diff --git a/src/api/handlers.rs b/src/api/handlers.rs
index 8f49e88..cd9b94b 100644
--- a/src/api/handlers.rs
+++ b/src/api/handlers.rs
@@ -2,7 +2,6 @@ use axum::{extract::State, Json};
 
 use crate::{
     api::response::{bad_request, ApiError, ApiResult},
-    engine::VectorEngine,
     models::{
         DeleteRequest, InsertRequest, MessageResponse, SearchRequest, SearchResponse,
     },
diff --git a/src/engine.rs b/src/engine.rs
index cfacc0c..95fb00c 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -4,6 +4,7 @@ pub trait VectorEngine {
     fn insert(&mut self, id: String, vector: Vec<f32>);
     fn search(&self, query: Vec<f32>, k: usize) -> Vec<SearchResult>;
     fn delete(&mut self, id: &str);
+    fn dimension(&self) -> Option<usize>;
 }
 
 #[derive(Default)]
@@ -15,10 +16,6 @@ impl FlatIndex {
     pub fn new() -> Self {
         Self::default()
     }
-
-    pub fn dimension(&self) -> Option<usize> {
-        self.vectors.first().map(|(_, vector)| vector.len())
-    }
 }
 
 impl VectorEngine for FlatIndex {
@@ -45,6 +42,10 @@ impl VectorEngine for FlatIndex {
     fn delete(&mut self, id: &str) {
         self.vectors.retain(|(stored_id, _)| stored_id != id);
     }
+
+    fn dimension(&self) -> Option<usize> {
+        self.vectors.first().map(|(_, vector)| vector.len())
+    }
 }
 
 fn cosine_similarity(left: &[f32], right: &[f32]) -> f32 {
diff --git a/src/state.rs b/src/state.rs
index ac3c248..9dd4b03 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -1,16 +1,16 @@
 use std::sync::{Arc, Mutex};
 
-use crate::engine::FlatIndex;
+use crate::engine::{FlatIndex, VectorEngine};
 
 #[derive(Clone)]
 pub struct AppState {
-    pub engine: Arc<Mutex<FlatIndex>>,
+    pub engine: Arc<Mutex<Box<dyn VectorEngine + Send>>>,
 }
 
 impl AppState {
     pub fn new() -> Self {
         Self {
-            engine: Arc::new(Mutex::new(FlatIndex::new())),
+            engine: Arc::new(Mutex::new(Box::new(FlatIndex::new()))),
         }
     }
 }