docs: add docs for firebase-database-ktx (firebase#841)

* docs: add docs for firebase-database-ktx

* docs: add database-ktx to README.md and FOSDC

Author: thatfiredev

.opensource/project.json

@@ -11,7 +11,8 @@
         "docs/ktx/firestore.md": "Firestore KTX",
         "docs/ktx/functions.md": "Functions KTX",
         "docs/ktx/remote-config.md": "Remote Config KTX",
-        "docs/ktx/storage.md": "Storage KTX"
+        "docs/ktx/storage.md": "Storage KTX",
+        "docs/ktx/database.md": "Realtime Database KTX"
     },
     "related": [
         "firebase/quickstart-android"

README.md

@@ -8,6 +8,7 @@ dependencies:
   * `firebase-common`
   * `firebase-common-ktx`
   * `firebase-database`
+  * `firebase-database-ktx`
   * `firebase-database-collection`
   * `firebase-datatransport`
   * `firebase-firestore`

docs/README.md

@@ -28,6 +28,7 @@ in your app:
   * [`firebase-functions`](ktx/functions.md)
   * [`firebase-remote-config`](ktx/remote-config.md)
   * [`firebase-storage`](ktx/storage.md)
+  * [`firebase-database`](ktx/database.md)
 
 [android-setup]: https://firebase.google.com/docs/android/setup
 [main-readme]: https://github.com/firebase/firebase-android-sdk/blob/master/README.md

docs/ktx/database.md

@@ -0,0 +1,82 @@
+# Realtime Database Kotlin Extensions
+
+## Getting Started
+
+To use the Firebase Realtime Database Android SDK with Kotlin Extensions, add the following
+to your app's `build.gradle` file:
+
+```groovy
+// See maven.google.com for the latest versions
+// This library transitively includes the firebase-database library
+implementation 'com.google.firebase:firebase-database-ktx:$VERSION'
+```
+
+## Features
+
+### Get an instance of FirebaseDatabase
+
+**Kotlin**
+```kotlin
+val database = FirebaseDatabase.getInstance()
+val anotherDatabase = FirebaseDatabase.getInstance(FirebaseApp.getInstance("myApp"))
+```
+
+**Kotlin + KTX**
+```kotlin
+val database = Firebase.database
+val anotherDatabase = Firebase.database(Firebase.app("myApp"))
+```
+
+### Get the FirebaseDatabase for the specified url
+
+**Kotlin**
+```kotlin
+val database = FirebaseDatabase.getInstance(url)
+```
+
+**Kotlin + KTX**
+```kotlin
+val database = Firebase.database(url)
+```
+
+
+### Get the FirebaseDatabase of the given FirebaseApp and url
+
+**Kotlin**
+```kotlin
+val database = FirebaseDatabase.getInstance(app, url)
+```
+
+**Kotlin + KTX**
+```kotlin
+val database = Firebase.database(app, url)
+```
+
+### Convert a DataSnapshot to a POJO
+
+**Kotlin**
+```kotlin
+val snapshot: DataSnapshot = ...
+val myObject = snapshot.getValue(MyClass::class.java)
+```
+
+**Kotlin + KTX**
+```kotlin
+val snapshot: DocumentSnapshot = ...
+val myObject = snapshot.getValue<MyClass>()
+```
+
+### Convert a DataSnapshot to generic types such as List or Map
+
+**Kotlin**
+```kotlin
+val snapshot: DataSnapshot = ...
+val typeIndicator = object : GenericTypeIndicator<List<Message>>() {}
+val messages: List<Message> = snapshot.getValue(t)
+```
+
+**Kotlin + KTX**
+```kotlin
+val snapshot: DocumentSnapshot = ...
+val messages: List<Message> = snapshot.getValue<List<@JvmSuppressWildcards Message>>()
+```