how to Create custom validation attribute mvc core ? #9271

2 Answer(s)

• 

  0

  EngincanV created 6 months ago

  Support Team .NET Developer

  Hi, it's the same as how to create it on the .NET side. You need to create an attribute that inherits from ValidationAttribute and implement the IsValid method:

  [AttributeUsage(AttributeTargets.Property)] //only can be used in properties
  public class YourCustomAttribute : ValidationAttribute
  {
      protected override ValidationResult IsValid(object value, ValidationContext validationContext)
      {
          //implement
      }
  }
  

  Then use the attribute on top of your property or class:

  public class CreateNewsDto
   {
        [Required(ErrorMessage = "The {0} field is required")]
        [StringLength(200, ErrorMessage = "The {0} must not exceed {1} characters")]
        [YourCustom] //your attribute
        public string TitleAr { get; set; }
        
        //...      
  }
  

  Since this is not related to ABP, you can refer to https://learn.microsoft.com/en-us/dotnet/csharp/advanced-topics/reflection-and-attributes/ for further info.

  Regards.

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• 

  0

  EngincanV created 5 months ago

  Support Team .NET Developer

  Which project can i implement YourCustomAttribute and also note that my Attribute will ensure that it is really image file not pdf and user just changed extension so i mean it is logic that's why i ask you which project will implement this attribute to put in mt dto which in contract project ?

  Hi, yes you can create and define your attribute in the *.Application.Contracts project. You should basically create an attribute, inherit it from the ValidationAttribute base class of .NET, then override the IsValid method and apply your own logic.

  Btw, in one of my old project, I had similar requirements and created an AllowedExtensionsAttribute as follows:

  public class AllowedExtensionsAttribute : ValidationAttribute
      {
          private readonly string[] _extensions;
          public AllowedExtensionsAttribute(string[] extensions)
          {
              _extensions = extensions;
          }
  
          protected override ValidationResult IsValid(
              object value, ValidationContext validationContext)
          {
              if (value == null)
              {
                  return ValidationResult.Success;
              }
              
              var file = value as IFormFile;
              var extension = Path.GetExtension(file.FileName);
              
              if (file.Length > 0 && file != null)
              {
                  if (!_extensions.Contains(extension.ToLower()))
                  {
                      return new ValidationResult(GetErrorMessage());
                  }
              }
  
              return ValidationResult.Success;
          }
  
          public string GetErrorMessage()
          {
              return $"This extension is not allowed!";
          }
      }
  

  and use the attribute:

  [AllowedExtensions(new string[] { ".jpg", ".png", ".jpeg" })]
  public IFormFile CoverImageFile { get; set; }
  

  ---

  Since this is not related to ABP, you can refer to https://learn.microsoft.com/en-us/dotnet/csharp/advanced-topics/reflection-and-attributes/ for further info.

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