# engine/base.py # Copyright (C) 2005-2013 the SQLAlchemy authors and contributors # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Defines :class:`.Connection` and :class:`.Engine`. """ from __future__ import with_statement import sys from .. import exc, schema, util, log, interfaces from ..sql import expression, util as sql_util from .interfaces import Connectable, Compiled from .util import _distill_params import contextlib class Connection(Connectable): """Provides high-level functionality for a wrapped DB-API connection. Provides execution support for string-based SQL statements as well as :class:`.ClauseElement`, :class:`.Compiled` and :class:`.DefaultGenerator` objects. Provides a :meth:`begin` method to return :class:`.Transaction` objects. The Connection object is **not** thread-safe. While a Connection can be shared among threads using properly synchronized access, it is still possible that the underlying DBAPI connection may not support shared access between threads. Check the DBAPI documentation for details. The Connection object represents a single dbapi connection checked out from the connection pool. In this state, the connection pool has no affect upon the connection, including its expiration or timeout state. For the connection pool to properly manage connections, connections should be returned to the connection pool (i.e. ``connection.close()``) whenever the connection is not in use. .. index:: single: thread safety; Connection """ def __init__(self, engine, connection=None, close_with_result=False, _branch=False, _execution_options=None, _dispatch=None, _has_events=False): """Construct a new Connection. The constructor here is not public and is only called only by an :class:`.Engine`. See :meth:`.Engine.connect` and :meth:`.Engine.contextual_connect` methods. """ self.engine = engine self.dialect = engine.dialect self.__connection = connection or engine.raw_connection() self.__transaction = None self.should_close_with_result = close_with_result self.__savepoint_seq = 0 self.__branch = _branch self.__invalid = False self.__can_reconnect = True if _dispatch: self.dispatch = _dispatch elif engine._has_events: self.dispatch = self.dispatch._join(engine.dispatch) self._has_events = _has_events or engine._has_events self._echo = self.engine._should_log_info() if _execution_options: self._execution_options =\ engine._execution_options.union(_execution_options) else: self._execution_options = engine._execution_options def _branch(self): """Return a new Connection which references this Connection's engine and connection; but does not have close_with_result enabled, and also whose close() method does nothing. This is used to execute "sub" statements within a single execution, usually an INSERT statement. """ return self.engine._connection_cls( self.engine, self.__connection, _branch=True, _has_events=self._has_events, _dispatch=self.dispatch) def _clone(self): """Create a shallow copy of this Connection. """ c = self.__class__.__new__(self.__class__) c.__dict__ = self.__dict__.copy() return c def __enter__(self): return self def __exit__(self, type, value, traceback): self.close() def execution_options(self, **opt): """ Set non-SQL options for the connection which take effect during execution. The method returns a copy of this :class:`.Connection` which references the same underlying DBAPI connection, but also defines the given execution options which will take effect for a call to :meth:`execute`. As the new :class:`.Connection` references the same underlying resource, it's usually a good idea to ensure that the copies would be discarded immediately, which is implicit if used as in:: result = connection.execution_options(stream_results=True).\\ execute(stmt) Note that any key/value can be passed to :meth:`.Connection.execution_options`, and it will be stored in the ``_execution_options`` dictionary of the :class:`.Connection`. It is suitable for usage by end-user schemes to communicate with event listeners, for example. The keywords that are currently recognized by SQLAlchemy itself include all those listed under :meth:`.Executable.execution_options`, as well as others that are specific to :class:`.Connection`. :param autocommit: Available on: Connection, statement. When True, a COMMIT will be invoked after execution when executed in 'autocommit' mode, i.e. when an explicit transaction is not begun on the connection. Note that DBAPI connections by default are always in a transaction - SQLAlchemy uses rules applied to different kinds of statements to determine if COMMIT will be invoked in order to provide its "autocommit" feature. Typically, all INSERT/UPDATE/DELETE statements as well as CREATE/DROP statements have autocommit behavior enabled; SELECT constructs do not. Use this option when invoking a SELECT or other specific SQL construct where COMMIT is desired (typically when calling stored procedures and such), and an explicit transaction is not in progress. :param compiled_cache: Available on: Connection. A dictionary where :class:`.Compiled` objects will be cached when the :class:`.Connection` compiles a clause expression into a :class:`.Compiled` object. It is the user's responsibility to manage the size of this dictionary, which will have keys corresponding to the dialect, clause element, the column names within the VALUES or SET clause of an INSERT or UPDATE, as well as the "batch" mode for an INSERT or UPDATE statement. The format of this dictionary is not guaranteed to stay the same in future releases. Note that the ORM makes use of its own "compiled" caches for some operations, including flush operations. The caching used by the ORM internally supersedes a cache dictionary specified here. :param isolation_level: Available on: Connection. Set the transaction isolation level for the lifespan of this connection. Valid values include those string values accepted by the ``isolation_level`` parameter passed to :func:`.create_engine`, and are database specific, including those for :ref:`sqlite_toplevel`, :ref:`postgresql_toplevel` - see those dialect's documentation for further info. Note that this option necessarily affects the underlying DBAPI connection for the lifespan of the originating :class:`.Connection`, and is not per-execution. This setting is not removed until the underlying DBAPI connection is returned to the connection pool, i.e. the :meth:`.Connection.close` method is called. :param no_parameters: When ``True``, if the final parameter list or dictionary is totally empty, will invoke the statement on the cursor as ``cursor.execute(statement)``, not passing the parameter collection at all. Some DBAPIs such as psycopg2 and mysql-python consider percent signs as significant only when parameters are present; this option allows code to generate SQL containing percent signs (and possibly other characters) that is neutral regarding whether it's executed by the DBAPI or piped into a script that's later invoked by command line tools. .. versionadded:: 0.7.6 :param stream_results: Available on: Connection, statement. Indicate to the dialect that results should be "streamed" and not pre-buffered, if possible. This is a limitation of many DBAPIs. The flag is currently understood only by the psycopg2 dialect. """ c = self._clone() c._execution_options = c._execution_options.union(opt) if 'isolation_level' in opt: c._set_isolation_level() return c def _set_isolation_level(self): self.dialect.set_isolation_level(self.connection, self._execution_options['isolation_level']) self.connection._connection_record.finalize_callback = \ self.dialect.reset_isolation_level @property def closed(self): """Return True if this connection is closed.""" return '_Connection__connection' not in self.__dict__ \ and not self.__can_reconnect @property def invalidated(self): """Return True if this connection was invalidated.""" return self.__invalid @property def connection(self): "The underlying DB-API connection managed by this Connection." try: return self.__connection except AttributeError: return self._revalidate_connection() def _revalidate_connection(self): if self.__can_reconnect and self.__invalid: if self.__transaction is not None: raise exc.InvalidRequestError( "Can't reconnect until invalid " "transaction is rolled back") self.__connection = self.engine.raw_connection() self.__invalid = False return self.__connection raise exc.ResourceClosedError("This Connection is closed") @property def _connection_is_valid(self): # use getattr() for is_valid to support exceptions raised in # dialect initializer, where the connection is not wrapped in # _ConnectionFairy return getattr(self.__connection, 'is_valid', False) @property def _still_open_and_connection_is_valid(self): return \ not self.closed and \ not self.invalidated and \ getattr(self.__connection, 'is_valid', False) @property def info(self): """Info dictionary associated with the underlying DBAPI connection referred to by this :class:`.Connection`, allowing user-defined data to be associated with the connection. The data here will follow along with the DBAPI connection including after it is returned to the connection pool and used again in subsequent instances of :class:`.Connection`. """ return self.connection.info def connect(self): """Returns a branched version of this :class:`.Connection`. The :meth:`.Connection.close` method on the returned :class:`.Connection` can be called and this :class:`.Connection` will remain open. This method provides usage symmetry with :meth:`.Engine.connect`, including for usage with context managers. """ return self._branch() def contextual_connect(self, **kwargs): """Returns a branched version of this :class:`.Connection`. The :meth:`.Connection.close` method on the returned :class:`.Connection` can be called and this :class:`.Connection` will remain open. This method provides usage symmetry with :meth:`.Engine.contextual_connect`, including for usage with context managers. """ return self._branch() def invalidate(self, exception=None): """Invalidate the underlying DBAPI connection associated with this Connection. The underlying DB-API connection is literally closed (if possible), and is discarded. Its source connection pool will typically lazily create a new connection to replace it. Upon the next usage, this Connection will attempt to reconnect to the pool with a new connection. Transactions in progress remain in an "opened" state (even though the actual transaction is gone); these must be explicitly rolled back before a reconnect on this Connection can proceed. This is to prevent applications from accidentally continuing their transactional operations in a non-transactional state. """ if self.invalidated: return if self.closed: raise exc.ResourceClosedError("This Connection is closed") if self._connection_is_valid: self.__connection.invalidate(exception) del self.__connection self.__invalid = True def detach(self): """Detach the underlying DB-API connection from its connection pool. This Connection instance will remain usable. When closed, the DB-API connection will be literally closed and not returned to its pool. The pool will typically lazily create a new connection to replace the detached connection. This method can be used to insulate the rest of an application from a modified state on a connection (such as a transaction isolation level or similar). Also see :class:`~sqlalchemy.interfaces.PoolListener` for a mechanism to modify connection state when connections leave and return to their connection pool. """ self.__connection.detach() def begin(self): """Begin a transaction and return a transaction handle. The returned object is an instance of :class:`.Transaction`. This object represents the "scope" of the transaction, which completes when either the :meth:`.Transaction.rollback` or :meth:`.Transaction.commit` method is called. Nested calls to :meth:`.begin` on the same :class:`.Connection` will return new :class:`.Transaction` objects that represent an emulated transaction within the scope of the enclosing transaction, that is:: trans = conn.begin() # outermost transaction trans2 = conn.begin() # "nested" trans2.commit() # does nothing trans.commit() # actually commits Calls to :meth:`.Transaction.commit` only have an effect when invoked via the outermost :class:`.Transaction` object, though the :meth:`.Transaction.rollback` method of any of the :class:`.Transaction` objects will roll back the transaction. See also: :meth:`.Connection.begin_nested` - use a SAVEPOINT :meth:`.Connection.begin_twophase` - use a two phase /XID transaction :meth:`.Engine.begin` - context manager available from :class:`.Engine`. """ if self.__transaction is None: self.__transaction = RootTransaction(self) return self.__transaction else: return Transaction(self, self.__transaction) def begin_nested(self): """Begin a nested transaction and return a transaction handle. The returned object is an instance of :class:`.NestedTransaction`. Nested transactions require SAVEPOINT support in the underlying database. Any transaction in the hierarchy may ``commit`` and ``rollback``, however the outermost transaction still controls the overall ``commit`` or ``rollback`` of the transaction of a whole. See also :meth:`.Connection.begin`, :meth:`.Connection.begin_twophase`. """ if self.__transaction is None: self.__transaction = RootTransaction(self) else: self.__transaction = NestedTransaction(self, self.__transaction) return self.__transaction def begin_twophase(self, xid=None): """Begin a two-phase or XA transaction and return a transaction handle. The returned object is an instance of :class:`.TwoPhaseTransaction`, which in addition to the methods provided by :class:`.Transaction`, also provides a :meth:`~.TwoPhaseTransaction.prepare` method. :param xid: the two phase transaction id. If not supplied, a random id will be generated. See also :meth:`.Connection.begin`, :meth:`.Connection.begin_twophase`. """ if self.__transaction is not None: raise exc.InvalidRequestError( "Cannot start a two phase transaction when a transaction " "is already in progress.") if xid is None: xid = self.engine.dialect.create_xid() self.__transaction = TwoPhaseTransaction(self, xid) return self.__transaction def recover_twophase(self): return self.engine.dialect.do_recover_twophase(self) def rollback_prepared(self, xid, recover=False): self.engine.dialect.do_rollback_twophase(self, xid, recover=recover) def commit_prepared(self, xid, recover=False): self.engine.dialect.do_commit_twophase(self, xid, recover=recover) def in_transaction(self): """Return True if a transaction is in progress.""" return self.__transaction is not None def _begin_impl(self): if self._echo: self.engine.logger.info("BEGIN (implicit)") if self._has_events: self.dispatch.begin(self) try: self.engine.dialect.do_begin(self.connection) except Exception, e: self._handle_dbapi_exception(e, None, None, None, None) def _rollback_impl(self): if self._has_events: self.dispatch.rollback(self) if self._still_open_and_connection_is_valid: if self._echo: self.engine.logger.info("ROLLBACK") try: self.engine.dialect.do_rollback(self.connection) self.__transaction = None except Exception, e: self._handle_dbapi_exception(e, None, None, None, None) else: self.__transaction = None def _commit_impl(self, autocommit=False): if self._has_events: self.dispatch.commit(self) if self._echo: self.engine.logger.info("COMMIT") try: self.engine.dialect.do_commit(self.connection) self.__transaction = None except Exception, e: self._handle_dbapi_exception(e, None, None, None, None) def _savepoint_impl(self, name=None): if self._has_events: self.dispatch.savepoint(self, name) if name is None: self.__savepoint_seq += 1 name = 'sa_savepoint_%s' % self.__savepoint_seq if self._still_open_and_connection_is_valid: self.engine.dialect.do_savepoint(self, name) return name def _rollback_to_savepoint_impl(self, name, context): if self._has_events: self.dispatch.rollback_savepoint(self, name, context) if self._still_open_and_connection_is_valid: self.engine.dialect.do_rollback_to_savepoint(self, name) self.__transaction = context def _release_savepoint_impl(self, name, context): if self._has_events: self.dispatch.release_savepoint(self, name, context) if self._still_open_and_connection_is_valid: self.engine.dialect.do_release_savepoint(self, name) self.__transaction = context def _begin_twophase_impl(self, xid): if self._echo: self.engine.logger.info("BEGIN TWOPHASE (implicit)") if self._has_events: self.dispatch.begin_twophase(self, xid) if self._still_open_and_connection_is_valid: self.engine.dialect.do_begin_twophase(self, xid) def _prepare_twophase_impl(self, xid): if self._has_events: self.dispatch.prepare_twophase(self, xid) if self._still_open_and_connection_is_valid: assert isinstance(self.__transaction, TwoPhaseTransaction) self.engine.dialect.do_prepare_twophase(self, xid) def _rollback_twophase_impl(self, xid, is_prepared): if self._has_events: self.dispatch.rollback_twophase(self, xid, is_prepared) if self._still_open_and_connection_is_valid: assert isinstance(self.__transaction, TwoPhaseTransaction) self.engine.dialect.do_rollback_twophase(self, xid, is_prepared) self.__transaction = None def _commit_twophase_impl(self, xid, is_prepared): if self._has_events: self.dispatch.commit_twophase(self, xid, is_prepared) if self._still_open_and_connection_is_valid: assert isinstance(self.__transaction, TwoPhaseTransaction) self.engine.dialect.do_commit_twophase(self, xid, is_prepared) self.__transaction = None def _autorollback(self): if not self.in_transaction(): self._rollback_impl() def close(self): """Close this :class:`.Connection`. This results in a release of the underlying database resources, that is, the DBAPI connection referenced internally. The DBAPI connection is typically restored back to the connection-holding :class:`.Pool` referenced by the :class:`.Engine` that produced this :class:`.Connection`. Any transactional state present on the DBAPI connection is also unconditionally released via the DBAPI connection's ``rollback()`` method, regardless of any :class:`.Transaction` object that may be outstanding with regards to this :class:`.Connection`. After :meth:`~.Connection.close` is called, the :class:`.Connection` is permanently in a closed state, and will allow no further operations. """ try: conn = self.__connection except AttributeError: pass else: if not self.__branch: conn.close() del self.__connection self.__can_reconnect = False self.__transaction = None def scalar(self, object, *multiparams, **params): """Executes and returns the first column of the first row. The underlying result/cursor is closed after execution. """ return self.execute(object, *multiparams, **params).scalar() def execute(self, object, *multiparams, **params): """Executes the a SQL statement construct and returns a :class:`.ResultProxy`. :param object: The statement to be executed. May be one of: * a plain string * any :class:`.ClauseElement` construct that is also a subclass of :class:`.Executable`, such as a :func:`~.expression.select` construct * a :class:`.FunctionElement`, such as that generated by :attr:`.func`, will be automatically wrapped in a SELECT statement, which is then executed. * a :class:`.DDLElement` object * a :class:`.DefaultGenerator` object * a :class:`.Compiled` object :param \*multiparams/\**params: represent bound parameter values to be used in the execution. Typically, the format is either a collection of one or more dictionaries passed to \*multiparams:: conn.execute( table.insert(), {"id":1, "value":"v1"}, {"id":2, "value":"v2"} ) ...or individual key/values interpreted by \**params:: conn.execute( table.insert(), id=1, value="v1" ) In the case that a plain SQL string is passed, and the underlying DBAPI accepts positional bind parameters, a collection of tuples or individual values in \*multiparams may be passed:: conn.execute( "INSERT INTO table (id, value) VALUES (?, ?)", (1, "v1"), (2, "v2") ) conn.execute( "INSERT INTO table (id, value) VALUES (?, ?)", 1, "v1" ) Note above, the usage of a question mark "?" or other symbol is contingent upon the "paramstyle" accepted by the DBAPI in use, which may be any of "qmark", "named", "pyformat", "format", "numeric". See `pep-249 `_ for details on paramstyle. To execute a textual SQL statement which uses bound parameters in a DBAPI-agnostic way, use the :func:`~.expression.text` construct. """ for c in type(object).__mro__: if c in Connection.executors: return Connection.executors[c]( self, object, multiparams, params) else: raise exc.InvalidRequestError( "Unexecutable object type: %s" % type(object)) def _execute_function(self, func, multiparams, params): """Execute a sql.FunctionElement object.""" return self._execute_clauseelement(func.select(), multiparams, params) def _execute_default(self, default, multiparams, params): """Execute a schema.ColumnDefault object.""" if self._has_events: for fn in self.dispatch.before_execute: default, multiparams, params = \ fn(self, default, multiparams, params) try: try: conn = self.__connection except AttributeError: conn = self._revalidate_connection() dialect = self.dialect ctx = dialect.execution_ctx_cls._init_default( dialect, self, conn) except Exception, e: self._handle_dbapi_exception(e, None, None, None, None) ret = ctx._exec_default(default, None) if self.should_close_with_result: self.close() if self._has_events: self.dispatch.after_execute(self, default, multiparams, params, ret) return ret def _execute_ddl(self, ddl, multiparams, params): """Execute a schema.DDL object.""" if self._has_events: for fn in self.dispatch.before_execute: ddl, multiparams, params = \ fn(self, ddl, multiparams, params) dialect = self.dialect compiled = ddl.compile(dialect=dialect) ret = self._execute_context( dialect, dialect.execution_ctx_cls._init_ddl, compiled, None, compiled ) if self._has_events: self.dispatch.after_execute(self, ddl, multiparams, params, ret) return ret def _execute_clauseelement(self, elem, multiparams, params): """Execute a sql.ClauseElement object.""" if self._has_events: for fn in self.dispatch.before_execute: elem, multiparams, params = \ fn(self, elem, multiparams, params) distilled_params = _distill_params(multiparams, params) if distilled_params: keys = distilled_params[0].keys() else: keys = [] dialect = self.dialect if 'compiled_cache' in self._execution_options: key = dialect, elem, tuple(keys), len(distilled_params) > 1 if key in self._execution_options['compiled_cache']: compiled_sql = self._execution_options['compiled_cache'][key] else: compiled_sql = elem.compile( dialect=dialect, column_keys=keys, inline=len(distilled_params) > 1) self._execution_options['compiled_cache'][key] = compiled_sql else: compiled_sql = elem.compile( dialect=dialect, column_keys=keys, inline=len(distilled_params) > 1) ret = self._execute_context( dialect, dialect.execution_ctx_cls._init_compiled, compiled_sql, distilled_params, compiled_sql, distilled_params ) if self._has_events: self.dispatch.after_execute(self, elem, multiparams, params, ret) return ret def _execute_compiled(self, compiled, multiparams, params): """Execute a sql.Compiled object.""" if self._has_events: for fn in self.dispatch.before_execute: compiled, multiparams, params = \ fn(self, compiled, multiparams, params) dialect = self.dialect parameters = _distill_params(multiparams, params) ret = self._execute_context( dialect, dialect.execution_ctx_cls._init_compiled, compiled, parameters, compiled, parameters ) if self._has_events: self.dispatch.after_execute(self, compiled, multiparams, params, ret) return ret def _execute_text(self, statement, multiparams, params): """Execute a string SQL statement.""" if self._has_events: for fn in self.dispatch.before_execute: statement, multiparams, params = \ fn(self, statement, multiparams, params) dialect = self.dialect parameters = _distill_params(multiparams, params) ret = self._execute_context( dialect, dialect.execution_ctx_cls._init_statement, statement, parameters, statement, parameters ) if self._has_events: self.dispatch.after_execute(self, statement, multiparams, params, ret) return ret def _execute_context(self, dialect, constructor, statement, parameters, *args): """Create an :class:`.ExecutionContext` and execute, returning a :class:`.ResultProxy`.""" try: try: conn = self.__connection except AttributeError: conn = self._revalidate_connection() context = constructor(dialect, self, conn, *args) except Exception, e: self._handle_dbapi_exception(e, str(statement), parameters, None, None) if context.compiled: context.pre_exec() cursor, statement, parameters = context.cursor, \ context.statement, \ context.parameters if not context.executemany: parameters = parameters[0] if self._has_events: for fn in self.dispatch.before_cursor_execute: statement, parameters = \ fn(self, cursor, statement, parameters, context, context.executemany) if self._echo: self.engine.logger.info(statement) self.engine.logger.info("%r", sql_util._repr_params(parameters, batches=10)) try: if context.executemany: self.dialect.do_executemany( cursor, statement, parameters, context) elif not parameters and context.no_parameters: self.dialect.do_execute_no_params( cursor, statement, context) else: self.dialect.do_execute( cursor, statement, parameters, context) except Exception, e: self._handle_dbapi_exception( e, statement, parameters, cursor, context) if self._has_events: self.dispatch.after_cursor_execute(self, cursor, statement, parameters, context, context.executemany) if context.compiled: context.post_exec() if context.isinsert and not context.executemany: context.post_insert() # create a resultproxy, get rowcount/implicit RETURNING # rows, close cursor if no further results pending result = context.get_result_proxy() if context.isinsert: if context._is_implicit_returning: context._fetch_implicit_returning(result) result.close(_autoclose_connection=False) result._metadata = None elif not context._is_explicit_returning: result.close(_autoclose_connection=False) result._metadata = None elif result._metadata is None: # no results, get rowcount # (which requires open cursor on some drivers # such as kintersbasdb, mxodbc), result.rowcount result.close(_autoclose_connection=False) if self.__transaction is None and context.should_autocommit: self._commit_impl(autocommit=True) if result.closed and self.should_close_with_result: self.close() return result def _cursor_execute(self, cursor, statement, parameters, context=None): """Execute a statement + params on the given cursor. Adds appropriate logging and exception handling. This method is used by DefaultDialect for special-case executions, such as for sequences and column defaults. The path of statement execution in the majority of cases terminates at _execute_context(). """ if self._has_events: for fn in self.dispatch.before_cursor_execute: statement, parameters = \ fn(self, cursor, statement, parameters, context, context.executemany if context is not None else False) if self._echo: self.engine.logger.info(statement) self.engine.logger.info("%r", parameters) try: self.dialect.do_execute( cursor, statement, parameters) except Exception, e: self._handle_dbapi_exception( e, statement, parameters, cursor, None) def _safe_close_cursor(self, cursor): """Close the given cursor, catching exceptions and turning into log warnings. """ try: cursor.close() except Exception, e: try: ex_text = str(e) except TypeError: ex_text = repr(e) if not self.closed: self.connection._logger.warn( "Error closing cursor: %s", ex_text) if isinstance(e, (SystemExit, KeyboardInterrupt)): raise _reentrant_error = False _is_disconnect = False def _handle_dbapi_exception(self, e, statement, parameters, cursor, context): exc_info = sys.exc_info() if not self._is_disconnect: self._is_disconnect = isinstance(e, self.dialect.dbapi.Error) and \ not self.closed and \ self.dialect.is_disconnect(e, self.__connection, cursor) if self._reentrant_error: util.raise_from_cause( exc.DBAPIError.instance(statement, parameters, e, self.dialect.dbapi.Error), exc_info ) self._reentrant_error = True try: # non-DBAPI error - if we already got a context, # or theres no string statement, don't wrap it should_wrap = isinstance(e, self.dialect.dbapi.Error) or \ (statement is not None and context is None) if should_wrap and context: if self._has_events: self.dispatch.dbapi_error(self, cursor, statement, parameters, context, e) context.handle_dbapi_exception(e) if not self._is_disconnect: if cursor: self._safe_close_cursor(cursor) self._autorollback() if should_wrap: util.raise_from_cause( exc.DBAPIError.instance( statement, parameters, e, self.dialect.dbapi.Error, connection_invalidated=self._is_disconnect), exc_info ) util.reraise(*exc_info) finally: del self._reentrant_error if self._is_disconnect: del self._is_disconnect dbapi_conn_wrapper = self.connection self.invalidate(e) if not hasattr(dbapi_conn_wrapper, '_pool') or \ dbapi_conn_wrapper._pool is self.engine.pool: self.engine.dispose() if self.should_close_with_result: self.close() # poor man's multimethod/generic function thingy executors = { expression.FunctionElement: _execute_function, expression.ClauseElement: _execute_clauseelement, Compiled: _execute_compiled, schema.SchemaItem: _execute_default, schema.DDLElement: _execute_ddl, basestring: _execute_text } def default_schema_name(self): return self.engine.dialect.get_default_schema_name(self) def transaction(self, callable_, *args, **kwargs): """Execute the given function within a transaction boundary. The function is passed this :class:`.Connection` as the first argument, followed by the given \*args and \**kwargs, e.g.:: def do_something(conn, x, y): conn.execute("some statement", {'x':x, 'y':y}) conn.transaction(do_something, 5, 10) The operations inside the function are all invoked within the context of a single :class:`.Transaction`. Upon success, the transaction is committed. If an exception is raised, the transaction is rolled back before propagating the exception. .. note:: The :meth:`.transaction` method is superseded by the usage of the Python ``with:`` statement, which can be used with :meth:`.Connection.begin`:: with conn.begin(): conn.execute("some statement", {'x':5, 'y':10}) As well as with :meth:`.Engine.begin`:: with engine.begin() as conn: conn.execute("some statement", {'x':5, 'y':10}) See also: :meth:`.Engine.begin` - engine-level transactional context :meth:`.Engine.transaction` - engine-level version of :meth:`.Connection.transaction` """ trans = self.begin() try: ret = self.run_callable(callable_, *args, **kwargs) trans.commit() return ret except: with util.safe_reraise(): trans.rollback() def run_callable(self, callable_, *args, **kwargs): """Given a callable object or function, execute it, passing a :class:`.Connection` as the first argument. The given \*args and \**kwargs are passed subsequent to the :class:`.Connection` argument. This function, along with :meth:`.Engine.run_callable`, allows a function to be run with a :class:`.Connection` or :class:`.Engine` object without the need to know which one is being dealt with. """ return callable_(self, *args, **kwargs) def _run_visitor(self, visitorcallable, element, **kwargs): visitorcallable(self.dialect, self, **kwargs).traverse_single(element) class Transaction(object): """Represent a database transaction in progress. The :class:`.Transaction` object is procured by calling the :meth:`~.Connection.begin` method of :class:`.Connection`:: from sqlalchemy import create_engine engine = create_engine("postgresql://scott:tiger@localhost/test") connection = engine.connect() trans = connection.begin() connection.execute("insert into x (a, b) values (1, 2)") trans.commit() The object provides :meth:`.rollback` and :meth:`.commit` methods in order to control transaction boundaries. It also implements a context manager interface so that the Python ``with`` statement can be used with the :meth:`.Connection.begin` method:: with connection.begin(): connection.execute("insert into x (a, b) values (1, 2)") The Transaction object is **not** threadsafe. See also: :meth:`.Connection.begin`, :meth:`.Connection.begin_twophase`, :meth:`.Connection.begin_nested`. .. index:: single: thread safety; Transaction """ def __init__(self, connection, parent): self.connection = connection self._parent = parent or self self.is_active = True def close(self): """Close this :class:`.Transaction`. If this transaction is the base transaction in a begin/commit nesting, the transaction will rollback(). Otherwise, the method returns. This is used to cancel a Transaction without affecting the scope of an enclosing transaction. """ if not self._parent.is_active: return if self._parent is self: self.rollback() def rollback(self): """Roll back this :class:`.Transaction`. """ if not self._parent.is_active: return self._do_rollback() self.is_active = False def _do_rollback(self): self._parent.rollback() def commit(self): """Commit this :class:`.Transaction`.""" if not self._parent.is_active: raise exc.InvalidRequestError("This transaction is inactive") self._do_commit() self.is_active = False def _do_commit(self): pass def __enter__(self): return self def __exit__(self, type, value, traceback): if type is None and self.is_active: try: self.commit() except: with util.safe_reraise(): self.rollback() else: self.rollback() class RootTransaction(Transaction): def __init__(self, connection): super(RootTransaction, self).__init__(connection, None) self.connection._begin_impl() def _do_rollback(self): if self.is_active: self.connection._rollback_impl() def _do_commit(self): if self.is_active: self.connection._commit_impl() class NestedTransaction(Transaction): """Represent a 'nested', or SAVEPOINT transaction. A new :class:`.NestedTransaction` object may be procured using the :meth:`.Connection.begin_nested` method. The interface is the same as that of :class:`.Transaction`. """ def __init__(self, connection, parent): super(NestedTransaction, self).__init__(connection, parent) self._savepoint = self.connection._savepoint_impl() def _do_rollback(self): if self.is_active: self.connection._rollback_to_savepoint_impl( self._savepoint, self._parent) def _do_commit(self): if self.is_active: self.connection._release_savepoint_impl( self._savepoint, self._parent) class TwoPhaseTransaction(Transaction): """Represent a two-phase transaction. A new :class:`.TwoPhaseTransaction` object may be procured using the :meth:`.Connection.begin_twophase` method. The interface is the same as that of :class:`.Transaction` with the addition of the :meth:`prepare` method. """ def __init__(self, connection, xid): super(TwoPhaseTransaction, self).__init__(connection, None) self._is_prepared = False self.xid = xid self.connection._begin_twophase_impl(self.xid) def prepare(self): """Prepare this :class:`.TwoPhaseTransaction`. After a PREPARE, the transaction can be committed. """ if not self._parent.is_active: raise exc.InvalidRequestError("This transaction is inactive") self.connection._prepare_twophase_impl(self.xid) self._is_prepared = True def _do_rollback(self): self.connection._rollback_twophase_impl(self.xid, self._is_prepared) def _do_commit(self): self.connection._commit_twophase_impl(self.xid, self._is_prepared) class Engine(Connectable, log.Identified): """ Connects a :class:`~sqlalchemy.pool.Pool` and :class:`~sqlalchemy.engine.interfaces.Dialect` together to provide a source of database connectivity and behavior. An :class:`.Engine` object is instantiated publicly using the :func:`~sqlalchemy.create_engine` function. See also: :doc:`/core/engines` :ref:`connections_toplevel` """ _execution_options = util.immutabledict() _has_events = False _connection_cls = Connection def __init__(self, pool, dialect, url, logging_name=None, echo=None, proxy=None, execution_options=None ): self.pool = pool self.url = url self.dialect = dialect self.pool._dialect = dialect if logging_name: self.logging_name = logging_name self.echo = echo self.engine = self log.instance_logger(self, echoflag=echo) if proxy: interfaces.ConnectionProxy._adapt_listener(self, proxy) if execution_options: self.update_execution_options(**execution_options) def update_execution_options(self, **opt): """Update the default execution_options dictionary of this :class:`.Engine`. The given keys/values in \**opt are added to the default execution options that will be used for all connections. The initial contents of this dictionary can be sent via the ``execution_options`` parameter to :func:`.create_engine`. .. seealso:: :meth:`.Connection.execution_options` :meth:`.Engine.execution_options` """ if 'isolation_level' in opt: raise exc.ArgumentError( "'isolation_level' execution option may " "only be specified on Connection.execution_options(). " "To set engine-wide isolation level, " "use the isolation_level argument to create_engine()." ) self._execution_options = \ self._execution_options.union(opt) def execution_options(self, **opt): """Return a new :class:`.Engine` that will provide :class:`.Connection` objects with the given execution options. The returned :class:`.Engine` remains related to the original :class:`.Engine` in that it shares the same connection pool and other state: * The :class:`.Pool` used by the new :class:`.Engine` is the same instance. The :meth:`.Engine.dispose` method will replace the connection pool instance for the parent engine as well as this one. * Event listeners are "cascaded" - meaning, the new :class:`.Engine` inherits the events of the parent, and new events can be associated with the new :class:`.Engine` individually. * The logging configuration and logging_name is copied from the parent :class:`.Engine`. The intent of the :meth:`.Engine.execution_options` method is to implement "sharding" schemes where multiple :class:`.Engine` objects refer to the same connection pool, but are differentiated by options that would be consumed by a custom event:: primary_engine = create_engine("mysql://") shard1 = primary_engine.execution_options(shard_id="shard1") shard2 = primary_engine.execution_options(shard_id="shard2") Above, the ``shard1`` engine serves as a factory for :class:`.Connection` objects that will contain the execution option ``shard_id=shard1``, and ``shard2`` will produce :class:`.Connection` objects that contain the execution option ``shard_id=shard2``. An event handler can consume the above execution option to perform a schema switch or other operation, given a connection. Below we emit a MySQL ``use`` statement to switch databases, at the same time keeping track of which database we've established using the :attr:`.Connection.info` dictionary, which gives us a persistent storage space that follows the DBAPI connection:: from sqlalchemy import event from sqlalchemy.engine import Engine shards = {"default": "base", shard_1: "db1", "shard_2": "db2"} @event.listens_for(Engine, "before_cursor_execute") def _switch_shard(conn, cursor, stmt, params, context, executemany): shard_id = conn._execution_options.get('shard_id', "default") current_shard = conn.info.get("current_shard", None) if current_shard != shard_id: cursor.execute("use %s" % shards[shard_id]) conn.info["current_shard"] = shard_id .. versionadded:: 0.8 .. seealso:: :meth:`.Connection.execution_options` - update execution options on a :class:`.Connection` object. :meth:`.Engine.update_execution_options` - update the execution options for a given :class:`.Engine` in place. """ return OptionEngine(self, opt) @property def name(self): """String name of the :class:`~sqlalchemy.engine.interfaces.Dialect` in use by this :class:`Engine`.""" return self.dialect.name @property def driver(self): """Driver name of the :class:`~sqlalchemy.engine.interfaces.Dialect` in use by this :class:`Engine`.""" return self.dialect.driver echo = log.echo_property() def __repr__(self): return 'Engine(%r)' % self.url def dispose(self): """Dispose of the connection pool used by this :class:`.Engine`. A new connection pool is created immediately after the old one has been disposed. This new pool, like all SQLAlchemy connection pools, does not make any actual connections to the database until one is first requested. This method has two general use cases: * When a dropped connection is detected, it is assumed that all connections held by the pool are potentially dropped, and the entire pool is replaced. * An application may want to use :meth:`dispose` within a test suite that is creating multiple engines. It is critical to note that :meth:`dispose` does **not** guarantee that the application will release all open database connections - only those connections that are checked into the pool are closed. Connections which remain checked out or have been detached from the engine are not affected. """ self.pool = self.pool._replace() def _execute_default(self, default): with self.contextual_connect() as conn: return conn._execute_default(default, (), {}) @contextlib.contextmanager def _optional_conn_ctx_manager(self, connection=None): if connection is None: with self.contextual_connect() as conn: yield conn else: yield connection def _run_visitor(self, visitorcallable, element, connection=None, **kwargs): with self._optional_conn_ctx_manager(connection) as conn: conn._run_visitor(visitorcallable, element, **kwargs) class _trans_ctx(object): def __init__(self, conn, transaction, close_with_result): self.conn = conn self.transaction = transaction self.close_with_result = close_with_result def __enter__(self): return self.conn def __exit__(self, type, value, traceback): if type is not None: self.transaction.rollback() else: self.transaction.commit() if not self.close_with_result: self.conn.close() def begin(self, close_with_result=False): """Return a context manager delivering a :class:`.Connection` with a :class:`.Transaction` established. E.g.:: with engine.begin() as conn: conn.execute("insert into table (x, y, z) values (1, 2, 3)") conn.execute("my_special_procedure(5)") Upon successful operation, the :class:`.Transaction` is committed. If an error is raised, the :class:`.Transaction` is rolled back. The ``close_with_result`` flag is normally ``False``, and indicates that the :class:`.Connection` will be closed when the operation is complete. When set to ``True``, it indicates the :class:`.Connection` is in "single use" mode, where the :class:`.ResultProxy` returned by the first call to :meth:`.Connection.execute` will close the :class:`.Connection` when that :class:`.ResultProxy` has exhausted all result rows. .. versionadded:: 0.7.6 See also: :meth:`.Engine.connect` - procure a :class:`.Connection` from an :class:`.Engine`. :meth:`.Connection.begin` - start a :class:`.Transaction` for a particular :class:`.Connection`. """ conn = self.contextual_connect(close_with_result=close_with_result) try: trans = conn.begin() except: with util.safe_reraise(): conn.close() return Engine._trans_ctx(conn, trans, close_with_result) def transaction(self, callable_, *args, **kwargs): """Execute the given function within a transaction boundary. The function is passed a :class:`.Connection` newly procured from :meth:`.Engine.contextual_connect` as the first argument, followed by the given \*args and \**kwargs. e.g.:: def do_something(conn, x, y): conn.execute("some statement", {'x':x, 'y':y}) engine.transaction(do_something, 5, 10) The operations inside the function are all invoked within the context of a single :class:`.Transaction`. Upon success, the transaction is committed. If an exception is raised, the transaction is rolled back before propagating the exception. .. note:: The :meth:`.transaction` method is superseded by the usage of the Python ``with:`` statement, which can be used with :meth:`.Engine.begin`:: with engine.begin() as conn: conn.execute("some statement", {'x':5, 'y':10}) See also: :meth:`.Engine.begin` - engine-level transactional context :meth:`.Connection.transaction` - connection-level version of :meth:`.Engine.transaction` """ with self.contextual_connect() as conn: return conn.transaction(callable_, *args, **kwargs) def run_callable(self, callable_, *args, **kwargs): """Given a callable object or function, execute it, passing a :class:`.Connection` as the first argument. The given \*args and \**kwargs are passed subsequent to the :class:`.Connection` argument. This function, along with :meth:`.Connection.run_callable`, allows a function to be run with a :class:`.Connection` or :class:`.Engine` object without the need to know which one is being dealt with. """ with self.contextual_connect() as conn: return conn.run_callable(callable_, *args, **kwargs) def execute(self, statement, *multiparams, **params): """Executes the given construct and returns a :class:`.ResultProxy`. The arguments are the same as those used by :meth:`.Connection.execute`. Here, a :class:`.Connection` is acquired using the :meth:`~.Engine.contextual_connect` method, and the statement executed with that connection. The returned :class:`.ResultProxy` is flagged such that when the :class:`.ResultProxy` is exhausted and its underlying cursor is closed, the :class:`.Connection` created here will also be closed, which allows its associated DBAPI connection resource to be returned to the connection pool. """ connection = self.contextual_connect(close_with_result=True) return connection.execute(statement, *multiparams, **params) def scalar(self, statement, *multiparams, **params): return self.execute(statement, *multiparams, **params).scalar() def _execute_clauseelement(self, elem, multiparams=None, params=None): connection = self.contextual_connect(close_with_result=True) return connection._execute_clauseelement(elem, multiparams, params) def _execute_compiled(self, compiled, multiparams, params): connection = self.contextual_connect(close_with_result=True) return connection._execute_compiled(compiled, multiparams, params) def connect(self, **kwargs): """Return a new :class:`.Connection` object. The :class:`.Connection` object is a facade that uses a DBAPI connection internally in order to communicate with the database. This connection is procured from the connection-holding :class:`.Pool` referenced by this :class:`.Engine`. When the :meth:`~.Connection.close` method of the :class:`.Connection` object is called, the underlying DBAPI connection is then returned to the connection pool, where it may be used again in a subsequent call to :meth:`~.Engine.connect`. """ return self._connection_cls(self, **kwargs) def contextual_connect(self, close_with_result=False, **kwargs): """Return a :class:`.Connection` object which may be part of some ongoing context. By default, this method does the same thing as :meth:`.Engine.connect`. Subclasses of :class:`.Engine` may override this method to provide contextual behavior. :param close_with_result: When True, the first :class:`.ResultProxy` created by the :class:`.Connection` will call the :meth:`.Connection.close` method of that connection as soon as any pending result rows are exhausted. This is used to supply the "connectionless execution" behavior provided by the :meth:`.Engine.execute` method. """ return self._connection_cls(self, self.pool.connect(), close_with_result=close_with_result, **kwargs) def table_names(self, schema=None, connection=None): """Return a list of all table names available in the database. :param schema: Optional, retrieve names from a non-default schema. :param connection: Optional, use a specified connection. Default is the ``contextual_connect`` for this ``Engine``. """ with self._optional_conn_ctx_manager(connection) as conn: if not schema: schema = self.dialect.default_schema_name return self.dialect.get_table_names(conn, schema) def has_table(self, table_name, schema=None): return self.run_callable(self.dialect.has_table, table_name, schema) def raw_connection(self): """Return a "raw" DBAPI connection from the connection pool. The returned object is a proxied version of the DBAPI connection object used by the underlying driver in use. The object will have all the same behavior as the real DBAPI connection, except that its ``close()`` method will result in the connection being returned to the pool, rather than being closed for real. This method provides direct DBAPI connection access for special situations. In most situations, the :class:`.Connection` object should be used, which is procured using the :meth:`.Engine.connect` method. """ return self.pool.unique_connection() class OptionEngine(Engine): def __init__(self, proxied, execution_options): self._proxied = proxied self.url = proxied.url self.dialect = proxied.dialect self.logging_name = proxied.logging_name self.echo = proxied.echo log.instance_logger(self, echoflag=self.echo) self.dispatch = self.dispatch._join(proxied.dispatch) self._execution_options = proxied._execution_options self.update_execution_options(**execution_options) def _get_pool(self): return self._proxied.pool def _set_pool(self, pool): self._proxied.pool = pool pool = property(_get_pool, _set_pool) def _get_has_events(self): return self._proxied._has_events or \ self.__dict__.get('_has_events', False) def _set_has_events(self, value): self.__dict__['_has_events'] = value _has_events = property(_get_has_events, _set_has_events)