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+### 1. **Should I have an `IEntityService` and then `EntityService` for each of my entities?**
+
+Not necessarily **for _every_** entity — only if it **makes sense**.
+
+- The Application Layer should expose **use cases** — not just CRUD logic for each entity.
+    
+- If an entity has business logic or interactions that need orchestration (e.g., validations, aggregations, calling repositories, etc.), then **yes**, create a service.
+    
+- Otherwise, for basic operations, **directly using a repository (via a unit of work or interface)** from the use case handler might be fine.
+### 2. **Is it OK to have services not related to a specific entity?**
+
+Absolutely, **yes**. In fact, that’s expected in a Clean Architecture setup.
+
+Examples:
+
+- A `ReportGenerationService` that combines bookings, customers, and payments.
+    
+- A `TokenService` for authentication tokens.
+    
+- A `CurrencyConversionService` that hits an external API.
+    
+- A `NotificationService` that sends emails or SMS.
+    
+
+👉 As long as these services **live in the Application Layer** and follow **dependency inversion** (i.e., they depend only on interfaces, not implementations), you’re doing great.
+
+### 3. **Is it necessary to have an interface for each service?**
+
+
+
+### 🔹 **What’s the Difference Between Services and Repositories?**
+
+| Aspect             | **Service**                                                            | **Repository**                                                  |
+| ------------------ | ---------------------------------------------------------------------- | --------------------------------------------------------------- |
+| **Layer**          | Application Layer                                                      | Domain Layer (interface), Infrastructure Layer (implementation) |
+| **Responsibility** | **Orchestrates business logic** / use cases                            | **Data access abstraction**                                     |
+| **Focus**          | Coordinates multiple domain/repo operations, validation, business flow | Fetching/storing data for a specific entity                     |
+| **Example**        | `PlaceOrderService`, `ReportService`                                   | `ICustomerRepository`, `IOrderRepository`                       |
+
+### What does `init` mean?
+
+`init` is an **access modifier for properties** that allows you to **set a property only during object initialization**, **but not after**.
+
+
+## Should I use `class` or `record` for DTOs in Clean Architecture?
+
+### 🔵 Short answer:
+
+> **Use `record` for DTOs when possible** — it's clean, immutable by default, and semantically perfect for data transfer.
+
+---
+
+### 🔍 Why `record` is a great fit for DTOs
+
+| Feature                 | `record`          | `class`                      |
+| ----------------------- | ----------------- | ---------------------------- |
+| Immutable by default    | ✅ (with `init`)   | ❌ (need manual setup)        |
+| Value-based equality    | ✅                 | ❌ (ref-based by default)     |
+| Concise syntax          | ✅                 | ❌ (more boilerplate)         |
+| Use for data containers | ✅ (perfect fit)   | ✅ (but more verbose)         |
+| Custom behavior/logic   | ❌ (less suitable) | ✅ (better for rich behavior) |
+### But when should you prefer `class`?
+
+Use `class` if your DTO or model:
+
+- Needs to be **mutable** after creation
+    
+- Has to **interact with legacy APIs/libraries**
+    
+- Needs **inheritance or polymorphism** (not well supported in `record`)
+    
+- Has **rich behavior** (logic, methods, validation, etc.)
+    
+
+> For example, in the Domain Layer (Entities, ValueObjects), you'll usually stick to **`class`** — because that's where behavior lives.
+
+## RESTful APIs:
+https://aws.amazon.com/what-is/restful-api/#:~:text=RESTful%20API%20is%20an%20interface,applications%20to%20perform%20various%20tasks.
+
+## What Conditions Make an API RESTful?
+
+### Key Principles of REST:
+
+1. **Statelessness**:
+    
+    - Each API call must contain all the information the server needs to fulfill the request (no session state). Each request is independent.
+        
+2. **Resource Identification**:
+    
+    - Resources (e.g., customers, orders) should be identified using URIs. Use nouns in URIs, not verbs.
+        
+3. **HTTP Methods**:
+    
+    - Use standard HTTP methods to represent actions:
+        
+        - **GET**: Retrieve a resource.
+            
+        - **POST**: Create a new resource.
+            
+        - **PUT**: Update a resource entirely.
+            
+        - **PATCH**: Update a resource partially.
+            
+        - **DELETE**: Remove a resource.
+            
+4. **Use of Standard Status Codes**:
+    
+    - Return appropriate HTTP status codes (e.g., `200 OK`, `201 Created`, `404 Not Found`, `500 Internal Server Error`).
+        
+5. **HATEOAS**:
+    
+    - (Hypermedia as the Engine of Application State) - Provide links to related resources within the responses.
+        
+
+### Multiple GET Methods in One Controller:
+
+- **Yes, you can have multiple GET methods in one controller**. The key is to differentiate them based on routes and parameters.
+    
+- For example:
+    
+
+```c#
+[ApiController] 
+[Route("api/[controller]")] 
+public class CustomerController : ControllerBase {     
+	
+	[HttpGet("{id}")]     
+	public IActionResult GetCustomerById(int id) { /*...*/ }      
+	
+	[HttpGet]     
+	public IActionResult GetAllCustomers() { /*...*/ }      
+	
+	[HttpGet("{id}/orders")]     
+	public IActionResult GetCustomerOrders(int id) { /*...*/ } 
+}
+```
+
+
+- **Routing**: ASP.NET Core uses route templates to differentiate these actions. The combination of route parameters, query strings, and action names can help separate the GET requests.
+
+
+## List-like stuff in `C#`
+Absolutely, let’s go over the main “list-like” data types in C#. They all serve similar purposes—holding multiple items—but differ in functionality, performance, and use cases. Here’s a detailed breakdown:
+
+🔷 1. `IEnumerable`
+
+- Namespace: System.Collections.Generic
+    
+- Most basic "list-like" abstraction.
+    
+- Read-only (forward-only iteration).
+    
+- You can use foreach on it.
+    
+- Doesn’t support indexing (no .Count, no [i]).
+    
+- Often used as the return type to expose a stream of data without giving full collection control.
+    
+
+Example:
+
+```csharp
+IEnumerable<int> numbers = GetNumbers(); // Lazy-loaded maybe
+foreach (var num in numbers)
+    Console.WriteLine(num);
+```
+
+💡 Ideal when:
+
+- You want to return a sequence without exposing modification.
+    
+- You’re using LINQ chains.
+    
+- You’re returning data from a database query.
+    
+
+---
+
+🔷 2. ICollection
+
+- Extends IEnumerable.
+    
+- Adds Count and Add/Remove/Clear methods.
+    
+- Still abstract—List and HashSet implement it.
+    
+
+💡 Useful when:
+
+- You want to expose a collection that can be modified (e.g. Add or Remove).
+    
+- You care about the Count.
+    
+
+---
+
+🔷 3. IList
+
+- Extends ICollection and IEnumerable.
+    
+- Adds index access: list[0] etc.
+    
+- Think of it like a mutable array with dynamic size.
+    
+
+💡 Use when:
+
+- You want ordered collection with indexing.
+    
+- You need to insert, remove, or replace items at specific positions.
+    
+
+---
+
+🔷 4. List
+
+- A concrete class (not interface).
+    
+- Implements IList, ICollection, IEnumerable.
+    
+- Backed by an array (auto-resizes).
+    
+- Fast read and write.
+    
+- Supports Add, Remove, Insert, IndexOf, etc.
+    
+
+Example:
+
+```csharp
+var list = new List<string>();
+list.Add("One");
+list.Add("Two");
+var second = list[1]; // "Two"
+```
+
+💡 Go-to general purpose collection.
+
+---
+
+🔷 5. IReadOnlyCollection & IReadOnlyList
+
+- IReadOnlyCollection: Just Count and IEnumerable.
+    
+- IReadOnlyList: Adds indexing without modification.
+    
+- Used to expose lists safely (read-only).
+    
+
+💡 Used when:
+
+- You want to return a list, but prevent any changes.
+    
+
+---
+
+🔷 6. Array (T[])
+
+- Fixed-size.
+    
+- Fastest for indexing.
+    
+- Cannot change size.
+    
+- Implements IList (via Array).
+    
+
+Example:
+
+```csharp
+int[] numbers = new int[5];
+numbers[0] = 42;
+```
+
+💡 Great for performance-sensitive or fixed-size data.
+
+---
+
+🔷 7. ObservableCollection
+
+- For WPF/Blazor/WinForms data-binding.
+    
+- Notifies UI when items are added/removed.
+    
+- Implements IList.
+    
+
+💡 Use in UI apps when the view needs to react to collection changes.
+
+---
+
+🔷 8. HashSet
+
+- Unordered, no duplicates.
+    
+- Implements ICollection, not IList.
+    
+- No index access.
+    
+
+💡 Best for fast membership checking (contains x).
+
+---
+
+🔷 Summary Table
+
+|Type|Indexing|Modifiable|Ordered|Duplicates|Use Case|
+|---|---|---|---|---|---|
+|IEnumerable|❌|❌|✔️|✔️|Basic read-only stream or LINQ chaining|
+|ICollection|❌|✔️|✔️|✔️|Expose modifiable group of items|
+|IList|✔️|✔️|✔️|✔️|Full-featured list abstraction|
+|List|✔️|✔️|✔️|✔️|Standard go-to collection|
+|IReadOnlyList|✔️|❌|✔️|✔️|Return data safely from service or repo|
+|Array (T[])|✔️|✔️|✔️|✔️|Fixed-size, performant indexing|
+|ObservableCollection|✔️|✔️|✔️|✔️|UI binding for collections|
+|HashSet|❌|✔️|❌|❌|Fast lookup, uniqueness enforcement|
+
+—
+
+If you tell me the scenario (e.g. search results, modifying a cart, populating a drop-down), I can recommend the best type for it. Want that?
@@ -0,0 +1,363 @@
+# Preparation: 
+The unedited conversation with Chat GPT, concerning almost all of the aspects of this session:
+(optional): read this to get a better understanding of the topic:
+https://chatgpt.com/share/67f18460-1c1c-8010-bc57-9f3b683ec87a
+
+# Branching
+- [ ]  Create the feature/transportation-search branch based on develop
+
+# DTO
+In order to develop transportation search flow, three DTOs need to be created in the application layer.
+
+- [ ]  Create DTOs related to transportation search flow
+
+📂 Suggested Folder: Application/DTOs/City`
+
+
+```cs
+public class CityDto
+{
+    public int Id { get; init; }
+    public required string Title { get; init; }
+}
+```
+
+📂 Suggested Folder: Application/DTOs/Transportation
+
+```cs
+public class TransportationSearchRequestDto
+{
+     public short? VehicleTypeId { get; init; }
+     public int? FromCityId { get; init; }
+     public int? ToCityId { get; init; }
+     public DateTime? StartDate { get; init; }
+     public DateTime? EndDate { get; init; }
+}
+```
+
+```cs
+public class TransportationSearchResultDto
+{
+    public long Id { get; init; }
+    public required string CompanyTitle { get; init; }   
+    public required string FromLocationTitle { get; init; }
+    public required string ToLocationTitle { get; init; }
+    public required string FromCityTitle { get; init; }
+    public required string ToCityTitle { get; init; }
+    public DateTime StartDateTime { get; init; }
+    public DateTime? EndDateTime { get; init; }
+    public decimal Price { get; init; } 
+}
+```
+
+# Repository
+There are a few things to be add to some repositories for transportation search flow.
+
+- [ ] Create DTOs related to transportation search flow
+
+📂 Suggested Folder: Domain/Framework/Interfaces/Repositories/
+TransportationRepositories
+
+```cs
+public interface ITransportationRepository : IRepository<Transportation, long>
+{
+    Task<IEnumerable<Transportation>> SearchTransportationsAsync(
+	    short? vehicleTypeId,
+        int? fromCityId,
+        int? toCityId, 
+        DateTime? startDate, 
+        DateTime? endDate);
+}
+```
+
+
+📂 Suggested Folder: Infrastructure/Services/Services/TransportationRepositories
+
+```cs
+public class TransportationRepository :
+        BaseRepository<ApplicationDBContext, Transportation, long>,
+        ITransportationRepository
+    {
+        public TransportationRepository(ApplicationDBContext dbContext) : base(dbContext)
+        {
+
+        }
+
+        public async Task<IEnumerable<Transportation>> SearchTransportationsAsync(
+            short? vehicleTypeId,
+            int? fromCityId,
+            int? toCityId,
+            DateTime? startDate,
+            DateTime? endDate)
+        {
+            var query = DbContext.Transportations
+                .Include(x => x.Vehicle)
+                .Include(x => x.FromLocation).ThenInclude(x => x.City)
+                .Include(x => x.ToLocation).ThenInclude(x => x.City)
+                .Include(x => x.Company)
+                .AsQueryable();
+            query = query.Where(x => vehicleTypeId == null || x.Vehicle.VehicleTypeId == vehicleTypeId.Value);
+            query = query.Where(x => fromCityId == null || x.FromLocation.CityId == fromCityId.Value);
+            query = query.Where(x => toCityId == null || x.ToLocation.CityId == toCityId.Value);
+            query = query.Where(x => startDate == null || x.StartDateTime.Date == startDate.Value.Date);
+            query = query.Where(x => endDate == null || (x.EndDateTime.HasValue && x.EndDateTime.Value == endDate.Value.Date));
+            
+            return await query.ToListAsync();
+        }
+    }
+```
+
+
+# Auto Mapper
+Auto Mapper simplifies mapping between aggregates and DTOs in both directions.
+
+- [ ] Create a `MappingProfile` that inherits `Profile`, and use it to add configurations for mappings
+
+📂 Suggested Folder: Application/Mappers/Profiles
+
+```cs
+public class MappingProfile : Profile
+{
+    public MappingProfile()
+    {
+        CreateMap<Transportation, TransportationSearchResultDto>()
+            .ForMember(dest => dest.CompanyTitle, 
+            opt => opt.MapFrom(src => src.Company.Title))
+            
+            .ForMember(dest => dest.FromLocationTitle, 
+            opt => opt.MapFrom(src => src.FromLocation.Title))
+            
+            .ForMember(dest => dest.ToLocationTitle, 
+            opt => opt.MapFrom(src => src.ToLocation.Title))
+            
+            .ForMember(dest => dest.FromCityTitle, 
+            opt => opt.MapFrom(src => src.FromLocation.City.Title))
+            
+             .ForMember(dest => dest.ToCityTitle, 
+             opt => opt.MapFrom(src => src.ToLocation.City.Title));
+
+        CreateMap<City, CityDto>();
+        }
+    }
+```
+
+- [ ] Register AutoMapper config file in `Program.cs` 
+
+```cs
+ .
+ .
+ .
+
+ builder.Services.AddAutoMapper(typeof(MappingProfile));
+ 
+ var app = builder.Build();
+
+ .
+ .
+ .
+```
+
+# Result & Result Status
+
+- [ ] Create `ResultStatus` enum and `Result` class
+📂 Suggested Folder: Application/Result
+
+
+Result is a template to transfer data between services and controllers (in backend), so will use a generic type
+
+```cs
+public class Result<T>
+{
+	public ResultStatus Status { get; set; }
+	public string? ErrorMessage { get; set; }
+	public T? Data { get; set; }
+	public bool IsSuccess => Status == ResultStatus.Success;
+
+	public static Result<T> Success(T data)
+	{
+		return new Result<T>
+		{
+			Status = ResultStatus.Success,
+			Data = data
+		};
+	}
+
+	public static Result<T> Error(T data)
+	{
+		return new Result<T>
+		{
+			Status = ResultStatus.Error,
+			Data = data
+		};
+	}
+
+	public static Result<T> NotFound(T data)
+	{
+		return new Result<T>
+		{
+			Status = ResultStatus.NotFound,
+			Data = data
+		};
+	}
+}
+```
+
+As you can see, there's a property of type ResultStatus, which is a enum for status of request
+
+```cs
+public enum ResultStatus
+{
+	Success,
+	NotFound,
+	ValidationError,
+	Conflict,
+	Unauthorized,
+	Forbidden,
+	Error
+}
+```
+
+You can read more about enums: [W3Schools](https://www.w3schools.com/cs/cs_enums.php)
+
+
+# `IService` & Service
+
+Now, use `I[Entity]Repositry` and `IUnitOfWork` in services to implement business logic
+
+- [ ] Create `I[Entity]Service` and `[Entity]Service` which implements it
+
+📂 Suggested Folder for `I[Entity]Service`: Application/Interfaces
+
+📂 Suggested Folder for Services: Application/Services
+
+
+- existence of an interface for each service class is optional
+- services can have multiple repositories in them -> logic-based structure
+
+An example of `I[Entity]Service`:
+
+```c#
+public interface ITransportationService
+{
+    Task<Result<IEnumerable<TransportationSearchResultDto>>> SearchTransportationsAsync(TransportationSearchRequestDto searchRequest);
+}
+```
+
+An example of `[Entity]Service`:
+
+```cs
+public class TransportationService : ITransportationService
+{
+	private readonly ITransportationRepository _transportationRepository;
+	private readonly IMapper _mapper;
+	private readonly IUnitOfWork _unitOfWork;
+
+	public TransportationService(ITransportationRepository transportationRepository, IMapper mapper, IUnitOfWork unitOfWork)
+	{
+		_transportationRepository = transportationRepository;
+		_mapper = mapper;
+		_unitOfWork = unitOfWork;
+	}
+
+	public async Task<Result<IEnumerable<TransportationSearchResultDto>>> SearchTransportationsAsync(TransportationSearchRequestDto requestDto)
+	{
+		var result = await _transportationRepository.SearchTransportationsAsync(
+			vehicleTypeId: requestDto.VehicleTypeId,
+			fromCityId: requestDto.FromCityId,
+			toCityId: requestDto.ToCityId,
+			startDateTime: requestDto.StartDate,
+			endDateTime: requestDto.EndDate);
+
+		if (result.Any())
+		{
+			var dto = _mapper.Map<IEnumerable<TransportationSearchResultDto>>(result);
+			return Result<IEnumerable<TransportationSearchResultDto>>.Success(dto);
+		}
+
+		return Result<IEnumerable<TransportationSearchResultDto>>.NotFound(null);
+	}
+}
+```
+
+- [ ] Register services in `Program.cs`:
+```c#
+.
+.
+.
+builder.Services.AddScoped<ITransportationService, TransportationService>();
+builder.Services.AddScoped<ICityService, CityService>();
+.
+.
+.
+```
+
+# Controller
+Now we're getting to endpoints, you should communicate with client side through web-api. So every controller uses Services in Application layer to receive requests and send responses with DTOs.
+
+- [ ] Create an APIController (right click on the folder, and then under Add, select Controller, and then make sure to select the APIController type)
+📂 Suggested Folder: WebAPI/Controller
+
+You should use ```[ApiController]``` attribute on top of them, route them and handle different status codes. TransportationController:
+
+```cs
+[ApiController]
+[Route("api/[controller]")]
+public class TransportationController : ControllerBase
+{
+	private readonly ITransportationService _transportationService;
+
+	public TransportationController(ITransportationService transportationService)
+	{
+		_transportationService = transportationService;
+	}
+
+	[HttpGet("search")]
+	public async Task<IActionResult> SearchTransportations([FromQuery] TransportationSearchRequestDto searchRequest)
+	{
+		if (searchRequest == null)
+		{
+			return BadRequest("Invalid search request");
+		}
+
+		var result = await _transportationService.SearchTransportationsAsync(searchRequest);
+		if (result.IsSuccess)
+		{
+			return Ok(result);
+		}
+
+		// any unsuccessful status
+		return result.Status switch
+		{
+			ResultStatus.NotFound => NotFound(result.ErrorMessage),
+			ResultStatus.ValidationError => BadRequest(result.ErrorMessage),
+			_ => StatusCode(500, result.ErrorMessage),
+		};
+	}
+}
+```
+
+- HttpGet: handles a GET request from client -> important for routing
+- Ok, BadRequest, NotFound and StatusCode are Json results to send through api
+- Use TransportationService to communicate with Application
+
+# Inserting Sample Data 
+
+For testing purposes, add some data into the related tables. 
+You are provided with a SQL script, that adds some sample data into the following tables
+
+ **Important Notes:** Note that different database names, and different table names will produce errors while executing the script. Consider adjusting these names before executing the script
+ 
+- Cities 
+- Companies 
+- LocationTypes
+- Locations 
+- VehicleTypes 
+- Vehicles
+- Transportation
+
+- [ ] Open `TransportationRelatedSampleData.sql` with SSMS, and execute the query
+
+
+# Merge
+- [ ] Create a PR and merge the current branch with develop
+