PostDao-DataSource.kt

@Dao
interface PostDao {
  @Insert(onConflict = OnConflictStrategy.IGNORE)
  fun insert(post: Post): Long

  @Update(onConflict = OnConflictStrategy.REPLACE)
  fun update(post: Post)

  @Transaction
  fun upsert(post: Post) {
      if (-1L == insert(post))
          update(post)
  }

  @Query("SELECT * FROM `post`")
  fun getPostList(): DataSource.Factory<Int, Post>
}