diff --git a/models/author_test.go b/models/author_test.go
index b93edc6..4948654 100644
--- a/models/author_test.go
+++ b/models/author_test.go
@@ -45,6 +45,7 @@ func TestAddOrUpdateAuthor(t *testing.T) {
 	// Pass an empty author to see if it fails
 	_, err = AddOrUpdateAuthor(Author{})
 	assert.Error(t, err)
+	assert.True(t, IsErrAuthorCannotBeEmpty(err))
 
 	// Update the author
 	testauthor.ID = author1.ID
@@ -62,4 +63,9 @@ func TestAddOrUpdateAuthor(t *testing.T) {
 	_, exists, err = GetAuthorByID(author1.ID)
 	assert.NoError(t, err)
 	assert.False(t, exists)
+
+	// Try deleting an author with ID = 0
+	err = DeleteAuthorByID(0)
+	assert.Error(t, err)
+	assert.True(t, IsErrIDCannotBeZero(err))
 }
diff --git a/models/authors_add_update.go b/models/authors_add_update.go
index 2ccd727..3473df7 100644
--- a/models/authors_add_update.go
+++ b/models/authors_add_update.go
@@ -1,7 +1,5 @@
 package models
 
-import "fmt"
-
 // AddOrUpdateAuthor adds a new author based on an author struct
 func AddOrUpdateAuthor(author Author) (newAuthor Author, err error) {
 
@@ -9,7 +7,7 @@ func AddOrUpdateAuthor(author Author) (newAuthor Author, err error) {
 	if author.ID == 0 {
 		// Check if the author is empty, only insert it if not
 		if author.Forename == "" && author.Lastname == "" {
-			return Author{}, fmt.Errorf("Author cannot be empty")
+			return Author{}, ErrAuthorCannotBeEmpty{}
 		}
 		_, err = x.Insert(&author)
 
diff --git a/models/authors_delete.go b/models/authors_delete.go
index e11edd3..a63ad2c 100644
--- a/models/authors_delete.go
+++ b/models/authors_delete.go
@@ -1,12 +1,10 @@
 package models
 
-import "fmt"
-
 // DeleteAuthorByID deletes an author by its ID
 func DeleteAuthorByID(id int64) error {
 	// Check if the id is 0
 	if id == 0 {
-		return fmt.Errorf("ID cannot be 0")
+		return ErrIDCannotBeZero{}
 	}
 
 	// Delete the author
diff --git a/models/book_test.go b/models/book_test.go
index ce696b7..70b8ec2 100644
--- a/models/book_test.go
+++ b/models/book_test.go
@@ -126,4 +126,9 @@ func TestAddOrUpdateBook(t *testing.T) {
 	_, exists, err = GetBookByID(book1.ID)
 	assert.NoError(t, err)
 	assert.False(t, exists)
+
+	// Try deleting one with ID = 0
+	err = DeleteBookByID(0)
+	assert.Error(t, err)
+	assert.True(t, IsErrIDCannotBeZero(err))
 }
diff --git a/models/books_delete.go b/models/books_delete.go
index 3a74e8c..63a9d87 100644
--- a/models/books_delete.go
+++ b/models/books_delete.go
@@ -1,12 +1,10 @@
 package models
 
-import "fmt"
-
 // DeleteBookByID deletes a book by its ID
 func DeleteBookByID(id int64) error {
 	// Check if the id is 0
 	if id == 0 {
-		return fmt.Errorf("ID cannot be 0")
+		return ErrIDCannotBeZero{}
 	}
 
 	// Delete the book
diff --git a/models/error.go b/models/error.go
index cd4e80c..70674f4 100644
--- a/models/error.go
+++ b/models/error.go
@@ -51,3 +51,31 @@ func IsErrUserDoesNotExist(err error) bool {
 func (err ErrUserDoesNotExist) Error() string {
 	return fmt.Sprintf("this user does not exist [user id: %d]", err.UserID)
 }
+
+// ErrIDCannotBeZero represents a "UsernameAlreadyExists" kind of error.
+type ErrIDCannotBeZero struct {}
+
+// IsErrIDCannotBeZero checks if an error is a ErrUsernameExists.
+func IsErrIDCannotBeZero(err error) bool {
+	_, ok := err.(ErrIDCannotBeZero)
+	return ok
+}
+
+func (err ErrIDCannotBeZero) Error() string {
+	return fmt.Sprintf("ID cannot be 0")
+}
+
+// ErrAuthorCannotBeEmpty represents a "AuthorCannotBeEmpty" kind of error.
+type ErrAuthorCannotBeEmpty struct {}
+
+// IsErrIDCannotBeZero checks if an error is a ErrUsernameExists.
+func IsErrAuthorCannotBeEmpty(err error) bool {
+	_, ok := err.(ErrAuthorCannotBeEmpty)
+	return ok
+}
+
+func (err ErrAuthorCannotBeEmpty) Error() string {
+	return fmt.Sprintf("author cannot be empty")
+}
+
+
diff --git a/models/item_test.go b/models/item_test.go
index 20bdcb7..1a1f801 100644
--- a/models/item_test.go
+++ b/models/item_test.go
@@ -85,4 +85,9 @@ func TestAddOrUpdateItem(t *testing.T) {
 	_, exists, err = GetItemByID(item1.ID)
 	assert.NoError(t, err)
 	assert.False(t, exists)
+
+	// Try deleting one with ID = 0
+	err = DeleteItemByID(0)
+	assert.Error(t, err)
+	assert.True(t, IsErrIDCannotBeZero(err))
 }
diff --git a/models/items_delete.go b/models/items_delete.go
index 28c80d1..e8c4ac5 100644
--- a/models/items_delete.go
+++ b/models/items_delete.go
@@ -1,12 +1,10 @@
 package models
 
-import "fmt"
-
 // DeleteItemByID deletes a item by its ID
 func DeleteItemByID(id int64) error {
 	// Check if the id is 0
 	if id == 0 {
-		return fmt.Errorf("ID cannot be 0")
+		return ErrIDCannotBeZero{}
 	}
 
 	// Delete the item
diff --git a/models/publisher_test.go b/models/publisher_test.go
index eb65c1b..794fd78 100644
--- a/models/publisher_test.go
+++ b/models/publisher_test.go
@@ -60,4 +60,9 @@ func TestAddOrUpdatePublisher(t *testing.T) {
 	_, exists, err = GetPublisherByID(publisher1.ID)
 	assert.NoError(t, err)
 	assert.False(t, exists)
+
+	// Try deleting one with ID = 0
+	err = DeletePublisherByID(0)
+	assert.Error(t, err)
+	assert.True(t, IsErrIDCannotBeZero(err))
 }
diff --git a/models/publishers_delete.go b/models/publishers_delete.go
index b317f74..353e37b 100644
--- a/models/publishers_delete.go
+++ b/models/publishers_delete.go
@@ -1,12 +1,10 @@
 package models
 
-import "fmt"
-
 // DeletePublisherByID deletes a publisher by its ID
 func DeletePublisherByID(id int64) error {
 	// Check if the id is 0
 	if id == 0 {
-		return fmt.Errorf("ID cannot be 0")
+		return ErrIDCannotBeZero{}
 	}
 
 	// Delete the publisher
diff --git a/models/user_delete.go b/models/user_delete.go
index 8eb357d..8ff6fa4 100644
--- a/models/user_delete.go
+++ b/models/user_delete.go
@@ -1,12 +1,10 @@
 package models
 
-import "fmt"
-
 // DeleteUserByID deletes a user by its ID
 func DeleteUserByID(id int64) error {
 	// Check if the id is 0
 	if id == 0 {
-		return fmt.Errorf("ID cannot be 0")
+		return ErrIDCannotBeZero{}
 	}
 
 	// Delete the user
diff --git a/routes/api/v1/author_delete.go b/routes/api/v1/author_delete.go
index d458a0e..ee88c43 100644
--- a/routes/api/v1/author_delete.go
+++ b/routes/api/v1/author_delete.go
@@ -34,6 +34,9 @@ func AuthorDelete(c echo.Context) error {
 	err = models.DeleteAuthorByID(authorID)
 
 	if err != nil {
+		if models.IsErrIDCannotBeZero(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Could not delete author."})
 	}
 
diff --git a/routes/api/v1/authors_add_update.go b/routes/api/v1/authors_add_update.go
index 238e5fe..4ddc2ee 100644
--- a/routes/api/v1/authors_add_update.go
+++ b/routes/api/v1/authors_add_update.go
@@ -62,6 +62,9 @@ func AuthorAddOrUpdate(c echo.Context) error {
 	newAuthor, err := models.AddOrUpdateAuthor(*datAuthor)
 
 	if err != nil {
+		if models.IsErrAuthorCannotBeEmpty(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Error"})
 	}
 
diff --git a/routes/api/v1/book_delete.go b/routes/api/v1/book_delete.go
index 2621cff..6901899 100644
--- a/routes/api/v1/book_delete.go
+++ b/routes/api/v1/book_delete.go
@@ -34,6 +34,9 @@ func BookDelete(c echo.Context) error {
 	err = models.DeleteBookByID(bookID)
 
 	if err != nil {
+		if models.IsErrIDCannotBeZero(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Could not delete book."})
 	}
 
diff --git a/routes/api/v1/books_add_update.go b/routes/api/v1/books_add_update.go
index 7d2f9a1..01a66cd 100644
--- a/routes/api/v1/books_add_update.go
+++ b/routes/api/v1/books_add_update.go
@@ -62,6 +62,9 @@ func BookAddOrUpdate(c echo.Context) error {
 	newBook, err := models.AddOrUpdateBook(*datBook)
 
 	if err != nil {
+		if models.IsErrAuthorCannotBeEmpty(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Error"})
 	}
 
diff --git a/routes/api/v1/items_delete.go b/routes/api/v1/items_delete.go
index be9c4df..31948ba 100644
--- a/routes/api/v1/items_delete.go
+++ b/routes/api/v1/items_delete.go
@@ -34,6 +34,9 @@ func ItemDelete(c echo.Context) error {
 	err = models.DeleteItemByID(itemID)
 
 	if err != nil {
+		if models.IsErrIDCannotBeZero(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Could not delete item."})
 	}
 
diff --git a/routes/api/v1/publishers_delete.go b/routes/api/v1/publishers_delete.go
index d6bf241..2c26ff4 100644
--- a/routes/api/v1/publishers_delete.go
+++ b/routes/api/v1/publishers_delete.go
@@ -34,6 +34,9 @@ func PublisherDelete(c echo.Context) error {
 	err = models.DeletePublisherByID(publisherID)
 
 	if err != nil {
+		if models.IsErrIDCannotBeZero(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Could not delete publisher."})
 	}
 
diff --git a/routes/api/v1/user_delete.go b/routes/api/v1/user_delete.go
index 348b8ea..0abd496 100644
--- a/routes/api/v1/user_delete.go
+++ b/routes/api/v1/user_delete.go
@@ -39,6 +39,9 @@ func UserDelete(c echo.Context) error {
 	err = models.DeleteUserByID(userID)
 
 	if err != nil {
+		if models.IsErrIDCannotBeZero(err) {
+			return c.JSON(http.StatusInternalServerError, models.Message{"Id cannot be 0"})
+		}
 		return c.JSON(http.StatusInternalServerError, models.Message{"Could not delete user."})
 	}