如何连接到Firebase Firestore？

// 引入Firebase SDK
import firebase from 'firebase/app';
import 'firebase/firestore';

// 初始化Firebase
const firebaseConfig = {
  // 配置信息
};
firebase.initializeApp(firebaseConfig);

// 获取Firestore实例
const firestore = firebase.firestore();

// 连接到Firestore
firestore.collection('users').get().then((querySnapshot) => {
  querySnapshot.forEach((doc) => {
    console.log(doc.id, ' => ', doc.data());
  });
});

// 引入Firebase SDK
import com.google.firebase.firestore.FirebaseFirestore;

// 获取Firestore实例
FirebaseFirestore db = FirebaseFirestore.getInstance();

// 连接到Firestore
db.collection("users")
    .get()
    .addOnCompleteListener(task -> {
        if (task.isSuccessful()) {
            for (QueryDocumentSnapshot document : task.getResult()) {
                Log.d(TAG, document.getId() + " => " + document.getData());
            }
        } else {
            Log.d(TAG, "Error getting documents: ", task.getException());
        }
    });

// 引入Firebase SDK
import Firebase

// 获取Firestore实例
let db = Firestore.firestore()

// 连接到Firestore
db.collection("users").getDocuments() { (querySnapshot, err) in
    if let err = err {
        print("Error getting documents: \(err)")
    } else {
        for document in querySnapshot!.documents {
            print("\(document.documentID) => \(document.data())")
        }
    }
}