We Keep Coding

Custom validation attribute that allows specific integer in C#

How to create a custom validation attribute that allows only specified integers. adding a custom error message.

Create a class and inherit from ValidationAttribute class.
Follow the example code below
public class IntegersAllowedAttribute : ValidationAttribute
{
private readonly int[] _values;
public IntegersAllowedAttribute(params int[] values)
{
_values = values;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
int valuesToValidate = (int)value;
if (!_values.Contains(valuesToValidate))
{
string errorMessage = FormatErrorMessage(validationContext.DisplayName);
return new ValidationResult(errorMessage);
}
return ValidationResult.Success;
}
}
Then place attribute on the property
public class Example
{
[IntValuesAllowed(1, 2, 3, ErrorMessage = "error message goes here")]
public int Values { get; set; }
}

How to validate document type using FileValidationAttribute?

I have this Dto class for the web api controller in .NET Core 2.2 MVC.
ApplicationDocumentType is an enum
public class DocumentUploadDto
{
[FileValidation]
public IFormFile File { get; set; }
public ApplicationDocumentType DocumentType { get; set; }
public Guid Id { get; set; }
}
and
public enum ApplicationDocumentType
{
BANKSTATEMENT,
NRIC
}
and the below class implements the [FileValidation]
public class FileValidationAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var file = value as IFormFile;
// some code removed for brevity
if (!AllowMimeTypes.Contains(file.ContentType))
{
ErrorMessage = "Invalid file type.";
return new ValidationResult(ErrorMessage);
}
return ValidationResult.Success;
}
}
Now I need to validate based on DocumentType. How do I pass DocumentType into FileValidationAttribute to do some validation?
Currently all DocumentType is having the same validation. But now I need to customize the validation based on DocumentType.
Thanks Richard for the clue, but I just keep getting the first enum value.
public class FileValidationAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var containerType = validationContext.ObjectType;
var documentType = containerType.GetProperty("DocumentType");
var file = value as IFormFile;
if (file == null)
return new ValidationResult("No file found.");
if (documentType != null)
{
var documentTypeValue = documentType.GetValue(validationContext.ObjectInstance, null);
if (documentTypeValue.ToString() == "NRIC"
&& file.ContentType == "application/pdf")
{
ErrorMessage = "Invalid file type. Pdf file type is not allowed for NRIC.";
return new ValidationResult(ErrorMessage);
}
}
// some code removed for brevity purpose.
}
}

If document type is static, you can simply add an attribute to your Attribute.
public class FileValidationAttribute : ValidationAttribute
{
public FileValidationAttribute(params string[] allowMimeTypes)
{
AllowMimeTypes = allowMimeTypes;
}
public string[] AllowMimeTypes { get; }
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var file = value as IFormFile;
// some code removed for brevity
if (!AllowMimeTypes.Contains(file.ContentType))
{
ErrorMessage = "Invalid file type.";
return new ValidationResult(ErrorMessage);
}
return ValidationResult.Success;
}
}
and then, in Dto, add allowed Mime Types
public class DocumentUploadDto
{
[FileValidation("text/javascript", "text/html")]
public IFormFile File { get; set; }
public ApplicationDocumentType DocumentType { get; set; }
public Guid Id { get; set; }
}
If you need to pass mime type dynamically, then I suggest looking at https://fluentvalidation.net/ which allows you to easily add data to validation context and write more fluent validators.

Pass Property of Class to ValidationAttribute

I am trying to write my own ValidationAttribute for which I want to pass the value of a parameter of my class to the ValidationAttribute. Very simple, if the boolean property is true, the property with the ValidationAttribute on top should not be null or empty.
My class:
public class Test
{
public bool Damage { get; set; }
[CheckForNullOrEmpty(Damage)]
public string DamageText { get; set; }
...
}
My Attribute:
public class CheckForNullOrEmpty: ValidationAttribute
{
private readonly bool _damage;
public RequiredForWanrnleuchte(bool damage)
{
_damage = damage;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
string damageText = validationContext.ObjectType.GetProperty(validationContext.MemberName).GetValue(validationContext.ObjectInstance).ToString();
if (_damage == true && string.IsNullOrEmpty(damageText))
return new ValidationResult(ErrorMessage);
return ValidationResult.Success;
}
}
However, I cannot simply pass the property inside the class to the ValidationAttribute like that. What would be a solution to pass the value of that property?

Instead of passing the bool value to the CheckForNullOrEmptyAttribute, you should pass the name of the corresponding property; within the attribute, you then can retrieve this bool value from the object instance being validated.
The CheckForNullOrEmptyAttribute below, can be applied on your model as shown here.
public class Test
{
public bool Damage { get; set; }
[CheckForNullOrEmpty(nameof(Damage))] // Pass the name of the property.
public string DamageText { get; set; }
}
public class CheckForNullOrEmptyAttribute : ValidationAttribute
{
public CheckForNullOrEmptyAttribute(string propertyName)
{
PropertyName = propertyName;
}
public string PropertyName { get; }
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var hasValue = !string.IsNullOrEmpty(value as string);
if (hasValue)
{
return ValidationResult.Success;
}
// Retrieve the boolean value.
var isRequired =
Convert.ToBoolean(
validationContext.ObjectInstance
.GetType()
.GetProperty(PropertyName)
.GetValue(validationContext.ObjectInstance)
);
if (isRequired)
{
return new ValidationResult(ErrorMessage);
}
return ValidationResult.Success;
}
}

c# conditional Required Attribute

how can i to put conditional Required Attribute into class? i tried the following code and it doesn't work.
public partial class Zone
{
[RequireCondition ]
public int LastCount { get; set; }
}
public class RequireCondition : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var Zone = (Zone)validationContext.ObjectInstance;
if (Zone.LastCount < 1)
{
return new ValidationResult("Last Count value must be greater than one.");
}
else
{
return ValidationResult.Success;
}
}
}

Try this?
public partial class Zone
{
[RequireCondition(1)]
public int LastCount { get; set; }
}
public class RequireConditionAttribute : ValidationAttribute
{
private int _comparisonValue;
public RequireCondition(int comparisonValue)
{
_comparisonValue = comparisonValue;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
if (value is int && (int)value < comparisonValue)
{
return new ValidationResult($"{validationContext.DisplayName} value must be greater than one.");
}
return ValidationResult.Success;
}
}

C# MVC5 Validate in Model with a List

Within a Class I have a Static List of values which are allowed
private static List<string> allowedClassNames = new List<string> {"Real Estate", "Factored Debt"};
And I also have an attribute of that class, which I want to restrict to being values in that list.
[Required]
public string assetClassName { get; set; }
I want to do this at the model level, so it works in either a REST or view context.
How would I implement forcing the value in the submission to be limited to that list?
Thanks!
Here's Where I wound up - Not fully tested yet, but to give an idea to future posters.
class MustContainAttribute : RequiredAttribute
{
public string Field { get; private set; }
List<string> allowed;
public MustContainAttribute(string validateField)
{
this.Field = validateField;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
switch (Field)
{
case "assetClassName":
allowed = new List<string> { "Real Estate", "Factored Debt" };
break;
default:
return ValidationResult.Success;
}
if (!allowed.Contains(Field))
{
return new ValidationResult("Invalid Value");
}else{
return ValidationResult.Success;
}
}
}

Create a custom validation attribute:
public class ClassNameRequiredAttribute : RequiredAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext context)
{
Object instance = context.ObjectInstance;
Type type = instance.GetType();
MyAssetClass myAssetClass = (MyAssetClass)type.GetProperty("MyAssetClass").GetValue(instance, null);
if (!string.IsNullOrEmpty(myAssetClass.assetClassName))
{
if (myAssetClass.allowedClassNames.Contains(myAssetClass.assetClassName))
{
return ValidationResult.Success;
}
}
return new ValidationResult(ErrorMessage);
}
}
And in your model:
[ClassNameRequired(ErrorMessage="Your error message.")]
public string assetClassName { get; set; }

As mentioned in the comments you can create your own ValidationAttribute. This is useful if you have this validation on multiple models or if you want to implement client side validation as well (JavaScript)
However, A quick and easy way to do one off validations like this is the IValidatableObject. You can use it as follows:
public class AssetModel:IValidatableObject
{
private static List<string> allowedClassNames = new List<string> {"Real Estate", "Factored Debt"};
[Required]
public string assetClassName { get; set; }
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
if (!allowedClassNames.Contains(assetClassName)
{
yield new ValidationResult("Not an allowed value", new string[] { "assetClassName" } );
}
}
}