Stage 2 - Core Services and Configuration

Q11. What is Dependency Injection in ASP.NET Core?

Quick interview answer: Dependency Injection is a pattern where required services are provided by ASP.NET Core instead of being created manually inside classes. It reduces coupling and makes code easier to test.

Study in detail: Dependency Injection (DI) - This article explains registration, injection, and lifetimes.

Q12. What are Transient, Scoped, and Singleton lifetimes?

Quick interview answer: Transient creates a new instance every time. Scoped creates one instance per HTTP request. Singleton creates one instance for the whole application.

Transient = every request for service
Scoped = one per HTTP request
Singleton = one for app lifetime

Study in detail: Dependency Injection (DI) - This article explains lifetime selection.

Q13. Which lifetime is commonly used for business services?

Quick interview answer: Scoped is commonly used for business services, repositories, and database-related services because one consistent instance is used during a single HTTP request.

Study in detail: Dependency Injection (DI) - This article explains real service examples.

Q14. Why should we not inject scoped services into singleton services?

Quick interview answer: A singleton lives for the entire application, while a scoped service lives only for one request. Injecting scoped into singleton can capture request-specific state and cause incorrect behavior.

Study in detail: Dependency Injection (DI) - This article explains lifetime mistakes.

Q15. What is appsettings.json?

Quick interview answer: appsettings.json is a configuration file used to store settings such as connection strings, logging levels, feature flags, API settings, and application options.

Study in detail: Configuration and appsettings.json - This article explains configuration sources and reading values.

Q16. How do you read configuration values?

Quick interview answer: Use builder.Configuration or inject IConfiguration.

var connectionString = builder.Configuration.GetConnectionString("SchoolDb");
var schoolName = builder.Configuration["School:Name"];

Study in detail: Configuration and appsettings.json - This article explains configuration keys and Options pattern.

Q17. What are environments in ASP.NET Core?

Quick interview answer: Environments let the same application behave differently in Development, Staging, and Production. For example, development can show detailed errors, while production should show safe messages.

Study in detail: Environments - Development, Staging, Production - This article explains environment-specific behavior.

Q18. How do you check the current environment?

Quick interview answer: Use app.Environment.

if (app.Environment.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}

Study in detail: Environments - Development, Staging, Production - This article explains IsDevelopment, IsStaging, and IsProduction.

Q19. What is logging in ASP.NET Core?

Quick interview answer: Logging records application events, warnings, and errors. ASP.NET Core uses ILogger<T> and supports different log levels such as Information, Warning, Error, and Critical.

Study in detail: Logging with ILogger - This article explains log levels and structured logging.

Q20. What is structured logging?

Quick interview answer: Structured logging stores message values separately using placeholders, making logs easier to search and filter.

_logger.LogInformation("Student {StudentId} loaded", id);

Study in detail: Logging with ILogger - This article explains logging best practices.