DEV Community: Sachin Ghatage

Find the difference

Sachin Ghatage — Tue, 14 Oct 2025 06:25:35 +0000

1)SELECT COUNT(*) FROM Employee;
2)SELECT COUNT(ManagerId) FROM Employee;

First statement counts all the records including nulls

Second statement counts only non null records

Difference is small but very much important

What happens when you inject scoped dependency into singleton?

Sachin Ghatage — Mon, 13 Oct 2025 10:21:53 +0000

leads to thread-safety issues and memory leaks due to EF’s Change Tracker.
It will give InvalidOperationException.
You registered your DbContext as Scoped → one instance per HTTP request.

You registered your repository/service as Singleton → one instance for the entire application lifetime.

Your Singleton service depends on Scoped DbContext.

Why this is dangerous

Even if somehow you delayed instantiation and it works:

You might accidentally share the same DbContext across multiple requests.

This causes thread-safety issues, stale data, and memory leaks

Suppose you have duplicate rows in a table. How can you delete all duplicates but keep one copy using SQL only?

Sachin Ghatage — Sun, 12 Oct 2025 08:01:44 +0000

using CTE + ROW_NUMBER()

WITH CTE AS (
SELECT *,
ROW_NUMBER() OVER (PARTITION BY Name, DeptId ORDER BY EmpId) AS rn
FROM Employees
)
DELETE FROM CTE
WHERE rn > 1;

This will number the records according to name and deptId , starts with 1 contiues until next record with different name and deptid is found this way it will delete all the duplicate records keeping one copy

What’s the difference between AddScoped, AddTransient, and AddSingleton in dependency injection?

Sachin Ghatage — Sun, 12 Oct 2025 07:41:21 +0000

AddSingleton - One instance is created and shared for the entire application lifetime (across all HTTP requests).
eg)Logging,Caching

AddScoped - A new instance is created per HTTP request and shared within that same request.
eg)DbContext

AddTransient - A new instance is created every time it’s requested (even within the same HTTP request).
eg)EmailService

What’s the difference between IActionResult and ActionResult in ASP.NET Core Web API?

Sachin Ghatage — Sun, 12 Oct 2025 07:13:37 +0000

IActionResult is an interface that represents a general action result. You can return any kind of HTTP response, such as Ok(), NotFound(), BadRequest(), etc. It doesn’t specify the type of data being returned.

public IActionResult GetUser()
{
var user = _userService.GetUser();
if (user == null)
return NotFound();
return Ok(user);
}

ActionResult is a generic type that allows you to return either a typed object (T) or an HTTP response. It combines the flexibility of IActionResult with the strong typing of T.

public ActionResult GetUser()
{
var user = _userService.GetUser();
if (user == null)
return NotFound();
return user; // Directly return T (User)
}

What’s the difference between AddScoped, AddTransient, and AddSingleton in dependency injection?

Sachin Ghatage — Sun, 12 Oct 2025 07:11:49 +0000

What’s the difference between AddScoped, AddTransient, and AddSingleton in dependency injection?

AddSingleton - One instance is created and shared for the entire application lifetime (across all HTTP requests).
eg)Logging,Caching

AddScoped - A new instance is created per HTTP request and shared within that same request.
eg)DbContext

AddTransient - A new instance is created every time it’s requested (even within the same HTTP request).
eg)EmailService

ASP.NET Core Middleware Order Explained: Why app.UseAuthentication() Must Come Before app.UseAuthorization()

Sachin Ghatage — Mon, 06 Oct 2025 09:05:49 +0000

When building an ASP.NET Core application, middleware order is critical. Two common middlewares are app.UseAuthentication() and app.UseAuthorization().

** What they do**

app.UseAuthentication(): Checks and validates the user's credentials. It sets the HttpContext.User property.

app.UseAuthorization(): Uses the authenticated identity to check whether the user has permission to access a resource.

✅** Correct Order**
app.UseAuthentication();
app.UseAuthorization();

This order is essential because authentication must happen before authorization. Authorization relies on an authenticated user identity to decide access rights.

⚠️ What happens if you reverse the order
app.UseAuthorization();
app.UseAuthentication();

If reversed:

UseAuthorization runs before UseAuthentication, so HttpContext.User will be empty.Authorization fails because the user hasn’t been authenticated yet.

The result: authorization will not work as expected, and access to protected resources will be denied even for valid users.

💡 Key takeaway

Always place app.UseAuthentication() before app.UseAuthorization() in your middleware pipeline. This ensures proper authentication and authorization flow.