Change the result type of searchAll* in *FtsDao as Flow to not block the

calling thread

core/data/src/main/java/com/google/samples/apps/nowinandroid/core/data/repository/DefaultSearchContentsRepository.kt

@@ -22,8 +22,13 @@ import com.google.samples.apps.nowinandroid.core.database.dao.TopicDao
 import com.google.samples.apps.nowinandroid.core.database.dao.TopicFtsDao
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.database.model.asFtsEntity
+import com.google.samples.apps.nowinandroid.core.network.Dispatcher
+import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.IO
+import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.flattenConcat
+import kotlinx.coroutines.withContext
 import javax.inject.Inject
 
 class DefaultSearchContentsRepository @Inject constructor(
@@ -31,11 +36,16 @@ class DefaultSearchContentsRepository @Inject constructor(
     private val newsResourceFtsDao: NewsResourceFtsDao,
     private val topicDao: TopicDao,
     private val topicFtsDao: TopicFtsDao,
+    @Dispatcher(IO) private val ioDispatcher: CoroutineDispatcher,
 ) : SearchContentsRepository {
 
-    override fun populateFtsData() {
-        newsResourceFtsDao.insertAll(newsResourceDao.getOneOffNewsResources().map { it.asFtsEntity() })
-        topicFtsDao.insertAll(topicDao.getOneOffTopicEntities().map { it.asFtsEntity() })
+    override suspend fun populateFtsData() {
+        withContext(ioDispatcher) {
+            newsResourceFtsDao.insertAll(
+                newsResourceDao.getOneOffNewsResources().map { it.asFtsEntity() },
+            )
+            topicFtsDao.insertAll(topicDao.getOneOffTopicEntities().map { it.asFtsEntity() })
+        }
     }
 
     override fun searchContents(searchQuery: String): Flow<SearchResult> {
@@ -44,14 +54,16 @@ class DefaultSearchContentsRepository @Inject constructor(
         val newsResourceIds = newsResourceFtsDao.searchAllNewsResources("*$searchQuery*")
         val topicIds = topicFtsDao.searchAllTopics("*$searchQuery*")
 
-        return combine(
-            newsResourceDao.getNewsResources(filterNewsIds = newsResourceIds.toSet()),
-            topicDao.getTopicEntities(topicIds.toSet()),
-        ) { newsResources, topics ->
-            SearchResult(
-                topics = topics.map { it.asExternalModel() },
-                newsResources = newsResources.map { it.asExternalModel() },
-            )
-        }
+        return combine(newsResourceIds, topicIds) { news, topics ->
+            combine(
+                newsResourceDao.getNewsResources(filterNewsIds = news.toSet()),
+                topicDao.getTopicEntities(topics.toSet()),
+            ) { newsResources, topics ->
+                SearchResult(
+                    topics = topics.map { it.asExternalModel() },
+                    newsResources = newsResources.map { it.asExternalModel() },
+                )
+            }
+        }.flattenConcat()
     }
 }

core/data/src/main/java/com/google/samples/apps/nowinandroid/core/data/repository/SearchContentsRepository.kt

@@ -20,8 +20,19 @@ import com.google.samples.apps.nowinandroid.core.model.data.NewsResource
 import com.google.samples.apps.nowinandroid.core.model.data.Topic
 import kotlinx.coroutines.flow.Flow
 
+/**
+ * Data layer interface for the search feature.
+ */
 interface SearchContentsRepository {
-    fun populateFtsData()
+
+    /**
+     * Populate the fts tables for the search contents.
+     */
+    suspend fun populateFtsData()
+
+    /**
+     * Query the contents matched with the [searchQuery] and returns it as a [Flow] of [SearchResult]
+     */
     fun searchContents(searchQuery: String): Flow<SearchResult>
 }
 

core/data/src/main/java/com/google/samples/apps/nowinandroid/core/data/repository/fake/FakeSearchContentsRepository.kt

@@ -26,7 +26,7 @@ import javax.inject.Inject
  */
 class FakeSearchContentsRepository @Inject constructor() : SearchContentsRepository {
 
-    override fun populateFtsData() {}
+    override suspend fun populateFtsData() {}
     override fun searchContents(searchQuery: String): Flow<SearchResult> {
         TODO("Not yet implemented")
     }

core/database/src/main/java/com/google/samples/apps/nowinandroid/core/database/DatabaseModule.kt

@@ -38,5 +38,5 @@ object DatabaseModule {
         "nia-database",
         // TODO: This is a workaround for executing read query in the main thread for search.
         // Figure out how other use cases avoid that
-    ).allowMainThreadQueries().build()
+    ).build()
 }

core/database/src/main/java/com/google/samples/apps/nowinandroid/core/database/dao/NewsResourceFtsDao.kt

@@ -21,6 +21,7 @@ import androidx.room.Insert
 import androidx.room.OnConflictStrategy
 import androidx.room.Query
 import com.google.samples.apps.nowinandroid.core.database.model.NewsResourceFtsEntity
+import kotlinx.coroutines.flow.Flow
 
 /**
  * DAO for [NewsResourceFtsEntity] access.
@@ -28,11 +29,11 @@ import com.google.samples.apps.nowinandroid.core.database.model.NewsResourceFtsE
 @Dao
 interface NewsResourceFtsDao {
     @Insert(onConflict = OnConflictStrategy.REPLACE)
-    fun insertAll(topics: List<NewsResourceFtsEntity>)
+    suspend fun insertAll(topics: List<NewsResourceFtsEntity>)
 
     @Query("SELECT newsResourceId FROM newsResourcesFts WHERE newsResourcesFts MATCH :query")
-    fun searchAllNewsResources(query: String): List<String>
+    fun searchAllNewsResources(query: String): Flow<List<String>>
 
     @Query("SELECT count(*) FROM newsResourcesFts")
-    fun getCount(): Int
+    suspend fun getCount(): Int
 }

core/database/src/main/java/com/google/samples/apps/nowinandroid/core/database/dao/TopicFtsDao.kt

@@ -21,6 +21,7 @@ import androidx.room.Insert
 import androidx.room.OnConflictStrategy
 import androidx.room.Query
 import com.google.samples.apps.nowinandroid.core.database.model.TopicFtsEntity
+import kotlinx.coroutines.flow.Flow
 
 /**
  * DAO for [TopicFtsEntity] access.
@@ -28,11 +29,11 @@ import com.google.samples.apps.nowinandroid.core.database.model.TopicFtsEntity
 @Dao
 interface TopicFtsDao {
     @Insert(onConflict = OnConflictStrategy.REPLACE)
-    fun insertAll(topics: List<TopicFtsEntity>)
+    suspend fun insertAll(topics: List<TopicFtsEntity>)
 
     @Query("SELECT topicId FROM topicsFts WHERE topicsFts MATCH :query")
-    fun searchAllTopics(query: String): List<String>
+    fun searchAllTopics(query: String): Flow<List<String>>
 
     @Query("SELECT count(*) FROM topicsFts")
-    fun getCount(): Int
+    suspend fun getCount(): Int
 }

core/domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/GetSearchContentsUseCase.kt

@@ -26,6 +26,9 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
 import javax.inject.Inject
 
+/**
+ * A use case which returns the searched contents matched with the search query.
+ */
 class GetSearchContentsUseCase @Inject constructor(
     private val searchContentsRepository: SearchContentsRepository,
     private val userDataRepository: UserDataRepository,

core/testing/src/main/java/com/google/samples/apps/nowinandroid/core/testing/repository/TestSearchContentsRepository.kt

@@ -28,7 +28,7 @@ class TestSearchContentsRepository : SearchContentsRepository {
     private val cachedTopics: MutableList<Topic> = mutableListOf()
     private val cachedNewsResources: MutableList<NewsResource> = mutableListOf()
 
-    override fun populateFtsData() {}
+    override suspend fun populateFtsData() {}
 
     override fun searchContents(searchQuery: String): Flow<SearchResult> {
         return flowOf(