ASP.NET Web Component for editing SQL tables

/*
 * Code Copyright 2012 by Bill Frisbie
 * 
 * This code is licensed under COPL license.
 * Users are free to use this code, modify it and include it in other work, including works for resale.
 * Please include this notice in the code.
 * Author provides code 'as-is', and assumes no liability for any losses whatsoever arising from its use
 * Contact author at bfrisbie@optonline.net with any questions or suggestions.
 */
using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace BFCS.Data.Common
{
    /// <summary>
    /// TableAdapter derived class for Date values
    /// </summary>
    class DateTableAdapter : TableAdapter, ITableAdapter
    {
        protected DateTime minDate = DateTime.MinValue;         // minimum allowed date
        protected DateTime maxDate = DateTime.MaxValue;         // maximum allowed date

        // JavaScript snippet template to validate date entry
        private const string JavaScriptValidateTemplate =
            @"if (this.value == '') {return true;} var d = new Date(this.value); if (d.ToString=='Invalid Date') {alert('Invalid date');return false;} var min = new Date('{0}'); var max = new Date('{1}'); if (min>d | d>max){alert('Date out of range');return false;} return true;";

        private string Validator;       // fully-qualified JavaScript validation code string
        /// <summary>
        /// Generic constructor for DateTableAdapter: all dates allowed
        /// </summary>
        /// <param name="validator">SQL statement DbValidator to use</param>
        /// <param name="ColumnName">Table column to use</param>
        public DateTableAdapter(DbValidator validator, string ColumnName)
            : base(validator, ColumnName, typeof(DateTime))
        {
            Validator = null;
        }
        /// <summary>
        /// Constructor that enforces min/max limits
        /// </summary>
        /// <param name="validator">SQL Statement DbValidator to use</param>
        /// <param name="ColumnName">Column to use</param>
        /// <param name="modifier">Modifier: should be [minDate],[maxDate]</param>
        /// <remarks>
        /// Use this constructor to create a TableAdapter that restricts the entered DateTime to minimum
        /// and maximum values; these are passed in the modifier argument
        /// </remarks>
        public DateTableAdapter(DbValidator validator, string ColumnName, string modifier)
            : this(validator, ColumnName)
        {
            string[] modifiers = modifier.Split(",".ToCharArray());
            if (modifiers.Length < 2)
                throw new ArgumentException("Modifier format: <minDate>,<maxDate>");
            if (!DateTime.TryParse(modifiers[0], out minDate))
                throw new ArgumentException(string.Format("MinDate '{0}' is not a valid date or time",
                    modifier[0]));
            if (!DateTime.TryParse(modifiers[1], out maxDate))
                throw new ArgumentException(string.Format("MaxDate '{0}' is not a valid date or time",
                    modifier[1]));
            if (maxDate < minDate)
                throw new ArgumentException(string.Format("MaxDate '{0}' is before MinDate '{1}'"));
            //Validator = string.Format(JavaScriptValidateTemplate, minDate, maxDate);
            Validator = JavaScriptValidateTemplate.Replace("{0}", minDate.ToString()).Replace("{1}", maxDate.ToString());
        }
        /// <summary>
        /// Convert a value to properly formatted displayable string
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        private string DisplayedText(object value)
        {
            if (value is DateTime)
                return ((DateTime)value).ToString("MM/dd/yyyy");
            value = value ?? "";
            return value.ToString();
        }

        #region ITableAdapter Members
        /// <summary>
        /// Given value from table, return control to display it (non-edit row)
        /// </summary>
        /// <param name="value"></param>
        /// <returns>Label that displayes formatted date string</returns>
        public Control DisplayValue(object value)
        {
            Label label = new Label();
            label.Text = DisplayedText(value);
            return label;
        }

        public System.Web.UI.Control EditValue(object value)
        {
            return EditValue(value, false);
        }
        /// <summary>
        /// Given initial value from table, return control used in edit or append row
        /// </summary>
        /// <param name="value">value from table</param>
        /// <param name="Appending">Flag: true if appending, false if editing</param>
        /// <returns>TextBox control for editing value (label if not appending and value is a key)</returns>
        public System.Web.UI.Control EditValue(object value, bool Appending)
        {
            if ((IsKey && !Appending) || !IsWriteable)
                return DisplayValue(value);
            TextBox t = new TextBox();
            t.Text = DisplayedText(value);
            t.MaxLength = 10;
            t.Attributes.Add("onchange", Validator);
            return t;
        }
        /// <summary>
        /// Convert entered value from Form collection to SQL insertion string, checking for error
        /// </summary>
        /// <param name="setting">Entered string from Form collection</param>
        /// <param name="error">(out) error message detected</param>
        /// <returns>value to insert into SQL statement (without delimiters)</returns>
        public virtual string SaveValue(string setting, out string error)
        {
            DateTime v;
            error = "";
            if (setting.Trim() == "")
                return "";          // allow blank string
            if (!DateTime.TryParse(setting, out v))
            {
                error = string.Format("{0} is not a valid date/time", setting);     // string is not a date
            }
            else
            {
                // Check to see if in legal range
                if (v < minDate || v > maxDate)
                    error = string.Format("{0} is not in valid date range {1} - {2}", minDate, maxDate);
            }
            return setting;
        }

        #endregion
    }
}