app/django/db/models/sql/datastructures.py
author Todd Larsen <tlarsen@google.com>
Fri, 26 Sep 2008 19:47:07 +0000
changeset 204 7075c27170f2
parent 54 03e267d67478
child 323 ff1a9aa48cfd
permissions -rw-r--r--
Add ModelWithFieldAttributes *before* PolyModel, so that everything does not become a "ModelWithFieldAttributes" in the Datastore. The way PolyModel works, each Model class hierarchy is stored in the Datastore as the class that directly inherited from PolyModel. So, we do not want to insert ModelWithFieldAttributes *after* PolyModel by inheriting *from* PolyModel, or everything would just be a ModelWithFieldAttributes in the Datastore, instead of Person, Work, Group, etc.

"""
Useful auxilliary data structures for query construction. Not useful outside
the SQL domain.
"""

class EmptyResultSet(Exception):
    pass

class FullResultSet(Exception):
    pass

class MultiJoin(Exception):
    """
    Used by join construction code to indicate the point at which a
    multi-valued join was attempted (if the caller wants to treat that
    exceptionally).
    """
    def __init__(self, level):
        self.level = level

class Empty(object):
    pass

class RawValue(object):
    def __init__(self, value):
        self.value = value

class Aggregate(object):
    """
    Base class for all aggregate-related classes (min, max, avg, count, sum).
    """
    def relabel_aliases(self, change_map):
        """
        Relabel the column alias, if necessary. Must be implemented by
        subclasses.
        """
        raise NotImplementedError

    def as_sql(self, quote_func=None):
        """
        Returns the SQL string fragment for this object.

        The quote_func function is used to quote the column components. If
        None, it defaults to doing nothing.

        Must be implemented by subclasses.
        """
        raise NotImplementedError

class Count(Aggregate):
    """
    Perform a count on the given column.
    """
    def __init__(self, col='*', distinct=False):
        """
        Set the column to count on (defaults to '*') and set whether the count
        should be distinct or not.
        """
        self.col = col
        self.distinct = distinct

    def relabel_aliases(self, change_map):
        c = self.col
        if isinstance(c, (list, tuple)):
            self.col = (change_map.get(c[0], c[0]), c[1])

    def as_sql(self, quote_func=None):
        if not quote_func:
            quote_func = lambda x: x
        if isinstance(self.col, (list, tuple)):
            col = ('%s.%s' % tuple([quote_func(c) for c in self.col]))
        elif hasattr(self.col, 'as_sql'):
            col = self.col.as_sql(quote_func)
        else:
            col = self.col
        if self.distinct:
            return 'COUNT(DISTINCT %s)' % col
        else:
            return 'COUNT(%s)' % col

class Date(object):
    """
    Add a date selection column.
    """
    def __init__(self, col, lookup_type, date_sql_func):
        self.col = col
        self.lookup_type = lookup_type
        self.date_sql_func= date_sql_func

    def relabel_aliases(self, change_map):
        c = self.col
        if isinstance(c, (list, tuple)):
            self.col = (change_map.get(c[0], c[0]), c[1])

    def as_sql(self, quote_func=None):
        if not quote_func:
            quote_func = lambda x: x
        if isinstance(self.col, (list, tuple)):
            col = '%s.%s' % tuple([quote_func(c) for c in self.col])
        else:
            col = self.col
        return self.date_sql_func(self.lookup_type, col)