin, metaclass=FMeta):
         return F("toStartOfTenMinutes", d)
 
     @staticmethod
-    def toStartOfWeek(d, mode=0):
+    def toStartOfWeek(d):
         return F("toStartOfWeek", d)
 
     @staticmethod
@@ -572,8 +575,8 @@ class F(Cond, FunctionOperatorsMixin, metaclass=FMeta):
         return F("timeSlots", start_time, F.toUInt32(duration))
 
     @staticmethod
-    def formatDateTime(d, format, timezone=NO_VALUE):
+    def formatDateTime(d, fmt, timezone=NO_VALUE):
-        return F("formatDateTime", d, format, timezone)
+        return F("formatDateTime", d, fmt, timezone)
 
     @staticmethod
     def addDays(d, n, timezone=NO_VALUE):

src/clickhouse_orm/migrations.py

@@ -1,9 +1,12 @@
+import re
+import logging
+
 from .models import Model, BufferModel
 from .fields import DateField, StringField
 from .engines import MergeTree
 from .utils import get_subclass_names
 
-import logging
+# pylint: disable=R0903
 
 logger = logging.getLogger("migrations")
 
@@ -93,13 +96,15 @@ class AlterTable(ModelOperation):
                 self._alter_table(database, cmd)
 
             if is_regular_field:
-                # ALIAS and MATERIALIZED fields are not stored in the database, and raise DatabaseError
+                # ALIAS and MATERIALIZED fields are not stored in the database
+                # and raise DatabaseError
                 # (no AFTER column). So we will skip them
                 prev_name = name
 
         # Identify fields whose type was changed
         # 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
+        # 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, db=database)
@@ -159,7 +164,7 @@ class AlterConstraints(ModelOperation):
         logger.info("    Alter constraints for %s", self.table_name)
         existing = self._get_constraint_names(database)
         # Go over constraints in the model
-        for constraint in self.model_class._constraints.values():
+        for constraint in self.model_class._constraints.values():  # pylint: disable=W0212
             # Check if it's a new constraint
             if constraint.name not in existing:
                 logger.info("        Add constraint %s", constraint.name)
@@ -175,8 +180,6 @@ class AlterConstraints(ModelOperation):
         """
         Returns a set containing the names of existing constraints in the table.
         """
-        import re
-
         table_def = database.raw("SHOW CREATE TABLE $db.`%s`" % self.table_name)
         matches = re.findall(r"\sCONSTRAINT\s+`?(.+?)`?\s+CHECK\s", table_def)
         return set(matches)
@@ -204,7 +207,7 @@ class AlterIndexes(ModelOperation):
         existing = self._get_index_names(database)
         logger.info(existing)
         # Go over indexes in the model
-        for index in self.model_class._indexes.values():
+        for index in self.model_class._indexes.values():  # pylint: disable=W0212
             # Check if it's a new index
             if index.name not in existing:
                 logger.info("        Add index %s", index.name)
@@ -224,8 +227,6 @@ class AlterIndexes(ModelOperation):
         """
         Returns a set containing the names of existing indexes in the table.
         """
-        import re
-
         table_def = database.raw("SHOW CREATE TABLE $db.`%s`" % self.table_name)
         matches = re.findall(r"\sINDEX\s+`?(.+?)`?\s+", table_def)
         return set(matches)

src/clickhouse_orm/session.py

@@ -1,3 +1,11 @@
+"""
+ClickHouse sessions in the HTTP protocol.
+To do this, you need to use a context manager to add the session_id parameter to the request.
+By default, the session is terminated after 60 seconds of inactivity.
+
+https://clickhouse.com/docs/en/interfaces/http/
+"""
+
 import uuid
 from typing import Optional
 from contextvars import ContextVar, Token
@@ -7,6 +15,8 @@ ctx_session_timeout: ContextVar[float] = ContextVar("ck.session_timeout")
 
 
 class SessionContext:
+    """Session context manager"""
+
     def __init__(self, session: str, timeout: float):
         self.session = session
         self.timeout = timeout
@@ -24,5 +34,9 @@ class SessionContext:
 
 
 def in_session(session: Optional[str] = None, timeout: int = 60):
+    """
+    Add a session_id for subsequent requests
+    You can use this context manager safely in coroutines or threads
+    """
     session = session or str(uuid.uuid4())
     return SessionContext(session, timeout)

src/clickhouse_orm/system_models.py

@@ -30,7 +30,8 @@ class SystemPart(Model):
     partition = StringField()  # Name of the partition, in the format YYYYMM.
     name = StringField()  # Name of the part.
 
-    # This field is present in the docs (https://clickhouse.tech/docs/en/single/index.html#system-parts),
+    # This field is present in the docs
+    # https://clickhouse.tech/docs/en/single/index.html#system-parts
     # but is absent in ClickHouse (in version 1.1.54245)
     # replicated = UInt8Field()  # Whether the part belongs to replicated data.
 
@@ -44,7 +45,8 @@ class SystemPart(Model):
 
     bytes = UInt64Field()  # Number of bytes when compressed.
 
-    # Time the directory with the part was modified. Usually corresponds to the part's creation time.
+    # Time the directory with the part was modified.
+    # Usually corresponds to the part's creation time.
     modification_time = DateTimeField()
     remove_time = (
         DateTimeField()
@@ -166,7 +168,8 @@ class SystemPart(Model):
         Gets active data from system.parts table
 
         - `database`: A database object to fetch data from.
-        - `conditions`: WHERE clause conditions. Database and active conditions are added automatically
+        - `conditions`: WHERE clause conditions.
+            Database and active conditions are added automatically
 
         Returns: A list of SystemPart objects
         """