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from enum import Enum
from typing import Optional, Type
from django.db import DEFAULT_DB_ALIAS, connections, models
class PostgresTableLockMode(Enum):
"""List of table locking modes.
See: https://www.postgresql.org/docs/current/explicit-locking.html
"""
ACCESS_SHARE = "ACCESS SHARE"
ROW_SHARE = "ROW SHARE"
ROW_EXCLUSIVE = "ROW EXCLUSIVE"
SHARE_UPDATE_EXCLUSIVE = "SHARE UPDATE EXCLUSIVE"
SHARE = "SHARE"
SHARE_ROW_EXCLUSIVE = "SHARE ROW EXCLUSIVE"
EXCLUSIVE = "EXCLUSIVE"
ACCESS_EXCLUSIVE = "ACCESS EXCLUSIVE"
@property
def alias(self) -> str:
return (
"".join([word.title() for word in self.name.lower().split("_")])
+ "Lock"
)
def postgres_lock_table(
table_name: str,
lock_mode: PostgresTableLockMode,
*,
schema_name: Optional[str] = None,
using: str = DEFAULT_DB_ALIAS,
) -> None:
"""Locks the specified table with the specified mode.
The lock is held until the end of the current transaction.
Arguments:
table_name:
Unquoted table name to acquire the lock on.
lock_mode:
Type of lock to acquire.
schema_name:
Optionally, the unquoted name of the schema
the table to lock is in. If not specified,
the table name is resolved by PostgreSQL
using it's ``search_path``.
using:
Optional name of the database connection to use.
"""
connection = connections[using]
with connection.cursor() as cursor:
quoted_fqn = connection.ops.quote_name(table_name)
if schema_name:
quoted_fqn = (
connection.ops.quote_name(schema_name) + "." + quoted_fqn
)
cursor.execute(f"LOCK TABLE {quoted_fqn} IN {lock_mode.value} MODE")
def postgres_lock_model(
model: Type[models.Model],
lock_mode: PostgresTableLockMode,
*,
using: str = DEFAULT_DB_ALIAS,
schema_name: Optional[str] = None,
) -> None:
"""Locks the specified model with the specified mode.
The lock is held until the end of the current transaction.
Arguments:
model:
The model of which to lock the table.
lock_mode:
Type of lock to acquire.
schema_name:
Optionally, the unquoted name of the schema
the table to lock is in. If not specified,
the table name is resolved by PostgreSQL
using it's ``search_path``.
Django models always reside in the default
("public") schema. You should not specify
this unless you're doing something special.
using:
Optional name of the database connection to use.
"""
postgres_lock_table(
model._meta.db_table, lock_mode, schema_name=schema_name, using=using
)
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