如何在 Cloud Firestore 中查询不存在的文档键 [英] How to query Cloud Firestore for non-existing keys of documents

问题描述

假设我有一个带有一些可选属性的数据模型.例如，这可以是具有名字"、姓氏"和可选的网站"属性的用户对象.

在 Cloud Firestore 中，只有具有已知网站的用户文档才会设置网站"属性，对于所有其他用户文档，此属性将不存在.

我现在的问题是如何在没有网站"属性的情况下查询所有用户文档.

谢谢.

解决方案

文档可以包含具有 null 值数据类型的属性(请参阅

这仅返回文档 inuwlZOvZNTHuBakS6GV，因为文档 9Hf7uwORiiToOKz6zcsX 在 website 属性中包含一个字符串值.

我相信您通常在 Swift 中开发，不幸的是不支持自定义对象，但您可以使用 NSNull() 将 null 值写入 Firestore.例如(我不精通 Swift，所以请随时纠正任何问题):

//写入数据让 docData: [字符串: 任何] = ["firstname": "例子","lastname": "用户",网站":NSNull()]db.collection("data").document("one").setData(docData) { 输入错误如果让错误 = 错误 {print("写入文档时出错:(err)")} 别的 {print("文档写入成功！")}}//查询空值让查询 = db.collection("test").whereField("website", isEqualTo: NSNull())

文档没有提到查询不存在的值的方法，所以这似乎是下一个最佳方法.如果有人可以改进或提出替代方案，请这样做.

Let's say I have a data model with some optional properties. This could be for example a user object with a "firstname", a "lastname" and an optional "website" property.

In Cloud Firestore only user documents with a known website would have the "website" property set, for all other user documents this property would not exist.

My questions is now how to query for all user documents without a "website" property.

Thanks.

解决方案

Documents can contain properties with a null value data type (see data types documentation). This will then allow you to construct a query to limit results where the website property is null.

This is not quite the same as a missing property, but if you use custom objects to write data to Firestore, empty properties will automatically be saved as null rather than not at all. You can also manually/programmatically write a null value to the database.

In Android, I tested this using the following:

FirebaseFirestore.getInstance().collection("test").whereEqualTo("website", null).get();

Where my database structure looked like:

This returned only the document inuwlZOvZNTHuBakS6GV, because document 9Hf7uwORiiToOKz6zcsX contains a string value in the website property.

I believe you usually develop in Swift, where unfortunately custom objects aren't supported, but you can use NSNull() to write a null value to Firestore. For example (I'm not proficient in Swift, so feel free to correct any issues):

// Writing data
let docData: [String: Any] = [
    "firstname": "Example",
    "lastname": "User",
    "website": NSNull()
]
db.collection("data").document("one").setData(docData) { err in
    if let err = err {
        print("Error writing document: (err)")
    } else {
        print("Document successfully written!")
    }
}

// Querying for null values
let query = db.collection("test").whereField("website", isEqualTo: NSNull())

The documentation doesn't mention a method to query for values that don't exist, so this seems like the next best approach. If anyone can improve or suggest alternatives, please do.

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