mirror of
https://github.com/janeczku/calibre-web
synced 2024-12-11 10:40:32 +00:00
336 lines
13 KiB
Python
336 lines
13 KiB
Python
# sqlite/pysqlite.py
|
|
# Copyright (C) 2005-2013 the SQLAlchemy authors and contributors <see AUTHORS file>
|
|
#
|
|
# This module is part of SQLAlchemy and is released under
|
|
# the MIT License: http://www.opensource.org/licenses/mit-license.php
|
|
|
|
"""
|
|
.. dialect:: sqlite+pysqlite
|
|
:name: pysqlite
|
|
:dbapi: sqlite3
|
|
:connectstring: sqlite+pysqlite:///file_path
|
|
:url: http://docs.python.org/library/sqlite3.html
|
|
|
|
Note that ``pysqlite`` is the same driver as the ``sqlite3``
|
|
module included with the Python distribution.
|
|
|
|
Driver
|
|
------
|
|
|
|
When using Python 2.5 and above, the built in ``sqlite3`` driver is
|
|
already installed and no additional installation is needed. Otherwise,
|
|
the ``pysqlite2`` driver needs to be present. This is the same driver as
|
|
``sqlite3``, just with a different name.
|
|
|
|
The ``pysqlite2`` driver will be loaded first, and if not found, ``sqlite3``
|
|
is loaded. This allows an explicitly installed pysqlite driver to take
|
|
precedence over the built in one. As with all dialects, a specific
|
|
DBAPI module may be provided to :func:`~sqlalchemy.create_engine()` to control
|
|
this explicitly::
|
|
|
|
from sqlite3 import dbapi2 as sqlite
|
|
e = create_engine('sqlite+pysqlite:///file.db', module=sqlite)
|
|
|
|
|
|
Connect Strings
|
|
---------------
|
|
|
|
The file specification for the SQLite database is taken as the "database"
|
|
portion of the URL. Note that the format of a SQLAlchemy url is::
|
|
|
|
driver://user:pass@host/database
|
|
|
|
This means that the actual filename to be used starts with the characters to
|
|
the **right** of the third slash. So connecting to a relative filepath
|
|
looks like::
|
|
|
|
# relative path
|
|
e = create_engine('sqlite:///path/to/database.db')
|
|
|
|
An absolute path, which is denoted by starting with a slash, means you
|
|
need **four** slashes::
|
|
|
|
# absolute path
|
|
e = create_engine('sqlite:////path/to/database.db')
|
|
|
|
To use a Windows path, regular drive specifications and backslashes can be
|
|
used. Double backslashes are probably needed::
|
|
|
|
# absolute path on Windows
|
|
e = create_engine('sqlite:///C:\\\\path\\\\to\\\\database.db')
|
|
|
|
The sqlite ``:memory:`` identifier is the default if no filepath is
|
|
present. Specify ``sqlite://`` and nothing else::
|
|
|
|
# in-memory database
|
|
e = create_engine('sqlite://')
|
|
|
|
Compatibility with sqlite3 "native" date and datetime types
|
|
-----------------------------------------------------------
|
|
|
|
The pysqlite driver includes the sqlite3.PARSE_DECLTYPES and
|
|
sqlite3.PARSE_COLNAMES options, which have the effect of any column
|
|
or expression explicitly cast as "date" or "timestamp" will be converted
|
|
to a Python date or datetime object. The date and datetime types provided
|
|
with the pysqlite dialect are not currently compatible with these options,
|
|
since they render the ISO date/datetime including microseconds, which
|
|
pysqlite's driver does not. Additionally, SQLAlchemy does not at
|
|
this time automatically render the "cast" syntax required for the
|
|
freestanding functions "current_timestamp" and "current_date" to return
|
|
datetime/date types natively. Unfortunately, pysqlite
|
|
does not provide the standard DBAPI types in ``cursor.description``,
|
|
leaving SQLAlchemy with no way to detect these types on the fly
|
|
without expensive per-row type checks.
|
|
|
|
Keeping in mind that pysqlite's parsing option is not recommended,
|
|
nor should be necessary, for use with SQLAlchemy, usage of PARSE_DECLTYPES
|
|
can be forced if one configures "native_datetime=True" on create_engine()::
|
|
|
|
engine = create_engine('sqlite://',
|
|
connect_args={'detect_types': sqlite3.PARSE_DECLTYPES|sqlite3.PARSE_COLNAMES},
|
|
native_datetime=True
|
|
)
|
|
|
|
With this flag enabled, the DATE and TIMESTAMP types (but note - not the
|
|
DATETIME or TIME types...confused yet ?) will not perform any bind parameter
|
|
or result processing. Execution of "func.current_date()" will return a string.
|
|
"func.current_timestamp()" is registered as returning a DATETIME type in
|
|
SQLAlchemy, so this function still receives SQLAlchemy-level result processing.
|
|
|
|
.. _pysqlite_threading_pooling:
|
|
|
|
Threading/Pooling Behavior
|
|
---------------------------
|
|
|
|
Pysqlite's default behavior is to prohibit the usage of a single connection
|
|
in more than one thread. This is originally intended to work with older
|
|
versions of SQLite that did not support multithreaded operation under
|
|
various circumstances. In particular, older SQLite versions
|
|
did not allow a ``:memory:`` database to be used in multiple threads
|
|
under any circumstances.
|
|
|
|
Pysqlite does include a now-undocumented flag known as
|
|
``check_same_thread`` which will disable this check, however note that pysqlite
|
|
connections are still not safe to use in concurrently in multiple threads.
|
|
In particular, any statement execution calls would need to be externally
|
|
mutexed, as Pysqlite does not provide for thread-safe propagation of error
|
|
messages among other things. So while even ``:memory:`` databases can be
|
|
shared among threads in modern SQLite, Pysqlite doesn't provide enough
|
|
thread-safety to make this usage worth it.
|
|
|
|
SQLAlchemy sets up pooling to work with Pysqlite's default behavior:
|
|
|
|
* When a ``:memory:`` SQLite database is specified, the dialect by default
|
|
will use :class:`.SingletonThreadPool`. This pool maintains a single
|
|
connection per thread, so that all access to the engine within the current
|
|
thread use the same ``:memory:`` database - other threads would access a
|
|
different ``:memory:`` database.
|
|
* When a file-based database is specified, the dialect will use
|
|
:class:`.NullPool` as the source of connections. This pool closes and
|
|
discards connections which are returned to the pool immediately. SQLite
|
|
file-based connections have extremely low overhead, so pooling is not
|
|
necessary. The scheme also prevents a connection from being used again in
|
|
a different thread and works best with SQLite's coarse-grained file locking.
|
|
|
|
.. versionchanged:: 0.7
|
|
Default selection of :class:`.NullPool` for SQLite file-based databases.
|
|
Previous versions select :class:`.SingletonThreadPool` by
|
|
default for all SQLite databases.
|
|
|
|
|
|
Using a Memory Database in Multiple Threads
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
To use a ``:memory:`` database in a multithreaded scenario, the same connection
|
|
object must be shared among threads, since the database exists
|
|
only within the scope of that connection. The
|
|
:class:`.StaticPool` implementation will maintain a single connection
|
|
globally, and the ``check_same_thread`` flag can be passed to Pysqlite
|
|
as ``False``::
|
|
|
|
from sqlalchemy.pool import StaticPool
|
|
engine = create_engine('sqlite://',
|
|
connect_args={'check_same_thread':False},
|
|
poolclass=StaticPool)
|
|
|
|
Note that using a ``:memory:`` database in multiple threads requires a recent
|
|
version of SQLite.
|
|
|
|
Using Temporary Tables with SQLite
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Due to the way SQLite deals with temporary tables, if you wish to use a
|
|
temporary table in a file-based SQLite database across multiple checkouts
|
|
from the connection pool, such as when using an ORM :class:`.Session` where
|
|
the temporary table should continue to remain after :meth:`.commit` or
|
|
:meth:`.rollback` is called, a pool which maintains a single connection must
|
|
be used. Use :class:`.SingletonThreadPool` if the scope is only needed
|
|
within the current thread, or :class:`.StaticPool` is scope is needed within
|
|
multiple threads for this case::
|
|
|
|
# maintain the same connection per thread
|
|
from sqlalchemy.pool import SingletonThreadPool
|
|
engine = create_engine('sqlite:///mydb.db',
|
|
poolclass=SingletonThreadPool)
|
|
|
|
|
|
# maintain the same connection across all threads
|
|
from sqlalchemy.pool import StaticPool
|
|
engine = create_engine('sqlite:///mydb.db',
|
|
poolclass=StaticPool)
|
|
|
|
Note that :class:`.SingletonThreadPool` should be configured for the number
|
|
of threads that are to be used; beyond that number, connections will be
|
|
closed out in a non deterministic way.
|
|
|
|
Unicode
|
|
-------
|
|
|
|
The pysqlite driver only returns Python ``unicode`` objects in result sets,
|
|
never plain strings, and accommodates ``unicode`` objects within bound
|
|
parameter values in all cases. Regardless of the SQLAlchemy string type in
|
|
use, string-based result values will by Python ``unicode`` in Python 2.
|
|
The :class:`.Unicode` type should still be used to indicate those columns that
|
|
require unicode, however, so that non-``unicode`` values passed inadvertently
|
|
will emit a warning. Pysqlite will emit an error if a non-``unicode`` string
|
|
is passed containing non-ASCII characters.
|
|
|
|
.. _pysqlite_serializable:
|
|
|
|
Serializable Transaction Isolation
|
|
----------------------------------
|
|
|
|
The pysqlite DBAPI driver has a long-standing bug in which transactional
|
|
state is not begun until the first DML statement, that is INSERT, UPDATE
|
|
or DELETE, is emitted. A SELECT statement will not cause transactional
|
|
state to begin. While this mode of usage is fine for typical situations
|
|
and has the advantage that the SQLite database file is not prematurely
|
|
locked, it breaks serializable transaction isolation, which requires
|
|
that the database file be locked upon any SQL being emitted.
|
|
|
|
To work around this issue, the ``BEGIN`` keyword can be emitted
|
|
at the start of each transaction. The following recipe establishes
|
|
a :meth:`.ConnectionEvents.begin` handler to achieve this::
|
|
|
|
from sqlalchemy import create_engine, event
|
|
|
|
engine = create_engine("sqlite:///myfile.db", isolation_level='SERIALIZABLE')
|
|
|
|
@event.listens_for(engine, "begin")
|
|
def do_begin(conn):
|
|
conn.execute("BEGIN")
|
|
|
|
"""
|
|
|
|
from sqlalchemy.dialects.sqlite.base import SQLiteDialect, DATETIME, DATE
|
|
from sqlalchemy import exc, pool
|
|
from sqlalchemy import types as sqltypes
|
|
from sqlalchemy import util
|
|
|
|
import os
|
|
|
|
|
|
class _SQLite_pysqliteTimeStamp(DATETIME):
|
|
def bind_processor(self, dialect):
|
|
if dialect.native_datetime:
|
|
return None
|
|
else:
|
|
return DATETIME.bind_processor(self, dialect)
|
|
|
|
def result_processor(self, dialect, coltype):
|
|
if dialect.native_datetime:
|
|
return None
|
|
else:
|
|
return DATETIME.result_processor(self, dialect, coltype)
|
|
|
|
|
|
class _SQLite_pysqliteDate(DATE):
|
|
def bind_processor(self, dialect):
|
|
if dialect.native_datetime:
|
|
return None
|
|
else:
|
|
return DATE.bind_processor(self, dialect)
|
|
|
|
def result_processor(self, dialect, coltype):
|
|
if dialect.native_datetime:
|
|
return None
|
|
else:
|
|
return DATE.result_processor(self, dialect, coltype)
|
|
|
|
|
|
class SQLiteDialect_pysqlite(SQLiteDialect):
|
|
default_paramstyle = 'qmark'
|
|
|
|
colspecs = util.update_copy(
|
|
SQLiteDialect.colspecs,
|
|
{
|
|
sqltypes.Date: _SQLite_pysqliteDate,
|
|
sqltypes.TIMESTAMP: _SQLite_pysqliteTimeStamp,
|
|
}
|
|
)
|
|
|
|
# Py3K
|
|
#description_encoding = None
|
|
|
|
driver = 'pysqlite'
|
|
|
|
def __init__(self, **kwargs):
|
|
SQLiteDialect.__init__(self, **kwargs)
|
|
|
|
if self.dbapi is not None:
|
|
sqlite_ver = self.dbapi.version_info
|
|
if sqlite_ver < (2, 1, 3):
|
|
util.warn(
|
|
("The installed version of pysqlite2 (%s) is out-dated "
|
|
"and will cause errors in some cases. Version 2.1.3 "
|
|
"or greater is recommended.") %
|
|
'.'.join([str(subver) for subver in sqlite_ver]))
|
|
|
|
@classmethod
|
|
def dbapi(cls):
|
|
try:
|
|
from pysqlite2 import dbapi2 as sqlite
|
|
except ImportError, e:
|
|
try:
|
|
from sqlite3 import dbapi2 as sqlite # try 2.5+ stdlib name.
|
|
except ImportError:
|
|
raise e
|
|
return sqlite
|
|
|
|
@classmethod
|
|
def get_pool_class(cls, url):
|
|
if url.database and url.database != ':memory:':
|
|
return pool.NullPool
|
|
else:
|
|
return pool.SingletonThreadPool
|
|
|
|
def _get_server_version_info(self, connection):
|
|
return self.dbapi.sqlite_version_info
|
|
|
|
def create_connect_args(self, url):
|
|
if url.username or url.password or url.host or url.port:
|
|
raise exc.ArgumentError(
|
|
"Invalid SQLite URL: %s\n"
|
|
"Valid SQLite URL forms are:\n"
|
|
" sqlite:///:memory: (or, sqlite://)\n"
|
|
" sqlite:///relative/path/to/file.db\n"
|
|
" sqlite:////absolute/path/to/file.db" % (url,))
|
|
filename = url.database or ':memory:'
|
|
if filename != ':memory:':
|
|
filename = os.path.abspath(filename)
|
|
|
|
opts = url.query.copy()
|
|
util.coerce_kw_type(opts, 'timeout', float)
|
|
util.coerce_kw_type(opts, 'isolation_level', str)
|
|
util.coerce_kw_type(opts, 'detect_types', int)
|
|
util.coerce_kw_type(opts, 'check_same_thread', bool)
|
|
util.coerce_kw_type(opts, 'cached_statements', int)
|
|
|
|
return ([filename], opts)
|
|
|
|
def is_disconnect(self, e, connection, cursor):
|
|
return isinstance(e, self.dbapi.ProgrammingError) and \
|
|
"Cannot operate on a closed database." in str(e)
|
|
|
|
dialect = SQLiteDialect_pysqlite
|