diff --git a/app/src/main/java/com/example/dtf/dao/CategoryDao.kt b/app/src/main/java/com/example/dtf/dao/CategoryDao.kt
index 238be5c..316969b 100644
--- a/app/src/main/java/com/example/dtf/dao/CategoryDao.kt
+++ b/app/src/main/java/com/example/dtf/dao/CategoryDao.kt
@@ -27,4 +27,7 @@ interface CategoryDao {
 
     @Query("select * from category limit 1")
     fun getFirst() : Flow<Category>
+
+    @Query("select * from category where id >= :loadKey limit :limit")
+    fun getByLoadKey(loadKey: Int, limit: Int) : Flow<List<Category>>
 }
diff --git a/app/src/main/java/com/example/dtf/dao/CommentDao.kt b/app/src/main/java/com/example/dtf/dao/CommentDao.kt
index d89a301..d411302 100644
--- a/app/src/main/java/com/example/dtf/dao/CommentDao.kt
+++ b/app/src/main/java/com/example/dtf/dao/CommentDao.kt
@@ -22,6 +22,9 @@ interface CommentDao {
     @Query("select * from comment where comment.post_id = :postId ORDER BY id DESC")
     fun getByPost(postId: Int) : PagingSource<Int, Comment>
 
-    @Query("delete from comment where post_id = :query")
-    fun deleteByQuery(query: String)
+    @Query("select * from comment where id >= :loadKey and post_id = :postId order by id desc limit :limit")
+    fun getByLoadKeyInitial(postId: Int, loadKey: Int, limit: Int) : Flow<List<Comment>>
+
+    @Query("select * from comment where id <= :loadKey and post_id = :postId order by id desc limit :limit")
+    fun getByLoadKey(postId: Int, loadKey: Int, limit: Int) : Flow<List<Comment>>
 }
diff --git a/app/src/main/java/com/example/dtf/dao/PostDao.kt b/app/src/main/java/com/example/dtf/dao/PostDao.kt
index c2a762b..7a8d690 100644
--- a/app/src/main/java/com/example/dtf/dao/PostDao.kt
+++ b/app/src/main/java/com/example/dtf/dao/PostDao.kt
@@ -22,6 +22,6 @@ interface PostDao {
     @Query("select * from post where post.category_id = :categoryId ORDER BY date DESC")
     fun getByCategory(categoryId: String) : PagingSource<Int, Post>
 
-    @Query("delete from post where category_id = :query")
-    fun deleteByQuery(query: String)
+    @Query("select * from post where category_id = :categoryId and id >= :loadKey ORDER BY date DESC limit :limit")
+    fun getByLoadKey(categoryId: Int, loadKey: Int, limit: Int) : Flow<List<Post>>
 }
diff --git a/app/src/main/java/com/example/dtf/repositories/online/mediator/CategoryMediator.kt b/app/src/main/java/com/example/dtf/repositories/online/mediator/CategoryMediator.kt
index 445bb41..e0a053b 100644
--- a/app/src/main/java/com/example/dtf/repositories/online/mediator/CategoryMediator.kt
+++ b/app/src/main/java/com/example/dtf/repositories/online/mediator/CategoryMediator.kt
@@ -8,6 +8,7 @@ import androidx.room.withTransaction
 import com.example.dtf.api.ServerService
 import com.example.dtf.db.AppDatabase
 import com.example.dtf.models.Category
+import kotlinx.coroutines.flow.first
 import java.io.IOException
 
 @OptIn(ExperimentalPagingApi::class)
@@ -42,11 +43,14 @@ class CategoryMediator (
                 limit = state.config.pageSize
             )
 
-
             database.withTransaction {
+                val present = categoryDao.getByLoadKey(loadKey, state.config.pageSize).first()
+
                 if (loadType == LoadType.REFRESH) {
-                    for (category in response.categories) {
-                        categoryDao.delete(category)
+                    for (category in present) {
+                        if (category !in response.categories){
+                            categoryDao.delete(category)
+                        }
                     }
                 }
 
diff --git a/app/src/main/java/com/example/dtf/repositories/online/mediator/CommentMediator.kt b/app/src/main/java/com/example/dtf/repositories/online/mediator/CommentMediator.kt
index 8c28105..8b6b088 100644
--- a/app/src/main/java/com/example/dtf/repositories/online/mediator/CommentMediator.kt
+++ b/app/src/main/java/com/example/dtf/repositories/online/mediator/CommentMediator.kt
@@ -8,6 +8,7 @@ import androidx.room.withTransaction
 import com.example.dtf.api.ServerService
 import com.example.dtf.db.AppDatabase
 import com.example.dtf.models.Comment
+import kotlinx.coroutines.flow.first
 import java.io.IOException
 
 @OptIn(ExperimentalPagingApi::class)
@@ -46,8 +47,18 @@ class CommentMediator (
 
 
             database.withTransaction {
+                val present = if (loadKey == 0) {
+                    commentDao.getByLoadKeyInitial(query.toInt(), loadKey, state.config.pageSize).first()
+                } else {
+                    commentDao.getByLoadKey(query.toInt(), loadKey, state.config.pageSize).first()
+                }
+
                 if (loadType == LoadType.REFRESH) {
-                    commentDao.deleteByQuery(query)
+                    for (comment in present) {
+                        if (comment !in response.comments) {
+                            commentDao.delete(comment)
+                        }
+                    }
                 }
 
                 for (comment in response.comments) {
diff --git a/app/src/main/java/com/example/dtf/repositories/online/mediator/PostMediator.kt b/app/src/main/java/com/example/dtf/repositories/online/mediator/PostMediator.kt
index 97e166d..39a9e86 100644
--- a/app/src/main/java/com/example/dtf/repositories/online/mediator/PostMediator.kt
+++ b/app/src/main/java/com/example/dtf/repositories/online/mediator/PostMediator.kt
@@ -8,6 +8,7 @@ import androidx.room.withTransaction
 import com.example.dtf.api.ServerService
 import com.example.dtf.db.AppDatabase
 import com.example.dtf.models.Post
+import kotlinx.coroutines.flow.first
 import java.io.IOException
 
 @OptIn(ExperimentalPagingApi::class)
@@ -46,12 +47,18 @@ class PostMediator (
 
 
             database.withTransaction {
+                val present = postDao.getByLoadKey(query.toInt(), loadKey, state.config.pageSize).first()
+
                 if (loadType == LoadType.REFRESH) {
-                    postDao.deleteByQuery(query)
+                    for (post in present) {
+                        if (post !in response.posts) {
+                            postDao.delete(post)
+                        }
+                    }
                 }
 
-                for (comment in response.posts) {
-                    postDao.insert(comment)
+                for (post in response.posts) {
+                    postDao.insert(post)
                 }
             }