feat(services): add getBySlug method to MysqlService and refine getAll method

Added a new method getBySlug to retrieve a category by its slug in mysql.service.ts. Also, updated the getAll method by specifying the return type to Promise<Array<IDbCategory>> for better type checking.

Issue: #6
Signed-off-by: Mathis <yidhra@tuta.io>

src/services/mysql.service.ts

@@ -411,7 +411,7 @@ const MySqlService = {
 		 *                                       - The category objects are of type IDbCategory.
 		 *                                       - If an error occurs, the promise will be rejected with an Error object.
 		 */
-		getAll(handler: MysqlHandler) {
+		getAll(handler: MysqlHandler): Promise<Array<IDbCategory>> {
 			return new Promise((resolve, reject) => {
 				const _sql = "SELECT * FROM `categories`";
 				try {
@@ -420,6 +420,26 @@ const MySqlService = {
 					reject(err as Error);
 				}
 			});
+		},
+		/**
+		 * Retrieves a category from the database by its slug.
+		 *
+		 * @param {MysqlHandler} handler - The MySQL handler object to execute the query.
+		 * @param {string} slug - The slug of the category to retrieve.
+		 * @returns {Promise<IDbCategory>} - A promise that resolves with the retrieved category object.
+		 * @throws {Error} - If an error occurs while executing the query.
+		 */
+		getBySlug(handler: MysqlHandler, slug: string): Promise<IDbCategory> {
+			return new Promise((resolve, reject) => {
+				if (!slug) return reject('slug is undefined')
+				const _sql = "SELECT * FROM `categories` WHERE `slug_name` = ?";
+				const _values = [slug];
+				try {
+					resolve(handler.execute(_sql, _values) as unknown as IDbCategory);
+				} catch (err: unknown) {
+					reject(err as Error);
+				}
+			})
 		}
 	}
 }