Support for temporary tables

src/clickhouse_orm/database.py

@@ -156,6 +156,7 @@ class Database(object):
             raise DatabaseException("You can't create system table")
         if getattr(model_class, 'engine') is None:
             raise DatabaseException("%s class must define an engine" % model_class.__name__)
+        print(model_class.create_table_sql(self))
         self._send(model_class.create_table_sql(self))
 
     def drop_table(self, model_class: Type[MODEL]) -> None:
@@ -435,6 +436,8 @@ class Database(object):
             if model_class:
                 if model_class.is_system_model():
                     mapping['table'] = "`system`.`%s`" % model_class.table_name()
+                elif model_class.is_temporary_model():
+                    mapping['table'] = "`%s`" % model_class.table_name()
                 else:
                     mapping['table'] = "`%s`.`%s`" % (self.db_name, model_class.table_name())
             query = Template(query).safe_substitute(mapping)

src/clickhouse_orm/engines.py

@@ -92,9 +92,11 @@ class MergeTree(Engine):
         elif not self.date_col:
             # Can't import it globally due to circular import
             from clickhouse_orm.database import DatabaseException
-            raise DatabaseException("Custom partitioning is not supported before ClickHouse 1.1.54310. "
+            raise DatabaseException(
-                                    "Please update your server or use date_col syntax."
+                "Custom partitioning is not supported before ClickHouse 1.1.54310. "
-                                    "https://clickhouse.tech/docs/en/table_engines/custom_partitioning_key/")
+                "Please update your server or use date_col syntax."
+                "https://clickhouse.tech/docs/en/table_engines/custom_partitioning_key/"
+            )
         else:
             partition_sql = ''
 

src/clickhouse_orm/models.py

@@ -11,7 +11,7 @@ from .fields import Field, StringField
 from .utils import parse_tsv, NO_VALUE, get_subclass_names, arg_to_sql
 from .query import QuerySet
 from .funcs import F
-from .engines import Merge, Distributed
+from .engines import Merge, Distributed, Memory
 
 logger = getLogger('clickhouse_orm')
 
@@ -273,6 +273,8 @@ class Model(metaclass=ModelBase):
     # Create table, drop table, insert operations are restricted for system models
     _system = False
 
+    _temporary = False
+
     _database = None
 
     _fields: Dict[str, Field]
@@ -483,6 +485,13 @@ class Model(metaclass=ModelBase):
         """
         return cls._system
 
+    @classmethod
+    def is_temporary_model(cls):
+        """
+        Returns true if the model represents a temporary table.
+        """
+        return cls._temporary
+
 
 class BufferModel(Model):
 
@@ -603,8 +612,6 @@ class DistributedModel(Model):
         """
         assert isinstance(cls.engine, Distributed), "engine must be engines.Distributed instance"
 
-        cls.fix_engine_table()
-
         parts = [
             'CREATE TABLE IF NOT EXISTS `{0}`.`{1}` AS `{0}`.`{2}`'.format(
                 db.db_name, cls.table_name(), cls.engine.table_name),
@@ -612,6 +619,44 @@ class DistributedModel(Model):
         return '\n'.join(parts)
 
 
+class TemporaryModel(Model):
+    """Temporary Tables
+
+    Temporary tables disappear when the session ends, including if the connection is lost.
+    A temporary table uses the Memory engine only.
+    The DB can’t be specified for a temporary table. It is created outside of databases.
+    Impossible to create a temporary table with distributed DDL query on all cluster servers
+    (by using ON CLUSTER): this table exists only in the current session.
+    If a temporary table has the same name as another one and a query specifies the table name
+    without specifying the DB, the temporary table will be used.
+    For distributed query processing, temporary tables used in a query are passed to remote servers.
+
+    https://clickhouse.com/docs/en/sql-reference/statements/create/table/#temporary-tables
+    """
+    _temporary = True
+
+    @classmethod
+    def create_table_sql(cls, db) -> str:
+        assert isinstance(cls.engine, Memory), "engine must be engines.Memory instance"
+
+        parts = ['CREATE TEMPORARY TABLE IF NOT EXISTS `%s` (' % cls.table_name()]
+        # Fields
+        items = []
+        for name, field in cls.fields().items():
+            items.append('    %s %s' % (name, field.get_sql(db=db)))
+        # Constraints
+        for c in cls._constraints.values():
+            items.append('    %s' % c.create_table_sql())
+        # Indexes
+        for i in cls._indexes.values():
+            items.append('    %s' % i.create_table_sql())
+        parts.append(',\n'.join(items))
+        # Engine
+        parts.append(')')
+        parts.append('ENGINE = Memory')
+        return '\n'.join(parts)
+
+
 # Expose only relevant classes in import *
 MODEL = TypeVar('MODEL', bound=Model)
 __all__ = get_subclass_names(locals(), (Model, Constraint, Index))

src/clickhouse_orm/session.py

@@ -13,9 +13,10 @@ class SessionContext:
         self.token1 = None
         self.token2 = None
 
-    def __enter__(self):
+    def __enter__(self) -> str:
         self.token1 = ctx_session_id.set(self.session)
         self.token2 = ctx_session_timeout.set(self.timeout)
+        return self.session
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         ctx_session_id.reset(self.token1)