561 lines
20 KiB
Python
561 lines
20 KiB
Python
import time
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import warnings
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from collections import deque
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from contextlib import contextmanager
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from django.conf import settings
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from django.core.exceptions import ImproperlyConfigured
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from django.db import DEFAULT_DB_ALIAS
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from django.db.backends import utils
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from django.db.backends.signals import connection_created
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from django.db.transaction import TransactionManagementError
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from django.db.utils import DatabaseError, DatabaseErrorWrapper
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from django.utils import timezone
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from django.utils.functional import cached_property
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from django.utils.six.moves import _thread as thread
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try:
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import pytz
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except ImportError:
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pytz = None
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NO_DB_ALIAS = '__no_db__'
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class BaseDatabaseWrapper(object):
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"""
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Represents a database connection.
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"""
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# Mapping of Field objects to their column types.
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data_types = {}
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# Mapping of Field objects to their SQL suffix such as AUTOINCREMENT.
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data_types_suffix = {}
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# Mapping of Field objects to their SQL for CHECK constraints.
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data_type_check_constraints = {}
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ops = None
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vendor = 'unknown'
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SchemaEditorClass = None
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queries_limit = 9000
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def __init__(self, settings_dict, alias=DEFAULT_DB_ALIAS,
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allow_thread_sharing=False):
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# Connection related attributes.
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# The underlying database connection.
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self.connection = None
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# `settings_dict` should be a dictionary containing keys such as
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# NAME, USER, etc. It's called `settings_dict` instead of `settings`
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# to disambiguate it from Django settings modules.
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self.settings_dict = settings_dict
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self.alias = alias
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# Query logging in debug mode or when explicitly enabled.
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self.queries_log = deque(maxlen=self.queries_limit)
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self.force_debug_cursor = False
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# Transaction related attributes.
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# Tracks if the connection is in autocommit mode. Per PEP 249, by
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# default, it isn't.
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self.autocommit = False
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# Tracks if the connection is in a transaction managed by 'atomic'.
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self.in_atomic_block = False
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# Increment to generate unique savepoint ids.
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self.savepoint_state = 0
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# List of savepoints created by 'atomic'.
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self.savepoint_ids = []
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# Tracks if the outermost 'atomic' block should commit on exit,
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# ie. if autocommit was active on entry.
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self.commit_on_exit = True
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# Tracks if the transaction should be rolled back to the next
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# available savepoint because of an exception in an inner block.
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self.needs_rollback = False
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# Connection termination related attributes.
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self.close_at = None
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self.closed_in_transaction = False
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self.errors_occurred = False
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# Thread-safety related attributes.
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self.allow_thread_sharing = allow_thread_sharing
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self._thread_ident = thread.get_ident()
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@cached_property
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def timezone(self):
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"""
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Time zone for datetimes stored as naive values in the database.
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Returns a tzinfo object or None.
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This is only needed when time zone support is enabled and the database
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doesn't support time zones. (When the database supports time zones,
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the adapter handles aware datetimes so Django doesn't need to.)
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"""
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if not settings.USE_TZ:
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return None
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elif self.features.supports_timezones:
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return None
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elif self.settings_dict['TIME_ZONE'] is None:
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return timezone.utc
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else:
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# Only this branch requires pytz.
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return pytz.timezone(self.settings_dict['TIME_ZONE'])
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@cached_property
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def timezone_name(self):
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"""
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Name of the time zone of the database connection.
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"""
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if not settings.USE_TZ:
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return settings.TIME_ZONE
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elif self.settings_dict['TIME_ZONE'] is None:
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return 'UTC'
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else:
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return self.settings_dict['TIME_ZONE']
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@property
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def queries_logged(self):
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return self.force_debug_cursor or settings.DEBUG
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@property
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def queries(self):
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if len(self.queries_log) == self.queries_log.maxlen:
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warnings.warn(
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"Limit for query logging exceeded, only the last {} queries "
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"will be returned.".format(self.queries_log.maxlen))
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return list(self.queries_log)
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# ##### Backend-specific methods for creating connections and cursors #####
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def get_connection_params(self):
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"""Returns a dict of parameters suitable for get_new_connection."""
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raise NotImplementedError('subclasses of BaseDatabaseWrapper may require a get_connection_params() method')
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def get_new_connection(self, conn_params):
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"""Opens a connection to the database."""
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raise NotImplementedError('subclasses of BaseDatabaseWrapper may require a get_new_connection() method')
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def init_connection_state(self):
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"""Initializes the database connection settings."""
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raise NotImplementedError('subclasses of BaseDatabaseWrapper may require an init_connection_state() method')
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def create_cursor(self):
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"""Creates a cursor. Assumes that a connection is established."""
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raise NotImplementedError('subclasses of BaseDatabaseWrapper may require a create_cursor() method')
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# ##### Backend-specific methods for creating connections #####
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def connect(self):
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"""Connects to the database. Assumes that the connection is closed."""
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# Check for invalid configurations.
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self.check_settings()
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# In case the previous connection was closed while in an atomic block
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self.in_atomic_block = False
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self.savepoint_ids = []
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self.needs_rollback = False
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# Reset parameters defining when to close the connection
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max_age = self.settings_dict['CONN_MAX_AGE']
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self.close_at = None if max_age is None else time.time() + max_age
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self.closed_in_transaction = False
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self.errors_occurred = False
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# Establish the connection
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conn_params = self.get_connection_params()
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self.connection = self.get_new_connection(conn_params)
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self.set_autocommit(self.settings_dict['AUTOCOMMIT'])
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self.init_connection_state()
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connection_created.send(sender=self.__class__, connection=self)
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def check_settings(self):
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if self.settings_dict['TIME_ZONE'] is not None:
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if not settings.USE_TZ:
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raise ImproperlyConfigured(
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"Connection '%s' cannot set TIME_ZONE because USE_TZ is "
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"False." % self.alias)
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elif self.features.supports_timezones:
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raise ImproperlyConfigured(
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"Connection '%s' cannot set TIME_ZONE because its engine "
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"handles time zones conversions natively." % self.alias)
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elif pytz is None:
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raise ImproperlyConfigured(
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"Connection '%s' cannot set TIME_ZONE because pytz isn't "
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"installed." % self.alias)
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def ensure_connection(self):
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"""
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Guarantees that a connection to the database is established.
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"""
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if self.connection is None:
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with self.wrap_database_errors:
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self.connect()
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# ##### Backend-specific wrappers for PEP-249 connection methods #####
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def _cursor(self):
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self.ensure_connection()
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with self.wrap_database_errors:
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return self.create_cursor()
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def _commit(self):
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if self.connection is not None:
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with self.wrap_database_errors:
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return self.connection.commit()
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def _rollback(self):
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if self.connection is not None:
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with self.wrap_database_errors:
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return self.connection.rollback()
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def _close(self):
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if self.connection is not None:
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with self.wrap_database_errors:
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return self.connection.close()
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# ##### Generic wrappers for PEP-249 connection methods #####
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def cursor(self):
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"""
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Creates a cursor, opening a connection if necessary.
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"""
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self.validate_thread_sharing()
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if self.queries_logged:
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cursor = self.make_debug_cursor(self._cursor())
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else:
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cursor = self.make_cursor(self._cursor())
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return cursor
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def commit(self):
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"""
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Commits a transaction and resets the dirty flag.
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"""
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self.validate_thread_sharing()
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self.validate_no_atomic_block()
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self._commit()
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# A successful commit means that the database connection works.
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self.errors_occurred = False
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def rollback(self):
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"""
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Rolls back a transaction and resets the dirty flag.
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"""
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self.validate_thread_sharing()
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self.validate_no_atomic_block()
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self._rollback()
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# A successful rollback means that the database connection works.
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self.errors_occurred = False
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def close(self):
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"""
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Closes the connection to the database.
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"""
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self.validate_thread_sharing()
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# Don't call validate_no_atomic_block() to avoid making it difficult
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# to get rid of a connection in an invalid state. The next connect()
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# will reset the transaction state anyway.
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if self.closed_in_transaction or self.connection is None:
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return
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try:
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self._close()
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finally:
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if self.in_atomic_block:
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self.closed_in_transaction = True
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self.needs_rollback = True
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else:
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self.connection = None
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# ##### Backend-specific savepoint management methods #####
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def _savepoint(self, sid):
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with self.cursor() as cursor:
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cursor.execute(self.ops.savepoint_create_sql(sid))
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def _savepoint_rollback(self, sid):
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with self.cursor() as cursor:
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cursor.execute(self.ops.savepoint_rollback_sql(sid))
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def _savepoint_commit(self, sid):
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with self.cursor() as cursor:
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cursor.execute(self.ops.savepoint_commit_sql(sid))
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def _savepoint_allowed(self):
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# Savepoints cannot be created outside a transaction
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return self.features.uses_savepoints and not self.get_autocommit()
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# ##### Generic savepoint management methods #####
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def savepoint(self):
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"""
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Creates a savepoint inside the current transaction. Returns an
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identifier for the savepoint that will be used for the subsequent
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rollback or commit. Does nothing if savepoints are not supported.
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"""
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if not self._savepoint_allowed():
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return
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thread_ident = thread.get_ident()
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tid = str(thread_ident).replace('-', '')
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self.savepoint_state += 1
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sid = "s%s_x%d" % (tid, self.savepoint_state)
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self.validate_thread_sharing()
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self._savepoint(sid)
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return sid
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def savepoint_rollback(self, sid):
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"""
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Rolls back to a savepoint. Does nothing if savepoints are not supported.
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"""
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if not self._savepoint_allowed():
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return
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self.validate_thread_sharing()
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self._savepoint_rollback(sid)
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def savepoint_commit(self, sid):
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"""
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Releases a savepoint. Does nothing if savepoints are not supported.
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"""
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if not self._savepoint_allowed():
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return
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self.validate_thread_sharing()
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self._savepoint_commit(sid)
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def clean_savepoints(self):
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"""
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Resets the counter used to generate unique savepoint ids in this thread.
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"""
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self.savepoint_state = 0
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# ##### Backend-specific transaction management methods #####
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def _set_autocommit(self, autocommit):
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"""
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Backend-specific implementation to enable or disable autocommit.
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"""
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raise NotImplementedError('subclasses of BaseDatabaseWrapper may require a _set_autocommit() method')
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# ##### Generic transaction management methods #####
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def get_autocommit(self):
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"""
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Check the autocommit state.
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"""
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self.ensure_connection()
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return self.autocommit
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def set_autocommit(self, autocommit):
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"""
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Enable or disable autocommit.
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"""
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self.validate_no_atomic_block()
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self.ensure_connection()
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self._set_autocommit(autocommit)
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self.autocommit = autocommit
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def get_rollback(self):
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"""
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Get the "needs rollback" flag -- for *advanced use* only.
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"""
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if not self.in_atomic_block:
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raise TransactionManagementError(
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"The rollback flag doesn't work outside of an 'atomic' block.")
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return self.needs_rollback
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def set_rollback(self, rollback):
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"""
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Set or unset the "needs rollback" flag -- for *advanced use* only.
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"""
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if not self.in_atomic_block:
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raise TransactionManagementError(
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"The rollback flag doesn't work outside of an 'atomic' block.")
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self.needs_rollback = rollback
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def validate_no_atomic_block(self):
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"""
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Raise an error if an atomic block is active.
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"""
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if self.in_atomic_block:
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raise TransactionManagementError(
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"This is forbidden when an 'atomic' block is active.")
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def validate_no_broken_transaction(self):
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if self.needs_rollback:
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raise TransactionManagementError(
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"An error occurred in the current transaction. You can't "
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"execute queries until the end of the 'atomic' block.")
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# ##### Foreign key constraints checks handling #####
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@contextmanager
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def constraint_checks_disabled(self):
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"""
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Context manager that disables foreign key constraint checking.
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"""
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disabled = self.disable_constraint_checking()
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try:
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yield
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finally:
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if disabled:
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self.enable_constraint_checking()
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def disable_constraint_checking(self):
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"""
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Backends can implement as needed to temporarily disable foreign key
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constraint checking. Should return True if the constraints were
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disabled and will need to be reenabled.
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"""
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return False
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def enable_constraint_checking(self):
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"""
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Backends can implement as needed to re-enable foreign key constraint
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checking.
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"""
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pass
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def check_constraints(self, table_names=None):
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"""
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Backends can override this method if they can apply constraint
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checking (e.g. via "SET CONSTRAINTS ALL IMMEDIATE"). Should raise an
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IntegrityError if any invalid foreign key references are encountered.
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"""
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pass
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# ##### Connection termination handling #####
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def is_usable(self):
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"""
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Tests if the database connection is usable.
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This function may assume that self.connection is not None.
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Actual implementations should take care not to raise exceptions
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as that may prevent Django from recycling unusable connections.
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"""
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raise NotImplementedError(
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"subclasses of BaseDatabaseWrapper may require an is_usable() method")
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def close_if_unusable_or_obsolete(self):
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"""
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Closes the current connection if unrecoverable errors have occurred,
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or if it outlived its maximum age.
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"""
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if self.connection is not None:
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# If the application didn't restore the original autocommit setting,
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# don't take chances, drop the connection.
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if self.get_autocommit() != self.settings_dict['AUTOCOMMIT']:
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self.close()
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return
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# If an exception other than DataError or IntegrityError occurred
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# since the last commit / rollback, check if the connection works.
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if self.errors_occurred:
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if self.is_usable():
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self.errors_occurred = False
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else:
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self.close()
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return
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if self.close_at is not None and time.time() >= self.close_at:
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self.close()
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return
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# ##### Thread safety handling #####
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def validate_thread_sharing(self):
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"""
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Validates that the connection isn't accessed by another thread than the
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one which originally created it, unless the connection was explicitly
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authorized to be shared between threads (via the `allow_thread_sharing`
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property). Raises an exception if the validation fails.
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"""
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if not (self.allow_thread_sharing
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or self._thread_ident == thread.get_ident()):
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raise DatabaseError("DatabaseWrapper objects created in a "
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"thread can only be used in that same thread. The object "
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"with alias '%s' was created in thread id %s and this is "
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"thread id %s."
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% (self.alias, self._thread_ident, thread.get_ident()))
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# ##### Miscellaneous #####
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def prepare_database(self):
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"""
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Hook to do any database check or preparation, generally called before
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migrating a project or an app.
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"""
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pass
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@cached_property
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def wrap_database_errors(self):
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"""
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Context manager and decorator that re-throws backend-specific database
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exceptions using Django's common wrappers.
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"""
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return DatabaseErrorWrapper(self)
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def make_debug_cursor(self, cursor):
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"""
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Creates a cursor that logs all queries in self.queries_log.
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"""
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return utils.CursorDebugWrapper(cursor, self)
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def make_cursor(self, cursor):
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"""
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Creates a cursor without debug logging.
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"""
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return utils.CursorWrapper(cursor, self)
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@contextmanager
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def temporary_connection(self):
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"""
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Context manager that ensures that a connection is established, and
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if it opened one, closes it to avoid leaving a dangling connection.
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This is useful for operations outside of the request-response cycle.
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Provides a cursor: with self.temporary_connection() as cursor: ...
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"""
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must_close = self.connection is None
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cursor = self.cursor()
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try:
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yield cursor
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finally:
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cursor.close()
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if must_close:
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self.close()
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@cached_property
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def _nodb_connection(self):
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"""
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Alternative connection to be used when there is no need to access
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the main database, specifically for test db creation/deletion.
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This also prevents the production database from being exposed to
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potential child threads while (or after) the test database is destroyed.
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Refs #10868, #17786, #16969.
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"""
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settings_dict = self.settings_dict.copy()
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settings_dict['NAME'] = None
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nodb_connection = self.__class__(
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settings_dict,
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alias=NO_DB_ALIAS,
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allow_thread_sharing=False)
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return nodb_connection
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def _start_transaction_under_autocommit(self):
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"""
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Only required when autocommits_when_autocommit_is_off = True.
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"""
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raise NotImplementedError(
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'subclasses of BaseDatabaseWrapper may require a '
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'_start_transaction_under_autocommit() method'
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)
|
|
|
|
def schema_editor(self, *args, **kwargs):
|
|
"""
|
|
Returns a new instance of this backend's SchemaEditor.
|
|
"""
|
|
if self.SchemaEditorClass is None:
|
|
raise NotImplementedError(
|
|
'The SchemaEditorClass attribute of this database wrapper is still None')
|
|
return self.SchemaEditorClass(self, *args, **kwargs)
|