diff --git a/src/main/java/sg/com/smartinventory/repositories/CustomerRepository.java b/src/main/java/sg/com/smartinventory/repositories/CustomerRepository.java
index 19a2d75..50c89f1 100644
--- a/src/main/java/sg/com/smartinventory/repositories/CustomerRepository.java
+++ b/src/main/java/sg/com/smartinventory/repositories/CustomerRepository.java
@@ -11,7 +11,7 @@
 // We can also create custom queries using the JPA criteria API by simply creating a method with a certain naming convention specified by the query creation mechanism.
 public interface CustomerRepository extends JpaRepository<Customer, Long> {
     // Custom query to find all customers with a certain ID.
-    List<Customer> findById(long id);
+    // List<Customer> findById(long id);
 
     // Custom query to find all customers with a certain first name.
     List<Customer> findByFirstName(String firstName);
diff --git a/src/main/java/sg/com/smartinventory/repositories/ProductRepository.java b/src/main/java/sg/com/smartinventory/repositories/ProductRepository.java
index ada6ddd..ce18b85 100644
--- a/src/main/java/sg/com/smartinventory/repositories/ProductRepository.java
+++ b/src/main/java/sg/com/smartinventory/repositories/ProductRepository.java
@@ -11,7 +11,7 @@
 // We can also create custom queries using the JPA criteria API by simply creating a method with a certain naming convention specified by the query creation mechanism.
 public interface ProductRepository extends JpaRepository<Product, Long> {
     // Custom query to find all products with a certain ID.
-    List<Product> findById(long id);
+    // List<Product> findById(long id);
 
     // Custom query to find all products with a certain category.
     List<Product> findByCategory(String category);
diff --git a/src/main/java/sg/com/smartinventory/repositories/ReviewRepository.java b/src/main/java/sg/com/smartinventory/repositories/ReviewRepository.java
index 6675f29..be12b8d 100644
--- a/src/main/java/sg/com/smartinventory/repositories/ReviewRepository.java
+++ b/src/main/java/sg/com/smartinventory/repositories/ReviewRepository.java
@@ -11,7 +11,7 @@
 // We can also create custom queries using the JPA criteria API by simply creating a method with a certain naming convention specified by the query creation mechanism.
 public interface ReviewRepository extends JpaRepository<Review, Long> {
     // Custom query to find all reviews with a certain ID.
-    List<Review> findById(long id);
+    // List<Review> findById(long id);
 
     // Custom query to find all reviews with a certain category.
     List<Review> findByCategory(String category);
diff --git a/src/main/java/sg/com/smartinventory/serviceImpls/CustomerServiceImpl.java b/src/main/java/sg/com/smartinventory/serviceImpls/CustomerServiceImpl.java
index f5e469d..b6b2f15 100644
--- a/src/main/java/sg/com/smartinventory/serviceImpls/CustomerServiceImpl.java
+++ b/src/main/java/sg/com/smartinventory/serviceImpls/CustomerServiceImpl.java
@@ -7,7 +7,7 @@
 
 import sg.com.smartinventory.entities.Customer;
 // import sg.com.smartinventory.entities.Review;
-// import sg.com.smartinventory.exceptions.CustomerNotFoundException;
+import sg.com.smartinventory.exceptions.CustomerNotFoundException;
 import sg.com.smartinventory.repositories.CustomerRepository;
 import sg.com.smartinventory.services.CustomerService;
 
@@ -28,16 +28,14 @@ public Customer createCustomer(Customer customer) {
     }
 
     @Override
-    public Customer getCustomer(long id) {
+    public Customer getCustomer(Long id) {
         // Optional<Customer> optionalCustomer = customerRepository.findById(id);
         // if(optionalCustomer.isPresent()) {
         // Customer foundCustomer = optionalCustomer.get();
         // return foundCustomer;
         // }
         // throw new CustomerNotFoundException(id);
-        // return customerRepository.findById(id).orElseThrow(() -> new
-        // CustomerNotFoundException(id));
-        return customerRepository.findById(id).get(0);
+        return customerRepository.findById(id).orElseThrow(() -> new CustomerNotFoundException(id));
     }
 
     @Override
@@ -47,12 +45,10 @@ public ArrayList<Customer> getAllCustomers() {
     }
 
     @Override
-    public Customer updateCustomer(long id, Customer customer) {
+    public Customer updateCustomer(Long id, Customer customer) {
         // Retrieve the customer from the database.
-        // Customer customerToUpdate = customerRepository.findById(id).orElseThrow(() ->
-        // new
-        // CustomerNotFoundException(id));
-        Customer customerToUpdate = customerRepository.findById(id).get(0);
+        Customer customerToUpdate = customerRepository.findById(id)
+                .orElseThrow(() -> new CustomerNotFoundException(id));
 
         // Update the customer retrieved from the database.
         customerToUpdate.setFirstName(customer.getFirstName());
diff --git a/src/main/java/sg/com/smartinventory/serviceImpls/ProductServiceImpl.java b/src/main/java/sg/com/smartinventory/serviceImpls/ProductServiceImpl.java
index a18727f..c1abeeb 100644
--- a/src/main/java/sg/com/smartinventory/serviceImpls/ProductServiceImpl.java
+++ b/src/main/java/sg/com/smartinventory/serviceImpls/ProductServiceImpl.java
@@ -6,7 +6,7 @@
 import org.springframework.stereotype.Service;
 
 import sg.com.smartinventory.entities.Product;
-// import sg.com.smartinventory.exceptions.ProductNotFoundException;
+import sg.com.smartinventory.exceptions.ProductNotFoundException;
 import sg.com.smartinventory.repositories.ProductRepository;
 import sg.com.smartinventory.services.ProductService;
 
@@ -27,16 +27,14 @@ public Product createProduct(Product product) {
     }
 
     @Override
-    public Product getProduct(long id) {
+    public Product getProduct(Long id) {
         // Optional<Product> optionalProduct = productRepository.findById(id);
         // if(optionalProduct.isPresent()) {
         // Product foundProduct = optionalProduct.get();
         // return foundProduct;
         // }
         // throw new ProductNotFoundException(id);
-        // return productRepository.findById(id).orElseThrow(() -> new
-        // ProductNotFoundException(id));
-        return productRepository.findById(id).get(0);
+        return productRepository.findById(id).orElseThrow(() -> new ProductNotFoundException(id));
     }
 
     @Override
@@ -46,12 +44,9 @@ public ArrayList<Product> getAllProducts() {
     }
 
     @Override
-    public Product updateProduct(long id, Product product) {
+    public Product updateProduct(Long id, Product product) {
         // Retrieve the product from the database.
-        // Product productToUpdate = productRepository.findById(id).orElseThrow(() ->
-        // new
-        // ProductNotFoundException(id));
-        Product productToUpdate = productRepository.findById(id).get(0);
+        Product productToUpdate = productRepository.findById(id).orElseThrow(() -> new ProductNotFoundException(id));
 
         // Update the product retrieved from the database.
         productToUpdate.setCategory(product.getCategory());
diff --git a/src/main/java/sg/com/smartinventory/serviceImpls/ReviewServiceImpl.java b/src/main/java/sg/com/smartinventory/serviceImpls/ReviewServiceImpl.java
index 29addfb..8c51149 100644
--- a/src/main/java/sg/com/smartinventory/serviceImpls/ReviewServiceImpl.java
+++ b/src/main/java/sg/com/smartinventory/serviceImpls/ReviewServiceImpl.java
@@ -6,7 +6,7 @@
 import org.springframework.stereotype.Service;
 
 import sg.com.smartinventory.entities.Review;
-// import sg.com.smartinventory.exceptions.ReviewNotFoundException;
+import sg.com.smartinventory.exceptions.ReviewNotFoundException;
 import sg.com.smartinventory.repositories.ReviewRepository;
 import sg.com.smartinventory.services.ReviewService;
 
@@ -27,16 +27,14 @@ public Review createReview(Review review) {
     }
 
     @Override
-    public Review getReview(long id) {
+    public Review getReview(Long id) {
         // Optional<Review> optionalReview = reviewRepository.findById(id);
         // if(optionalReview.isPresent()) {
         // Review foundReview = optionalReview.get();
         // return foundReview;
         // }
         // throw new ReviewNotFoundException(id);
-        // return reviewRepository.findById(id).orElseThrow(() -> new
-        // ReviewNotFoundException(id));
-        return reviewRepository.findById(id).get(0);
+        return reviewRepository.findById(id).orElseThrow(() -> new ReviewNotFoundException(id));
     }
 
     @Override
@@ -46,11 +44,9 @@ public ArrayList<Review> getAllReviews() {
     }
 
     @Override
-    public Review updateReview(long id, Review review) {
+    public Review updateReview(Long id, Review review) {
         // Retrieve the review from the database.
-        // Review reviewToUpdate = reviewRepository.findById(id).orElseThrow(() -> new
-        // ReviewNotFoundException(id));
-        Review reviewToUpdate = reviewRepository.findById(id).get(0);
+        Review reviewToUpdate = reviewRepository.findById(id).orElseThrow(() -> new ReviewNotFoundException(id));
 
         // Update the review retrieved from the database.
         reviewToUpdate.setCategory(review.getCategory());
diff --git a/src/main/java/sg/com/smartinventory/services/CustomerService.java b/src/main/java/sg/com/smartinventory/services/CustomerService.java
index 38c7bae..60d536c 100644
--- a/src/main/java/sg/com/smartinventory/services/CustomerService.java
+++ b/src/main/java/sg/com/smartinventory/services/CustomerService.java
@@ -8,11 +8,11 @@
 public interface CustomerService {
     Customer createCustomer(Customer customer);
 
-    Customer getCustomer(long id);
+    Customer getCustomer(Long id);
 
     ArrayList<Customer> getAllCustomers();
 
-    Customer updateCustomer(long id, Customer customer);
+    Customer updateCustomer(Long id, Customer customer);
 
     void deleteCustomer(long id);
 
diff --git a/src/main/java/sg/com/smartinventory/services/ProductService.java b/src/main/java/sg/com/smartinventory/services/ProductService.java
index ad915be..9db88ab 100644
--- a/src/main/java/sg/com/smartinventory/services/ProductService.java
+++ b/src/main/java/sg/com/smartinventory/services/ProductService.java
@@ -7,11 +7,11 @@
 public interface ProductService {
     Product createProduct(Product product);
 
-    Product getProduct(long id);
+    Product getProduct(Long id);
 
     ArrayList<Product> getAllProducts();
 
-    Product updateProduct(long id, Product product);
+    Product updateProduct(Long id, Product product);
 
     void deleteProduct(long id);
 }
\ No newline at end of file
diff --git a/src/main/java/sg/com/smartinventory/services/ReviewService.java b/src/main/java/sg/com/smartinventory/services/ReviewService.java
index de37da9..3c34e09 100644
--- a/src/main/java/sg/com/smartinventory/services/ReviewService.java
+++ b/src/main/java/sg/com/smartinventory/services/ReviewService.java
@@ -7,11 +7,11 @@
 public interface ReviewService {
     Review createReview(Review review);
 
-    Review getReview(long id);
+    Review getReview(Long id);
 
     ArrayList<Review> getAllReviews();
 
-    Review updateReview(long id, Review review);
+    Review updateReview(Long id, Review review);
 
     void deleteReview(long id);