.. currentmodule:: psycopg Connection classes ================== The `Connection` and `AsyncConnection` classes are the main wrappers for a PostgreSQL database session. You can imagine them similar to a :program:`psql` session. One of the differences compared to :program:`psql` is that a `Connection` usually handles a transaction automatically: other sessions will not be able to see the changes until you have committed them, more or less explicitly. Take a look to :ref:`transactions` for the details. The `!Connection` class ----------------------- .. autoclass:: Connection() This class implements a `DBAPI-compliant interface`__. It is what you want to use if you write a "classic", blocking program (eventually using threads or Eventlet/gevent for concurrency). If your program uses `asyncio` you might want to use `AsyncConnection` instead. .. __: https://www.python.org/dev/peps/pep-0249/#connection-objects Connections behave as context managers: on block exit, the current transaction will be committed (or rolled back, in case of exception) and the connection will be closed. .. automethod:: connect :param conninfo: The `connection string`__ (a ``postgresql://`` url or a list of ``key=value`` pairs) to specify where and how to connect. :param kwargs: Further parameters specifying the connection string. They override the ones specified in `!conninfo`. :param autocommit: If `!True` don't start transactions automatically. See :ref:`transactions` for details. :param row_factory: The row factory specifying what type of records to create fetching data (default: `~psycopg.rows.tuple_row()`). See :ref:`row-factories` for details. :param cursor_factory: Initial value for the `cursor_factory` attribute of the connection (new in Psycopg 3.1). :param prepare_threshold: Initial value for the `prepare_threshold` attribute of the connection (new in Psycopg 3.1). More specialized use: :param context: A context to copy the initial adapters configuration from. It might be an `~psycopg.adapt.AdaptersMap` with customized loaders and dumpers, used as a template to create several connections. See :ref:`adaptation` for further details. .. __: https://www.postgresql.org/docs/current/libpq-connect.html #LIBPQ-CONNSTRING This method is also aliased as `psycopg.connect()`. .. seealso:: - the list of `the accepted connection parameters`__ - the `environment variables`__ affecting connection .. __: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS .. __: https://www.postgresql.org/docs/current/libpq-envars.html .. versionchanged:: 3.1 added `!prepare_threshold` and `!cursor_factory` parameters. .. attribute:: adapters :type: ~adapt.AdaptersMap The adapters configuration used to convert Python parameters and PostgreSQL results for the queries executed on this cursor. It affects all the cursors created by this connection afterwards. .. automethod:: close .. note:: You can use:: with psycopg.connect() as conn: ... to close the connection automatically when the block is exited. See :ref:`with-connection`. .. autoattribute:: closed .. autoattribute:: broken .. method:: cursor(*, binary: bool = False, \ row_factory: Optional[RowFactory] = None) -> Cursor .. method:: cursor(name: str, *, binary: bool = False, \ row_factory: Optional[RowFactory] = None, \ scrollable: Optional[bool] = None, withhold: bool = False) -> ServerCursor :noindex: Return a new cursor to send commands and queries to the connection. :param name: If not specified create a client-side cursor, if specified create a server-side cursor. See :ref:`cursor-types` for details. :param binary: If `!True` return binary values from the database. All the types returned by the query must have a binary loader. See :ref:`binary-data` for details. :param row_factory: If specified override the `row_factory` set on the connection. See :ref:`row-factories` for details. :param scrollable: Specify the `~ServerCursor.scrollable` property of the server-side cursor created. :param withhold: Specify the `~ServerCursor.withhold` property of the server-side cursor created. :return: A cursor of the class specified by `cursor_factory` (or `server_cursor_factory` if `!name` is specified). .. note:: You can use:: with conn.cursor() as cur: ... to close the cursor automatically when the block is exited. .. autoattribute:: cursor_factory The type, or factory function, returned by `cursor()` and `execute()`. Default is `psycopg.Cursor`. .. autoattribute:: server_cursor_factory The type, or factory function, returned by `cursor()` when a name is specified. Default is `psycopg.ServerCursor`. .. autoattribute:: row_factory The row factory defining the type of rows returned by `~Cursor.fetchone()` and the other cursor fetch methods. The default is `~psycopg.rows.tuple_row`, which means that the fetch methods will return simple tuples. .. seealso:: See :ref:`row-factories` for details about defining the objects returned by cursors. .. automethod:: execute :param query: The query to execute. :type query: `~typing.LiteralString`, `!bytes`, `sql.SQL`, `sql.Composed`, or `~string.templatelib.Template` :param params: The parameters to pass to the query, if any. Can't be specified if ``query`` is a `!Template`. :type params: Sequence or Mapping :param prepare: Force (`!True`) or disallow (`!False`) preparation of the query. By default (`!None`) prepare automatically. See :ref:`prepared-statements`. :param binary: If `!True` the cursor will return binary values from the database. All the types returned by the query must have a binary loader. See :ref:`binary-data` for details. The method simply creates a `Cursor` instance, `~Cursor.execute()` the query requested, and returns it. See :ref:`query-parameters` for all the details about executing queries. .. automethod:: pipeline The method is a context manager: you should call it using:: with conn.pipeline() as p: ... At the end of the block, a synchronization point is established and the connection returns in normal mode. You can call the method recursively from within a pipeline block. Innermost blocks will establish a synchronization point on exit, but pipeline mode will be kept until the outermost block exits. See :ref:`pipeline-mode` for details. .. versionadded:: 3.1 .. rubric:: Transaction management methods For details see :ref:`transactions`. .. automethod:: commit .. automethod:: rollback .. automethod:: transaction .. note:: The method must be called with a syntax such as:: with conn.transaction(): ... with conn.transaction() as tx: ... The latter is useful if you need to interact with the `Transaction` object. See :ref:`transaction-context` for details. Inside a transaction block it will not be possible to call `commit()` or `rollback()`. .. autoattribute:: autocommit The property is writable for sync connections, read-only for async ones: you should call `!await` `~AsyncConnection.set_autocommit` :samp:`({value})` instead. .. automethod:: set_autocommit .. versionadded:: 3.2 The following three properties control the characteristics of new transactions. See :ref:`transaction-characteristics` for details. .. autoattribute:: isolation_level `!None` means use the default set in the default_transaction_isolation__ configuration parameter of the server. .. __: https://www.postgresql.org/docs/current/runtime-config-client.html #GUC-DEFAULT-TRANSACTION-ISOLATION .. automethod:: set_isolation_level .. versionadded:: 3.2 .. autoattribute:: read_only `!None` means use the default set in the default_transaction_read_only__ configuration parameter of the server. .. __: https://www.postgresql.org/docs/current/runtime-config-client.html #GUC-DEFAULT-TRANSACTION-READ-ONLY .. automethod:: set_read_only .. versionadded:: 3.2 .. autoattribute:: deferrable `!None` means use the default set in the default_transaction_deferrable__ configuration parameter of the server. .. __: https://www.postgresql.org/docs/current/runtime-config-client.html #GUC-DEFAULT-TRANSACTION-DEFERRABLE .. automethod:: set_deferrable .. versionadded:: 3.2 .. rubric:: Checking and configuring the connection state .. attribute:: pgconn :type: psycopg.pq.PGconn The `~pq.PGconn` libpq connection wrapper underlying the `!Connection`. It can be used to send low level commands to PostgreSQL and access features not currently wrapped by Psycopg. .. autoattribute:: info .. autoattribute:: prepare_threshold See :ref:`prepared-statements` for details. .. autoattribute:: prepared_max If more queries need to be prepared, old ones are deallocated__. Specifying `!None` can be useful for middleware that don't support deallocation; see :ref:`prepared statements notes `. .. __: https://www.postgresql.org/docs/current/sql-deallocate.html .. versionchanged:: 3.2 Added support for the `!None` value. .. rubric:: Methods you can use to do something cool .. automethod:: cancel_safe .. note:: You can use the `~Capabilities.has_cancel_safe` capability to check if `!cancel_safe()` will not fall back on the legacy libpq functions. .. warning:: The `timeout` parameter has no effect for libpq older than version 17. .. warning:: This method shouldn't be used as a `~signal.signal` handler. Please use `cancel()` instead. .. versionadded:: 3.2 .. automethod:: cancel .. warning:: The `!cancel()` method is implemented using the :pq:`PQcancel` function, which is deprecated since PostgreSQL 17, and has a few shortcomings: - it is blocking even on async connections, - it `might use an insecure connection`__ even if the original connection was secure. Therefore you should use the `cancel_safe()` method whenever possible. .. __: https://www.postgresql.org/docs/devel/libpq-cancel.html #LIBPQ-CANCEL-DEPRECATED .. note:: Unlike `cancel_safe()`, it is safe to call this method as a `~signal.signal` handler. This is pretty much the only case in which you might want to use this function. .. automethod:: notifies Notifies are received after using :sql:`LISTEN` in a connection, when any sessions in the database generates a :sql:`NOTIFY` on one of the listened channels. .. versionchanged:: 3.2 Added `!timeout` and `!stop_after` parameters. .. automethod:: add_notify_handler See :ref:`async-notify` for details. .. automethod:: remove_notify_handler .. automethod:: add_notice_handler See :ref:`async-messages` for details. .. automethod:: remove_notice_handler .. automethod:: fileno .. _tpc-methods: .. rubric:: Two-Phase Commit support methods .. versionadded:: 3.1 .. seealso:: :ref:`two-phase-commit` for an introductory explanation of these methods. .. automethod:: xid .. automethod:: tpc_begin :param xid: The id of the transaction :type xid: Xid or str This method should be called outside of a transaction (i.e. nothing may have executed since the last `commit()` or `rollback()` and `~ConnectionInfo.transaction_status` is `~pq.TransactionStatus.IDLE`). Furthermore, it is an error to call `!commit()` or `!rollback()` within the TPC transaction: in this case a `ProgrammingError` is raised. The `!xid` may be either an object returned by the `xid()` method or a plain string: the latter allows to create a transaction using the provided string as PostgreSQL transaction id. See also `tpc_recover()`. .. automethod:: tpc_prepare A `ProgrammingError` is raised if this method is used outside of a TPC transaction. After calling `!tpc_prepare()`, no statements can be executed until `tpc_commit()` or `tpc_rollback()` will be called. .. seealso:: The |PREPARE TRANSACTION|_ PostgreSQL command. .. |PREPARE TRANSACTION| replace:: :sql:`PREPARE TRANSACTION` .. _PREPARE TRANSACTION: https://www.postgresql.org/docs/current/static/sql-prepare-transaction.html .. automethod:: tpc_commit :param xid: The id of the transaction :type xid: Xid or str When called with no arguments, `!tpc_commit()` commits a TPC transaction previously prepared with `tpc_prepare()`. If `!tpc_commit()` is called prior to `!tpc_prepare()`, a single phase commit is performed. A transaction manager may choose to do this if only a single resource is participating in the global transaction. When called with a transaction ID `!xid`, the database commits the given transaction. If an invalid transaction ID is provided, a `ProgrammingError` will be raised. This form should be called outside of a transaction, and is intended for use in recovery. On return, the TPC transaction is ended. .. seealso:: The |COMMIT PREPARED|_ PostgreSQL command. .. |COMMIT PREPARED| replace:: :sql:`COMMIT PREPARED` .. _COMMIT PREPARED: https://www.postgresql.org/docs/current/static/sql-commit-prepared.html .. automethod:: tpc_rollback :param xid: The id of the transaction :type xid: Xid or str When called with no arguments, `!tpc_rollback()` rolls back a TPC transaction. It may be called before or after `tpc_prepare()`. When called with a transaction ID `!xid`, it rolls back the given transaction. If an invalid transaction ID is provided, a `ProgrammingError` is raised. This form should be called outside of a transaction, and is intended for use in recovery. On return, the TPC transaction is ended. .. seealso:: The |ROLLBACK PREPARED|_ PostgreSQL command. .. |ROLLBACK PREPARED| replace:: :sql:`ROLLBACK PREPARED` .. _ROLLBACK PREPARED: https://www.postgresql.org/docs/current/static/sql-rollback-prepared.html .. automethod:: tpc_recover Returns a list of `Xid` representing pending transactions, suitable for use with `tpc_commit()` or `tpc_rollback()`. If a transaction was not initiated by Psycopg, the returned Xids will have attributes `~Xid.format_id` and `~Xid.bqual` set to `!None` and the `~Xid.gtrid` set to the PostgreSQL transaction ID: such Xids are still usable for recovery. Psycopg uses the same algorithm of the `PostgreSQL JDBC driver`__ to encode a XA triple in a string, so transactions initiated by a program using such driver should be unpacked correctly. .. __: https://jdbc.postgresql.org/ Xids returned by `!tpc_recover()` also have extra attributes `~Xid.prepared`, `~Xid.owner`, `~Xid.database` populated with the values read from the server. .. seealso:: the |pg_prepared_xacts|_ system view. .. |pg_prepared_xacts| replace:: `pg_prepared_xacts` .. _pg_prepared_xacts: https://www.postgresql.org/docs/current/static/view-pg-prepared-xacts.html The `!AsyncConnection` class ---------------------------- .. autoclass:: AsyncConnection() This class implements a DBAPI-inspired interface, with all the blocking methods implemented as coroutines. Unless specified otherwise, non-blocking methods are shared with the `Connection` class. The following methods have the same behaviour of the matching `!Connection` methods, but should be called using the `await` keyword. .. automethod:: connect .. versionchanged:: 3.1 Automatically resolve domain names asynchronously. In previous versions, name resolution blocks, unless the `!hostaddr` parameter is specified, or the `~psycopg._dns.resolve_hostaddr_async()` function is used. .. automethod:: close .. note:: You can use ``async with`` to close the connection automatically when the block is exited, but be careful about the async quirkness: see :ref:`async-with` for details. .. method:: cursor(*, binary: bool = False, \ row_factory: Optional[RowFactory] = None) -> AsyncCursor .. method:: cursor(name: str, *, binary: bool = False, \ row_factory: Optional[RowFactory] = None, \ scrollable: Optional[bool] = None, withhold: bool = False) -> AsyncServerCursor :noindex: .. note:: You can use:: async with conn.cursor() as cur: ... to close the cursor automatically when the block is exited. .. autoattribute:: cursor_factory Default is `psycopg.AsyncCursor`. .. autoattribute:: server_cursor_factory Default is `psycopg.AsyncServerCursor`. .. autoattribute:: row_factory .. automethod:: execute .. automethod:: pipeline .. note:: It must be called as:: async with conn.pipeline() as p: ... .. automethod:: commit .. automethod:: rollback .. automethod:: transaction .. note:: It must be called as:: async with conn.transaction() as tx: ... .. automethod:: cancel_safe .. versionadded:: 3.2 .. automethod:: notifies .. versionchanged:: 3.2 Added `!timeout` and `!stop_after` parameters. .. automethod:: set_autocommit .. automethod:: set_isolation_level .. automethod:: set_read_only .. automethod:: set_deferrable .. automethod:: tpc_prepare .. automethod:: tpc_commit .. automethod:: tpc_rollback .. automethod:: tpc_recover