Paging with network and database

app/build.gradle

@@ -67,6 +67,7 @@ dependencies {
     implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycleVersion"
     implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycleVersion"
     implementation "androidx.room:room-runtime:$roomVersion"
+    implementation "androidx.room:room-ktx:$roomVersion"
     implementation "androidx.paging:paging-runtime:$pagingVersion"
     kapt "androidx.lifecycle:lifecycle-compiler:$lifecycleVersion"
     kapt "androidx.room:room-compiler:$roomVersion"

app/src/main/java/com/example/android/codelabs/paging/Injection.kt

@@ -20,7 +20,9 @@ import android.content.Context
 import androidx.lifecycle.ViewModelProvider
 import com.example.android.codelabs.paging.api.GithubService
 import com.example.android.codelabs.paging.data.GithubRepository
+import com.example.android.codelabs.paging.db.RepoDatabase
 import com.example.android.codelabs.paging.ui.ViewModelFactory
+import kotlinx.coroutines.Dispatchers
 
 /**
  * Class that handles object creation.
@@ -33,15 +35,19 @@ object Injection {
      * Creates an instance of [GithubRepository] based on the [GithubService] and a
      * [GithubLocalCache]
      */
-    private fun provideGithubRepository(): GithubRepository {
-        return GithubRepository(GithubService.create())
+    private fun provideGithubRepository(context: Context): GithubRepository {
+        return GithubRepository(GithubService.create(), provideDatabase(context), Dispatchers.IO)
+    }
+
+    private fun provideDatabase(context: Context): RepoDatabase {
+        return RepoDatabase.getInstance(context)
     }
 
     /**
      * Provides the [ViewModelProvider.Factory] that is then used to get a reference to
      * [ViewModel] objects.
      */
-    fun provideViewModelFactory(): ViewModelProvider.Factory {
-        return ViewModelFactory(provideGithubRepository())
+    fun provideViewModelFactory(context: Context): ViewModelProvider.Factory {
+        return ViewModelFactory(provideGithubRepository(context))
     }
 }

app/src/main/java/com/example/android/codelabs/paging/data/GithubPagingSource.kt

@@ -16,6 +16,7 @@
 
 package com.example.android.codelabs.paging.data
 
+import android.util.Log
 import androidx.paging.PagingSource
 import com.example.android.codelabs.paging.api.GithubService
 import com.example.android.codelabs.paging.api.IN_QUALIFIER
@@ -25,7 +26,7 @@ import retrofit2.HttpException
 import java.io.IOException
 
 // GitHub page API is 1 based: https://developer.github.com/v3/#pagination
-private const val GITHUB_STARTING_PAGE_INDEX = 1
+const val GITHUB_STARTING_PAGE_INDEX = 1
 
 @ExperimentalCoroutinesApi
 class GithubPagingSource(

app/src/main/java/com/example/android/codelabs/paging/data/GithubRemoteMediator.kt

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.codelabs.paging.data
+
+import android.util.Log
+import androidx.paging.LoadType
+import androidx.paging.PagingSource
+import androidx.paging.PagingState
+import androidx.paging.RemoteMediator
+import androidx.room.withTransaction
+import com.example.android.codelabs.paging.data.GithubRepository.Companion.NETWORK_PAGE_SIZE
+import com.example.android.codelabs.paging.db.RepoDatabase
+import com.example.android.codelabs.paging.model.Repo
+import kotlinx.coroutines.withContext
+import kotlin.coroutines.CoroutineContext
+
+class GithubRemoteMediator(
+        private val pagingSource: GithubPagingSource,
+        private val repoDatabase: RepoDatabase,
+        private val ioDispatcher: CoroutineContext
+) : RemoteMediator<Int, Repo>() {
+
+    override suspend fun load(loadType: LoadType, state: PagingState<Int, Repo>?): MediatorResult {
+        Log.d("GithubRemoteMediator", "load type: $loadType, state: $state")
+
+        val key = when (loadType) {
+            LoadType.REFRESH -> GITHUB_STARTING_PAGE_INDEX
+            LoadType.START -> state?.pages?.last()?.prevKey ?: GITHUB_STARTING_PAGE_INDEX
+            LoadType.END -> state?.pages?.last()?.nextKey ?: GITHUB_STARTING_PAGE_INDEX
+        }
+
+        val result = pagingSource.load(PagingSource.LoadParams(
+                loadType = loadType,
+                key = key,
+                loadSize = NETWORK_PAGE_SIZE,
+                placeholdersEnabled = false,
+                pageSize = NETWORK_PAGE_SIZE
+        ))
+
+        return when (result) {
+            is PagingSource.LoadResult.Page -> {
+                withContext(ioDispatcher) {
+                    repoDatabase.withTransaction {
+                        if (loadType == LoadType.REFRESH) {
+                            repoDatabase.reposDao().clearRepos()
+                        }
+                        repoDatabase.reposDao().insert(result.data)
+                    }
+                }
+                MediatorResult.Success(hasMoreData = result.nextKey != null)
+            }
+            is PagingSource.LoadResult.Error -> MediatorResult.Error(result.throwable)
+
+        }
+    }
+}

app/src/main/java/com/example/android/codelabs/paging/data/GithubRepository.kt

@@ -21,15 +21,21 @@ import androidx.paging.PagingConfig
 import androidx.paging.PagingData
 import androidx.paging.PagingDataFlow
 import com.example.android.codelabs.paging.api.GithubService
+import com.example.android.codelabs.paging.db.RepoDatabase
 import com.example.android.codelabs.paging.model.Repo
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
+import kotlin.coroutines.CoroutineContext
 
 /**
  * Repository class that works with local and remote data sources.
  */
 @ExperimentalCoroutinesApi
-class GithubRepository(private val service: GithubService) {
+class GithubRepository(
+        private val service: GithubService,
+        private val database: RepoDatabase,
+        private val ioDispatcher: CoroutineContext
+) {
 
     /**
      * Search repositories whose names match the query, exposed as a stream of data that will emit
@@ -38,13 +44,19 @@ class GithubRepository(private val service: GithubService) {
     fun getSearchResultStream(query: String): Flow<PagingData<Repo>> {
         Log.d("GithubRepository", "New query: $query")
 
+        val pagingSourceFactory = database.reposDao().reposByName().asPagingSourceFactory()
         return PagingDataFlow(
                 config = PagingConfig(pageSize = NETWORK_PAGE_SIZE),
-                pagingSourceFactory = { GithubPagingSource(service, query) }
+                remoteMediator = GithubRemoteMediator(
+                        GithubPagingSource(service, query),
+                        database,
+                        ioDispatcher
+                ),
+                pagingSourceFactory = pagingSourceFactory
         )
     }
 
     companion object {
-        private const val NETWORK_PAGE_SIZE = 50
+        const val NETWORK_PAGE_SIZE = 50
     }
 }

app/src/main/java/com/example/android/codelabs/paging/db/RepoDao.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.codelabs.paging.db
+
+import androidx.paging.DataSource
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.OnConflictStrategy
+import androidx.room.Query
+import com.example.android.codelabs.paging.model.Repo
+
+/**
+ * Room data access object for accessing the [Repo] table.
+ */
+@Dao
+interface RepoDao {
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun insert(posts: List<Repo>)
+
+    // Do a similar query as the search API:
+    // Look for repos that contain the query string in the name or in the description
+    // and order those results descending, by the number of stars and then by name
+    @Query("SELECT * FROM repos ORDER BY stars DESC, name ASC")
+    fun reposByName(): DataSource.Factory<Int, Repo>
+
+    @Query("DELETE FROM repos")
+    suspend fun clearRepos()
+}

app/src/main/java/com/example/android/codelabs/paging/db/RepoDatabase.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.codelabs.paging.db
+
+import androidx.room.Database
+import androidx.room.Room
+import androidx.room.RoomDatabase
+import android.content.Context
+import com.example.android.codelabs.paging.model.Repo
+
+/**
+ * Database schema that holds the list of repos.
+ */
+@Database(
+        entities = [Repo::class],
+        version = 1,
+        exportSchema = false
+)
+abstract class RepoDatabase : RoomDatabase() {
+
+    abstract fun reposDao(): RepoDao
+
+    companion object {
+
+        @Volatile
+        private var INSTANCE: RepoDatabase? = null
+
+        fun getInstance(context: Context): RepoDatabase =
+                INSTANCE ?: synchronized(this) {
+                    INSTANCE
+                            ?: buildDatabase(context).also { INSTANCE = it }
+                }
+
+        private fun buildDatabase(context: Context) =
+                Room.databaseBuilder(context.applicationContext,
+                        RepoDatabase::class.java, "Github.db")
+                        .build()
+    }
+}

app/src/main/java/com/example/android/codelabs/paging/ui/SearchRepositoriesActivity.kt

@@ -50,7 +50,7 @@ class SearchRepositoriesActivity : AppCompatActivity() {
         setContentView(view)
 
         // get the view model
-        viewModel = ViewModelProvider(this, Injection.provideViewModelFactory())
+        viewModel = ViewModelProvider(this, Injection.provideViewModelFactory(applicationContext))
                 .get(SearchRepositoriesViewModel::class.java)
 
         // add dividers between RecyclerView's row items

build.gradle

@@ -35,7 +35,7 @@ allprojects {
     repositories {
         google()
         jcenter()
-        maven { url 'https://androidx-dev-prod.appspot.com/snapshots/builds/6295087/artifacts/repository' }
+        maven { url 'https://androidx-dev-prod.appspot.com/snapshots/builds/6345264/artifacts/repository' }
     }
 }