ASP.NET Core Web API Interview Question #35

How does validation work in ASP.NET Core Web API?

DTOs, Model Binding, Validation & API Responses Junior Beginner

Quick Interview Answer

Validation checks whether incoming data satisfies the rules defined for the request contract. Data Annotation attributes such as Required, StringLength, Range, and EmailAddress can describe common validation rules.

Detailed Explanation

Validation checks whether incoming data satisfies the rules defined for the request contract. Data Annotation attributes such as Required, StringLength, Range, and EmailAddress can describe common validation rules.

With ApiController, invalid model state normally causes an automatic 400 response before the action executes. Business rules that require application or database context should be validated separately.

Code Example

public sealed class RegisterRequest
{
    [Required]
    [EmailAddress]
    public string Email { get; init; } = "";

    [Required]
    [MinLength(8)]
    public string Password { get; init; } = "";
}