在 Google App Engine 中，如何在处理表单提交时保持最终一致性? [英] In Google App Engine, how can I work with eventual consistency in handling form submissions?

问题描述

我注意到，在最终一致性的情况下，我习惯的通用表单处理工作流程(提交 -> 创建/更新记录 -> 重定向 -> 重新加载)不起作用.重定向后，新记录(可能)将无法显示.我应该如何处理表单以便在重新加载时显示更新?

I've noticed that, with eventual consistency, the common form-processing workflow that I am used to (submit -> create/update record -> redirect -> reload) doesn't work. Upon redirect, the new record (probably) won't be available for display. How should I handle forms so that updates are displayed upon reload?

我可以尝试使用强一致性，但作为 App Engine 文档 注释，更新仅限于 每秒更新一次.

I could try to use strong consistency, but as the App Engine documentation notes, updates are limited to one update per second.

那么，我如何处理提供即时用户反馈并最终保持一致性的表单?

So how can I process a form providing immediate user feedback with eventual consistency?

推荐答案

尝试重构您的代码，以便您按关键字获取(它始终为您提供最新数据)而不是执行查询.我意识到这并不总是可行的，但我会举一个最近对我有用的例子.

Try to restructure your code so that you are getting by key (which always gives you the most recent data) instead of doing a query. I realize this isn't always possible, but I'll give you a recent example of something that worked for me.

我有一个用户仪表板，用户可以在其中创建和删除项目".我的实体看起来像这样:

I have a user dashboard where a user can create and delete "items". My entities looked like this:

class User(ndb.Model)
    ...

class Item(ndb.Model)
    user = ndb.KeyProperty(User, required=True)

过去，我会在响应用户仪表板的 GET 请求时执行这样的查询.

In the past, I would do a query like this when responding to a GET request for the user dashboard.

items = Item.query(user=user.key)

这是一种糟糕的体验，因为用户会删除一个项目，并且在 POST/重定向/GET 之后，由于最终的一致性，刚刚删除的项目将再次出现在仪表板中.

This was a bad experience because a user would delete an item and after the POST/redirect/GET the just deleted item would again appear in the dashboard because of eventual consistency.

为了解决这个问题，我将我的用户实体更改为具有这样的项目列表:

To fix this, I changed my User entity to have a list of Items like this:

class User(ndb.Model)
    items = ndb.KeyProperty(repeated=True)
    ...

现在，当我显示仪表板时，我会这样做:

Now, when I show the dashboard, I do this:

items = ndb.get_multi(user.items)

由于我现在是按密钥获取的，因此数据始终是最新的.

Since I am now getting by key, the data is always up to date.

这对我有用，因为用户不会有那么多项目.但是，如果用户可以拥有数千个项目，由于实体大小限制，这种方法将不起作用.

This works for me because a user won't have that many items. If a user could have thousands of items, however, this approach wouldn't work because of the entity size limit.

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