How can I define a IDataErrorInfo Error Property for multiple BO properties

Question

I\'m starting to implement validation in my WPF project via the IDataErrorInfo interface. My business object contains multiple properties with validation info. How do I get a l

Answer 1

I think it is much easier to use the Validation attributes.

class MyBusinessObject {
    [Required(ErrorMessage="Must enter customer")]
    public string Customer { get; set; }

    [Range(10,99, ErrorMessage="Price must be between 10 and 99")]
    public decimal Price { get; set; }

    // I have also created some custom attributes, e.g. validate paths
    [File(FileValidation.IsDirectory, ErrorMessage = "Must enter an importfolder")]
    public string ImportFolder { get; set; }

    public string this[string columnName] {
        return InputValidation.Validate(this, columnName);
    }

    public ICollection AllErrors() {
        return InputValidation.Validate(this);
    }
}

The helper class InputValidation looks like this

internal static class InputValidation
    where T : IDataErrorInfo
{
    /// 

    /// Validate a single column in the source
    /// 
    /// 
    /// Usually called from IErrorDataInfo.this[]
    /// Instance to validate
    /// Name of column to validate
    /// Error messages separated by newline or string.Empty if no errors
    public static string Validate(T source, string columnName) {
       KeyValuePair, ValidationAttribute[]> validators;
       if (mAllValidators.TryGetValue(columnName, out validators)) {
           var value = validators.Key(source);
           var errors = validators.Value.Where(v => !v.IsValid(value)).Select(v => v.ErrorMessage ?? "").ToArray();
           return string.Join(Environment.NewLine, errors);
       }
       return string.Empty;
    }

    /// 

    /// Validate all columns in the source
    /// 
    /// Instance to validate
    /// List of all error messages. Empty list if no errors
    public static ICollection Validate(T source) {
        List messages = new List();
        foreach (var validators in mAllValidators.Values) {
            var value = validators.Key(source);
            messages.AddRange(validators.Value.Where(v => !v.IsValid(value)).Select(v => v.ErrorMessage ?? ""));
        }
        return messages;
    }

    /// 

    /// Get all validation attributes on a property
    /// 
    /// 
    /// 
    private static ValidationAttribute[] GetValidations(PropertyInfo property) {
        return (ValidationAttribute[])property.GetCustomAttributes(typeof(ValidationAttribute), true);
    }

    /// 

    /// Create a lambda to receive a property value
    /// 
    /// 
    /// 
    private static Func CreateValueGetter(PropertyInfo property) {
        var instance = Expression.Parameter(typeof(T), "i");
        var cast = Expression.TypeAs(Expression.Property(instance, property), typeof(object));
        return (Func)Expression.Lambda(cast, instance).Compile();
    }

    private static readonly Dictionary, ValidationAttribute[]>>  mAllValidators;

    static InputValidation() {
        mAllValidators = new Dictionary, ValidationAttribute[]>>();
        foreach (var property in typeof(T).GetProperties()) {
            var validations = GetValidations(property);
            if (validations.Length > 0)
                mAllValidators.Add(property.Name,
                       new KeyValuePair, ValidationAttribute[]>(
                         CreateValueGetter(property), validations));
        }       
    }
}