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schema.py
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schema.py
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from django.conf import settings
from django.db.backends.postgresql.schema import DatabaseSchemaEditor
from timescale.db.models.fields import TimescaleDateTimeField
class TimescaleSchemaEditor(DatabaseSchemaEditor):
sql_is_hypertable = '''SELECT * FROM timescaledb_information.hypertables
WHERE hypertable_name = {table}{extra_condition}'''
sql_assert_is_hypertable = (
'DO $do$ BEGIN '
'IF EXISTS ( '
+ sql_is_hypertable +
') '
'THEN NULL; '
'ELSE RAISE EXCEPTION {error_message}; '
'END IF;'
'END; $do$'
)
sql_assert_is_not_hypertable = (
'DO $do$ BEGIN '
'IF EXISTS ( '
+ sql_is_hypertable +
') '
'THEN RAISE EXCEPTION {error_message}; '
'ELSE NULL; '
'END IF;'
'END; $do$'
)
sql_drop_primary_key = 'ALTER TABLE {table} DROP CONSTRAINT {pkey}'
sql_add_hypertable = (
"SELECT create_hypertable("
"{table}, {partition_column}, "
"chunk_time_interval => interval {interval}, "
"migrate_data => {migrate})"
)
sql_set_chunk_time_interval = 'SELECT set_chunk_time_interval({table}, interval {interval})'
sql_hypertable_is_in_schema = '''hypertable_schema = {schema_name}'''
def _assert_is_hypertable(self, model):
"""
Assert if the table is a hyper table
"""
table = self.quote_value(model._meta.db_table)
error_message = self.quote_value("assert failed - " + table + " should be a hyper table")
extra_condition = self._get_extra_condition()
sql = self.sql_assert_is_hypertable.format(table=table, error_message=error_message,
extra_condition=extra_condition)
self.execute(sql)
def _assert_is_not_hypertable(self, model):
"""
Assert if the table is not a hyper table
"""
table = self.quote_value(model._meta.db_table)
error_message = self.quote_value("assert failed - " + table + " should not be a hyper table")
extra_condition = self._get_extra_condition()
sql = self.sql_assert_is_not_hypertable.format(table=table, error_message=error_message,
extra_condition=extra_condition)
self.execute(sql)
def _drop_primary_key(self, model):
"""
Hypertables can't partition if the primary key is not
the partition column.
So we drop the mandatory primary key django creates.
"""
db_table = model._meta.db_table
table = self.quote_name(db_table)
pkey = self.quote_name(f'{db_table}_pkey')
sql = self.sql_drop_primary_key.format(table=table, pkey=pkey)
self.execute(sql)
def _create_hypertable(self, model, field, should_migrate=False):
"""
Create the hypertable with the partition column being the field.
"""
# assert that the table is not already a hypertable
self._assert_is_not_hypertable(model)
# drop primary key of the table
self._drop_primary_key(model)
partition_column = self.quote_value(field.column)
interval = self.quote_value(field.interval)
table = self.quote_value(model._meta.db_table)
migrate = "true" if should_migrate else "false"
if should_migrate and getattr(settings, "TIMESCALE_MIGRATE_HYPERTABLE_WITH_FRESH_TABLE", False):
# TODO migrate with fresh table [https://github.com/schlunsen/django-timescaledb/issues/16]
raise NotImplementedError()
else:
sql = self.sql_add_hypertable.format(
table=table, partition_column=partition_column, interval=interval, migrate=migrate
)
self.execute(sql)
def _set_chunk_time_interval(self, model, field):
"""
Change time interval for hypertable
"""
# assert if already a hypertable
self._assert_is_hypertable(model)
table = self.quote_value(model._meta.db_table)
interval = self.quote_value(field.interval)
sql = self.sql_set_chunk_time_interval.format(table=table, interval=interval)
self.execute(sql)
def create_model(self, model):
super().create_model(model)
# scan if any field is of instance `TimescaleDateTimeField`
for field in model._meta.local_fields:
if isinstance(field, TimescaleDateTimeField):
# create hypertable, with the field as partition column
self._create_hypertable(model, field)
break
def add_field(self, model, field):
super().add_field(model, field)
# check if this field is type `TimescaleDateTimeField`
if isinstance(field, TimescaleDateTimeField):
# migrate existing table to hypertable
self._create_hypertable(model, field, True)
def alter_field(self, model, old_field, new_field, strict=False):
super().alter_field(model, old_field, new_field, strict)
# check if old_field is not type `TimescaleDateTimeField` and new_field is
if not isinstance(old_field, TimescaleDateTimeField) and isinstance(new_field, TimescaleDateTimeField):
# migrate existing table to hypertable
self._create_hypertable(model, new_field, True)
# check if old_field and new_field is type `TimescaleDateTimeField` and `interval` is changed
elif isinstance(old_field, TimescaleDateTimeField) and isinstance(new_field, TimescaleDateTimeField) \
and old_field.interval != new_field.interval:
# change chunk-size
self._set_chunk_time_interval(model, new_field)
def _get_extra_condition(self):
extra_condition = ''
try:
if self.connection.schema_name:
schema_name = self.quote_value(self.connection.schema_name)
extra_condition = ' AND ' + self.sql_hypertable_is_in_schema.format(schema_name=schema_name)
except:
pass
return extra_condition