1 # -*- coding: utf-8 -*-

     2 #

     3 # PgManager - manage database connections

     4 #

     5 # Requires: Python 2.6, psycopg2

     6 #

     7 # Copyright (c) 2010, 2011  Radek Brich <radek.brich@devl.cz>

     8 #

     9 # Permission is hereby granted, free of charge, to any person obtaining a copy

    10 # of this software and associated documentation files (the "Software"), to deal

    11 # in the Software without restriction, including without limitation the rights

    12 # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

    13 # copies of the Software, and to permit persons to whom the Software is

    14 # furnished to do so, subject to the following conditions:

    15 #

    16 # The above copyright notice and this permission notice shall be included in

    17 # all copies or substantial portions of the Software.

    18 #

    19 # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

    20 # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

    21 # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

    22 # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

    23 # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

    24 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

    25 # THE SOFTWARE.

    26 

    27 """Postgres database connection manager

    28 

    29 PgManager wraps psycopg2 connect function, adding following features:

    30 

    31  * Manage database connection parameters - link connection parameters

    32    to an unique identifier, retrieve connection object by this identifier

    33 

    34  * Connection pooling - connections with same identifier are pooled and reused

    35 

    36  * Easy query using the with statement - retrieve cursor directly by connection

    37    identifier, don't worry about connections

    38 

    39  * Dict rows - cursor has additional methods like fetchall_dict(), which

    40    returns dict row instead of ordinary list-like row

    41 

    42 Example:

    43 

    44 import pgmanager

    45 

    46 pgm = pgmanager.get_instance()

    47 pgm.create_conn(hostaddr='127.0.0.1', dbname='postgres')

    48 

    49 with pgm.cursor() as curs:

    50     curs.execute('SELECT now() AS now')

    51     row = curs.fetchone_dict()

    52     print row.now

    53 

    54 First, we have obtained PgManager instance. This is like calling

    55 PgManager(), although in our example the instance is global. That means

    56 getting the instance in another module brings us all the defined connections

    57 etc.

    58 

    59 On second line we created connection named 'default' (this name can be left out).

    60 The with statement obtains connection (actually connects to database when needed),

    61 then returns cursor for this connection. On exit, the connection is returned

    62 to the pool or closed (depending on number of connections on pool and setting

    63 of keep_open parameter).

    64 

    65 The row returned by fetchone_dict() is special dict object, which can be accessed

    66 using item or attribute access, that is row['now'] or row.now.

    67 """

    68 

    69 from contextlib import contextmanager

    70 import logging

    71 import threading

    72 import select

    73 

    74 import psycopg2

    75 import psycopg2.extensions

    76 

    77 from psycopg2 import DatabaseError, IntegrityError

    78 

    79 

    80 class PgManagerError(Exception):

    81 

    82     pass

    83 

    84 

    85 class ConnectionInfo:

    86 

    87     def __init__(self, dsn, isolation_level=None, init_statement=None, keep_open=1):

    88         self.dsn = dsn

    89         self.isolation_level = isolation_level

    90         self.init_statement = init_statement

    91         self.keep_open = keep_open

    92 

    93 

    94 class RowDict(dict):

    95 

    96     def __getattr__(self, key):

    97         return self[key]

    98 

    99 

   100 class Cursor(psycopg2.extensions.cursor):

   101 

   102     def execute(self, query, args=None):

   103         try:

   104             return super(Cursor, self).execute(query, args)

   105         finally:

   106             log.debug(self.query)

   107 

   108     def callproc(self, procname, args=None):

   109         try:

   110             return super(Cursor, self).callproc(procname, args)

   111         finally:

   112             log.debug(self.query)

   113 

   114     def row_dict(self, row, lstrip=None):

   115         adjustname = lambda a: a

   116         if lstrip:

   117             adjustname = lambda a: a.lstrip(lstrip)

   118         return RowDict(zip([adjustname(desc[0]) for desc in self.description], row))

   119 

   120     def fetchone_dict(self, lstrip=None):

   121         row = super(Cursor, self).fetchone()

   122         if not row:

   123             return row

   124         return self.row_dict(row, lstrip)

   125 

   126     def fetchall_dict(self, lstrip=None):

   127         rows = super(Cursor, self).fetchall()

   128         return [self.row_dict(row, lstrip) for row in rows]

   129 

   130 

   131 class Connection(psycopg2.extensions.connection):

   132 

   133     def cursor(self, name=None):

   134         if name is None:

   135             return super(Connection, self).cursor(cursor_factory=Cursor)

   136         else:

   137             return super(Connection, self).cursor(name, cursor_factory=Cursor)

   138 

   139 

   140 class PgManager:

   141 

   142     def __init__(self):

   143         self.conn_known = {}  # available connections

   144         self.conn_pool = {}

   145         self.lock = threading.Lock()

   146 

   147     def __del__(self):

   148         for conn in tuple(self.conn_known.keys()):

   149             self.destroy_conn(conn)

   150 

   151     def create_conn(self, name='default', isolation_level=None, dsn=None, **kw):

   152         '''Create named connection.'''

   153         if name in self.conn_known:

   154             raise PgManagerError('Connection name "%s" already registered.', name)

   155 

   156         if dsn is None:

   157             dsn = ' '.join([x[0]+'='+str(x[1]) for x in kw.items()])

   158 

   159         isolation_level = self._normalize_isolation_level(isolation_level)

   160         ci = ConnectionInfo(dsn, isolation_level)

   161 

   162         self.conn_known[name] = ci

   163         self.conn_pool[name] = []

   164 

   165     def close_conn(self, name='default'):

   166         '''Close all connections of given name.

   167         

   168         Connection credentials are still saved.

   169         

   170         '''

   171         while len(self.conn_pool[name]):

   172             conn = self.conn_pool[name].pop()

   173             conn.close()

   174 

   175     def destroy_conn(self, name='default'):

   176         '''Destroy connection.

   177         

   178         Counterpart of create_conn.

   179         

   180         '''

   181         if not name in self.conn_known:

   182             raise PgManagerError('Connection name "%s" not registered.', name)

   183 

   184         self.close_conn(name)

   185 

   186         del self.conn_known[name]

   187         del self.conn_pool[name]

   188 

   189     def get_conn(self, name='default'):

   190         '''Get connection of name 'name' from pool.'''

   191         self.lock.acquire()

   192         try:

   193             if not name in self.conn_known:

   194                 raise PgManagerError("Connection name '%s' not registered.", name)

   195 

   196             conn = None

   197             while len(self.conn_pool[name]) and conn is None:

   198                 conn = self.conn_pool[name].pop()

   199                 if conn.closed:

   200                     conn = None

   201 

   202             if conn is None:

   203                 ci = self.conn_known[name]

   204                 conn = psycopg2.connect(ci.dsn, connection_factory=Connection)

   205                 if not ci.isolation_level is None:

   206                     conn.set_isolation_level(ci.isolation_level)

   207                 if ci.init_statement:

   208                     curs = conn.cursor()

   209                     curs.execute(ci.init_statement)

   210                     curs.close()

   211         finally:

   212             self.lock.release()

   213         return conn

   214 

   215     def put_conn(self, conn, name='default'):

   216         '''Put connection back to pool.

   217         

   218         Name must be same as used for get_conn,

   219         otherwise things become broken.

   220         

   221         '''

   222         self.lock.acquire()

   223         try:

   224             if not name in self.conn_known:

   225                 raise PgManagerError("Connection name '%s' not registered.", name)

   226 

   227             if len(self.conn_pool[name]) >= self.conn_known[name].keep_open:

   228                 conn.close()

   229                 return

   230 

   231             if conn.get_transaction_status() == psycopg2.extensions.TRANSACTION_STATUS_UNKNOWN:

   232                 conn.close()

   233                 return

   234 

   235             # connection returned to the pool must not be in transaction

   236             if conn.get_transaction_status() != psycopg2.extensions.TRANSACTION_STATUS_IDLE:

   237                 conn.rollback()

   238 

   239             self.conn_pool[name].append(conn)

   240         finally:

   241             self.lock.release()

   242 

   243     @contextmanager

   244     def cursor(self, name='default'):

   245         '''Cursor context.

   246         

   247         Uses any connection of name 'name' from pool

   248         and returns cursor for that connection.

   249         

   250         '''

   251         conn = self.get_conn(name)

   252 

   253         try:

   254             curs = conn.cursor()

   255             yield curs

   256         finally:

   257             curs.close()

   258             self.put_conn(conn, name)

   259 

   260     def wait_for_notify(self, name='default', timeout=5):

   261         '''Wait for asynchronous notifies, return the last one.

   262         

   263         Returns None on timeout.

   264         

   265         '''

   266         conn = self.get_conn(name)

   267         

   268         try:

   269             # any residual notify?

   270             # then return it, that should not break anything

   271             if conn.notifies:

   272                 return conn.notifies.pop()

   273 

   274             if select.select([conn], [], [], timeout) == ([], [], []):

   275                 # timeout

   276                 return None

   277             else:

   278                 conn.poll()

   279 

   280                 # return just the last notify (we do not care for older ones)

   281                 if conn.notifies:

   282                     return conn.notifies.pop()

   283                 return None

   284         finally:

   285             # clean notifies

   286             while conn.notifies:

   287                 conn.notifies.pop()

   288             self.put_conn(conn, name)

   289 

   290     def _normalize_isolation_level(self, level):

   291         if type(level) == str:

   292             if level.lower() == 'autocommit':

   293                 return psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT

   294             if level.lower() == 'read_committed':

   295                 return psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED

   296             if level.lower() == 'serializable':

   297                 return psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE

   298             raise PgManagerError('Unknown isolation level name: "%s"', level)

   299         return level

   300 

   301 

   302 try:

   303     NullHandler = logging.NullHandler

   304 except AttributeError:

   305     class NullHandler(logging.Handler):

   306         def emit(self, record):

   307             pass

   308 

   309 

   310 log = logging.getLogger("pgmanager")

   311 log.addHandler(NullHandler())

   312 

   313 

   314 instance = None

   315 

   316 

   317 def get_instance():

   318     global instance

   319     if instance is None:

   320         instance = PgManager()

   321     return instance

   322 

   323