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Diffstat (limited to 'lib/_json.py')
| -rw-r--r-- | lib/_json.py | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/lib/_json.py b/lib/_json.py new file mode 100644 index 0000000..536dd58 --- /dev/null +++ b/lib/_json.py @@ -0,0 +1,194 @@ +"""Implementation of the JSON adaptation objects + +This module exists to avoid a circular import problem: pyscopg2.extras depends +on psycopg2.extension, so I can't create the default JSON typecasters in +extensions importing register_json from extras. +""" + +# psycopg/_json.py - Implementation of the JSON adaptation objects +# +# Copyright (C) 2012 Daniele Varrazzo <daniele.varrazzo@gmail.com> +# +# psycopg2 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 3 of the License, or +# (at your option) any later version. +# +# In addition, as a special exception, the copyright holders give +# permission to link this program with the OpenSSL library (or with +# modified versions of OpenSSL that use the same license as OpenSSL), +# and distribute linked combinations including the two. +# +# You must obey the GNU Lesser General Public License in all respects for +# all of the code used other than OpenSSL. +# +# psycopg2 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. + +import sys + +from psycopg2._psycopg import ISQLQuote, QuotedString +from psycopg2._psycopg import new_type, new_array_type, register_type + + +# import the best json implementation available +if sys.version_info[:2] >= (2,6): + import json +else: + try: + import simplejson as json + except ImportError: + json = None + + +# oids from PostgreSQL 9.2 +JSON_OID = 114 +JSONARRAY_OID = 199 + +class Json(object): + """ + An `~psycopg2.extensions.ISQLQuote` wrapper to adapt a Python object to + :sql:`json` data type. + + `!Json` can be used to wrap any object supported by the provided *dumps* + function. If none is provided, the standard :py:func:`json.dumps()` is + used (`!simplejson` for Python < 2.6; + `~psycopg2.extensions.ISQLQuote.getquoted()` will raise `!ImportError` if + the module is not available). + + """ + def __init__(self, adapted, dumps=None): + self.adapted = adapted + + if dumps is not None: + self._dumps = dumps + elif json is not None: + self._dumps = json.dumps + else: + self._dumps = None + + def __conform__(self, proto): + if proto is ISQLQuote: + return self + + def dumps(self, obj): + """Serialize *obj* in JSON format. + + The default is to call `!json.dumps()` or the *dumps* function + provided in the constructor. You can override this method to create a + customized JSON wrapper. + """ + dumps = self._dumps + if dumps is not None: + return dumps(obj) + else: + raise ImportError( + "json module not available: " + "you should provide a dumps function") + + def getquoted(self): + s = self.dumps(self.adapted) + return QuotedString(s).getquoted() + + +def register_json(conn_or_curs=None, globally=False, loads=None, + oid=None, array_oid=None): + """Create and register typecasters converting :sql:`json` type to Python objects. + + :param conn_or_curs: a connection or cursor used to find the :sql:`json` + and :sql:`json[]` oids; the typecasters are registered in a scope + limited to this object, unless *globally* is set to `!True`. It can be + `!None` if the oids are provided + :param globally: if `!False` register the typecasters only on + *conn_or_curs*, otherwise register them globally + :param loads: the function used to parse the data into a Python object. If + `!None` use `!json.loads()`, where `!json` is the module chosen + according to the Python version (see above) + :param oid: the OID of the :sql:`json` type if known; If not, it will be + queried on *conn_or_curs* + :param array_oid: the OID of the :sql:`json[]` array type if known; + if not, it will be queried on *conn_or_curs* + + The connection or cursor passed to the function will be used to query the + database and look for the OID of the :sql:`json` type. No query is + performed if *oid* and *array_oid* are provided. Raise + `~psycopg2.ProgrammingError` if the type is not found. + + """ + if oid is None: + oid, array_oid = _get_json_oids(conn_or_curs) + + JSON, JSONARRAY = _create_json_typecasters(oid, array_oid, loads) + + register_type(JSON, not globally and conn_or_curs or None) + + if JSONARRAY is not None: + register_type(JSONARRAY, not globally and conn_or_curs or None) + + return JSON, JSONARRAY + +def register_default_json(conn_or_curs=None, globally=False, loads=None): + """ + Create and register :sql:`json` typecasters for PostgreSQL 9.2 and following. + + Since PostgreSQL 9.2 :sql:`json` is a builtin type, hence its oid is known + and fixed. This function allows specifying a customized *loads* function + for the default :sql:`json` type without querying the database. + All the parameters have the same meaning of `register_json()`. + """ + return register_json(conn_or_curs=conn_or_curs, globally=globally, + loads=loads, oid=JSON_OID, array_oid=JSONARRAY_OID) + +def _create_json_typecasters(oid, array_oid, loads=None): + """Create typecasters for json data type.""" + if loads is None: + if json is None: + raise ImportError("no json module available") + else: + loads = json.loads + + def typecast_json(s, cur): + if s is None: + return None + return loads(s) + + JSON = new_type((oid, ), 'JSON', typecast_json) + if array_oid is not None: + JSONARRAY = new_array_type((array_oid, ), "JSONARRAY", JSON) + else: + JSONARRAY = None + + return JSON, JSONARRAY + +def _get_json_oids(conn_or_curs): + # lazy imports + from psycopg2.extensions import STATUS_IN_TRANSACTION + from psycopg2.extras import _solve_conn_curs + + conn, curs = _solve_conn_curs(conn_or_curs) + + # Store the transaction status of the connection to revert it after use + conn_status = conn.status + + # column typarray not available before PG 8.3 + typarray = conn.server_version >= 80300 and "typarray" or "NULL" + + # get the oid for the hstore + curs.execute( + "SELECT t.oid, %s FROM pg_type t WHERE t.typname = 'json';" + % typarray) + r = curs.fetchone() + + # revert the status of the connection as before the command + if (conn_status != STATUS_IN_TRANSACTION and not conn.autocommit): + conn.rollback() + + if not r: + raise conn.ProgrammingError("json data type not found") + + return r + + + |