Call getNewsResourceIds instead of getNewsResources

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

@@ -80,17 +80,14 @@ class OfflineFirstNewsRepository @Inject constructor(
                 val hasOnboarded = userData.shouldHideOnboarding
                 val followedTopicIds = userData.followedTopics
 
-                // TODO: Make this more efficient, there is no need to retrieve populated
-                //  news resources when all that's needed are the ids
                 val existingNewsResourceIdsThatHaveChanged = when {
-                    hasOnboarded -> newsResourceDao.getNewsResources(
+                    hasOnboarded -> newsResourceDao.getNewsResourceIds(
                         useFilterTopicIds = true,
                         filterTopicIds = followedTopicIds,
                         useFilterNewsIds = true,
                         filterNewsIds = changedIds.toSet(),
                     )
                         .first()
-                        .map { it.entity.id }
                         .toSet()
                     // No need to retrieve anything if notifications won't be sent
                     else -> emptySet()

core/data/src/test/java/com/google/samples/apps/nowinandroid/core/data/testdoubles/TestNewsResourceDao.kt

@@ -67,6 +67,33 @@ class TestNewsResourceDao : NewsResourceDao {
                 result
             }
 
+    override fun getNewsResourceIds(
+        useFilterTopicIds: Boolean,
+        filterTopicIds: Set<String>,
+        useFilterNewsIds: Boolean,
+        filterNewsIds: Set<String>,
+    ): Flow<List<String>> =
+        entitiesStateFlow
+            .map { newsResourceEntities ->
+                newsResourceEntities.map { entity ->
+                    entity.asPopulatedNewsResource(topicCrossReferences)
+                }
+            }
+            .map { resources ->
+                var result = resources
+                if (useFilterTopicIds) {
+                    result = result.filter { resource ->
+                        resource.topics.any { it.id in filterTopicIds }
+                    }
+                }
+                if (useFilterNewsIds) {
+                    result = result.filter { resource ->
+                        resource.entity.id in filterNewsIds
+                    }
+                }
+                result.map { it.entity.id }
+            }
+
     override suspend fun insertOrIgnoreNewsResources(
         entities: List<NewsResourceEntity>,
     ): List<Long> {

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

@@ -65,6 +65,33 @@ interface NewsResourceDao {
         filterNewsIds: Set<String> = emptySet(),
     ): Flow<List<PopulatedNewsResource>>
 
+    @Transaction
+    @Query(
+       value = """
+            SELECT id FROM news_resources
+            WHERE 
+                CASE WHEN :useFilterNewsIds
+                    THEN id IN (:filterNewsIds)
+                    ELSE 1
+                END
+             AND
+                CASE WHEN :useFilterTopicIds
+                    THEN id IN
+                        (
+                            SELECT news_resource_id FROM news_resources_topics
+                            WHERE topic_id IN (:filterTopicIds)
+                        )
+                    ELSE 1
+                END
+            ORDER BY publish_date DESC
+    """)
+    fun getNewsResourceIds(
+        useFilterTopicIds: Boolean = false,
+        filterTopicIds: Set<String> = emptySet(),
+        useFilterNewsIds: Boolean = false,
+        filterNewsIds: Set<String> = emptySet(),
+    ): Flow<List<String>>
+
     /**
      * Inserts [entities] into the db if they don't exist, and ignores those that do
      */