
# 1. Configurations
## Preparation 
- [ ] Read the documentation:
https://learn.microsoft.com/en-us/ef/core/modeling/

## Branching
- [ ] Create the feature/entity-configurations branch based on develop

## Where Should You Place Configuration Files?

✅ **Best Practice:** Place all configuration files in the **Infrastructure** layer.  
📂 Suggested Folder: `Infrastructure/Configurations`
### **Reason:**

- The **Domain layer** should be **clean** (only entities, no database-related logic).
- The **Infrastructure layer** handles **database interactions**, so configurations belong here.

 
## Create configuration classes
- [ ] Create the classes with this format: `[Entity]Configutaion.cs`
- [ ] The class should implement the `IEntityTypeConfiguration<[Entity]>`
## Examples and Details


### **Use this as a reference:**
https://github.com/MehrdadShirvani/AlibabaClone-Backend/tree/develop/AlibabaClone.Infrastructure/Configurations
---

### **How to Define Keys (Primary Keys & Identity)**

You **don’t** need to explicitly define the **primary key (PK)** if you follow EF Core conventions (`Id` or `EntityNameId`). However, if you want to be explicit:

```csharp
public class TicketConfiguration : IEntityTypeConfiguration<Ticket>
{
    public void Configure(EntityTypeBuilder<Ticket> builder)
    {
        builder.HasKey(t => t.Id); // Explicitly defining PK (optional)

        builder.Property(t => t.Id)
               .ValueGeneratedOnAdd(); // Sets Identity (auto-increment)
    }
}
```

> 🛑 **NOTE:** If you’re using a GUID as the ID, you might need `.ValueGeneratedNever()` instead.

---

### **How to Define Foreign Keys?**

Use `HasOne()` and `WithMany()` for **one-to-many** relationships.

```csharp
public class TicketConfiguration : IEntityTypeConfiguration<Ticket>
{
    public void Configure(EntityTypeBuilder<Ticket> builder)
    {
        builder.HasKey(t => t.Id);

        // Foreign Key - Ticket to Transportation
        builder.HasOne(t => t.Transportation) 
               .WithMany(tr => tr.Tickets)   
               .HasForeignKey(t => t.TransportationId)
               .OnDelete(DeleteBehavior.Restrict); // Optional: No cascade delete
    }
}
```

---

### **How to Introduce Navigation Properties with Different Names?**

If your navigation property **doesn’t match** the entity name, you should explicitly specify it using `HasOne()` and `WithMany()`.

### **Example: Ticket has a Buyer (which is an Account)**

```csharp
builder.HasOne(t => t.Buyer)  // Navigation property (Ticket → Account)
       .WithMany(a => a.TicketsBought) // Corresponding collection in Account
       .HasForeignKey(t => t.BuyerId);
```

> **Tip:** If your navigation property names don't match table names, always define them explicitly in the Fluent API.

---

### **How to Configure Column Types? (nvarchar, date, etc.)**

You can **manually specify column types** using `.HasColumnType()`.

### **All Strings Should Be `nvarchar` with Specific Lengths**

```csharp
builder.Property(t => t.TicketNumber)
       .IsRequired()
       .HasMaxLength(20) // Limits nvarchar length
       .HasColumnType("nvarchar(20)");
```

### **Store Some DateTime Fields as SQL `DATE` Instead of `DATETIME2`**

```csharp
builder.Property(t => t.PurchaseDate)
       .HasColumnType("date");  // Instead of default "datetime2"
```

> 🚀 **Best Practice:** Always set **string lengths** to avoid `nvarchar(MAX)`, which hurts performance.

---

### **How to Define Constraints? (Not Null, Length, etc.)**

Use `.IsRequired()` for **NOT NULL** and `.HasMaxLength()` for length constraints.

### **Example: Ticket Number Must Be Unique & Required**

```csharp
builder.Property(t => t.TicketNumber)
       .IsRequired() // NOT NULL
       .HasMaxLength(20);

builder.HasIndex(t => t.TicketNumber)
       .IsUnique();  // Unique constraint
```

---

### **Final Configuration File Example (TicketConfiguration.cs)**

Here’s a **complete** example of a configuration file:

```csharp
public class TicketConfiguration : IEntityTypeConfiguration<Ticket>
{
    public void Configure(EntityTypeBuilder<Ticket> builder)
    {
        builder.HasKey(t => t.Id);

        builder.Property(t => t.TransportationId)
            .IsRequired();

        builder.Property(t => t.SeatId)
            .IsRequired();

        builder.Property(t => t.BuyerId)
            .IsRequired();

        builder.Property(t => t.TravelerId)
            .IsRequired();

        builder.Property(t => t.CreatedAt)
            .IsRequired();

        builder.Property(t => t.CompanionId)
            .IsRequired(false);

        builder.Property(t => t.TicketStatusId)
            .IsRequired();

        builder.Property(t => t.SerialNumber)
            .IsRequired()
            .HasMaxLength(50)
            .IsUnicode(false);

        builder.Property(t => t.Description)
            .HasMaxLength(200)
            .IsUnicode(false);

        // Relationships
        builder.HasOne(t => t.Transportation)
            .WithMany(t => t.Tickets)
            .HasForeignKey(t => t.TransportationId)
            .OnDelete(DeleteBehavior.Restrict);

        builder.HasOne(t => t.Seat)
            .WithMany(s => s.Tickets)
            .HasForeignKey(t => t.SeatId)
            .OnDelete(DeleteBehavior.Restrict);

        builder.HasOne(t => t.Buyer)
            .WithMany(a => a.BoughtTickets)
            .HasForeignKey(t => t.BuyerId)
            .OnDelete(DeleteBehavior.Restrict);

        builder.HasOne(t => t.Traveler)
            .WithMany(p => p.TraveledTickets)
            .HasForeignKey(t => t.TravelerId)
            .OnDelete(DeleteBehavior.Restrict);

        builder.HasOne(t => t.Companion)
            .WithMany()
            .HasForeignKey(t => t.CompanionId)
            .OnDelete(DeleteBehavior.Restrict);

        builder.HasOne(t => t.TicketStatus)
            .WithMany()
            .HasForeignKey(t => t.TicketStatusId)
            .OnDelete(DeleteBehavior.Restrict);
    }
}
```

---

### **Summary & Best Practices**

✅ **Store Configuration Files in:** `Infrastructure/Configurations`  
✅ **Define Foreign Keys:** Use `HasOne()` and `WithMany()`  
✅ **Explicitly Define Navigation Properties** if the names differ  
✅ **Column Types:** Use `.HasColumnType()` for `nvarchar`, `date`, etc.  
✅ **Constraints:** Use `.IsRequired()`, `.HasMaxLength()`, `.IsUnique()`

---



### **1. Join Tables with Multiple IDs**

In many-to-many relationships, a join table is created to link two entities. This join table typically contains foreign keys referencing the primary keys of the two entities involved in the relationship.

#### **Example of a Join Table**

Suppose we have two entities, `Student` and `Course`, and we want to create a many-to-many relationship between them. We'll create a join table called `StudentCourses`.

#### **Entities**

```csharp
public class Student : Entity<long>
{
    public required string Name { get; set; }
    public virtual ICollection<StudentCourse> StudentCourses { get; set; }
}

public class Course : Entity<long>
{
    public required string Title { get; set; }
    public virtual ICollection<StudentCourse> StudentCourses { get; set; }
}

public class StudentCourse
{
    public long StudentId { get; set; }
    public virtual Student Student { get; set; }

    public long CourseId { get; set; }
    public virtual Course Course { get; set; }
}
```

#### **Configuration for Join Table**

You would configure the join table using the Fluent API:

```csharp
public class StudentCourseConfiguration : IEntityTypeConfiguration<StudentCourse>
{
    public void Configure(EntityTypeBuilder<StudentCourse> builder)
    {
        // Composite Primary Key
        builder.HasKey(sc => new { sc.StudentId, sc.CourseId });

        // Foreign Key Relationships
        builder.HasOne(sc => sc.Student)
            .WithMany(s => s.StudentCourses)
            .HasForeignKey(sc => sc.StudentId);

        builder.HasOne(sc => sc.Course)
            .WithMany(c => c.StudentCourses)
            .HasForeignKey(sc => sc.CourseId);
    }
}
```

#### **Key Points for Join Tables**

- **Composite Primary Key**: The join table uses a composite key made up of both foreign keys.
- **Navigation Properties**: This enables navigation from `Student` to `Course` and vice versa.

---

### **2. Using GUIDs That Should Be Auto-Generated**

GUIDs (Globally Unique Identifiers) can be used as primary keys in your entities. In EF Core, you can configure them to auto-generate when a new entity is created.

#### **Example Entity Using GUID**

```csharp
public class SomeEntity
{
    public Guid Id { get; set; } = Guid.NewGuid(); // Auto-generate GUID
    public string Name { get; set; }
}
```

#### **Configuration for GUID**

When configuring an entity with a GUID as the primary key, you don’t need a specific setup in the configuration, but you can enforce that the `Id` is generated on addition.

```csharp
builder.Property(e => e.Id)
    .ValueGeneratedOnAdd()
    .HasDefaultValueSql("NEWSEQUENTIALID()"); // Optionally use NEWID() for random GUID
```

#### **How It Works**

- **`Guid.NewGuid()`** generates a new GUID when a new entity instance is created.
- **Database**: If you use `NEWSEQUENTIALID()` in SQL Server, it generates sequential GUIDs, which can improve indexing performance.

#### **Example Configuration in DbContext**

Here's how you might define an entity with GUIDs in your `DbContext`:

```csharp
public class ApplicationDbContext : DbContext
{
    public DbSet<SomeEntity> SomeEntities { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<SomeEntity>(builder =>
        {
            builder.HasKey(e => e.Id);
            builder.Property(e => e.Id)
                .ValueGeneratedOnAdd()
                .HasDefaultValueSql("NEWSEQUENTIALID()");
        });
    }
}
```

---


## Merge
- [ ] Create a PR and merge the current branch with develop

# 2. Application DBContext and ConnectionString Configurations

## Preparation 
- [ ] Read the documentation:
https://learn.microsoft.com/en-us/ef/core/modeling/

## Branching
- [ ] Create the feature/setup-dbContext branch based on develop

## Database Context
- [ ] Create ApplicationDBContext 
	- [ ] Location: Infrastructure/ApplicationDbContext.cs
	- [ ] Inherits DbContext
	- [ ] Create the constructor like the code below
	- [ ] Add the Needed DbSets
	- [ ] Override `OnModelCreating` and `OnConfiguring` as below

```csharp
using AlibabaClone.Domain.Aggregates.AccountAggregates;

using Microsoft.EntityFrameworkCore;

namespace AlibabaClone.Infrastructure
{
    public class ApplicationDBContext : DbContext
    {
        public ApplicationDBContext(DbContextOptions<ApplicationDBContext> options) : base(options)
        {

        }

        public DbSet<Account> Accounts { get; set; }
        public DbSet<AccountRole> AccountRoles { get; set; }
        public DbSet<Gender> Genders{ get; set; }
        public DbSet<Person> People { get; set; }
        public DbSet<Role> Roles { get; set; }

		//... Add other DbSets as well

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.ApplyConfigurationsFromAssembly(typeof(ApplicationDBContext).Assembly);
            base.OnModelCreating(modelBuilder);
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseLazyLoadingProxies();
        }
    }
}

```



---

## Configuring the Database in ASP.NET Core

### 📌 **Connection String **
- [ ] Modify `appsettings.json` and add the following. (They might have a type or something... search the web to make sure)

- [ ] Adjust the ConnectionString to meet your needs
### Option 1:
```json
{
  "ConnectionStrings": {
    "DefaultConnection": "Server=YOUR_SERVER;Database=YourDb;User Id=USERNAME;Password=PASSWORD;Trusted_Connection=True;TrustServerCertificate=True"
  }
}
```
### Option 2:
```json
{
  "ConnectionStrings": {
    "DefaultConnection": "Server=YOUR_SERVER;Database=YourDb;Integrated Security=TRUE;Trusted_Connection=True;TrustServerCertificate=True"
  }
}
```
- [ ] Put this `appsettings.json` in **`gitignore`** if you think is needed 
### **Registering EF Core in `Program.cs`**
- [ ] Modify `Program.cs`
 
```csharp
using Infrastructure.Persistence;
using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

var app = builder.Build();
app.Run();
```
## Merge
- [ ] Create a PR and merge the current branch with develop
---

# Migrations and Database Setup
## Branching
- [ ] Create the feature/migrations branch based on develop

## Using Package Manager Console 
- [ ] Make sure to set the project to Infrastructure
- [ ] Make sure you have installed Microsoft.EntityFrameworkCore.Tools
- [ ] Run the following command
```
Add-Migration InitialCreate
```
- [ ] In case of scuccues:
```
Update-Database
```
## Merge
- [ ] Create a PR and merge the current branch with develop
---

# Additional Notes
## Cardinality
### Cardinality in Database Relationships

Cardinality in databases refers to the number of relationships between records in two tables. It defines how many instances of one entity can be associated with instances of another entity. Cardinality is a crucial concept in database design because it ensures data integrity and optimizes query performance.

---

### **Types of Cardinality**

1. **One-to-One (1:1)**
    
    - Each record in Table A is related to exactly one record in Table B, and vice versa.
        
    - Example: A _person_ has one _passport_, and a _passport_ belongs to only one _person_.
        
    - Implementation: Typically enforced with a **unique foreign key**.
        
2. **One-to-Many (1:M)**
    
    - A record in Table A can have multiple related records in Table B, but a record in Table B is linked to only one record in Table A.
        
    - Example: A _customer_ can place multiple _orders_, but each _order_ is placed by only one _customer_.
        
    - Implementation: A **foreign key** in Table B referring to the primary key in Table A.
        
3. **Many-to-Many (M:M)**
    
    - Multiple records in Table A can relate to multiple records in Table B.
        
    - Example: _Students_ enroll in multiple _courses_, and each _course_ has multiple _students_.
        
    - Implementation: A **junction (bridge) table** with foreign keys referencing both tables.
        

---

### **Cardinality Constraints**

Cardinality can be further specified using **minimum and maximum** constraints:

- **(0,1): Optional One** → A record may or may not be related.
    
- **(1,1): Mandatory One** → A record must always be related to exactly one record.
    
- **(0,N): Optional Many** → A record may have many related records or none.
    
- **(1,N): Mandatory Many** → A record must have at least one related record.
    

---

### **Practical Example**

Consider a database with `Students` and `Courses`:

- **One-to-Many:** A _teacher_ teaches multiple _courses_, but each _course_ has only one _teacher_.
    
- **Many-to-Many:** _Students_ enroll in multiple _courses_, and _courses_ have multiple _students_. This is implemented using a **StudentCourses** junction table.
    

Would you like a more detailed example or SQL implementation? 🚀

## 