Question

I’m using code-first EF 4.1 to insert data into a SQL Server database. When a string property has a value longer than the maximum set in the mapping, EF throws a DbEntityValidationException whose EntityValidationsErrors contains the details of the issue.

Is there any way to resolve the errors programmatically?

Specifically I would like to truncate the property in question, record a “Property X Truncated” notification for later use and re-attempt the SaveChanges().

I’ve created a custom ValidationAttribute that checks the length of the annotated property but can’t figure out if I can change the property’s length at the same time.

public class TruncateAttribute : ValidationAttribute
{
    public int TruncateLength { get; set; }

    public TruncateAttribute(object truncateLength)
    {
        this.TruncateLength = (int) truncateLength;
    }
    protected override ValidationResult IsValid(object value, 
          ValidationContext validationContext)
    {
        var original = (string) value;
        if (original.Length > this.TruncateLength)
        {
            value = original.Substring(0, 
                     this.TruncateLength); // doesn't work
            return new ValidationResult(
                string.Format("{0} is longer than {1} characters",
                  validationContext.DisplayName, this.TruncateLength),
                new[] {validationContext.MemberName});
        }
        else
        {
            return ValidationResult.Success;
        }
    }
}

Answer 1

From everything I’ve read, it is not possible to alter a property’s value during the ValidationAttribute‘s IsValid() call. I can’t find anything that specifically says it isn’t possible but all signs point to no.