util.py 文件源码

def randomize_unitofwork():
    """Use random-ordering sets within the unit of work in order
    to detect unit of work sorting issues.

    This is a utility function that can be used to help reproduce
    inconsistent unit of work sorting issues.   For example,
    if two kinds of objects A and B are being inserted, and
    B has a foreign key reference to A - the A must be inserted first.
    However, if there is no relationship between A and B, the unit of work
    won't know to perform this sorting, and an operation may or may not
    fail, depending on how the ordering works out.   Since Python sets
    and dictionaries have non-deterministic ordering, such an issue may
    occur on some runs and not on others, and in practice it tends to
    have a great dependence on the state of the interpreter.  This leads
    to so-called "heisenbugs" where changing entirely irrelevant aspects
    of the test program still cause the failure behavior to change.

    By calling ``randomize_unitofwork()`` when a script first runs, the
    ordering of a key series of sets within the unit of work implementation
    are randomized, so that the script can be minimized down to the
    fundamental mapping and operation that's failing, while still reproducing
    the issue on at least some runs.

    This utility is also available when running the test suite via the
    ``--reversetop`` flag.

    .. versionadded:: 0.8.1 created a standalone version of the
       ``--reversetop`` feature.

    """
    from sqlalchemy.orm import unitofwork, session, mapper, dependency
    from sqlalchemy.util import topological
    from sqlalchemy.testing.util import RandomSet
    topological.set = unitofwork.set = session.set = mapper.set = \
        dependency.set = RandomSet