问题描述
我对MongoDB完全陌生...我错过了一个新手"标签，因此专家们不必看到这个问题.
I am totally new to MongoDB... I am missing a "newbie" tag, so the experts would not have to see this question.
我正在尝试使用表达式更新集合中的所有文档.我期望解决的查询是:
I am trying to update all documents in a collection using an expression. The query I was expecting to solve this was:
db.QUESTIONS.update({}, { $set: { i_pp : i_up * 100 - i_down * 20 } }, false, true);
但是，这会导致以下错误消息:
That, however, results in the following error message:
与此同时，数据库在吃这个方面没有任何问题:
At the same time, the database did not have any problem with eating this one:
db.QUESTIONS.update({}, { $set: { i_pp : 0 } }, false, true);
我是否必须一次完成一份文档?这似乎太复杂了.
Do I have to do this one document at a time or something? That just seems excessively complicated.
更新谢谢塞尔吉奥·图伦采夫(Sergio Tulentsev)告诉我它不起作用.现在，我真的在为如何做到这一点而苦苦挣扎.我向乐于助人的灵魂提供500个利润点，他们可以用MongoDB理解的方式编写此信息.如果您在我们的论坛上注册，我可以在此处将利润点添加到您的帐户中.
UpdateThank you Sergio Tulentsev for telling me that it does not work. Now, I am really struggling with how to do this. I offer 500 Profit Points to the helpful soul, who can write this in a way that MongoDB understands. If you register on our forum I can add the Profit Points to your account there.
推荐答案
您不能在更新中使用表达式.或者，相反，您不能使用依赖于文档字段的表达式.简单的自包含数学表达式就可以了(例如2 * 2).
You can't use expressions in updates. Or, rather, you can't use expressions that depend on fields of the document. Simple self-containing math expressions are fine (e.g. 2 * 2).
如果要为所有文档设置一个新字段，这是其他字段的功能，则必须遍历它们并手动更新.多次更新在这里无济于事.
If you want to set a new field for all documents that is a function of other fields, you have to loop over them and update manually. Multi-update won't help here.
这篇关于用表达式而不是值更新的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！