C# attribute to check whether one date is earlier

问题:

I have a ViewModel for my MVC4 Prject containing two DateTime properties:

[Required]
[DataType(DataType.Date)]
public DateTime RentDate { get; set; }

[Required]
[DataType(DataType.Date)]
public DateTime ReturnDate { get; set; }

Is there a simple way to use C# attributes as [Compare("someProperty")] to check weather the value of RentDate property is earlier than the value of ReturnDate?

回答1:

Here is a very quick basic implementation (without error checking etc.) that should do what you ask (only on server side...it will not do asp.net client side javascript validation). I haven't tested it, but should be enough to get you started.

using System;
using System.ComponentModel.DataAnnotations;

namespace Test
{
   [AttributeUsage(AttributeTargets.Property)]
   public class DateGreaterThanAttribute : ValidationAttribute
   {
      public DateGreaterThanAttribute(string dateToCompareToFieldName)
      {
          DateToCompareToFieldName = dateToCompareToFieldName;
      }

       private string DateToCompareToFieldName { get; set; }

       protected override ValidationResult IsValid(object value, ValidationContext validationContext)
       {
           DateTime earlierDate = (DateTime)value;

           DateTime laterDate = (DateTime)validationContext.ObjectType.GetProperty(DateToCompareToFieldName).GetValue(validationContext.ObjectInstance, null);

           if (laterDate > earlierDate)
           {
               return ValidationResult.Success;
           }
           else
           {
               return new ValidationResult("Date is not later");
           }
       }
   }


   public class TestClass
   {
       [DateGreaterThan("ReturnDate")]
       public DateTime RentDate { get; set; }

       public DateTime ReturnDate { get; set; }
   }
}

回答2:

It looks like you're using DataAnnotations so another alternative is to implement IValidatableObject in the view model:

public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
    if (this.RentDate > this.ReturnDate)
    {
        yield return new ValidationResult("Rent date must be prior to return date", new[] { "RentDate" });
    }
}

回答3:

If you're using .Net Framework 3.0 or higher you could do it as a class extension...

    /// <summary>
    /// Determines if a <code>DateTime</code> falls before another <code>DateTime</code> (inclusive)
    /// </summary>
    /// <param name="dt">The <code>DateTime</code> being tested</param>
    /// <param name="compare">The <code>DateTime</code> used for the comparison</param>
    /// <returns><code>bool</code></returns>
    public static bool isBefore(this DateTime dt, DateTime compare)
    {
        return dt.Ticks <= compare.Ticks;
    }

    /// <summary>
    /// Determines if a <code>DateTime</code> falls after another <code>DateTime</code> (inclusive)
    /// </summary>
    /// <param name="dt">The <code>DateTime</code> being tested</param>
    /// <param name="compare">The <code>DateTime</code> used for the comparison</param>
    /// <returns><code>bool</code></returns>
    public static bool isAfter(this DateTime dt, DateTime compare)
    {
        return dt.Ticks >= compare.Ticks;
    }

回答4:

Not sure of it's use in MVC/Razor, but..

You can use DateTime.Compare(t1, t2) - t1 and t2 being the times you want to compare. It will return either -1, 0 or 1 depending on what the results are.

Read more here: http://msdn.microsoft.com/en-us/library/system.datetime.compare.aspx

回答5:

Model:

[DateCorrectRange(ValidateStartDate = true, ErrorMessage = "Start date shouldn't be older than the current date")]
public DateTime StartDate { get; set; }

 [DateCorrectRange(ValidateEndDate = true, ErrorMessage = "End date can't be younger than start date")]
public DateTime EndDate { get; set; }

Attribute class:

[AttributeUsage(AttributeTargets.Property)]
    public class DateCorrectRangeAttribute : ValidationAttribute
    {
        public bool ValidateStartDate { get; set; }
        public bool ValidateEndDate { get; set; }

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

            if (model != null)
            {
                if (model.StartDate > model.EndDate && ValidateEndDate
                    || model.StartDate > DateTime.Now.Date && ValidateStartDate)
                {
                    return new ValidationResult(string.Empty);
                }
            }

            return ValidationResult.Success;
        }
    }

回答6:

Nothing like that exists in the framework. A common similar attribute is the RequiredIf. It is described in this post.

RequiredIf Conditional Validation Attribute