775 lines
26 KiB
Markdown
775 lines
26 KiB
Markdown
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### ⚠ Important Tip
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If your `agent.ts` uses `useAuthStore().token` **at the top level**, remember:
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- On very first load, Zustand will **rehydrate** from storage _after_ initial render, so token may be `null` until rehydration is done.
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- Fix: either delay access until after `hasHydrated`, or refactor `agent` to inject token per request.
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To **safely handle concurrency** in your `CreateTicketOrderAsync` method — particularly for **seat reservation** on the same `Transportation` — you need to **prevent race conditions** where two users might reserve the same seat or oversell capacity.
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This is a **classic critical section problem**, and you can solve it using **application-level locking**, **database-level locking**, or both.
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---
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## ✅ Recommended: **Database-level concurrency control + optional distributed lock**
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### 👇 Here’s what you should do:
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---
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## ✅ 1. Use **pessimistic concurrency** (row-level locking) on the `Transportation` row
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### Why?
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You need to **lock the transportation row** to prevent multiple reservations from modifying the related seats/capacity **at the same time**.
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### How?
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Use EF Core's **raw SQL or transaction-scoped SELECT ... FOR UPDATE** (which translates to SQL row locks):
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```csharp
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using var transaction = await _context.Database.BeginTransactionAsync(IsolationLevel.Serializable);
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var transportation = await _context.Transportations
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.FromSqlRaw("SELECT * FROM Transportations WITH (UPDLOCK, ROWLOCK) WHERE Id = {0}", dto.TransportationId)
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.FirstOrDefaultAsync();
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```
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- `UPDLOCK`: prevents others from reading for update
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- `ROWLOCK`: locks only the specific row
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> If using PostgreSQL or MySQL, you’d use `FOR UPDATE` instead.
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---
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## ✅ 2. Alternatively, use **distributed locking** if you have multiple app instances
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Use something like:
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- **Redis distributed lock**
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- **SQL application locks** (`sp_getapplock`)
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- **SemaphoreSlim static lock** (only for single-instance apps — not safe in web farms)
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### Example using `sp_getapplock` (SQL Server):
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```sql
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EXEC sp_getapplock @Resource = 'lock_transportation_123', @LockMode = 'Exclusive', @LockTimeout = 10000;
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```
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EF version:
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```csharp
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await _dbContext.Database.ExecuteSqlRawAsync(
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$"EXEC sp_getapplock @Resource = 'transportation_lock_{dto.TransportationId}', @LockMode = 'Exclusive', @LockTimeout = 10000;");
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```
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✅ This will ensure **only one thread** gets to proceed per `TransportationId`.
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---
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## ✅ 3. Wrap the reservation logic in a **transaction**
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```csharp
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using var transaction = await _context.Database.BeginTransactionAsync(IsolationLevel.Serializable);
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// locking query here
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// seat validation
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// insert tickets
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// save ticket order
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// commit
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await _unitOfWork.SaveChangesAsync();
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await transaction.CommitAsync();
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```
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Use `IsolationLevel.Serializable` or `RepeatableRead` if you’re not doing explicit locking.
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---
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## ✅ 4. Add a **unique constraint** on `SeatId + TransportationId` (if not already)
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To **enforce uniqueness at DB level** and prevent race conditions from succeeding:
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```sql
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ALTER TABLE Tickets ADD CONSTRAINT UQ_Tickets_Seat_Transport UNIQUE (SeatId, TicketStatusId)
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WHERE TicketStatusId != 3; -- exclude cancelled
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```
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Or make a logic-safe alternative depending on your schema.
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---
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## ✅ Final version: Summary of changes
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### In your service:
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```csharp
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using var transaction = await _dbContext.Database.BeginTransactionAsync(IsolationLevel.Serializable);
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// Optional: Lock the transportation row to prevent race
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await _dbContext.Database.ExecuteSqlRawAsync(
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$"EXEC sp_getapplock @Resource = 'transportation_lock_{dto.TransportationId}', @LockMode = 'Exclusive', @LockTimeout = 10000;");
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// Re-fetch transportation + tickets
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var transportation = await _transportationRepository.GetByIdWithTickets(dto.TransportationId);
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// Validate seats
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var seatCheck = ValidateTransportationAndSeats(transportation, dto.Travelers);
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if (!string.IsNullOrEmpty(seatCheck)) return Result<long>.Error(0, seatCheck);
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// Proceed with reservation
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...
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await _unitOfWork.SaveChangesAsync();
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await transaction.CommitAsync();
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```
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---
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## 🧠 Summary Table
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|Strategy|Prevents Race?|Web-farm Safe|Recommended For|
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|---|---|---|---|
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|`sp_getapplock`|✅ Yes|✅ Yes|SQL Server web apps|
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|EF raw SQL `WITH (UPDLOCK)`|✅ Yes|✅ Yes|SQL Server monoliths|
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|`SemaphoreSlim`|✅ Yes|❌ No|Local-only apps|
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|`FOR UPDATE`|✅ Yes|✅ Yes|PostgreSQL, MySQL|
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---
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Let me know your DB provider and environment (single-instance or multi-instance), and I can generate exact code tailored for that.
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Perfect — you're absolutely right to want **the whole process to be atomic**:
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→ **Seat allocation**,
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→ **Ticket creation**,
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→ **Balance checking & payment**,
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→ **Transaction creation**,
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→ **Traveler creation/upsert**, etc.
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This needs more than just _database-level locks_. You want to **serialize execution** for the same transportation to avoid concurrency conflicts — **across the entire flow**, not just the DB writes.
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---
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## ✅ Your Goal
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> **For a given `TransportationId`, only one call to `CreateTicketOrderAsync` should execute at a time**, regardless of app instance or user.
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This includes logic **outside EF** (like payment, seat assignment, person creation, etc.).
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---
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## 🛠️ The Right Solution: **Distributed Application Locking**
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### Use **SQL Server’s `sp_getapplock`** to lock **by `TransportationId`**
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Why?
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- It locks **application-level logic**, not just SQL rows
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- It works across threads, processes, and even app servers
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- It ensures only **one process** can work on that transportation at a time
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---
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## ✅ How to Implement in Your Method
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### 🔒 Step 1: Lock by Transportation ID
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Add this at the **start** of your method:
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```csharp
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await _dbContext.Database.ExecuteSqlRawAsync(
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$"EXEC sp_getapplock @Resource = 'transportation_lock_{dto.TransportationId}', " +
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"@LockMode = 'Exclusive', @LockTimeout = 10000;");
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```
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This ensures that **only one call per transportation** runs at a time.
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If a second request tries to lock the same ID, it waits up to 10 seconds.
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---
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### 🔁 Step 2: Begin EF Transaction
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This will include all EF operations in a single atomic unit:
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```csharp
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using var transaction = await _dbContext.Database.BeginTransactionAsync();
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```
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---
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### 🧠 Step 3: Keep the Full Logic As Is, But Within Transaction
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Like this:
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```csharp
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public async Task<Result<long>> CreateTicketOrderAsync(long accountId, CreateTicketOrderDto dto)
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{
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// 🔒 Lock to prevent concurrency per transportation
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await _dbContext.Database.ExecuteSqlRawAsync(
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$"EXEC sp_getapplock @Resource = 'transportation_lock_{dto.TransportationId}', " +
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"@LockMode = 'Exclusive', @LockTimeout = 10000;");
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// 🧾 Begin transaction
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using var transaction = await _dbContext.Database.BeginTransactionAsync();
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// 💰 Load account and transportation
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var account = await _accountRepository.GetByIdAsync(accountId);
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if (account == null) return Result<long>.Error(0, "Account not found");
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var transportation = await _transportationRepository.GetByIdAsync(dto.TransportationId);
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if (transportation == null) return Result<long>.Error(0, "Transportation not found");
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// 💵 Check balance
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var price = transportation.BasePrice * dto.Travelers.Count;
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if (account.CurrentBalance < price)
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return Result<long>.Error(0, "Not enough money");
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// ✅ Validate seat availability
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var seatCheck = ValidateTransportationAndSeats(transportation, dto.Travelers);
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if (!string.IsNullOrEmpty(seatCheck))
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return Result<long>.Error(0, seatCheck);
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// 🪑 Assign seats (if dynamic logic)
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await AssignSeatsIfDynamic(transportation.VehicleId, dto.Travelers);
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// 👤 Upsert travelers (can also use same transaction)
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await UpsertTravelers(account.Id, dto.Travelers);
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// 🎟️ Create ticket order
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var ticketOrder = new TicketOrder
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{
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BuyerId = account.Id,
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CreatedAt = DateTime.UtcNow,
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Description = "",
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SerialNumber = Guid.NewGuid().ToString("N"),
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TransportationId = dto.TransportationId,
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};
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await _ticketOrderRepository.AddAsync(ticketOrder);
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// 🎫 Add tickets
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foreach (var traveler in dto.Travelers)
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{
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var ticket = new Ticket
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{
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CreatedAt = DateTime.UtcNow,
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Description = traveler.Description,
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SeatId = traveler.SeatId!.Value,
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SerialNumber = Guid.NewGuid().ToString("N"),
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TicketOrder = ticketOrder,
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TicketStatusId = 1,
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TravelerId = traveler.Id,
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};
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await _ticketRepository.AddAsync(ticket);
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}
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// 💳 Commit everything
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await _unitOfWork.SaveChangesAsync();
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// 💸 Withdraw money and create transaction
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await _accountService.PayForTicketOrderAsync(account.Id, ticketOrder.Id, price);
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// ✅ Commit transaction
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await transaction.CommitAsync();
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return Result<long>.Success(ticketOrder.Id);
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}
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```
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---
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## 🧱 Summary of Protection
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|Step|Protected?|How|
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|---|---|---|
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|Prevent concurrent seat assignment|✅|`sp_getapplock` per `TransportationId`|
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|Prevent concurrent DB changes|✅|EF `DbTransaction`|
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|Prevent double-spend|✅|Balance check inside the same lock + transaction|
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|Ensure traveler upserts/tickets are safe|✅|Wrapped in same transaction|
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---
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## ⚠️ Important Note
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Make sure all the operations (`AssignSeatsIfDynamic`, `UpsertTravelers`, etc.):
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- Use the **same `DbContext`/UnitOfWork**
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- Don’t commit changes prematurely (no `SaveChangesAsync()` before you're ready to commit the whole transaction)
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---
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## ✅ Optional (Safety): Add retry logic
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In case of a **deadlock or lock timeout**, you might want to retry the whole operation once.
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---
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Let me know if you want me to extract this into a reusable helper like:
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```csharp
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await _appLockService.ExecuteWithLockAsync($"transportation_lock_{dto.TransportationId}", async () => {
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// your reservation logic
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});
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```
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That would clean things up nicely.
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Sure. Let’s break down everything you need to know about **transactions** in Entity Framework Core (EF Core) — especially for your case where you're doing **complex operations that must all succeed or fail together**.
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---
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## 🧾 What is a Transaction?
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A **transaction** is a unit of work that is treated as a **single, indivisible operation**. Either **all of it succeeds** (committed), or **none of it does** (rolled back).
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### 🧠 Properties of a transaction (ACID):
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|Property|Meaning|
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|---|---|
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|**Atomicity**|All steps succeed or none do|
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|**Consistency**|DB remains valid before and after|
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|**Isolation**|Transactions don’t interfere with each other|
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|**Durability**|Once committed, data is persisted permanently|
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---
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## ✅ Why You Need Transactions
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In your case, you’re:
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- Assigning seats
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- Creating or updating people
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- Creating a `TicketOrder`
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- Creating multiple `Tickets`
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- Updating account balance & transaction history
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All of these must either:
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- Complete **fully and safely**, or
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- **Fail entirely**, with no partial data left behind.
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---
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## 🧰 Transaction in EF Core: Full Example
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### 🔧 Step-by-step Example:
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```csharp
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public async Task<Result<long>> CreateTicketOrderAsync(long accountId, CreateTicketOrderDto dto)
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{
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// Begin EF Core transaction
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using var transaction = await _dbContext.Database.BeginTransactionAsync();
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try
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{
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// Load required entities
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var account = await _accountRepository.GetByIdAsync(accountId);
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if (account == null)
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return Result<long>.Error(0, "Account not found");
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var transportation = await _transportationRepository.GetByIdAsync(dto.TransportationId);
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if (transportation == null)
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return Result<long>.Error(0, "Transportation not found");
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var price = transportation.BasePrice * dto.Travelers.Count;
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if (account.CurrentBalance < price)
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return Result<long>.Error(0, "Not enough money");
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// Validate seat assignment
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var seatCheck = ValidateTransportationAndSeats(transportation, dto.Travelers);
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if (!string.IsNullOrEmpty(seatCheck))
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return Result<long>.Error(0, seatCheck);
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await AssignSeatsIfDynamic(transportation.VehicleId, dto.Travelers);
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await UpsertTravelers(account.Id, dto.Travelers);
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// Create ticket order
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var ticketOrder = new TicketOrder
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{
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BuyerId = account.Id,
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CreatedAt = DateTime.UtcNow,
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SerialNumber = Guid.NewGuid().ToString("N"),
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TransportationId = dto.TransportationId,
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};
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await _ticketOrderRepository.AddAsync(ticketOrder);
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foreach (var traveler in dto.Travelers)
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{
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await _ticketRepository.AddAsync(new Ticket
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{
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CreatedAt = DateTime.UtcNow,
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Description = traveler.Description,
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SeatId = traveler.SeatId.Value,
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SerialNumber = Guid.NewGuid().ToString("N"),
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TicketOrder = ticketOrder,
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TicketStatusId = 1,
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TravelerId = traveler.Id,
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});
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}
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// Save changes
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await _unitOfWork.SaveChangesAsync();
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// Withdraw money from account
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await _accountService.PayForTicketOrderAsync(account.Id, ticketOrder.Id, price);
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|
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// Commit transaction
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await transaction.CommitAsync();
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return Result<long>.Success(ticketOrder.Id);
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}
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catch (Exception ex)
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{
|
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// Rollback if anything failed
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await transaction.RollbackAsync();
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return Result<long>.Error(0, "Reservation failed: " + ex.Message);
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}
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}
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```
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|
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---
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|
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## 🔄 Isolation Levels (Advanced)
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|
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### You can specify isolation level when beginning a transaction:
|
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|
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```csharp
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using var transaction = await _dbContext.Database.BeginTransactionAsync(IsolationLevel.Serializable);
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```
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|
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### Common levels:
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|
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|Isolation Level|Description|Use Case|
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|---|---|---|
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|`ReadCommitted` (default)|No dirty reads|Usually enough|
|
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|`RepeatableRead`|Prevents non-repeatable reads|Seat assignment logic|
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|`Serializable`|Full isolation (slower, safer)|Financial or reservation systems|
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|
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---
|
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|
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## 🧩 When `SaveChangesAsync()` Commits vs. Not
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|
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Calling `SaveChangesAsync()` **does not commit** the outer transaction — it just writes pending changes to the database.
|
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|
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The real commit happens only when you call:
|
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|
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```csharp
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await transaction.CommitAsync();
|
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```
|
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|
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If anything fails before that, the changes are **not persisted**.
|
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|
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---
|
||
|
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## ✅ Best Practices for Transactions in EF Core
|
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|
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|Best Practice|Why|
|
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|---|---|
|
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|Keep transactions **short**|Locks and contention increase with time|
|
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|Catch exceptions and **rollback**|Prevent dirty/incomplete data|
|
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|Use **only one DbContext** inside the transaction|EF tracks entities via one unit of work|
|
||
|Don’t call SaveChanges too early|May break the atomicity|
|
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|Use **appropriate isolation level**|Based on your concurrency needs|
|
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|Consider retry policy for transient errors|Especially in distributed systems|
|
||
|
||
---
|
||
|
||
## ❗ Common Pitfalls
|
||
|
||
|Mistake|Problem|
|
||
|---|---|
|
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|Mixing DbContext instances inside one transaction|Breaks consistency|
|
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|Committing too early|Later failure still leaves partial data|
|
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|Forgetting rollback in catch|Leaves transaction open or inconsistent|
|
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|Async code outside transaction scope|Could break atomicity or introduce race|
|
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|
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---
|
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|
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## 🧠 Summary: Transaction Essentials
|
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|
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|Concept|Description|
|
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|---|---|
|
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|`BeginTransactionAsync()`|Starts a manual transaction|
|
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|`SaveChangesAsync()`|Writes changes but doesn’t commit outer transaction|
|
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|`CommitAsync()`|Finalizes all DB changes|
|
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|`RollbackAsync()`|Reverts all changes since the transaction began|
|
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|Scope|All EF/DB actions done within the transaction block|
|
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|
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---
|
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|
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If you'd like, I can create a **generic transaction helper**, or even make this a **middleware** or **interceptor**, depending on how reusable you want this to be.
|
||
|
||
Let me know!
|
||
Great! These questions show deep thinking about **how transactions and locks actually work** in EF Core and layered architecture. Let’s answer them one by one with real clarity and direction.
|
||
|
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---
|
||
|
||
## ❓ 1. _"I have this method in my `TicketOrderService`, and I don't have access to `_dbContext`."_
|
||
|
||
### ✅ Solution:
|
||
|
||
If you're using **Repository + UnitOfWork pattern**, your `UnitOfWork` should expose a method to access the underlying **DbContext** or allow you to start a transaction.
|
||
|
||
**👉 Extend your `IUnitOfWork` interface like this:**
|
||
|
||
```csharp
|
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public interface IUnitOfWork
|
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{
|
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Task<int> SaveChangesAsync();
|
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Task<IDbContextTransaction> BeginTransactionAsync(IsolationLevel level = IsolationLevel.ReadCommitted);
|
||
DbContext Context { get; } // optional
|
||
}
|
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```
|
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|
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And in your implementation:
|
||
|
||
```csharp
|
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public class UnitOfWork : IUnitOfWork
|
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{
|
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private readonly AppDbContext _context;
|
||
|
||
public UnitOfWork(AppDbContext context) => _context = context;
|
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|
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public Task<int> SaveChangesAsync() => _context.SaveChangesAsync();
|
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|
||
public Task<IDbContextTransaction> BeginTransactionAsync(IsolationLevel level = IsolationLevel.ReadCommitted)
|
||
=> _context.Database.BeginTransactionAsync(level);
|
||
|
||
public DbContext Context => _context;
|
||
}
|
||
```
|
||
|
||
### ✅ Then in your `TicketOrderService`:
|
||
|
||
```csharp
|
||
using var transaction = await _unitOfWork.BeginTransactionAsync();
|
||
// your operations
|
||
await _unitOfWork.SaveChangesAsync();
|
||
await transaction.CommitAsync();
|
||
```
|
||
|
||
This keeps your `Service` clean and architecture-respecting.
|
||
|
||
---
|
||
|
||
## ❓ 2. _"How does the transaction hold stuff? Wouldn’t `unitOfWork.SaveChangesAsync()` just save everything?"_
|
||
|
||
### 🔍 Clarification:
|
||
|
||
- `SaveChangesAsync()` **writes the changes to the database**, but…
|
||
|
||
- **If you're in a transaction**, the database holds those changes in a **temporary, invisible state** until you explicitly call:
|
||
|
||
|
||
```csharp
|
||
await transaction.CommitAsync();
|
||
```
|
||
|
||
💡 If you **don’t commit**, or you **rollback**, then **those changes are discarded**, even if you called `SaveChangesAsync()`.
|
||
|
||
### 👇 Timeline of how EF works in a transaction:
|
||
|
||
1. EF tracks entities in memory.
|
||
|
||
2. You call `SaveChangesAsync()`.
|
||
|
||
3. Changes are written to the DB — but:
|
||
|
||
- If inside a transaction, they are **not visible to others yet**.
|
||
|
||
- They are held until `CommitAsync()`.
|
||
|
||
4. If you call `RollbackAsync()`, all writes are undone.
|
||
|
||
|
||
---
|
||
|
||
## ❓ 3. _"How would the lock know that the work with that transportation is finished?"_
|
||
|
||
### 🔒 About `sp_getapplock`:
|
||
|
||
This SQL Server feature locks a **named resource** (like `transportation_lock_123`) for **the duration of the current SQL connection and transaction**.
|
||
|
||
Here’s how it works:
|
||
|
||
|Action|Result|
|
||
|---|---|
|
||
|You call `sp_getapplock`|SQL Server grants an exclusive lock for the resource|
|
||
|You complete the transaction (commit or rollback)|Lock is **automatically released**|
|
||
|Your connection is closed or disposed|Lock is released|
|
||
|
||
### 🔍 So you don’t need to manually release the lock.
|
||
|
||
Just make sure:
|
||
|
||
- The **lock and transaction use the same connection**
|
||
|
||
- You commit or rollback after the work is done
|
||
|
||
|
||
✅ EF Core handles all that automatically when using `Database.BeginTransactionAsync()`.
|
||
|
||
---
|
||
|
||
## ✅ Final Advice Recap
|
||
|
||
|Question|Answer|
|
||
|---|---|
|
||
|I don’t have access to `_dbContext`|Expose `BeginTransactionAsync` on your `IUnitOfWork`|
|
||
|How does transaction matter if I save mid-way?|It isolates changes — no one sees them until committed|
|
||
|How does lock get released?|Automatically when transaction completes or connection closes|
|
||
|
||
---
|
||
|
||
Let me know if you want:
|
||
|
||
- Sample `UnitOfWork` and `Repository` setup for full support
|
||
|
||
- A lock + transaction helper method
|
||
|
||
- Unit tests to simulate concurrent reservations
|
||
|
||
|
||
You're doing great — this is how robust, real-world software gets built.
|
||
|
||
You've unpacked crucial concerns around **transactions**, **unit-of-work (UoW)**, and **application-wide consistency**. Here's a polished breakdown with clear answers and guidance:
|
||
|
||
---
|
||
|
||
### ✅ 1. Is it okay to use both Transactions **and** Unit of Work?
|
||
|
||
- **Yes, absolutely.** UoW is a design pattern that groups multiple repository operations into one logical unit, while a _transaction_ ensures these operations either all succeed or all fail atomically ([antondevtips.com](https://antondevtips.com/blog/implementing-unit-of-work-pattern-in-ef-core?utm_source=chatgpt.com "Implementing Unit of Work Pattern in EF Core - Anton DevTips")).
|
||
|
||
- In EF Core, the **DbContext itself implements UoW**, collecting changes in memory until `SaveChangesAsync()` is called ([reddit.com](https://www.reddit.com/r/dotnet/comments/17npjtx/unit_of_work_pattern_still_necessary_in_net_8/?utm_source=chatgpt.com "Unit of Work Pattern still necessary in .NET 8? : r/dotnet - Reddit")).
|
||
|
||
- When you execute **multiple SaveChanges**, or include non-repository logic (e.g., balance updates, payment creation, seat locking), **explicit transactions** ensure the entire flow remains atomic .
|
||
|
||
|
||
---
|
||
|
||
### ✅ 2. How exactly to open/close transactions? Where to be careful?
|
||
|
||
#### ✨ Use EF to manage transactions in your UoW:
|
||
|
||
1. **Extend your `IUnitOfWork`** to include transaction methods:
|
||
|
||
```csharp
|
||
Task<IDbContextTransaction> BeginTransactionAsync(IsolationLevel level = ReadCommitted);
|
||
Task<int> SaveChangesAsync();
|
||
```
|
||
|
||
2. **In your service**, do:
|
||
|
||
```csharp
|
||
using var tx = await _unitOfWork.BeginTransactionAsync();
|
||
try {
|
||
// perform all operations (seat locks, entity changes, balance, tickets)
|
||
await _unitOfWork.SaveChangesAsync();
|
||
await tx.CommitAsync();
|
||
} catch {
|
||
await tx.RollbackAsync();
|
||
throw;
|
||
}
|
||
```
|
||
|
||
3. **Know the boundaries**: Keep the transaction as short as possible. Open it before critical operations and close it after the final `CommitAsync()`.
|
||
|
||
|
||
> 💡 Use `(IsolationLevel.Serializable)` for scenarios like seat reservation where concurrent writes must be prevented ([milanjovanovic.tech](https://www.milanjovanovic.tech/blog/working-with-transactions-in-ef-core?utm_source=chatgpt.com "Working With Transactions In EF Core"), [learn.microsoft.com](https://learn.microsoft.com/en-us/aspnet/mvc/overview/older-versions/getting-started-with-ef-5-using-mvc-4/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application?utm_source=chatgpt.com "Implementing the Repository and Unit of Work Patterns in an ASP ...")).
|
||
|
||
---
|
||
|
||
### ✅ 3. Why did things “work” without explicit transactions?
|
||
|
||
- **Simple SaveChanges** calls act like atomic units—if they fail, nothing is saved. With just one SaveChanges call, EF wraps it in a default transaction ([stackoverflow.com](https://stackoverflow.com/questions/24636352/unit-of-work-i-dont-need-to-use-transactions?utm_source=chatgpt.com "c# - unit of work - I don't need to use transactions? - Stack Overflow")).
|
||
|
||
- However, as soon as your workflow involves **multiple SaveChanges**, **external services**, or **cross-repository updates**, the default behavior is no longer sufficient. A failure midway could leave your data in a partial state.
|
||
|
||
- That's where **explicit transaction scopes** come in—to guarantee everything is batched and rolled back if any part fails ([antondevtips.com](https://antondevtips.com/blog/implementing-unit-of-work-pattern-in-ef-core?utm_source=chatgpt.com "Implementing Unit of Work Pattern in EF Core - Anton DevTips")).
|
||
|
||
|
||
---
|
||
|
||
### 🧠 TL;DR Summary
|
||
|
||
|Concept|Purpose|When Needed|
|
||
|---|---|---|
|
||
|**Unit of Work**|Organizes multiple EF operations into one commit|Always used with EF DbContext|
|
||
|**Implicit transaction**|EF wraps each SaveChanges automatically|Ok for single SaveChanges calls|
|
||
|**Explicit transaction**|Manually control commit/rollback across many operations|Needed when multiple SaveChanges, external services, concurrency, etc.|
|
||
|**IsolationLevel.Serializable**|Highest locking level to prevent concurrent conflicts|Use for critical resource locks (e.g., seat booking)|
|
||
|**Be careful**|Keep transactions short to avoid locks and deadlocks|Avoid long-running operations inside the transaction|
|
||
|
||
---
|
||
|
||
If you want, I can provide:
|
||
|
||
- **Code templates** for UoW with transaction management
|
||
|
||
- **Interceptor or decorator** to automate transaction handling in your services
|
||
|
||
- **Concurrency demos** to test seat reservation under load
|
||
|
||
|
||
Just say the word!
|
||
Absolutely! Let’s clarify both of your statements with authoritative sources:
|
||
|
||
---
|
||
|
||
## 1. If I haven't called `BeginTransaction` and call `SaveChanges`, will changes be saved?
|
||
|
||
✅ **Yes.** EF Core automatically wraps **every** `SaveChanges()` call in its **own transaction**. This means:
|
||
|
||
- If **all operations succeed**, the data is saved.
|
||
- If **anything fails**, the entire set is **rolled back**, leaving the DB unchanged. citeturn0search0turn0search9
|
||
|
||
🔁 So even without explicitly starting a transaction, `SaveChanges()` ensures atomicity for that batch of changes.
|
||
|
||
---
|
||
|
||
## 2. If I have called `BeginTransaction`, and then call `SaveChanges`, do changes go to the DB immediately?
|
||
|
||
✅ **Yes, but context matters.** When you wrap operations in an explicit transaction:
|
||
|
||
- Each `SaveChanges()` writes within that transaction.
|
||
- However, **none** of these writes become visible to other connections until you call `Commit()`.
|
||
|
||
EF also uses **savepoints** internally (for multiple `SaveChanges()` calls) to enable partial rollbacks without rolling back the entire transaction. citeturn0search0turn0search2turn0search3
|
||
|
||
---
|
||
|
||
### 🧩 In Plain English
|
||
|
||
| Scenario | SaveChanges Only | BeginTransaction + SaveChanges |
|
||
|------------------|--------------------------------------------------|----------------------------------------------------|
|
||
| No transaction | Auto-wrapped in its own transaction–immediate. | — |
|
||
| With explicit transaction | Writes are within the transaction, not yet committed. | ✔ |
|
||
| Rollback before commit | Not possible. SaveChanges is final. | ✔ Rolls everything back. |
|
||
|
||
---
|
||
|
||
### ✅ TL;DR
|
||
|
||
- ✅ **Without `BeginTransaction`**: `SaveChanges()` is atomic per call—commits or rolls back automatically.
|
||
- ✅ **With `BeginTransaction`**: `SaveChanges()` writes into the transaction, but the changes are **held until** you call `Commit()`; `Rollback()` discards them all.
|
||
|
||
---
|
||
|
||
Want some **ready-to-use code** to introduce `BeginTransaction()` into your UnitOfWork and services? Just let me know and I’ll supply a clean implementation! |