พื้นฐาน Cloud Firestore

Cloud Firestore คืออะไร

รับอินสแตนซ์ Firestore

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore

val db = Firebase.firestore

val usersRef = db.collection("users")
val oneUser = db.collection("users").document("abc123")

ออกแบบโครงสร้างข้อมูล

data class Note(
    val title: String = "",
    val body: String = "",
    val done: Boolean = false,
    val createdAt: Long = 0L
)

เขียนเอกสาร

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore
import kotlinx.coroutines.tasks.await

suspend fun addNote(note: Note): String {
    val ref = Firebase.firestore
        .collection("notes")
        .add(note)          // auto-generated ID
        .await()
    return ref.id
}

อ่านเอกสาร

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore
import kotlinx.coroutines.tasks.await

suspend fun loadNote(id: String): Note? {
    val snapshot = Firebase.firestore
        .collection("notes")
        .document(id)
        .get()
        .await()
    return if (snapshot.exists()) snapshot.toObject(Note::class.java) else null
}

อัปเดตและลบ

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore
import kotlinx.coroutines.tasks.await

suspend fun markDone(id: String) {
    Firebase.firestore.collection("notes").document(id)
        .update("done", true)
        .await()
}

suspend fun removeNote(id: String) {
    Firebase.firestore.collection("notes").document(id)
        .delete()
        .await()
}

สืบค้นคอลเลกชัน

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore
import kotlinx.coroutines.tasks.await

suspend fun pendingNotes(): List<Note> {
    val snap = Firebase.firestore.collection("notes")
        .whereEqualTo("done", false)
        .orderBy("createdAt")
        .limit(20)
        .get()
        .await()
    return snap.documents.mapNotNull { it.toObject(Note::class.java) }
}

ตัวติดตามแบบเรียลไทม์

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore

val registration = Firebase.firestore.collection("notes")
    .whereEqualTo("done", false)
    .addSnapshotListener { snapshot, error ->
        if (error != null || snapshot == null) return@addSnapshotListener
        val notes = snapshot.toObjects(Note::class.java)
        println("Now have ${notes.size} pending notes")
    }

// Later: registration.remove()

ข้อมูลเรียลไทม์ในรูปแบบ Flow

import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore
import kotlinx.coroutines.channels.awaitClose
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.callbackFlow

fun notesFlow(): Flow<List<Note>> = callbackFlow {
    val reg = Firebase.firestore.collection("notes")
        .addSnapshotListener { snap, err ->
            if (err == null && snap != null) {
                trySend(snap.toObjects(Note::class.java))
            }
        }
    awaitClose { reg.remove() }
}

แสดงข้อมูลใน Compose

@Composable
fun NotesScreen(viewModel: NotesViewModel) {
    val notes by viewModel.notes.collectAsStateWithLifecycle()

    LazyColumn {
        items(notes) { note ->
            ListItem(
                headlineContent = { Text(note.title) },
                supportingContent = { Text(note.body) }
            )
        }
    }
}

กฎความปลอดภัยมีความสำคัญ

// firestore.rules
rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId}/{document=**} {
      allow read, write: if request.auth != null
                         && request.auth.uid == userId;
    }
  }
}

ตรวจสอบความเข้าใจ

สรุป: Firestore