django/db/backends/base/base.py
import _thread
import copy
import datetime
import logging
import threading
import time
import warnings
import zoneinfo
from collections import deque
from contextlib import contextmanager
from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.db import DEFAULT_DB_ALIAS, DatabaseError, NotSupportedError
from django.db.backends import utils
from django.db.backends.base.validation import BaseDatabaseValidation
from django.db.backends.signals import connection_created
from django.db.backends.utils import debug_transaction
from django.db.transaction import TransactionManagementError
from django.db.utils import DatabaseErrorWrapper, ProgrammingError
from django.utils.asyncio import async_unsafe
from django.utils.functional import cached_property
NO_DB_ALIAS = "__no_db__"
RAN_DB_VERSION_CHECK = set()
logger = logging.getLogger("django.db.backends.base")
class BaseDatabaseWrapper:
"""Represent a database connection."""
# Mapping of Field objects to their column types.
data_types = {}
# Mapping of Field objects to their SQL suffix such as AUTOINCREMENT.
data_types_suffix = {}
# Mapping of Field objects to their SQL for CHECK constraints.
data_type_check_constraints = {}
ops = None
vendor = "unknown"
display_name = "unknown"
SchemaEditorClass = None
# Classes instantiated in __init__().
client_class = None
creation_class = None
features_class = None
introspection_class = None
ops_class = None
validation_class = BaseDatabaseValidation
queries_limit = 9000
def __init__(self, settings_dict, alias=DEFAULT_DB_ALIAS):
# Connection related attributes.
# The underlying database connection.
self.connection = None
# `settings_dict` should be a dictionary containing keys such as
# NAME, USER, etc. It's called `settings_dict` instead of `settings`
# to disambiguate it from Django settings modules.
self.settings_dict = settings_dict
self.alias = alias
# Query logging in debug mode or when explicitly enabled.
self.queries_log = deque(maxlen=self.queries_limit)
self.force_debug_cursor = False
# Transaction related attributes.
# Tracks if the connection is in autocommit mode. Per PEP 249, by
# default, it isn't.
self.autocommit = False
# Tracks if the connection is in a transaction managed by 'atomic'.
self.in_atomic_block = False
# Increment to generate unique savepoint ids.
self.savepoint_state = 0
# List of savepoints created by 'atomic'.
self.savepoint_ids = []
# Stack of active 'atomic' blocks.
self.atomic_blocks = []
# Tracks if the outermost 'atomic' block should commit on exit,
# ie. if autocommit was active on entry.
self.commit_on_exit = True
# Tracks if the transaction should be rolled back to the next
# available savepoint because of an exception in an inner block.
self.needs_rollback = False
self.rollback_exc = None
# Connection termination related attributes.
self.close_at = None
self.closed_in_transaction = False
self.errors_occurred = False
self.health_check_enabled = False
self.health_check_done = False
# Thread-safety related attributes.
self._thread_sharing_lock = threading.Lock()
self._thread_sharing_count = 0
self._thread_ident = _thread.get_ident()
# A list of no-argument functions to run when the transaction commits.
# Each entry is an (sids, func, robust) tuple, where sids is a set of
# the active savepoint IDs when this function was registered and robust
# specifies whether it's allowed for the function to fail.
self.run_on_commit = []
# Should we run the on-commit hooks the next time set_autocommit(True)
# is called?
self.run_commit_hooks_on_set_autocommit_on = False
# A stack of wrappers to be invoked around execute()/executemany()
# calls. Each entry is a function taking five arguments: execute, sql,
# params, many, and context. It's the function's responsibility to
# call execute(sql, params, many, context).
self.execute_wrappers = []
self.client = self.client_class(self)
self.creation = self.creation_class(self)
self.features = self.features_class(self)
self.introspection = self.introspection_class(self)
self.ops = self.ops_class(self)
self.validation = self.validation_class(self)
def __repr__(self):
return (
f"<{self.__class__.__qualname__} "
f"vendor={self.vendor!r} alias={self.alias!r}>"
)
def ensure_timezone(self):
"""
Ensure the connection's timezone is set to `self.timezone_name` and
return whether it changed or not.
"""
return False
@cached_property
def timezone(self):
"""
Return a tzinfo of the database connection time zone.
This is only used when time zone support is enabled. When a datetime is
read from the database, it is always returned in this time zone.
When the database backend supports time zones, it doesn't matter which
time zone Django uses, as long as aware datetimes are used everywhere.
Other users connecting to the database can choose their own time zone.
When the database backend doesn't support time zones, the time zone
Django uses may be constrained by the requirements of other users of
the database.
"""
if not settings.USE_TZ:
return None
elif self.settings_dict["TIME_ZONE"] is None:
return datetime.timezone.utc
else:
return zoneinfo.ZoneInfo(self.settings_dict["TIME_ZONE"])
@cached_property
def timezone_name(self):
"""
Name of the time zone of the database connection.
"""
if not settings.USE_TZ:
return settings.TIME_ZONE
elif self.settings_dict["TIME_ZONE"] is None:
return "UTC"
else:
return self.settings_dict["TIME_ZONE"]
@property
def queries_logged(self):
return self.force_debug_cursor or settings.DEBUG
@property
def queries(self):
if len(self.queries_log) == self.queries_log.maxlen:
warnings.warn(
"Limit for query logging exceeded, only the last {} queries "
"will be returned.".format(self.queries_log.maxlen)
)
return list(self.queries_log)
def get_database_version(self):
"""Return a tuple of the database's version."""
raise NotImplementedError(
"subclasses of BaseDatabaseWrapper may require a get_database_version() "
"method."
)
def check_database_version_supported(self):
"""
Raise an error if the database version isn't supported by this
version of Django.
"""
if (
self.features.minimum_database_version is not None
and self.get_database_version() < self.features.minimum_database_version
):
db_version = ".".join(map(str, self.get_database_version()))
min_db_version = ".".join(map(str, self.features.minimum_database_version))
raise NotSupportedError(
f"{self.display_name} {min_db_version} or later is required "
f"(found {db_version})."
)
# ##### Backend-specific methods for creating connections and cursors #####
def get_connection_params(self):
"""Return a dict of parameters suitable for get_new_connection."""
raise NotImplementedError(
"subclasses of BaseDatabaseWrapper may require a get_connection_params() "
"method"
)
def get_new_connection(self, conn_params):
"""Open a connection to the database."""
raise NotImplementedError(
"subclasses of BaseDatabaseWrapper may require a get_new_connection() "
"method"
)
def init_connection_state(self):
"""Initialize the database connection settings."""
global RAN_DB_VERSION_CHECK
if self.alias not in RAN_DB_VERSION_CHECK:
self.check_database_version_supported()
RAN_DB_VERSION_CHECK.add(self.alias)
def create_cursor(self, name=None):
"""Create a cursor. Assume that a connection is established."""
raise NotImplementedError(
"subclasses of BaseDatabaseWrapper may require a create_cursor() method"
)
# ##### Backend-specific methods for creating connections #####
@async_unsafe
def connect(self):
"""Connect to the database. Assume that the connection is closed."""
# Check for invalid configurations.
self.check_settings()
# In case the previous connection was closed while in an atomic block
self.in_atomic_block = False
self.savepoint_ids = []
self.atomic_blocks = []
self.needs_rollback = False
# Reset parameters defining when to close/health-check the connection.
self.health_check_enabled = self.settings_dict["CONN_HEALTH_CHECKS"]
max_age = self.settings_dict["CONN_MAX_AGE"]
self.close_at = None if max_age is None else time.monotonic() + max_age
self.closed_in_transaction = False
self.errors_occurred = False
# New connections are healthy.
self.health_check_done = True
# Establish the connection
conn_params = self.get_connection_params()
self.connection = self.get_new_connection(conn_params)
self.set_autocommit(self.settings_dict["AUTOCOMMIT"])
self.init_connection_state()
connection_created.send(sender=self.__class__, connection=self)
self.run_on_commit = []
def check_settings(self):
if self.settings_dict["TIME_ZONE"] is not None and not settings.USE_TZ:
raise ImproperlyConfigured(
"Connection '%s' cannot set TIME_ZONE because USE_TZ is False."
% self.alias
)
@async_unsafe
def ensure_connection(self):
"""Guarantee that a connection to the database is established."""
if self.connection is None:
if self.in_atomic_block and self.closed_in_transaction:
raise ProgrammingError(
"Cannot open a new connection in an atomic block."
)
with self.wrap_database_errors:
self.connect()
# ##### Backend-specific wrappers for PEP-249 connection methods #####
def _prepare_cursor(self, cursor):
"""
Validate the connection is usable and perform database cursor wrapping.
"""
self.validate_thread_sharing()
if self.queries_logged:
wrapped_cursor = self.make_debug_cursor(cursor)
else:
wrapped_cursor = self.make_cursor(cursor)
return wrapped_cursor
def _cursor(self, name=None):
self.close_if_health_check_failed()
self.ensure_connection()
with self.wrap_database_errors:
return self._prepare_cursor(self.create_cursor(name))
def _commit(self):
if self.connection is not None:
with debug_transaction(self, "COMMIT"), self.wrap_database_errors:
return self.connection.commit()
def _rollback(self):
if self.connection is not None:
with debug_transaction(self, "ROLLBACK"), self.wrap_database_errors:
return self.connection.rollback()
def _close(self):
if self.connection is not None:
with self.wrap_database_errors:
return self.connection.close()
# ##### Generic wrappers for PEP-249 connection methods #####
@async_unsafe
def cursor(self):
"""Create a cursor, opening a connection if necessary."""
return self._cursor()
@async_unsafe
def commit(self):
"""Commit a transaction and reset the dirty flag."""
self.validate_thread_sharing()
self.validate_no_atomic_block()
self._commit()
# A successful commit means that the database connection works.
self.errors_occurred = False
self.run_commit_hooks_on_set_autocommit_on = True
@async_unsafe
def rollback(self):
"""Roll back a transaction and reset the dirty flag."""
self.validate_thread_sharing()
self.validate_no_atomic_block()
self._rollback()
# A successful rollback means that the database connection works.
self.errors_occurred = False
self.needs_rollback = False
self.run_on_commit = []
@async_unsafe
def close(self):
"""Close the connection to the database."""
self.validate_thread_sharing()
self.run_on_commit = []
# Don't call validate_no_atomic_block() to avoid making it difficult
# to get rid of a connection in an invalid state. The next connect()
# will reset the transaction state anyway.
if self.closed_in_transaction or self.connection is None:
return
try:
self._close()
finally:
if self.in_atomic_block:
self.closed_in_transaction = True
self.needs_rollback = True
else:
self.connection = None
# ##### Backend-specific savepoint management methods #####
def _savepoint(self, sid):
with self.cursor() as cursor:
cursor.execute(self.ops.savepoint_create_sql(sid))
def _savepoint_rollback(self, sid):
with self.cursor() as cursor:
cursor.execute(self.ops.savepoint_rollback_sql(sid))
def _savepoint_commit(self, sid):
with self.cursor() as cursor:
cursor.execute(self.ops.savepoint_commit_sql(sid))
def _savepoint_allowed(self):
# Savepoints cannot be created outside a transaction
return self.features.uses_savepoints and not self.get_autocommit()
# ##### Generic savepoint management methods #####
@async_unsafe
def savepoint(self):
"""
Create a savepoint inside the current transaction. Return an
identifier for the savepoint that will be used for the subsequent
rollback or commit. Do nothing if savepoints are not supported.
"""
if not self._savepoint_allowed():
return
thread_ident = _thread.get_ident()
tid = str(thread_ident).replace("-", "")
self.savepoint_state += 1
sid = "s%s_x%d" % (tid, self.savepoint_state)
self.validate_thread_sharing()
self._savepoint(sid)
return sid
@async_unsafe
def savepoint_rollback(self, sid):
"""
Roll back to a savepoint. Do nothing if savepoints are not supported.
"""
if not self._savepoint_allowed():
return
self.validate_thread_sharing()
self._savepoint_rollback(sid)
# Remove any callbacks registered while this savepoint was active.
self.run_on_commit = [
(sids, func, robust)
for (sids, func, robust) in self.run_on_commit
if sid not in sids
]
@async_unsafe
def savepoint_commit(self, sid):
"""
Release a savepoint. Do nothing if savepoints are not supported.
"""
if not self._savepoint_allowed():
return
self.validate_thread_sharing()
self._savepoint_commit(sid)
@async_unsafe
def clean_savepoints(self):
"""
Reset the counter used to generate unique savepoint ids in this thread.
"""
self.savepoint_state = 0
# ##### Backend-specific transaction management methods #####
def _set_autocommit(self, autocommit):
"""
Backend-specific implementation to enable or disable autocommit.
"""
raise NotImplementedError(
"subclasses of BaseDatabaseWrapper may require a _set_autocommit() method"
)
# ##### Generic transaction management methods #####
def get_autocommit(self):
"""Get the autocommit state."""
self.ensure_connection()
return self.autocommit
def set_autocommit(
self, autocommit, force_begin_transaction_with_broken_autocommit=False
):
"""
Enable or disable autocommit.
The usual way to start a transaction is to turn autocommit off.
SQLite does not properly start a transaction when disabling
autocommit. To avoid this buggy behavior and to actually enter a new
transaction, an explicit BEGIN is required. Using
force_begin_transaction_with_broken_autocommit=True will issue an
explicit BEGIN with SQLite. This option will be ignored for other
backends.
"""
self.validate_no_atomic_block()
self.close_if_health_check_failed()
self.ensure_connection()
start_transaction_under_autocommit = (
force_begin_transaction_with_broken_autocommit
and not autocommit
and hasattr(self, "_start_transaction_under_autocommit")
)
if start_transaction_under_autocommit:
self._start_transaction_under_autocommit()
elif autocommit:
self._set_autocommit(autocommit)
else:
with debug_transaction(self, "BEGIN"):
self._set_autocommit(autocommit)
self.autocommit = autocommit
if autocommit and self.run_commit_hooks_on_set_autocommit_on:
self.run_and_clear_commit_hooks()
self.run_commit_hooks_on_set_autocommit_on = False
def get_rollback(self):
"""Get the "needs rollback" flag -- for *advanced use* only."""
if not self.in_atomic_block:
raise TransactionManagementError(
"The rollback flag doesn't work outside of an 'atomic' block."
)
return self.needs_rollback
def set_rollback(self, rollback):
"""
Set or unset the "needs rollback" flag -- for *advanced use* only.
"""
if not self.in_atomic_block:
raise TransactionManagementError(
"The rollback flag doesn't work outside of an 'atomic' block."
)
self.needs_rollback = rollback
def validate_no_atomic_block(self):
"""Raise an error if an atomic block is active."""
if self.in_atomic_block:
raise TransactionManagementError(
"This is forbidden when an 'atomic' block is active."
)
def validate_no_broken_transaction(self):
if self.needs_rollback:
raise TransactionManagementError(
"An error occurred in the current transaction. You can't "
"execute queries until the end of the 'atomic' block."
) from self.rollback_exc
# ##### Foreign key constraints checks handling #####
@contextmanager
def constraint_checks_disabled(self):
"""
Disable foreign key constraint checking.
"""
disabled = self.disable_constraint_checking()
try:
yield
finally:
if disabled:
self.enable_constraint_checking()
def disable_constraint_checking(self):
"""
Backends can implement as needed to temporarily disable foreign key
constraint checking. Should return True if the constraints were
disabled and will need to be reenabled.
"""
return False
def enable_constraint_checking(self):
"""
Backends can implement as needed to re-enable foreign key constraint
checking.
"""
pass
def check_constraints(self, table_names=None):
"""
Backends can override this method if they can apply constraint
checking (e.g. via "SET CONSTRAINTS ALL IMMEDIATE"). Should raise an
IntegrityError if any invalid foreign key references are encountered.
"""
pass
# ##### Connection termination handling #####
def is_usable(self):
"""
Test if the database connection is usable.
This method may assume that self.connection is not None.
Actual implementations should take care not to raise exceptions
as that may prevent Django from recycling unusable connections.
"""
raise NotImplementedError(
"subclasses of BaseDatabaseWrapper may require an is_usable() method"
)
def close_if_health_check_failed(self):
"""Close existing connection if it fails a health check."""
if (
self.connection is None
or not self.health_check_enabled
or self.health_check_done
):
return
if not self.is_usable():
self.close()
self.health_check_done = True
def close_if_unusable_or_obsolete(self):
"""
Close the current connection if unrecoverable errors have occurred
or if it outlived its maximum age.
"""
if self.connection is not None:
self.health_check_done = False
# If the application didn't restore the original autocommit setting,
# don't take chances, drop the connection.
if self.get_autocommit() != self.settings_dict["AUTOCOMMIT"]:
self.close()
return
# If an exception other than DataError or IntegrityError occurred
# since the last commit / rollback, check if the connection works.
if self.errors_occurred:
if self.is_usable():
self.errors_occurred = False
self.health_check_done = True
else:
self.close()
return
if self.close_at is not None and time.monotonic() >= self.close_at:
self.close()
return
# ##### Thread safety handling #####
@property
def allow_thread_sharing(self):
with self._thread_sharing_lock:
return self._thread_sharing_count > 0
def inc_thread_sharing(self):
with self._thread_sharing_lock:
self._thread_sharing_count += 1
def dec_thread_sharing(self):
with self._thread_sharing_lock:
if self._thread_sharing_count <= 0:
raise RuntimeError(
"Cannot decrement the thread sharing count below zero."
)
self._thread_sharing_count -= 1
def validate_thread_sharing(self):
"""
Validate that the connection isn't accessed by another thread than the
one which originally created it, unless the connection was explicitly
authorized to be shared between threads (via the `inc_thread_sharing()`
method). Raise an exception if the validation fails.
"""
if not (self.allow_thread_sharing or self._thread_ident == _thread.get_ident()):
raise DatabaseError(
"DatabaseWrapper objects created in a "
"thread can only be used in that same thread. The object "
"with alias '%s' was created in thread id %s and this is "
"thread id %s." % (self.alias, self._thread_ident, _thread.get_ident())
)
# ##### Miscellaneous #####
def prepare_database(self):
"""
Hook to do any database check or preparation, generally called before
migrating a project or an app.
"""
pass
@cached_property
def wrap_database_errors(self):
"""
Context manager and decorator that re-throws backend-specific database
exceptions using Django's common wrappers.
"""
return DatabaseErrorWrapper(self)
def chunked_cursor(self):
"""
Return a cursor that tries to avoid caching in the database (if
supported by the database), otherwise return a regular cursor.
"""
return self.cursor()
def make_debug_cursor(self, cursor):
"""Create a cursor that logs all queries in self.queries_log."""
return utils.CursorDebugWrapper(cursor, self)
def make_cursor(self, cursor):
"""Create a cursor without debug logging."""
return utils.CursorWrapper(cursor, self)
@contextmanager
def temporary_connection(self):
"""
Context manager that ensures that a connection is established, and
if it opened one, closes it to avoid leaving a dangling connection.
This is useful for operations outside of the request-response cycle.
Provide a cursor: with self.temporary_connection() as cursor: ...
"""
must_close = self.connection is None
try:
with self.cursor() as cursor:
yield cursor
finally:
if must_close:
self.close()
@contextmanager
def _nodb_cursor(self):
"""
Return a cursor from an alternative connection to be used when there is
no need to access the main database, specifically for test db
creation/deletion. This also prevents the production database from
being exposed to potential child threads while (or after) the test
database is destroyed. Refs #10868, #17786, #16969.
"""
conn = self.__class__({**self.settings_dict, "NAME": None}, alias=NO_DB_ALIAS)
try:
with conn.cursor() as cursor:
yield cursor
finally:
conn.close()
def schema_editor(self, *args, **kwargs):
"""
Return 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)
def on_commit(self, func, robust=False):
if not callable(func):
raise TypeError("on_commit()'s callback must be a callable.")
if self.in_atomic_block:
# Transaction in progress; save for execution on commit.
self.run_on_commit.append((set(self.savepoint_ids), func, robust))
elif not self.get_autocommit():
raise TransactionManagementError(
"on_commit() cannot be used in manual transaction management"
)
else:
# No transaction in progress and in autocommit mode; execute
# immediately.
if robust:
try:
func()
except Exception as e:
logger.error(
f"Error calling {func.__qualname__} in on_commit() (%s).",
e,
exc_info=True,
)
else:
func()
def run_and_clear_commit_hooks(self):
self.validate_no_atomic_block()
current_run_on_commit = self.run_on_commit
self.run_on_commit = []
while current_run_on_commit:
_, func, robust = current_run_on_commit.pop(0)
if robust:
try:
func()
except Exception as e:
logger.error(
f"Error calling {func.__qualname__} in on_commit() during "
f"transaction (%s).",
e,
exc_info=True,
)
else:
func()
@contextmanager
def execute_wrapper(self, wrapper):
"""
Return a context manager under which the wrapper is applied to suitable
database query executions.
"""
self.execute_wrappers.append(wrapper)
try:
yield
finally:
self.execute_wrappers.pop()
def copy(self, alias=None):
"""
Return a copy of this connection.
For tests that require two connections to the same database.
"""
settings_dict = copy.deepcopy(self.settings_dict)
if alias is None:
alias = self.alias
return type(self)(settings_dict, alias)