from django.db.models.sql import compiler

class SQLCompiler(compiler.SQLCompiler):

    def resolve_columns(self, row, fields=()):

        # If this query has limit/offset information, then we expect the

        # first column to be an extra "_RN" column that we need to throw

        # away.

        if self.query.high_mark is not None or self.query.low_mark:

            rn_offset = 1

        else:

            rn_offset = 0

        index_start = rn_offset + len(self.query.extra_select.keys())

        values = [self.query.convert_values(v, None, connection=self.connection)

                  for v in row[rn_offset:index_start]]

        for value, field in map(None, row[index_start:], fields):

            values.append(self.query.convert_values(value, field, connection=self.connection))

        return tuple(values)

    def as_sql(self, with_limits=True, with_col_aliases=False):

        """

        Creates the SQL for this query. Returns the SQL string and list

        of parameters.  This is overriden from the original Query class

        to handle the additional SQL Oracle requires to emulate LIMIT

        and OFFSET.

        If 'with_limits' is False, any limit/offset information is not

        included in the query.

        """

        # The `do_offset` flag indicates whether we need to construct

        # the SQL needed to use limit/offset with Oracle.

        do_offset = with_limits and (self.query.high_mark is not None

                                     or self.query.low_mark)

        if not do_offset:

            sql, params = super(SQLCompiler, self).as_sql(with_limits=False,

                    with_col_aliases=with_col_aliases)

        else:

            sql, params = super(SQLCompiler, self).as_sql(with_limits=False,

                                                    with_col_aliases=True)

            # Wrap the base query in an outer SELECT * with boundaries on

            # the "_RN" column.  This is the canonical way to emulate LIMIT

            # and OFFSET on Oracle.

            high_where = ''

            if self.query.high_mark is not None:

                high_where = 'WHERE ROWNUM <= %d' % (self.query.high_mark,)

            sql = 'SELECT * FROM (SELECT ROWNUM AS "_RN", "_SUB".* FROM (%s) "_SUB" %s) WHERE "_RN" > %d' % (sql, high_where, self.query.low_mark)

        return sql, params

class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):

    pass

class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):

    pass

class SQLUpdateCompiler(compiler.SQLUpdateCompiler, SQLCompiler):

    pass

class SQLAggregateCompiler(compiler.SQLAggregateCompiler, SQLCompiler):

    pass

class SQLDateCompiler(compiler.SQLDateCompiler, SQLCompiler):

    pass