diff --git a/src/api/book.rs b/src/api/book.rs
index 18f78fb..94e63d6 100644
--- a/src/api/book.rs
+++ b/src/api/book.rs
@@ -46,7 +46,7 @@ async fn get_all_books_handler(
     let mut books: Vec<BookItem> = Vec::new();
     for b in all_books {
         let book_resp = BookItem {
-            id: b.id,
+            id: b.id.into(),
             name: b.name,
         };
         books.push(book_resp);
@@ -72,7 +72,7 @@ async fn get_book_by_id_handler(
     match book_query {
         Some(b) => {
             book_resp = BookItem {
-                id: b.id,
+                id: b.id.into(),
                 name: b.name,
             };
         }
diff --git a/src/model/http_body/book.rs b/src/model/http_body/book.rs
index c88651c..f37b201 100644
--- a/src/model/http_body/book.rs
+++ b/src/model/http_body/book.rs
@@ -1,8 +1,10 @@
 use serde::{Serialize, Deserialize};
+use super::common::{number_stringify, OptionalI64};
 
 #[derive(Serialize)]
 pub struct BookItem {
-    pub id: i64,
+    #[serde(with="number_stringify")]
+    pub id: OptionalI64,
     pub name: String,
 }