python-storm 0.19-1 / usr / share / pyshared / storm / database.py

#
# Copyright (c) 2006, 2007 Canonical
#
# Written by Gustavo Niemeyer <gustavo@niemeyer.net>
#
# This file is part of Storm Object Relational Mapper.
#
# Storm is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as
# published by the Free Software Foundation; either version 2.1 of
# the License, or (at your option) any later version.
#
# Storm is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

"""Basic database interfacing mechanisms for Storm.

This is the common code for database support; specific databases are
supported in modules in L{storm.databases}.
"""

from storm.expr import Expr, State, compile
# Circular import: imported at the end of the module.
# from storm.tracer import trace
from storm.variables import Variable
from storm.exceptions import (
    ClosedError, ConnectionBlockedError, DatabaseError, DisconnectionError,
    Error)
from storm.uri import URI
import storm


__all__ = ["Database", "Connection", "Result",
           "convert_param_marks", "create_database", "register_scheme"]


STATE_CONNECTED = 1
STATE_DISCONNECTED = 2
STATE_RECONNECT = 3


class Result(object):
    """A representation of the results from a single SQL statement."""

    _closed = False

    def __init__(self, connection, raw_cursor):
        self._connection = connection # Ensures deallocation order.
        self._raw_cursor = raw_cursor
        if raw_cursor.arraysize == 1:
            # Default of 1 is silly.
            self._raw_cursor.arraysize = 10

    def __del__(self):
        """Close the cursor."""
        try:
            self.close()
        except:
            pass

    def close(self):
        """Close the underlying raw cursor, if it hasn't already been closed.
        """
        if not self._closed:
            self._closed = True
            self._raw_cursor.close()
            self._raw_cursor = None

    def get_one(self):
        """Fetch one result from the cursor.

        The result will be converted to an appropriate format via
        L{from_database}.

        @raise DisconnectionError: Raised when the connection is lost.
            Reconnection happens automatically on rollback.

        @return: A converted row or None, if no data is left.
        """
        row = self._connection._check_disconnect(self._raw_cursor.fetchone)
        if row is not None:
            return tuple(self.from_database(row))
        return None

    def get_all(self):
        """Fetch all results from the cursor.

        The results will be converted to an appropriate format via
        L{from_database}.

        @raise DisconnectionError: Raised when the connection is lost.
            Reconnection happens automatically on rollback.
        """
        result = self._connection._check_disconnect(self._raw_cursor.fetchall)
        if result:
            return [tuple(self.from_database(row)) for row in result]
        return result

    def __iter__(self):
        """Yield all results, one at a time.

        The results will be converted to an appropriate format via
        L{from_database}.

        @raise DisconnectionError: Raised when the connection is lost.
            Reconnection happens automatically on rollback.
        """
        while True:
            results = self._connection._check_disconnect(
                self._raw_cursor.fetchmany)
            if not results:
                break
            for result in results:
                yield tuple(self.from_database(result))

    @property
    def rowcount(self):
        """
        See PEP 249 for further details on rowcount.

        @return: the number of affected rows, or None if the database
            backend does not provide this information. Return value
            is undefined if all results have not yet been retrieved.
        """
        if self._raw_cursor.rowcount == -1:
            return None
        return self._raw_cursor.rowcount

    def get_insert_identity(self, primary_columns, primary_variables):
        """Get a query which will return the row that was just inserted.

        This must be overridden in database-specific subclasses.

        @rtype: L{storm.expr.Expr}
        """
        raise NotImplementedError

    @staticmethod
    def set_variable(variable, value):
        """Set the given variable's value from the database."""
        variable.set(value, from_db=True)

    @staticmethod
    def from_database(row):
        """Convert a row fetched from the database to an agnostic format.

        This method is intended to be overridden in subclasses, but
        not called externally.

        If there are any peculiarities in the datatypes returned from
        a database backend, this method should be overridden in the
        backend subclass to convert them.
        """
        return row


class Connection(object):
    """A connection to a database.

    @cvar result_factory: A callable which takes this L{Connection}
        and the backend cursor and returns an instance of L{Result}.
    @type param_mark: C{str}
    @cvar param_mark: The dbapi paramstyle that the database backend expects.
    @type compile: L{storm.expr.Compile}
    @cvar compile: The compiler to use for connections of this type.
    """

    result_factory = Result
    param_mark = "?"
    compile = compile

    _blocked = False
    _closed = False
    _state = STATE_CONNECTED

    def __init__(self, database, event=None):
        self._database = database # Ensures deallocation order.
        self._event = event
        self._raw_connection = self._database.raw_connect()

    def __del__(self):
        """Close the connection."""
        try:
            self.close()
        except:
            pass

    def block_access(self):
        """Block access to the connection.

        Attempts to execute statements or commit a transaction will
        result in a C{ConnectionBlockedError} exception.  Rollbacks
        are permitted as that operation is often used in case of
        failures.
        """
        self._blocked = True

    def unblock_access(self):
        """Unblock access to the connection."""
        self._blocked = False

    def execute(self, statement, params=None, noresult=False):
        """Execute a statement with the given parameters.

        @type statement: L{Expr} or C{str}
        @param statement: The statement to execute. It will be
            compiled if necessary.
        @param noresult: If True, no result will be returned.

        @raise ConnectionBlockedError: Raised if access to the connection
            has been blocked with L{block_access}.
        @raise DisconnectionError: Raised when the connection is lost.
            Reconnection happens automatically on rollback.

        @return: The result of C{self.result_factory}, or None if
            C{noresult} is True.
        """
        if self._closed:
            raise ClosedError("Connection is closed")
        if self._blocked:
            raise ConnectionBlockedError("Access to connection is blocked")
        if self._event:
            self._event.emit("register-transaction")
        self._ensure_connected()
        if isinstance(statement, Expr):
            if params is not None:
                raise ValueError("Can't pass parameters with expressions")
            state = State()
            statement = self.compile(statement, state)
            params = state.parameters
        statement = convert_param_marks(statement, "?", self.param_mark)
        raw_cursor = self.raw_execute(statement, params)
        if noresult:
            self._check_disconnect(raw_cursor.close)
            return None
        return self.result_factory(self, raw_cursor)

    def close(self):
        """Close the connection if it is not already closed."""
        if not self._closed:
            self._closed = True
            if self._raw_connection is not None:
                self._raw_connection.close()
                self._raw_connection = None

    def commit(self):
        """Commit the connection.

        @raise ConnectionBlockedError: Raised if access to the connection
            has been blocked with L{block_access}.
        @raise DisconnectionError: Raised when the connection is lost.
            Reconnection happens automatically on rollback.

        """
        self._ensure_connected()
        self._check_disconnect(self._raw_connection.commit)

    def rollback(self):
        """Rollback the connection."""
        if self._state == STATE_CONNECTED:
            try:
                self._raw_connection.rollback()
            except Error, exc:
                if self.is_disconnection_error(exc):
                    self._raw_connection = None
                    self._state = STATE_RECONNECT
                else:
                    raise
        else:
            self._state = STATE_RECONNECT

    @staticmethod
    def to_database(params):
        """Convert some parameters into values acceptable to a database backend.

        It is acceptable to override this method in subclasses, but it
        is not intended to be used externally.

        This delegates conversion to any L{Variable}s in the parameter
        list, and passes through all other values untouched.
        """
        for param in params:
            if isinstance(param, Variable):
                yield param.get(to_db=True)
            else:
                yield param

    def build_raw_cursor(self):
        """Get a new dbapi cursor object.

        It is acceptable to override this method in subclasses, but it
        is not intended to be called externally.
        """
        return self._raw_connection.cursor()

    def raw_execute(self, statement, params=None):
        """Execute a raw statement with the given parameters.

        It's acceptable to override this method in subclasses, but it
        is not intended to be called externally.

        If the global C{DEBUG} is True, the statement will be printed
        to standard out.

        @return: The dbapi cursor object, as fetched from L{build_raw_cursor}.
        """
        raw_cursor = self._check_disconnect(self.build_raw_cursor)
        self._check_disconnect(
            trace, "connection_raw_execute", self, raw_cursor,
            statement, params or ())
        if params:
            args = (statement, tuple(self.to_database(params)))
        else:
            args = (statement,)
        try:
            self._check_disconnect(raw_cursor.execute, *args)
        except Exception, error:
            self._check_disconnect(
                trace, "connection_raw_execute_error", self, raw_cursor,
                statement, params or (), error)
            raise
        else:
            self._check_disconnect(
                trace, "connection_raw_execute_success", self, raw_cursor,
                statement, params or ())
        return raw_cursor

    def _ensure_connected(self):
        """Ensure that we are connected to the database.

        If the connection is marked as dead, or if we can't reconnect,
        then raise DisconnectionError.
        """
        if self._blocked:
            raise ConnectionBlockedError("Access to connection is blocked")
        if self._state == STATE_CONNECTED:
            return
        elif self._state == STATE_DISCONNECTED:
            raise DisconnectionError("Already disconnected")
        elif self._state == STATE_RECONNECT:
            try:
                self._raw_connection = self._database.raw_connect()
            except DatabaseError, exc:
                self._state = STATE_DISCONNECTED
                self._raw_connection = None
                raise DisconnectionError(str(exc))
            else:
                self._state = STATE_CONNECTED

    def is_disconnection_error(self, exc, extra_disconnection_errors=()):
        """Check whether an exception represents a database disconnection.

        This should be overridden by backends to detect whichever
        exception values are used to represent this condition.
        """
        return False

    def _check_disconnect(self, function, *args, **kwargs):
        """Run the given function, checking for database disconnections."""
        # Allow the caller to specify additional exception types that
        # should be treated as possible disconnection errors.
        extra_disconnection_errors = kwargs.pop(
            'extra_disconnection_errors', ())
        try:
            return function(*args, **kwargs)
        except Exception, exc:
            if self.is_disconnection_error(exc, extra_disconnection_errors):
                self._state = STATE_DISCONNECTED
                self._raw_connection = None
                raise DisconnectionError(str(exc))
            else:
                raise

    def preset_primary_key(self, primary_columns, primary_variables):
        """Process primary variables before an insert happens.

        This method may be overwritten by backends to implement custom
        changes in primary variables before an insert happens.
        """


class Database(object):
    """A database that can be connected to.

    This should be subclassed for individual database backends.

    @cvar connection_factory: A callable which will take this database
        and should return an instance of L{Connection}.
    """

    connection_factory = Connection

    def connect(self, event=None):
        """Create a connection to the database.

        It calls C{self.connection_factory} to allow for ease of
        customization.

        @param event: The event system to broadcast messages with. If
            not specified, then no events will be broadcast.

        @return: An instance of L{Connection}.
        """
        return self.connection_factory(self, event)

    def raw_connect(self):
        """Create a raw database connection.

        This is used by L{Connection} objects to connect to the
        database.  It should be overriden in subclasses to do any
        database-specific connection setup.

        @return: A DB-API connection object.
        """
        raise NotImplementedError


def convert_param_marks(statement, from_param_mark, to_param_mark):
    # TODO: Add support for $foo$bar$foo$ literals.
    if from_param_mark == to_param_mark or from_param_mark not in statement:
        return statement
    tokens = statement.split("'")
    for i in range(0, len(tokens), 2):
        tokens[i] = tokens[i].replace(from_param_mark, to_param_mark)
    return "'".join(tokens)


_database_schemes = {}

def register_scheme(scheme, factory):
    """Register a handler for a new database URI scheme.

    @param scheme: the database URI scheme
    @param factory: a function taking a URI instance and returning a database.
    """
    _database_schemes[scheme] = factory


def create_database(uri):
    """Create a database instance.

    @param uri: An URI instance, or a string describing the URI. Some examples:
        - "sqlite:" An in memory sqlite database.
        - "sqlite:example.db" A SQLite database called example.db
        - "postgres:test" The database 'test' from the local postgres server.
        - "postgres://user:password@host/test" The database test on machine host
          with supplied user credentials, using postgres.
        - "anything:..." Where 'anything' has previously been registered
          with L{register_scheme}.
    """
    if isinstance(uri, basestring):
        uri = URI(uri)
    if uri.scheme in _database_schemes:
        factory = _database_schemes[uri.scheme]
    else:
        module = __import__("%s.databases.%s" % (storm.__name__, uri.scheme),
                            None, None, [""])
        factory = module.create_from_uri
    return factory(uri)

# Deal with circular import.        
from storm.tracer import trace