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假设我有类 Dog()、Walrus()、Boot()。我想让它这样你就不能更新 Walrus 对象，尽管你可以删除它们并且你永远不能删除 Boot 对象。所以如果这样做：

dog1 = Dog("DogName")
walrus1 = Walrus("WalrusName")
boot1 = Boot("BootName")
session.add(dog1)
session.add(walrus1)
session.add(boot1)
session.flush()
transaction.commit()
dog1.name = "Fluffy"
walrus1.name = "Josh"
boot1.name = "Pogo"
session.flush()
transaction.commit()

它会在更改海象名称时引发异常，但允许更改其他名称。如果我试图删除 boot1 它会抛出异常。

我对事件监听器进行了几次尝试，但我接触的两种方式都没有让我一路走好：

#One possibility
#I don't know how to tell that it's just an update though
#The is_modified seems to take inserts as well

@event.listens_for(Session, 'before_flush')
def listener(thissession, flush_context, instances):
    for obj in thissession:
        if isinstance(obj, Walrus):
            if thissession.is_modified(obj, include_collections=False):
                thissession.expunge(obj)


#Possiblity two
#It says before_update but it seems to take in inserts as well
#Also documentation says it's not completely reliable to capture all statements
#where an update will occur
@event.listens_for(Walrus, 'before_update', raw=True)
def pleasework(mapper, connection, target):
    print "\n\nInstance %s being updated\n\n" % target
    object_session(target).expunge(target)

编辑1：

@event.listens_for(Walrus, 'before_update', raw=True)
def prevent_walrus_update(mapper, connection, target):
    print "\n\nInstance %s being updated\n\n" % target
    if target not None:
        raise

@event.listens_for(Boot, 'before_delete', raw=True)
def prevent_boot_delete(mapper, connection, target):
    print "\n\nInstance %s being deleted\n\n" % target
    if target not None:
        raise

我已经让这个工作，它不允许我更新 Walrus 或删除 Boot，但是任何试图尝试都会崩溃的 AttributeError 的提示，我似乎没有任何能力捕捉到。例如，如果我运行 Walrus1.name = "Josh" 然后任何查询，即使是 get，AttributeError 都会使应用程序崩溃。我比以前走得更远，但仍然相当不便。

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1 回答 1

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您发布的第一个解决方案看起来应该可以工作，如果您只是将循环更改为：

for obj in thissession.dirty:

before_flush您可以通过循环使用相同的事件来防止删除 Boot 对象thissession.deleted。

于 2013-01-30T09:04:56.703 回答