ValidationHelper

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Reflection;

namespace Core {

    /// <summary>
    /// Helper class used to validate components the use the 'System.ComponentModel.DataAnnotations' validation attributes
    /// </summary>
    public class ValidationHelper {
        /// <summary>
        /// Validates the component's "Required" and "StringLength" Attributes and returns a dictionary with the Property Name as the key and the error message as the value;
        /// Note: If a propery has more than one 'error message' the error message will be delimeted by a NewLine
        /// </summary>
        /// <param name="component">The object to validate with "Required" and "StringLength" Attributes</param>
        /// <param name="errors">A dictionary used to add Property Name as the key and the error message as the value</param>
        public static void AppendValidationErrors(object component,Dictionary<string,string> errors) {

            //Test for required fields
            var requiredProps = TypeHelper.GetAttributes<RequiredAttribute>(component);

            foreach(MemberInfo propname in requiredProps.Keys) {

                var att = requiredProps[propname];
                object propvalue = TypeHelper.GetValue(component,propname.Name);
                if(!att.IsValid(propvalue)) {
                    string errmsg = att.ErrorMessage;
                    if(errmsg.IsNullOrEmptyTrim())
                        errmsg = propname + " is required";

                    //append or add the error message for the propertyname
                    if(errors.ContainsKey(propname.Name))
                        errors[propname.Name] += "\r\n" + errmsg;
                    else
                        errors.Add(propname.Name,errmsg);
                }
            }

            //Test for string lengths either max or min
            var stringLengthProps = TypeHelper.GetAttributes<StringLengthAttribute>(component);
            foreach(MemberInfo propname in stringLengthProps.Keys) {
                var att = stringLengthProps[propname];
                var propvalue = TypeHelper.GetValue(component,propname.Name);

                if(!att.IsValid(propvalue)) {
                    string errmsg = att.ErrorMessage;
                    if(errmsg.IsNullOrEmptyTrim()) {
                        if(att.MinimumLength == 0) {
                            errmsg = propname + " must be not greater than {0} characters".FormatString(att.MaximumLength);
                        }
                        else if(att.MaximumLength > 0 && att.MinimumLength > 0) {
                            errmsg = propname + " must be between {0} and {1} characters".FormatString(att.MinimumLength,att.MaximumLength);
                        }
                        else
                            errmsg = propname + " string length is invalid";
                    }

                    //append or add the error message for the propertyname
                    if(errors.ContainsKey(propname.Name))
                        errors[propname.Name] += "\r\n" + errmsg;
                    else
                        errors.Add(propname.Name,errmsg);

                }
            }
        }
    }

}