ModelState.AddModelError
ModelState.AddModelError is an ASP.NET Core MVC operation that adds a validation error associated with a model key or field.
ASP.NET Core in Action, 3e
AddModelError is a model-state operation that adds a validation error associated with a key or model field.
- How it is used
- Adds server-side business-rule errors to ModelState so forms display them with DataAnnotation errors.
- How deep it goes
- Explains the purpose and handler flow, but does not provide a detailed AddModelError call or key-selection example.
- Examples
- Uses product existence checks and errors returned by a different system as examples of additional validation.
- What you can do after
- Apply it via ModelState in a Razor Pages handler to redisplay invalid forms before saving.
Read how ASP.NET Core in Action, 3e explains ModelState.AddModelError →
Pro ASP.NET Core 7, Tenth Edition
AddModelError is an ASP.NET Core MVC ModelState operation that adds a validation error associated with a model key.
- How it is used
- Adds explicit MVC validation errors when model binding and declarative validation cannot express application rules.
- How deep it goes
- Explains property and model-level keys, validation-state checks, display configuration, and controller tests without covering framework internals.
- Examples
- Uses positive-price validation, database-backed identifier checks, cross-property product rules, and empty-cart checkout validation.
- What you can do after
- Apply it via ASP.NET Core MVC controllers to reject invalid submissions and redisplay actionable errors.
Read how Pro ASP.NET Core 7, Tenth Edition explains ModelState.AddModelError →
Related concepts
- ModelStateuses · ModelState is an ASP.NET Core representation of request model-binding and validation state, including bound values and associated errors.
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