152 lines
6.8 KiB
Python
152 lines
6.8 KiB
Python
"""
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Custom Query class for Oracle.
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Derives from: django.db.models.sql.query.Query
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"""
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import datetime
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from django.db.backends import util
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from django.utils.encoding import force_unicode
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# Cache. Maps default query class to new Oracle query class.
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_classes = {}
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def query_class(QueryClass, Database):
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"""
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Returns a custom django.db.models.sql.query.Query subclass that is
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appropriate for Oracle.
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The 'Database' module (cx_Oracle) is passed in here so that all the setup
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required to import it only needs to be done by the calling module.
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"""
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global _classes
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try:
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return _classes[QueryClass]
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except KeyError:
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pass
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class OracleQuery(QueryClass):
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def __reduce__(self):
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"""
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Enable pickling for this class (normal pickling handling doesn't
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work as Python can only pickle module-level classes by default).
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"""
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if hasattr(QueryClass, '__getstate__'):
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assert hasattr(QueryClass, '__setstate__')
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data = self.__getstate__()
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else:
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data = self.__dict__
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return (unpickle_query_class, (QueryClass,), data)
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def resolve_columns(self, row, fields=()):
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# If this query has limit/offset information, then we expect the
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# first column to be an extra "_RN" column that we need to throw
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# away.
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if self.high_mark is not None or self.low_mark:
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rn_offset = 1
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else:
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rn_offset = 0
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index_start = rn_offset + len(self.extra_select.keys())
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values = [self.convert_values(v, None)
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for v in row[rn_offset:index_start]]
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for value, field in map(None, row[index_start:], fields):
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values.append(self.convert_values(value, field))
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return values
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def convert_values(self, value, field):
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if isinstance(value, Database.LOB):
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value = value.read()
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if field and field.get_internal_type() == 'TextField':
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value = force_unicode(value)
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# Oracle stores empty strings as null. We need to undo this in
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# order to adhere to the Django convention of using the empty
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# string instead of null, but only if the field accepts the
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# empty string.
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if value is None and field and field.empty_strings_allowed:
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value = u''
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# Convert 1 or 0 to True or False
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elif value in (1, 0) and field and field.get_internal_type() in ('BooleanField', 'NullBooleanField'):
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value = bool(value)
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# Force floats to the correct type
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elif value is not None and field and field.get_internal_type() == 'FloatField':
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value = float(value)
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# Convert floats to decimals
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elif value is not None and field and field.get_internal_type() == 'DecimalField':
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value = util.typecast_decimal(field.format_number(value))
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# cx_Oracle always returns datetime.datetime objects for
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# DATE and TIMESTAMP columns, but Django wants to see a
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# python datetime.date, .time, or .datetime. We use the type
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# of the Field to determine which to cast to, but it's not
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# always available.
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# As a workaround, we cast to date if all the time-related
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# values are 0, or to time if the date is 1/1/1900.
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# This could be cleaned a bit by adding a method to the Field
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# classes to normalize values from the database (the to_python
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# method is used for validation and isn't what we want here).
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elif isinstance(value, Database.Timestamp):
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# In Python 2.3, the cx_Oracle driver returns its own
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# Timestamp object that we must convert to a datetime class.
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if not isinstance(value, datetime.datetime):
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value = datetime.datetime(value.year, value.month,
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value.day, value.hour, value.minute, value.second,
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value.fsecond)
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if field and field.get_internal_type() == 'DateTimeField':
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pass
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elif field and field.get_internal_type() == 'DateField':
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value = value.date()
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elif field and field.get_internal_type() == 'TimeField' or (value.year == 1900 and value.month == value.day == 1):
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value = value.time()
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elif value.hour == value.minute == value.second == value.microsecond == 0:
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value = value.date()
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return value
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def as_sql(self, with_limits=True, with_col_aliases=False):
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"""
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Creates the SQL for this query. Returns the SQL string and list
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of parameters. This is overriden from the original Query class
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to handle the additional SQL Oracle requires to emulate LIMIT
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and OFFSET.
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If 'with_limits' is False, any limit/offset information is not
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included in the query.
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"""
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# The `do_offset` flag indicates whether we need to construct
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# the SQL needed to use limit/offset with Oracle.
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do_offset = with_limits and (self.high_mark is not None
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or self.low_mark)
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if not do_offset:
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sql, params = super(OracleQuery, self).as_sql(with_limits=False,
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with_col_aliases=with_col_aliases)
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else:
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sql, params = super(OracleQuery, self).as_sql(with_limits=False,
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with_col_aliases=True)
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# Wrap the base query in an outer SELECT * with boundaries on
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# the "_RN" column. This is the canonical way to emulate LIMIT
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# and OFFSET on Oracle.
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high_where = ''
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if self.high_mark is not None:
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high_where = 'WHERE ROWNUM <= %d' % (self.high_mark,)
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sql = 'SELECT * FROM (SELECT ROWNUM AS "_RN", "_SUB".* FROM (%s) "_SUB" %s) WHERE "_RN" > %d' % (sql, high_where, self.low_mark)
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return sql, params
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_classes[QueryClass] = OracleQuery
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return OracleQuery
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def unpickle_query_class(QueryClass):
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"""
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Utility function, called by Python's unpickling machinery, that handles
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unpickling of Oracle Query subclasses.
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"""
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# XXX: Would be nice to not have any dependency on cx_Oracle here. Since
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# modules can't be pickled, we need a way to know to load the right module.
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import cx_Oracle
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klass = query_class(QueryClass, cx_Oracle)
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return klass.__new__(klass)
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unpickle_query_class.__safe_for_unpickling__ = True
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