Gold Creek Group

Automatically set MAXLENGTH on text input fields in ASP.net MVC 3

2011-12-13T18:55:00.000-08:00

It seemed to me that ASP.net MVC 3 should know what the max string length is for any given database field and set it in the MAXLENGTH attribute on the corresponding web form.

I went looking for a way to get the built-in Html.EditorFor to do it, but didn't find any.

Here's a new helper called "LimitedEditorFor" which automatically adds the correct MAXLENGTH attribute to the text input tag. Call this exactly the same way you would call Html.EditorFor.

 
namespace ExtensionMethods
{
   public static class MyExtensions
   {
     public static MvcHtmlString LimitedEditorFor<TModel, TValue>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TValue>> expression)
     {
       string S = htmlHelper.EditorFor(expression).ToString().Replace("/>", "MAXLENGTH=\"" + GetLengthLimit(expression) + "\"/>");
       return new MvcHtmlString(S);
     }
  
     private static int GetLengthLimit(Expression expression)
     {
       MemberExpression ME = GetMemberInfo(expression);
       Type type = ME.Member.ReflectedType;
       string field = ME.Member.Name;
       PropertyInfo prop = type.GetProperty(field);
       // Find the Linq 'Column' attribute
       // e.g. [Column(Storage="_FileName", DbType="NChar(256) NOT NULL", CanBeNull=false)]
       object[] info = prop.GetCustomAttributes(typeof(ColumnAttribute), true);
  
       if (info.Length != 1) return 0;  // Assume there is just one
  
       ColumnAttribute ca = (ColumnAttribute)info[0];
       string dbtype = ca.DbType;
       if (!dbtype.StartsWith("NChar") && !dbtype.StartsWith("NVarChar")) return 0;
  
       Regex pattern = new Regex("\\((.+)\\)");
       Match m = pattern.Match(dbtype);
       if (!m.Success) return 0;
  
       return Convert.ToInt16(m.Groups[1].Value);
     }
  
     private static MemberExpression GetMemberInfo(Expression method)
     {
       LambdaExpression lambda = method as LambdaExpression; 
       if (lambda == null) throw new ArgumentNullException("method"); 
       MemberExpression memberExpr = null; 
  
       if (lambda.Body.NodeType == ExpressionType.Convert)
       {
         memberExpr = ((UnaryExpression)lambda.Body).Operand as MemberExpression;
       } 
       else if (lambda.Body.NodeType == ExpressionType.MemberAccess)
       {
         memberExpr = lambda.Body as MemberExpression;
       } 
  
       if (memberExpr == null) throw new ArgumentException("method"); 
  
       return memberExpr;
     }
   }
}

This was a huge help: http://joaodepaula.com/articles/columnsizereflection.html

Bare-Bones Script

2010-01-07T16:48:00.000-08:00

This is the smaller version of the client-side code to capture Javascript errors. See description here.

This version does not save code snippets, but does crunch down to 267 bytes.  The full-featured version requires 678 bytes of minimized Javascript.

// !!!! IMPORTANT !!!!

// This must be the first script that runs.

// It cannot catch errors in script that

// appears higher up the page.

onerror =   // assign our own handler to the Window.onerror event

function(d, p, l) // d: Error Description; p: Path; l: Line

  // NOTE!!  ScriptCanary will only log requests from registered customers.

  // See http://ScriptCanary.com

  // ScriptCanary version number

  new Image().src = "http://ScriptCanary.com/log.aspx?v=1" +

  // Error Description

  "&d=" + encodeURIComponent(d) +

  // Error Line #

  "&l=" + l +

  // User Agent

  "&u=" + encodeURIComponent(navigator.userAgent) +

  // OS/Device

  "&o=" + encodeURIComponent(navigator.platform) +

  // URL

  "&p=" + encodeURIComponent(p) +

  // Random # to circumvent caching

  "&r=" + Math.random();

  onerror = null

How to capture Javascript errors

2009-12-23T11:01:00.000-08:00

Introduction

Why let some bugs slip through the cracks when they're so easy to identify? This article explains how to trap all those pesky Javascript errors that would otherwise take much longer to find. Early detection before release is the key to keeping development costs low, and early detection after release helps rein in support costs.

The Root of the Problem

You can usually count on your test team to find serious rendering problems or 50x server errors -- they're too obvious to overlook.

However, Javascript errors often go unnoticed before release. Testers can forget to turn on error notification in all the browsers they're using to test the new web site code. Overall test coverage is usually lower in the less-popular browsers. New browser variants can gain popularity before your team can react.

After release, you're counting on customers to tell your support team about the problems they see. However, most browsers by default do not show error alerts. Certainly customers aren't bothered by seeing the yellow shield in the status bar. What if there's functionality they can't see because of the errors? What if it's a serious issue -- do you really want to wait through the support lag to find out?

The Solution

By adding a little bit of code to your web pages and building or using an existing error-capturing service, you can collect all of the errors that testers and real users are encountering.

All you need to do is:

1) Add code to your page that triggers on the first error event.
2) Have that code send the details of the error to a web service. See the description of the ScriptCanary.com code below to get started.
3) Create a web service that captures the error reports and saves them in a database.
4) Develop a reporting mechanism so that your team knows when there's a new error to review.

For steps 3) and 4), use any platform and technology you prefer. Or, sign up with ScriptCanary.com and skip those steps completely.

ScriptCanary's Client-Side Error Handling Code

2009-12-18T16:18:00.000-08:00

Here's a detailed walk-through of the ScriptCanary client code.

The first thing we're doing here is attaching an event handler to the Window.Onerror event.

The handler's tasks are simple:

1) Grab a few lines of the erroneous source code if possible.

2) Send the source code and other details of the error report to the ScriptCanary web service.

At the very top of the script we have:

onerror =   // assign our own handler to the Window.onerror event

function(d, p, l) // d: Error Description; p: Path; l: Line

Next, we make the standard bare-Javascript moves to get the XMLHTTPREQUEST object:

try

        R = new XMLHttpRequest();

    catch (E)

try

...et cetera. Next, we see why we need the XMLHTTP object.

We're going to attempt to do a synchronous read of the problem source code file and grab the exact source lines as they appear at this moment.

This guarantees that the lines will be available when it's time to view the error, and won't cause cross-site access errors when the user is reviewing the bug details later. 

R.open("GET", p, true);

R.onreadystatechange =

function()

    if (R.readyState == 4)

        if (R.status == 200)

            // Split the file into an array of lines.

            A = R.responseText.split(new RegExp("(\r\n){1}"));

            // Find only the lines around the error,

            // and insert the line numbers

            for (i = 0; i < A.length; i++)

                if (i > l - 4 && i < l + 2)

                s += (i + 1) + ': ' + A[i] + "\n";

R.send(null);

Now we can send the log entry via a simple fire-and-forget GET request on a new Image object.

NOTE!! ScriptCanary will only log requests from registered customers.

new Image().src =

"http://scriptcanary.com/log.aspx?" +

   // Error Description

   "&d=" + encodeURIComponent(d) +

   // Error Line #

   "&l=" + l +

   // User Agent

   "&u=" + encodeURIComponent(navigator.userAgent) +

   // OS/Device

   "&o=" + encodeURIComponent(navigator.platform) +

   // URL

   "&p=" + encodeURIComponent(p) +

   // ScriptCanary version number

   "&v=1" +

   // Source code (note this can be truncated by the browser to the max url length)

   "&s=" + encodeURIComponent(s);

Finally, disable our error handler. Subsequent errors tend to be noise -- cascading effects from the first problem.

 onerror = null;

Huge thanks go out to Eric Lawrence for his help with this script.

Please send along questions and feedback in the comments, or through our feedback form on ScriptCanary.com.

Coming soon: The less-is-more version of the ScriptCanary client code -- only 204 bytes of pure sizzle!

Announcing ScriptCanary.com - Javascript Error Reporting

2009-12-17T14:41:00.000-08:00

Finally!

http://ScriptCanary.com

Check out the super low intro price for all you bleeding-edge early adopters.

More blog posts to come, including a detailed explanation of the client-side code.