Firestore-检查是否存在要更新的文档 [英] Firestore - Check if the document which is being updated exists

问题描述

据我所知-为了检查document是否存在，我应该使用get函数并查看它是否存在.

As far as I know - In order to check whether a document exists or not, I should use the get function and see if it does.

我的问题是关于更新时进行检查-是否可以?(考虑到document在更新发生时可能会消失).

My question is about checking while updating - Is it possible? (Considering that the document might be gone when the update occurs).

我试图更新一个空的document，但出现一个错误，提示该文档不存在，但我认为这可能不是检查此文档的成功方法.

I have tried to update an empty document and I got an error which says that the document doesn't exist, but I think this might not be the successful way to check this.

推荐答案

有几种方法可以将数据写入Cloud Firestore:

There are a few ways to write data to Cloud Firestore:

• update()-更改文档中已存在的字段.如果文档不存在，则失败.
• set()-覆盖文档中的数据，如果尚不存在则创建该文档.如果您只想部分更新文档，请使用SetOptions.merge().
• create()-仅在服务器端SDK中可用，类似于set()，但如果文档已存在则失败.

• update() - change fields on a document that already exists. Fails if the document does not exist.
• set() - overwrite the data in a document, creating the document if it does not already exist. If you want to only partially update a document, use SetOptions.merge().
• create() - only available in the server-side SDKs, similar to set() but fails if the document already exists.

因此，您只需要针对用例使用正确的操作即可.如果要在不知道文档是否存在的情况下更新文档，则要使用带有merge()选项的set()，如下所示(此示例适用于Java):

So you just need to use the correct operation for your use case. If you want to update a document without knowing if it exists or not, you want to use a set() with the merge() option like this (this example is for Java):

// Update one field, creating the document if it does not already exist.
Map<String, Object> data = new HashMap<>();
data.put("capital", true);

db.collection("cities").document("BJ")
        .set(data, SetOptions.merge());

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