检查包含具有特定值的字段的文档是否存在的最佳方法是什么 - Firestore？

Question

I want to check if a field nam has a specific value and return a boolen if true(or check by something else - whatever). Here is my code which actually does check but still returns something (some autogenerated stuff from the server) and if I check for null of course it will never be null.

So, whats the easiest and best way to do this? And is it better to do it server-side? PS I want to inform the user that a field with this value was found!

Here is my current code:

var type_of_vendor = db().collection(this.state.vendor_type).where('nam', '==', this.state.vendor_name);
type_of_vendor.get()
    .then((user) => {
        if (user.exists) {
            this.state.error = true;
            let errorMessage = 'error message';
            this.setState({ errorMessage: errorMessage });
        } else {
            this._signUpVendorvalidateHandler();
        }
    });

Answer 1

Your code looks fine to me. The only think I'd change is add .limit(1) to the query, so that you never retrieve more than 1 document, even if there are multiple matches.

Doing this server-side is possible with either Cloud Functions, or on a server you already control.

If you do this on the server, you will only have to return whether the document exists (a boolean), instead of the entire document. So you're saving some bandwidth there.