How to Effectively Implement Model Validation in ASP.NET Web API?

Model Validation in ASP.NET Web API

Model validation is a crucial aspect of developing a robust web API. ASP.NET Web API provides a comprehensive system for validating incoming model data.

Implementing Model Validation

To implement Model Validation, follow these steps:

1. Enable Model Validation: Enable automatic validation in your Web API configuration:

   config.Filters.Add(new ValidateModelFilter());

2. Annotate Your Model: Use data annotations to specify validation rules for your model properties. For example:

   public class Enquiry
   {
       [Key]
       public int EnquiryId { get; set; }
       [Required]
       public DateTime EnquiryDate { get; set; }
       [Required]
       public string CustomerAccountNumber { get; set; }
       [Required]
       public string ContactName { get; set; }
   }

3. Use a Custom Action Filter: Create a custom action filter to handle model validation errors. Register this filter globally or at the controller level:

   public class ValidationActionFilter : ActionFilterAttribute
   {
       public override void OnActionExecuting(HttpActionContext actionContext)
       {
           var modelState = actionContext.ModelState;
   
           if (!modelState.IsValid)
               actionContext.Response = actionContext.Request
                    .CreateErrorResponse(HttpStatusCode.BadRequest, modelState);
       }
   }

Handling Validation Failures

When a model validation fails:

• The ModelState property of the HttpActionContext will contain a list of validation errors.
• The custom action filter can access this property and create an appropriate error response.

Additional Considerations

• You can access the validation errors via the Errors property of the ModelState.
• Customize the error message returned to the client.
• Ensure model validation is consistent throughout your API.

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