如何检查一个值，例如名称是否存在于Cloud Firestore中任何文档的集合中? [英] How can I check if a value e.g. name exists in a collection within any of documents in Cloud Firestore?

问题描述

我想检查是否有一个值，例如(名称:"John")存在于我的Cloud Firestore中任何文档的集合中，因为如果这样的话，我不想创建具有该名称的新文档(在本例中为"John").如何检查名称是否存在?

I want to check if a value e.g. (name: ‘John’) exists in the collection of any document in my Cloud Firestore, because if it does I do not want to create a new document with that name (in this case ‘John’). How can I check if the name exists?

推荐答案

假定您在Firestore中有一个名为"users"的集合，以检查是否有名称为"John"的用户.已经存在，请使用以下代码行:

Assuming you have in Firestore a collection called "users", to check if a user with the name of "John" already exists, please use the following lines of code:

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference usersRef = rootRef.collection("users");
Query queryUsersByName = usersRef.whereEqualTo("name", "John");
queryUsersByName.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (DocumentSnapshot document : task.getResult()) {
                if (document.exists()) {
                    Log.d("TAG", "name already exists");
                } else {
                    //Do what you need to do
                }
            }
        } else {
            Log.d("TAG", "Error getting documents: ", task.getException());
        }
    }
});

如果名称为"John"的用户被拒绝，则上述代码的结果将是带有消息名称已存在"的日志语句.已经存在于用户"列表中.集合.

The result of the above code will be a log statement with the message "name already exists", if a user with the name of "John" already exists in the "users" collection.

这篇关于如何检查一个值，例如名称是否存在于Cloud Firestore中任何文档的集合中?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IT屋！