Model binding

Model binding maps HTTP request data—route values, query strings, form fields, JSON bodies—to action parameters and complex types automatically.

Sources (priority order varies)

• Form fields → properties by name (Email → model.Email)
• Route tokens → {id} parameters
• Query string → ?page=2
• JSON body → API actions with [FromBody]

Complex type binding

public IActionResult Create(ProductEditModel model) {
    if (!ModelState.IsValid) return View(model);
    // save
}

[FromQuery], [FromRoute], [FromBody]

Disambiguate when names collide or for minimal APIs—be explicit in APIs with multiple primitive parameters.

Important interview questions and answers

1. Q: Model binding vs manual Request.Form?
   A: Binding is declarative and testable; manual parsing is error-prone for complex types.
2. Q: Nullable binding failures?
   A: Missing required non-nullable value types may fail validation—use nullable or defaults intentionally.

Self-check

1. How does POST form data reach a view model?
2. When use [FromBody]?

Pitfall: Binding POST data directly to EF entities enables over-posting—use view models with only the fields the form should set.