Interview Q&A

Answer: filter is a component that allows logic to be executed before or after parts of the request pipeline, such as authorization, action execution, or result processing.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Filters are ASP.NET Core’s plug-in points that allow you to inject logic before or after

specific pipeline stages such as:

• Authorization
• Resource execution
• Action execution
• Results processing
• Exception handling

They help you implement cross-cutting concerns without cluttering controllers or actions.

In enterprise systems, filters are indispensable for:

• Logging
• Validation
• Authorization
• Error handling
• Performance profiling
• Policy enforcement

Middleware is a component in the HTTP request pipeline that can:

• Handle requests,
• Pass requests to the next middleware,
• Or short-circuit the pipeline.

Middleware can:

• Perform actions before and/or after the next middleware executes.
• Be used for logging, authentication, error handling, etc.

Middleware executes in the order it's added in Program.cs.

Answer: ction filters wrap the action method; result filters wrap the returned result (like ObjectResult or ViewResult).

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: RequestDelegate is a delegate representing the next middleware in the pipeline: public delegate Task RequestDelegate(HttpContext context); In custom middleware, it allows passing control to the next component.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

The sequence in which filters run. Lower Order value = earlier execution.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Dependency Injection (DI) is a design pattern that allows you to inject dependencies (services) into classes instead of hard-coding them.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Used for filters that require custom instantiation logic.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• MVC (Model-View-Controller) is a pattern for organizing code into:
• Model: Data and business logic
• View: UI rendering
• Controller: Input handling and app flow
• Built on a modular, cross-platform framework.
• Uses dependency injection by default.
• Unified Web API + MVC pipeline.
• Lightweight and middleware-based request processing.

How does it differ from MVC in

“older” ASP.NET?

• MVC (Model-View-Controller) is a pattern for organizing code into:
• Model: Data and business logic
• View: UI rendering
• Controller: Input handling and app flow

🔹 Key differences in ASP.NET Core:

• Built on a modular, cross-platform framework.
• Uses dependency injection by default.
• Unified Web API + MVC pipeline.
• Lightweight and middleware-based request processing.

SP.NET Core 2.0.

• Each .cshtml file has an associated PageModel class (like a view +

controller combined).

• Best for simple UI-focused apps or CRUD pages.

✅ Use Razor Pages for:

• Simpler, page-focused apps

✅ Use MVC for:

• Complex, controller-based routing or large, structured apps

When to use Razor Pages instead of

MVC?

• Razor Pages is a page-based programming model introduced in

ASP.NET Core 2.0.

• Each .cshtml file has an associated PageModel class (like a view +

controller combined).

• Best for simple UI-focused apps or CRUD pages.

✅ Use Razor Pages for:

• Simpler, page-focused apps

✅ Use MVC for:

• Complex, controller-based routing or large, structured apps

REST (Representational State Transfer) is an architectural style for

building scalable web services. RESTful APIs follow standard HTTP

methods (GET, POST, PUT, DELETE) and stateless communication.

✅ Key principles for RESTful API in ASP.NET Core:

• Use HTTP verbs for operations.
• Use nouns (resources) in URIs, not verbs.
• Support stateless operations.
• Return appropriate HTTP status codes.
• Implement HATEOAS (optional for hypermedia).

How to design RESTful APIs in ASP.NET Core

REST (Representational State Transfer) is an architectural style for

building scalable web services. RESTful APIs follow standard HTTP

methods (GET, POST, PUT, DELETE) and stateless communication.

✅ Key principles for RESTful API in ASP.NET Core:

• Use HTTP verbs for operations.
• Use nouns (resources) in URIs, not verbs.
• Support stateless operations.
• Return appropriate HTTP status codes.
• Implement HATEOAS (optional for hypermedia).

Answer: SP.NET Core. ✅ Benefits: Automatic model validation Infer [FromBody] / [FromQuery], etc. 400 BadRequest returned automatically if model state is invalid. Improved parameter binding behavior

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

The [ApiController] attribute is used to denote Web API controllers in

ASP.NET Core.

✅ Benefits:

• Automatic model validation
• Infer [FromBody] / [FromQuery], etc.
• 400 BadRequest returned automatically if model state is invalid.
• Improved parameter binding behavior

Answer: ction (What are you allowed to do?) In ASP.NET Core, both are handled via middleware and attributes like [Authorize], roles, nd policies.

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• Authentication: Verifying the identity of a user (Who are you?)
• Authorization: Determining if the authenticated user has permission to perform an

action (What are you allowed to do?)

In ASP.NET Core, both are handled via middleware and attributes like [Authorize], roles,

and policies.

Answer: uthorizationHandler<MinimumAgeRequirement> { protected override Task HandleRequirementAsync(...) { // logic } } Register in DI and use with [Authorize(Policy = "...")].

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Filters run in a specific order depending on their type:

• Authorization filters run first.
• Resource filters run next.
• Model binding happens after resource filters.
• Action filters run around the action execution.
• Exception filters handle exceptions thrown during action or result execution.
• Result filters run around result execution.

Within each type, filters can be ordered by their Order property and whether they are global,

controller-level, or action-level.

Filters receive context objects (e.g., ActionExecutingContext) providing:

• HTTP context and request data.
• Access to action parameters.
• Ability to modify or cancel execution (e.g., short-circuit).
• Access to the result or exceptions.
• Ability to set result or modify response.

This allows filters to inspect, modify, or block processing at their stage.

Filters can short-circuit by setting the result early, preventing further execution:

public void OnActionExecuting(ActionExecutingContext context)
{
if (!IsAuthorized())
{
context.Result = new UnauthorizedResult(); // stops pipeline

here

}
}

This prevents action execution and later filters from running.

CORS (Cross-Origin Resource Sharing) is a browser security feature that restricts web

pages from making requests to a different domain than the one that served the web page, to

prevent cross-site attacks.

CORS defines a way for servers to allow controlled access to resources from a different

origin.

• IActionResult: Represents a non-generic result of an action method. Can return any

HTTP response (Ok, NotFound, Redirect, etc.).

• ActionResult<T>: Combines a result with a typed value (T). It allows returning typed

data or an HTTP response. Improves clarity and enables better OpenAPI docs.

• In .NET 5 and earlier, Startup configures services and middleware.
• In .NET 6+ minimal hosting model, the Program.cs file combines service

registration and middleware setup with a simplified, top-level statement style.

• Startup can still be used for organization, but not required.