I have a simple input model for my blazor server side component. I want to use the build in validation for two DateTime properties.

[DataType(DataType.Date)]
public DateTime? FromDate { get; set; }
[DataType(DataType.Date)]
public DateTime? ToDate { get; set; }

How can I only accept ToDate > FromDate?

CodePudding user response：

Solution using custom ValidationAttribute:

public class DateMustBeAfterAttribute : ValidationAttribute
{
    public DateMustBeAfterAttribute(string propertyName)
        => PropertyName = propertyName;

    public string PropertyName { get; }

    public string GetErrorMessage() =>
        $"Date must be after {PropertyName}.";

    protected override ValidationResult? IsValid(
        object? value, ValidationContext validationContext)
    {
        var model = (DateTimeModel)validationContext.ObjectInstance;

        if ((DateTime?)value < (DateTime?)model.GetType().GetProperty(PropertyName)?.GetValue(model, null))
        {
            return new ValidationResult(GetErrorMessage());
        }

        return ValidationResult.Success;
    }
}

Usage:

public class DateTimeModel
{
    [Required]
    [DataType(DataType.Date)]
    public DateTime? FromDate { get; set; }

    [Required]
    [DateMustBeAfter(nameof(FromDate))]
    [DataType(DataType.Date)]   
    public DateTime? ToDate { get; set; }
}

Blazor fiddle example

GitHub repository with demo

Solution using IValidatableObject:

To do more complex validation checks, your model can inherit from IValidatableObject interface and implement the Validate method:

public class ExampleModel : IValidatableObject
{
    [DataType(DataType.Date)]
    public DateTime? FromDate { get; set; }

    [DataType(DataType.Date)]
    public DateTime? ToDate { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (ToDate < FromDate)
        {
            yield return new ValidationResult("ToDate must be after FromDate", new[] { nameof(ToDate) });
        }
    }
}

Blazor fiddle example

CodePudding user response：

I am afraid you cannot achieve this using the built-in validation. You need to create your own validation component. See for more info here and here.