Backend Systems

Relevant source files

The following files were used as context for generating this wiki page:

• MercaditoMovil/MercaditoMovil.Infrastructure/Tools/Scripts/create_csvs.py
• MercaditoMovil/MercaditoMovil.Infrastructure/Repositories/CsvUserRepository.cs
• MercaditoMovil/Mercadito.Domain/Entities/User/User.cs
• MercaditoMovil/MercaditoMovil.Application/Service/AuthService.cs
• MercaditoMovil/MercaditoMovil/Controllers/LoginController.cs
• MercaditoMovil/MercaditoMovil.Application/Validators/UserValidator.cs
• MercaditoMovil/Mercadito.Domain/Interfaces/Interface1.cs
• MercaditoMovil/MercaditoMovil.Application/Features/UserManagement/IAuthService.cs
• MercaditoMovil/MercaditoMovil/Program.cs
• MercaditoMovil/MercaditoMovil/Views/Form1.Designer.cs
• MercaditoMovil/MercaditoMovil/Views/Form1.cs

The backend for MercaditoMovil is built using a layered architecture in C# (.NET) and is responsible for business logic, data persistence, and user authentication. The data storage is file-based, utilizing CSV files as a simple database. A supplementary Python script is used for generating the initial dataset, including users, markets, and products, which populates these CSV files.

The core backend functionality revolves around user management, providing services for user login and registration. The system is designed with a separation of concerns, dividing responsibilities into distinct layers: Presentation (WinForms), Application (Services), Domain (Entities and Interfaces), and Infrastructure (Data Repositories). This structure facilitates maintainability and isolates data access logic from business rules.

System Architecture

The application follows a classic layered architecture pattern. The layers communicate in a top-down fashion, where the UI (Presentation) interacts with Application Services via controllers, and the services orchestrate calls to the Infrastructure layer for data operations, all while using entities defined in the Domain layer.

This diagram illustrates the dependency flow between the major components of the backend system.

Data Persistence Layer

The persistence layer is implemented using CSV files, abstracting file I/O operations behind a repository pattern. This design choice avoids the need for a formal database system.

Sources: MercaditoMovil.Infrastructure/Repositories/CsvUserRepository.cs, MercaditoMovil.Infrastructure/Tools/Scripts/create_csvs.py

CSV Repository (CsvUserRepository)

The CsvUserRepository class is the concrete implementation for user data access. It reads from and writes to users.csv.

• GetByUsername(string username): This method performs a sequential scan of the users.csv file. It reads the file line by line, skipping the header, and compares the username field in a case-insensitive manner. It returns a User object on the first match or null if no user is found. It uses TextFieldParser to correctly handle fields enclosed in quotes.
• Add(User user, out string error): This method appends a new user record to the users.csv file. It ensures the directory and file exist, creating them and writing a header if necessary. All string values are quoted and have internal quotes escaped to maintain CSV integrity.

Sources: MercaditoMovil.Infrastructure/Repositories/CsvUserRepository.cs:33-60, 65-103

Data Schema

The data is organized across several CSV files. The Python script create_csvs.py is responsible for generating these files and their content. The following diagram shows the main entities and their relationships as defined by the CSV columns.

This ER diagram outlines the structure of the CSV files and the foreign key relationships between them.

Domain Model

The Domain layer contains the core business entities and interfaces.

Sources: Mercadito.Domain/Entities/User/User.cs, Mercadito.Domain/Interfaces/Interface1.cs

User Entity

The User class is a sealed class representing an application user. All its properties are strings and are guarded against null values in the constructor, defaulting to empty strings.

This class diagram shows the User entity and the interfaces for the repository and authentication service.

The table below details the properties of the User entity.

Property	Type	Description
UserId	string	Unique identifier for the user (e.g., USR-XXXXXXXX).
Username	string	The user's login name.
Password	string	The user's password (stored in plain text).
FirstName	string	The user's first name.
LastName1	string	The user's first last name.
LastName2	string	The user's second last name.
NationalId	string	The user's national identification number.
Email	string	The user's email address.
Phone	string	The user's phone number.
ExactAddress	string	The user's detailed street address.
Province	string	The province of the user's address.
Canton	string	The canton of the user's address.
District	string	The district of the user's address.
MarketId	string	The ID of the market assigned to the user. Defaults to MKT-000.

Sources: Mercadito.Domain/Entities/User/User.cs:8-22, 48

Application Services

The Application layer contains the business logic and orchestrates operations between the presentation and data layers.

Authentication Service (AuthService)

AuthService implements the IAuthService interface and provides the core logic for user authentication and registration. It depends on an IUserRepository to interact with the data store.

• Login(string username, string password, out string message):

  1. Validates that username and password are not empty using UserValidator.
  2. Retrieves the user from the repository via _repo.GetByUsername(username).
  3. Compares the provided password with the one stored in the retrieved User object.
  4. Returns true for a successful login, false otherwise, with an appropriate output message.

• Register(User user, out string message):

  1. Validates the required fields of the User object using UserValidator.
  2. Checks if a user with the same username already exists by calling _repo.GetByUsername(user.Username).
  3. If validation passes and the username is unique, it calls _repo.Add(user, out repoError) to persist the new user.
  4. Returns a success message, which varies depending on whether the user was assigned to a valid market (MarketId != "MKT-000").

Sources: MercaditoMovil.Application/Service/AuthService.cs:19-57, MercaditoMovil.Application/Validators/UserValidator.cs:11-40

The following sequence diagram illustrates the login process.

Initial Data Generation

A Python script, create_csvs.py, is provided to bootstrap the application with a set of realistic, randomly generated data. This script does not have external dependencies and can be run from any location.

Script Functionality

The script performs the following actions in order:

1. gen_markets(): Writes a predefined list of markets to markets.csv.
2. gen_users(): Generates approximately 30 user records, including two fixed users and 28 randomly generated ones, and writes them to users.csv. It can optionally use locations.csv to generate more realistic geographic data.
3. gen_producers(): Creates 30 producer records (a mix of individuals and companies) and saves them to producers.csv.
4. gen_catalog(): Populates product_catalog.csv from a hardcoded list of products.
5. gen_producer_products(): Links producers with products from the catalog, assigning random prices and other attributes, and writes the results to producer_products.csv.

This flowchart shows the main execution flow of the data generation script.

Conclusion

The backend of MercaditoMovil is a pragmatic system designed for a desktop application environment. It employs a clean, layered architecture in C# that separates concerns effectively. The use of CSV files for data persistence, managed through a repository pattern, simplifies deployment and setup. An accompanying Python script for data generation is a key component, enabling rapid development and testing by providing a rich initial dataset. The core functionalities are centered around user authentication and registration, forming a solid foundation for the application's features.