Session01 Backend

🛠️ Task Checklist

Preparation

EF Core Code First

• Watch this video

🚧 Branching

• Create the develop branch
• Create the feature/domain-entities branch based on develop

IEntity.cs

• Create the IEntity interface 📂 Suggested Folder: Domain/Framework/Interfaces

public interface IEntity<TKey>
{
    public TKey Id { get; set; }
}

Entity.cs

• Create the Entity class 📂 Suggested Folder: Domain/Framework/Base

public class Entity<TKey> : IEntity<TKey>
{
    public TKey Id{ get; set; }
}

Create Entities

📂 Suggested Folder: Domain/Aggregates/[RelatedFolder] Entities represent the core business objects in our domain model. By defining them explicitly and consistently, we ensure that:

• Our domain logic remains clear and maintainable.
• We follow Domain-Driven Design (DDD) principles, keeping the business rules close to the data they govern.
• All developers have a standardized structure to follow, improving code readability and collaboration.

Guidelines

1. Base Class
   • All entities (except join tables) must inherit from Entity and explicitly specify the datatype of their Id.
2. Properties
   • Use the latest version of the ERD to define properties and relationships.
3. Reference Project
   • For implementation details, you can refer to this project:
     👉 AlibabaClone-Backend Domain Layer
4. ERD Reference
   • Latest ERD available here:
     👉 Project ERD One Example:

Example

public class Account : Entity<long>
{
    public required string PhoneNumber { get; set; }
    public required string Password { set; get; }
    public string? Email { get; set; }
    public long? PersonId { get; set; }
    //...
}

Add Navigation Properties

Navigation properties in Entity Framework Core (EF Core) represent relationships between entities. They allow you to navigate (follow) the relationships between different tables using C# objects instead of writing SQL joins manually.

Add the needed navigation properties inside entities

• Figure out what navigation properties are needed based on the ERD, and use this project as a reference: https://github.com/MehrdadShirvani/AlibabaClone-Backend/tree/develop/AlibabaClone.Domain/Aggregates
• Don’t forget to mark all the navigation properties as virtual

🔹 Examples of Defining Navigation Properties

These are just examples, and not how the project should look like

🔹 One-to-Many Example

A Buyer can have multiple Tickets, but each Ticket belongs to one Buyer.

public class Buyer
{
    public int Id { get; set; }
    public string Name { get; set; }
 
    // Navigation Property (One Buyer → Many Tickets)
    public virtual ICollection<Ticket> Tickets { get; set; } = new List<Ticket>();
}
 
public class Ticket
{
    public int Id { get; set; }
    public int BuyerId { get; set; }
 
    // Navigation Property (Many Tickets → One Buyer)
    public virtual Buyer Buyer { get; set; }
}

🔹 One-to-One Example

A Ticket can have only one Transaction, and a Transaction belongs to exactly one Ticket.

public class Ticket
{
    public int Id { get; set; }
 
    // One-to-One Navigation Property
    public virtual Transaction Transaction { get; set; }
}
 
public class Transaction
{
    public int Id { get; set; }
    public int TicketId { get; set; }
 
    // One-to-One Navigation Property
    public virtual Ticket Ticket { get; set; }
}

🔹 Many-to-Many Example

A Buyer can buy many Tickets, and each Ticket can be bought by many Buyers (if resale is allowed).

public class Buyer
{
    public int Id { get; set; }
    public string Name { get; set; }
 
    // Many-to-Many Navigation Property
    public virtual ICollection<Ticket> Tickets { get; set; } = new List<Ticket>();
}
 
public class Ticket
{
    public int Id { get; set; }
 
    // Many-to-Many Navigation Property
    public virtual ICollection<Buyer> Buyers { get; set; } = new List<Buyer>();
}

Add Packages to Infrastructure Project

• Add Microsoft.EntityFrameworkCore.Proxies to Infrastructure Project

🚧 Merge

• Create a PR and merge the current branch with develop

🧠 Hints & Notes

• Mark navigation properties virtual

🙌 Acknowledgements

• ChatGPT for snippet refinement and explanations

🔍 References

Session01 Additional Info