Add functions to Query

* Add readValue to read single objects
* Add readList to read complex types (e.g.: List)

Author: lucasvsme

app/src/androidTest/java/kotlinx/coroutines/experimental/firebase/android/app/DatabaseReferenceIntegrationTest.kt

@@ -23,14 +23,19 @@ class DatabaseReferenceIntegrationTest : BaseIntegrationTest() {
 
         val firstMessageNode = messagesNode.child("1")
         val secondMessageNode = messagesNode.child("2")
+        val thirdMessageNode = messagesNode.child("3")
 
         try {
             firstMessageNode.saveValue("Call Mary tomorrow morning")
             secondMessageNode.saveValue("See the new TV show season")
+            thirdMessageNode.saveValue("Spread Kotlin word")
 
             val first = firstMessageNode.readValue<String>()
             val second = secondMessageNode.readValue(String::class.java)
+            val third = messagesNode.orderByValue().limitToFirst(1).readList<String>()
 
+            assertThat(third.size, `is`(equalTo(1)))
+            assertThat(third[0], `is`(equalTo("Call Mary tomorrow morning")))
             assertThat(first, `is`(equalTo("Call Mary tomorrow morning")))
             assertThat(second, `is`(equalTo("See the new TV show season")))
         } catch (exception: FirebaseException) {

kotlinx-coroutines-firebase-android/src/main/java/kotlinx/coroutines/experimental/firebase/android/DatabaseReference.kt

@@ -4,6 +4,8 @@ import com.google.firebase.FirebaseException
 import com.google.firebase.database.DataSnapshot
 import com.google.firebase.database.DatabaseError
 import com.google.firebase.database.DatabaseReference
+import com.google.firebase.database.GenericTypeIndicator
+import com.google.firebase.database.Query
 import com.google.firebase.database.ValueEventListener
 import kotlinx.coroutines.experimental.suspendCancellableCoroutine
 
@@ -106,21 +108,6 @@ suspend fun <T : Any> DatabaseReference.readValue(type: Class<T>): T = readRefer
  */
 suspend inline fun <reified T : Any> DatabaseReference.readValue(): T = readValue(T::class.java)
 
-/**
- * Coroutine to read a collection of values from Firebase Database
- *
- * This method is not intended to be used in the code. It's just a base function that contains the
- * main coroutine code that reads a collection of values from Firebase Database. To use it's
- * functionality call [kotlinx.coroutines.experimental.firebase.android.readValue] function.
- *
- * The implementation consists of a [suspendCancellableCoroutine] that encapsulates a
- * [ValueEventListener].
- *
- * @param reference The Firebase Database node to be read.
- * @param type Expected type wrapped in a Class instance.
- * @param T The type of the expected value from Firebase Database.
- * @return The persisted object of the type T informed.
- */
 private suspend fun <T : Any> readReferences(
         reference: DatabaseReference,
         type: Class<T>
@@ -217,4 +204,48 @@ suspend inline fun <reified T : Any> DatabaseReference.readList(): List<T> = rea
 suspend fun <T : Any> DatabaseReference.saveValue(value: T): Unit =
         setValue(value).await().let { Unit }
 
-suspend fun <T: Any> DatabaseReference.pushValue(value: T): Unit = push().saveValue(value)
+suspend fun <T : Any> DatabaseReference.pushValue(value: T): Unit = push().saveValue(value)
+
+private suspend fun <T : Any> awaitQuerySingleValue(query: Query, type: Class<T>): T =
+        suspendCancellableCoroutine { continuation ->
+            val listener = object : ValueEventListener {
+                override fun onDataChange(snapshot: DataSnapshot) = try {
+                    continuation.resume(snapshot.getValue(type)!!)
+                } catch (exception: Exception) {
+                    continuation.resumeWithException(exception)
+                }
+
+                override fun onCancelled(error: DatabaseError) =
+                        continuation.resumeWithException(error.toException())
+            }
+
+            query.addListenerForSingleValueEvent(listener)
+            continuation.invokeOnCompletion { query.removeEventListener(listener) }
+        }
+
+suspend fun <T : Any> Query.readValue(type: Class<T>): T = awaitQuerySingleValue(this, type)
+
+suspend inline fun <reified T : Any> Query.readValue(): T = readValue(T::class.java)
+
+private suspend fun <T : Any> awaitQueryListValue(query: Query, type: Class<T>): List<T> =
+        suspendCancellableCoroutine { continuation ->
+            val listener = object : ValueEventListener {
+                override fun onDataChange(snapshot: DataSnapshot) = try {
+                    val data: List<T> = snapshot.children.toHashSet().map { it.getValue(type)!! }
+
+                    continuation.resume(data)
+                } catch (exception: Exception) {
+                    continuation.resumeWithException(exception)
+                }
+
+                override fun onCancelled(error: DatabaseError) =
+                        continuation.resumeWithException(error.toException())
+            }
+
+            query.addListenerForSingleValueEvent(listener)
+            continuation.invokeOnCompletion { query.removeEventListener(listener) }
+        }
+
+suspend fun <T : Any> Query.readList(type: Class<T>): List<T> = awaitQueryListValue(this, type)
+
+suspend inline fun <reified T : Any> Query.readList(): List<T> = readList(T::class.java)