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[mod] sqlitedb: access to SQLite databases a little more convenient.
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
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Markus Heiser
Markus Heiser
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commit
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8
docs/src/searx.sqlitedb.rst
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docs/src/searx.sqlitedb.rst
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.. _sqlite db:
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=========
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SQLite DB
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=========
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.. automodule:: searx.sqlitedb
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:members:
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323
searx/sqlitedb.py
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searx/sqlitedb.py
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# SPDX-License-Identifier: AGPL-3.0-or-later
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"""Implementations to make access to SQLite databases a little more convenient.
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:py:obj:`SQLiteAppl`
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Abstract class with which DB applications can be implemented.
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:py:obj:`SQLiteProperties`:
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Class to manage properties stored in a database.
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----
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"""
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from __future__ import annotations
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import sys
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import re
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import sqlite3
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import threading
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import abc
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from searx import logger
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logger = logger.getChild('sqlitedb')
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class SQLiteAppl(abc.ABC):
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"""Abstract base class for implementing convenient DB access in SQLite
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applications. In the constructor, a :py:obj:`SQLiteProperties` instance is
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already aggregated under ``self.properties``."""
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DDL_CREATE_TABLES: dict[str, str] = {}
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DB_SCHEMA: int = 1
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"""As soon as changes are made to the DB schema, the version number must be
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increased. Changes to the version number require the DB to be recreated (or
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migrated / if an migration path exists and is implemented)."""
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SQLITE_THREADING_MODE = {
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0: "single-thread",
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1: "multi-thread",
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3: "serialized"}[sqlite3.threadsafety] # fmt:skip
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"""Threading mode of the SQLite library. Depends on the options used at
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compile time and is different for different distributions and architectures.
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Possible values are 0:``single-thread``, 1:``multi-thread``,
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3:``serialized`` (see :py:obj:`sqlite3.threadsafety`). Pre- Python 3.11
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this value was hard coded to 1.
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Depending on this value, optimizations are made, e.g. in “serialized” mode
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it is not necessary to create a separate DB connector for each thread.
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"""
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SQLITE_JOURNAL_MODE = "WAL"
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SQLITE_CONNECT_ARGS = {
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# "timeout": 5.0,
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# "detect_types": 0,
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"check_same_thread": bool(SQLITE_THREADING_MODE != "serialized"),
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"cached_statements": 0, # https://github.com/python/cpython/issues/118172
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# "uri": False,
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"autocommit": False,
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} # fmt:skip
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"""Connection arguments (:py:obj:`sqlite3.connect`)
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``check_same_thread``:
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Is disabled by default when :py:obj:`SQLITE_THREADING_MODE` is
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``serialized``. The check is more of a hindrance in this case because it
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would prevent a DB connector from being used in multiple threads.
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``autocommit``:
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Is disabled by default. Note: autocommit option has been added in Python
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3.12.
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``cached_statements``:
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Is set to ``0`` by default. Note: Python 3.12+ fetch result are not
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consistent in multi-threading application and causing an API misuse error.
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The multithreading use in SQLiteAppl is intended and supported if
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threadsafety is set to 3 (aka "serialized"). CPython supports “serialized”
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from version 3.12 on, but unfortunately only with errors:
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- https://github.com/python/cpython/issues/118172
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- https://github.com/python/cpython/issues/123873
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The workaround for SQLite3 multithreading cache inconsistency ist to set
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option ``cached_statements`` to ``0`` by default.
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"""
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def __init__(self, db_url):
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self.db_url = db_url
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self.properties = SQLiteProperties(db_url)
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self.thread_local = threading.local()
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self._init_done = False
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self._compatibility()
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def _compatibility(self):
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if self.SQLITE_THREADING_MODE == "serialized":
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self._DB = None
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else:
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msg = (
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f"SQLite library is compiled with {self.SQLITE_THREADING_MODE} mode,"
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" read https://docs.python.org/3/library/sqlite3.html#sqlite3.threadsafety"
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)
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if threading.active_count() > 1:
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logger.error(msg)
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else:
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logger.warning(msg)
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if sqlite3.sqlite_version_info <= (3, 35):
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# See "Generalize UPSERT:" in https://sqlite.org/releaselog/3_35_0.html
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logger.critical(
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"SQLite runtime library version %s is not supported (require >= 3.35)", sqlite3.sqlite_version
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)
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def connect(self) -> sqlite3.Connection:
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"""Creates a new DB connection (:py:obj:`SQLITE_CONNECT_ARGS`). If not
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already done, the DB schema is set up
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"""
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if sys.version_info < (3, 12):
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# Prior Python 3.12 there is no "autocommit" option
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self.SQLITE_CONNECT_ARGS.pop("autocommit", None)
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self.init()
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logger.debug("%s: connect to DB: %s // %s", self.__class__.__name__, self.db_url, self.SQLITE_CONNECT_ARGS)
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conn = sqlite3.Connection(self.db_url, **self.SQLITE_CONNECT_ARGS) # type: ignore
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conn.execute(f"PRAGMA journal_mode={self.SQLITE_JOURNAL_MODE}")
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self.register_functions(conn)
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return conn
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def register_functions(self, conn):
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"""Create user-defined_ SQL functions.
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``REGEXP(<pattern>, <field>)`` : 0 | 1
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`re.search`_ returns (int) 1 for a match and 0 for none match of
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``<pattern>`` in ``<field>``.
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.. code:: sql
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SELECT '12' AS field WHERE REGEXP('^[0-9][0-9]$', field)
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-- 12
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SELECT REGEXP('[0-9][0-9]', 'X12Y')
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-- 1
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SELECT REGEXP('[0-9][0-9]', 'X1Y')
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-- 0
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.. _user-defined: https://docs.python.org/3/library/sqlite3.html#sqlite3.Connection.create_function
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.. _deterministic: https://sqlite.org/deterministic.html
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.. _re.search: https://docs.python.org/3/library/re.html#re.search
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"""
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conn.create_function('regexp', 2, lambda x, y: 1 if re.search(x, y) else 0, deterministic=True)
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@property
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def DB(self) -> sqlite3.Connection:
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"""Provides a DB connection. The connection is a *singleton* and
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therefore well suited for read access. If
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:py:obj:`SQLITE_THREADING_MODE` is ``serialized`` only one DB connection
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is created for all threads.
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.. note::
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For dedicated `transaction control`_, it is recommended to create a
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new connection (:py:obj:`SQLiteAppl.connect`).
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.. _transaction control:
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https://docs.python.org/3/library/sqlite3.html#sqlite3-controlling-transactions
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"""
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if getattr(self.thread_local, 'DB', None) is None:
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self.thread_local.DB = self.connect()
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# Theoretically it is possible to reuse the DB cursor across threads as
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# of Python 3.12, in practice the threading of the cursor seems to me to
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# be so faulty that I prefer to establish one connection per thread
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self.thread_local.DB.commit()
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return self.thread_local.DB
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# In "serialized" mode, SQLite can be safely used by multiple threads
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# with no restriction.
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#
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# if self.SQLITE_THREADING_MODE != "serialized":
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# if getattr(self.thread_local, 'DB', None) is None:
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# self.thread_local.DB = self.connect()
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# return self.thread_local.DB
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#
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# if self._DB is None:
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# self._DB = self.connect() # pylint: disable=attribute-defined-outside-init
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# return self._DB
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def init(self):
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"""Initializes the DB schema and properties, is only executed once even
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if called several times."""
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if self._init_done:
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return
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self._init_done = True
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logger.debug("init DB: %s", self.db_url)
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self.properties.init()
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ver = self.properties("DB_SCHEMA")
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if ver is None:
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with self.properties.DB:
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self.create_schema(self.properties.DB)
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else:
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ver = int(ver)
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if ver != self.DB_SCHEMA:
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raise sqlite3.DatabaseError("Expected DB schema v%s, DB schema is v%s" % (self.DB_SCHEMA, ver))
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logger.debug("DB_SCHEMA = %s", ver)
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def create_schema(self, conn):
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logger.debug("create schema ..")
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with conn:
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for table_name, sql in self.DDL_CREATE_TABLES.items():
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conn.execute(sql)
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self.properties.set(f"Table {table_name} created", table_name)
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self.properties.set("DB_SCHEMA", self.DB_SCHEMA)
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self.properties.set("LAST_MAINTENANCE", "")
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class SQLiteProperties(SQLiteAppl):
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"""Simple class to manage properties of a DB application in the DB. The
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object has its own DB connection and transaction area.
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.. code:: sql
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CREATE TABLE IF NOT EXISTS properties (
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name TEXT,
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value TEXT,
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m_time INTEGER DEFAULT (strftime('%s', 'now')),
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PRIMARY KEY (name))
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"""
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SQLITE_JOURNAL_MODE = "WAL"
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DDL_PROPERTIES = """\
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CREATE TABLE IF NOT EXISTS properties (
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name TEXT,
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value TEXT,
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m_time INTEGER DEFAULT (strftime('%s', 'now')), -- last modified (unix epoch) time in sec.
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PRIMARY KEY (name))"""
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"""Table to store properties of the DB application"""
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SQL_GET = "SELECT value FROM properties WHERE name = ?"
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SQL_M_TIME = "SELECT m_time FROM properties WHERE name = ?"
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SQL_SET = (
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"INSERT INTO properties (name, value) VALUES (?, ?)"
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" ON CONFLICT(name) DO UPDATE"
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" SET value=excluded.value, m_time=strftime('%s', 'now')"
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)
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SQL_TABLE_EXISTS = (
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"SELECT name FROM sqlite_master"
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" WHERE type='table' AND name='properties'"
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) # fmt:skip
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SQLITE_CONNECT_ARGS = dict(SQLiteAppl.SQLITE_CONNECT_ARGS)
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SQLITE_CONNECT_ARGS["autocommit"] = True # This option has no effect before Python 3.12
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def __init__(self, db_url: str): # pylint: disable=super-init-not-called
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self.db_url = db_url
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self.thread_local = threading.local()
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self._init_done = False
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self._compatibility()
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def init(self):
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"""Initializes DB schema of the properties in the DB."""
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if self._init_done:
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return
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self._init_done = True
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logger.debug("init properties of DB: %s", self.db_url)
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with self.DB as conn:
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res = conn.execute(self.SQL_TABLE_EXISTS)
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if res.fetchone() is None: # DB schema needs to be be created
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self.create_schema(conn)
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def __call__(self, name, default=None):
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"""Returns the value of the property ``name`` or ``default`` if property
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not exists in DB."""
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res = self.DB.execute(self.SQL_GET, (name,)).fetchone()
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if res is None:
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return default
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return res[0]
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def set(self, name, value):
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"""Set ``value`` of property ``name`` in DB. If property already
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exists, update the ``m_time`` (and the value)."""
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self.DB.execute(self.SQL_SET, (name, value))
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if sys.version_info <= (3, 12):
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# Prior Python 3.12 there is no "autocommit" option / lets commit
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# explicitely.
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self.DB.commit()
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def row(self, name, default=None):
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"""Returns the DB row of property ``name`` or ``default`` if property
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not exists in DB."""
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cur = self.DB.cursor()
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cur.execute("SELECT * FROM properties WHERE name = ?", (name,))
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res = cur.fetchone()
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if res is None:
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return default
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col_names = [column[0] for column in cur.description]
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return dict(zip(col_names, res))
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def m_time(self, name, default: int = 0) -> int:
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"""Last modification time of this property."""
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res = self.DB.execute(self.SQL_M_TIME, (name,)).fetchone()
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if res is None:
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return default
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return int(res[0])
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def create_schema(self, conn):
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with conn:
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conn.execute(self.DDL_PROPERTIES)
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