get_object源码分析

django\db\models\query.py
class QuerySet:
    def filter(self, *args, **kwargs):
        """
        Return a new QuerySet instance with the args ANDed to the existing
        set.
        """
        return self._filter_or_exclude(False, *args, **kwargs)

    def exclude(self, *args, **kwargs):
        """
        Return a new QuerySet instance with NOT (args) ANDed to the existing
        set.
        """
        return self._filter_or_exclude(True, *args, **kwargs)

    def _filter_or_exclude(self, negate, *args, **kwargs):
        if args or kwargs:
            assert self.query.can_filter(), \
                "Cannot filter a query once a slice has been taken."

        clone = self._chain()
        if negate:
            clone.query.add_q(~Q(*args, **kwargs))
        else:
            clone.query.add_q(Q(*args, **kwargs))

根据negate的值,发现执行这个过程
clone.query.add_q(Q(*args, **kwargs))

class Q(tree.Node):
    """
    Encapsulate filters as objects that can then be combined logically (using
    `&` and `|`).
    """
    # Connection types
    AND = 'AND'
    OR = 'OR'
    default = AND
    conditional = True

    def __init__(self, *args, **kwargs):
        connector = kwargs.pop('_connector', None)
        negated = kwargs.pop('_negated', False)
        super().__init__(children=list(args) + sorted(kwargs.items()), connector=connector, negated=negated)
        
 class Node:
    """
    A single internal node in the tree graph. A Node should be viewed as a
    connection (the root) with the children being either leaf nodes or other
    Node instances.
    """
    # Standard connector type. Clients usually won't use this at all and
    # subclasses will usually override the value.
    default = 'DEFAULT'

    def __init__(self, children=None, connector=None, negated=False):
        """Construct a new Node. If no connector is given, use the default."""
        self.children = children[:] if children else []
        self.connector = connector or self.default
        self.negated = negated
 
 返回Q对象
 执行add_q函数
     def add_q(self, q_object):
        """
        A preprocessor for the internal _add_q(). Responsible for doing final
        join promotion.
        """
        # For join promotion this case is doing an AND for the added q_object
        # and existing conditions. So, any existing inner join forces the join
        # type to remain inner. Existing outer joins can however be demoted.
        # (Consider case where rel_a is LOUTER and rel_a__col=1 is added - if
        # rel_a doesn't produce any rows, then the whole condition must fail.
        # So, demotion is OK.
        existing_inner = {a for a in self.alias_map if self.alias_map[a].join_type == INNER}
        clause, _ = self._add_q(q_object, self.used_aliases)
        if clause:
            self.where.add(clause, AND)
        self.demote_joins(existing_inner)
demote_joins 最终执行这个过程? 这个过滤的谜题没有解决?