# Cloud Firestore on Android (Kotlin)

This guide walks you through using Cloud Firestore in your Android app using
Kotlin.

### Enable Firestore via CLI

Before adding dependencies in your app, make sure you enable the Firestore
service in your Firebase Project using the Firebase CLI:

```bash
npx -y firebase-tools@latest init firestore
```

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### 1. Add Dependencies

In your module-level `build.gradle.kts` (usually `app/build.gradle.kts`), add
the dependency for Cloud Firestore:

```kotlin
dependencies {
    // [AGENT] Fetch the latest available BoM version from https://firebase.google.com/support/release-notes/android before adding this
    implementation(platform("com.google.firebase:firebase-bom:<latest_bom_version>"))

    // Add the dependency for the Cloud Firestore library
    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-firestore")
}
```

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### 2. Initialize Firestore

In your Activity or Fragment, initialize the `FirebaseFirestore` instance:

```kotlin
import com.google.firebase.firestore.FirebaseFirestore
import com.google.firebase.firestore.ktx.firestore
import com.google.firebase.ktx.Firebase

class MainActivity : AppCompatActivity() {

    private lateinit var db: FirebaseFirestore

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val db = Firebase.firestore
        
        setContent {
            MaterialTheme {
                Text("Firestore initialized!")
            }
        }
    }
}
```

#### Jetpack Compose (Modern)

Initialize inside a `ComponentActivity` using `setContent`:

```kotlin
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
import com.google.firebase.Firebase
import com.google.firebase.firestore.firestore

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val db = Firebase.firestore
        
        setContent {
            MaterialTheme {
                Text("Firestore initialized!")
            }
        }
    }
}
```

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### 3. Add Data

Add a new document with a generated ID using `add()`:

```kotlin
// Create a new user with a first and last name
val user = hashMapOf(
    "first" to "Ada",
    "last" to "Lovelace",
    "born" to 1815
)

// Add a new document with a generated ID
db.collection("users")
    .add(user)
    .addOnSuccessListener { documentReference ->
        Log.d(TAG, "DocumentSnapshot added with ID: ${documentReference.id}")
    }
    .addOnFailureListener { e ->
        Log.w(TAG, "Error adding document", e)
    }
```

Or set a document with a specific ID using `set()`:

```kotlin
val city = hashMapOf(
    "name" to "Los Angeles",
    "state" to "CA",
    "country" to "USA"
)

db.collection("cities").document("LA")
    .set(city)
    .addOnSuccessListener { Log.d(TAG, "DocumentSnapshot successfully written!") }
    .addOnFailureListener { e -> Log.w(TAG, "Error writing document", e) }
```

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### 4. Read Data

Read a single document using `get()`:

```kotlin
val docRef = db.collection("cities").document("SF")
docRef.get()
    .addOnSuccessListener { document ->
        if (document != null && document.exists()) {
            Log.d(TAG, "DocumentSnapshot data: ${document.data}")
        } else {
            Log.d(TAG, "No such document")
        }
    }
    .addOnFailureListener { exception ->
        Log.d(TAG, "get failed with ", exception)
    }
```

Read multiple documents using a query:

```kotlin
db.collection("cities")
    .whereEqualTo("capital", true)
    .get()
    .addOnSuccessListener { documents ->
        for (document in documents) {
            Log.d(TAG, "${document.id} => ${document.data}")
        }
    }
    .addOnFailureListener { exception ->
        Log.w(TAG, "Error getting documents: ", exception)
    }
```

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### 5. Update Data

Update some fields of a document using `update()` without overwriting the entire
document:

```kotlin
val washingtonRef = db.collection("cities").document("DC")

// Set the "isCapital" field to true
washingtonRef
    .update("capital", true)
    .addOnSuccessListener { Log.d(TAG, "DocumentSnapshot successfully updated!") }
    .addOnFailureListener { e -> Log.w(TAG, "Error updating document", e) }
```

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### 6. Delete Data

Delete a document using `delete()`:

```kotlin
db.collection("cities").document("DC")
    .delete()
    .addOnSuccessListener { Log.d(TAG, "DocumentSnapshot successfully deleted!") }
    .addOnFailureListener { e -> Log.w(TAG, "Error deleting document", e) }
```