NestJS
Dependency injection, request lifecycle, validation, and database integration.
What is the Nest request lifecycle?
The request lifecycle is the order in which Nest processes an incoming request and produces a response. Different extension points handle different concerns, such as access checks, input conversion and response wrapping. Knowing the order helps explain why code in one stage cannot rely on work that happens later.
How do global, controller and route handlers interact?
Nest can attach request handlers at global, controller and route scopes. Scope determines which requests a handler applies to, while handler type determines execution order. Interceptors wrap inner work and unwind on the response path; exception filters select a matching handler rather than form a normal middleware chain.
Guard vs pipe vs interceptor vs filter?
Guards, pipes, interceptors and filters are separate request extension points with different jobs. A guard decides whether work may proceed; a pipe validates or transforms arguments; an interceptor wraps execution; a filter handles uncaught errors. Choosing the correct point avoids mixing authentication, validation and formatting into business methods.
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