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refactor: clean project based sesstion04 notes

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MehrdadShirvani
2025-07-18 11:33:54 +03:30
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ProjectOrientedSessions/Session04/Session04 Additional Info.md
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### 1. **Should I have an `IEntityService` and then `EntityService` for each of my entities?**
## *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?**
## **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?**
## **Is it necessary to have an interface for each service?**
### 🔹 **What’s the Difference Between Services and Repositories?**
## **What’s the Difference Between Services and Repositories?**
| Aspect | **Service** | **Repository** |
| ------------------ | ---------------------------------------------------------------------- | --------------------------------------------------------------- |
@@ -37,7 +27,7 @@ Examples:
| **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?
## 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**.
@@ -62,21 +52,15 @@ Examples:
### 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.
[read more](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:
@@ -140,22 +124,15 @@ public class CustomerController : ControllerBase {
## 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:
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:
@@ -166,42 +143,28 @@ foreach (var num in numbers)
```
💡 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.
🔷 3. `IList`
- Extends `ICollection` and `IEnumerable`.
- Adds index access: `list[0]` etc.
- Think of it like a mutable array with dynamic size.
💡 Use when:
@@ -215,15 +178,10 @@ foreach (var num in numbers)
🔷 4. List
- A concrete class (not interface).
- Implements IList, ICollection, IEnumerable.
- Implements `IList`, `ICollection`, `IEnumerable`.
- Backed by an array (auto-resizes).
- Fast read and write.
- Supports Add, Remove, Insert, IndexOf, etc.
- Supports `Add`, `Remove`, `Insert`, `IndexOf`, etc.
Example:
@@ -238,32 +196,23 @@ var second = list[1]; // "Two"
---
🔷 5. IReadOnlyCollection & IReadOnlyList
🔷 5. `IReadOnlyCollection` & `IReadOnlyList`
- IReadOnlyCollection: Just Count and IEnumerable.
- IReadOnlyList: Adds indexing without modification.
- `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[])
🔷 6. `Array(T[])`
- Fixed-size.
- Fastest for indexing.
- Cannot change size.
- Implements IList (via Array).
- Implements `IList` (via Array).
Example:
@@ -276,27 +225,20 @@ numbers[0] = 42;
---
🔷 7. ObservableCollection
🔷 7. `ObservableCollection`
- For WPF/Blazor/WinForms data-binding.
- 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.
- Implements `ICollection`, not `IList`.
- No index access.
💡 Best for fast membership checking (contains x).
@@ -315,6 +257,3 @@ numbers[0] = 42;
|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?
ProjectOrientedSessions/Session04/Session04 Backend.md
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# Preparation:
# 🛠️ Task Checklist
## 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
## 🚧Branching
- [ ]  Create the feature/transportation-search branch based on develop
# DTO
## 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
{
@@ -23,34 +24,35 @@ public class CityDto
```
📂 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; }
}
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; }
}
public int VehicleTypeId { get; init; }
public string? VehicleTitle { 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; }
public int RemainingCapacity { get; init; }
```
# Repository
## Repository
There are a few things to be add to some repositories for transportation search flow.
- [ ] Create DTOs related to transportation search flow
@@ -108,7 +110,7 @@ public class TransportationRepository :
```
# Auto Mapper
## 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
@@ -157,7 +159,7 @@ public class MappingProfile : Profile
.
```
# Result & Result Status
## Result & Result Status
- [ ] Create `ResultStatus` enum and `Result` class
📂 Suggested Folder: Application/Result
@@ -220,22 +222,18 @@ public enum ResultStatus
You can read more about enums: [W3Schools](https://www.w3schools.com/cs/cs_enums.php)
# `IService` & Service
## `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
{
@@ -244,7 +242,6 @@ public interface ITransportationService
```
An example of `[Entity]Service`:
```cs
public class TransportationService : ITransportationService
{
@@ -291,7 +288,7 @@ builder.Services.AddScoped<ICityService, CityService>();
.
```
# Controller
## 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)
@@ -336,17 +333,16 @@ public class TransportationController : ControllerBase
}
```
- 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
- `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
## 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
@@ -356,8 +352,14 @@ You are provided with a SQL script, that adds some sample data into the followin
- Transportation
- [ ] Open `TransportationRelatedSampleData.sql` with SSMS, and execute the query
> Note: there has been changes in database structure since this note and this file has been written.
# Merge
## 🚧Merge
- [ ] Create a PR and merge the current branch with develop
# 🧠 Hints & Notes
# 🙌 Acknowledgements
- ChatGPT for snippet refinement and explanations
# 🔍 References