Diffference Between RegEx.IsMatch and the RegularExpressionAttribute

-

I was working on some code that stores a month as CCYYMM string. Of course I wanted to validate the string with Regex so I had the pattern

^20[0-2][0-9](0[1-9])|(1[0-2])$

Everything was fine as long as I was using Regex.IsMatch. The problems started when I used the RegularExpressionAttribute. Suddenly, I was getting errors everywhere. I constructed a little test to verify that there was a difference. What I found was that using the same string and pattern, yielded different results.

Here’s my unit test.

[TestMethod]
public void DifferenceBetweenIsMatchAndRegExAttribute()
{
  var pattern = "^20[0-2][0-9](0[1-9])|(1[0-2])$";
  int cnt = 0;
  var months = new string[]
  {
  "201001",
  "201002",
  "201003",
  "201004",
  "201005",
  "201006",
  "201007",
  "201008",
  "201009",
  "201010",
  "201011",
  "201012" };
  var attribute = new RegularExpressionAttribute(pattern);
  bool isMatchOk = false;
  bool isAttrOk = false;
 
  foreach (var month in months)
  {
    isMatchOk = System.Text.RegularExpressions.Regex.IsMatch(month, pattern);
    isAttrOk = attribute.IsValid(month);
 
    if (isMatchOk & isAttrOk)
    { cnt += 1; }
  }
 
  Assert.AreEqual(12, cnt);
}

You would expect the number of matches to be 12 but it’s actually 9. Why? Because the attribute is matching only the first half of our pattern. It stops at the pipe (|). To prove this, I flipped the sides of the pipe and got 3. If I add parens around both sides of the logical or I will get the answer I’m looking for.

^20[0-2][0-9]((0[1-9])|(1[0-2]))$

While it seems logical that the RegularExpressionAttribute would use Regex.IsMatch underneath, it apparently is not the case. I’m betting the reason has to do with JavaScript compatibility. Remember, the attribute must also validate client side.

Cheers!

Comments

Post a Comment

Popular posts from this blog

Migrating Legacy Apps to the New SimpleMembership Provider

-
Image
Asp.Net MVC4 uses the new SimpleMembership provider, changes the table structure and adds a new hashing algorithm. The reasons for the changes can be found in this article by Jon Galloway. This article shows how to migrate your existing apps to the new provider. I’m assuming that you stored your passwords in the unrecoverable SHA-1 format. If you didn’t, then you’ll have to change a couple of things. All of my apps are done this way so… I’m also assuming that you have created the basic skeleton of the new app and ran it once so the correct tables will be created. First, we’ll look at the new tables. Previously, we had all of those aspnet_xxxxxx tables. Here’s the new ones. UserProfile Contains all of the elements relevant to the user. This is a combination of the aspnet_Users table and the aspnet_Profiles table. webpages_Membership Stores the password info when not using OAuth, Live, Facebook, etc. This table is somewhat of a match to the aspnet_Membership table. webpage
Read more

Windows 8 Keyboard Shortcuts

-
Image
There are numerous posts on the keyboard shortcuts in Windows 8. I’m not going to regurgitate those. Here are the common things you’ll want to do. Shut Your Computer Off, Network / Wi-Fi, Volume, Keyboard Press Windows+I which brings up the Settings bar (below left). Search, Change Application Settings, Manage Devices Windows+C which brings up the Charms bar (above right). Want to find a song or artist in Music, use The rest of the story If you want to read about other short-cuts and print a handy-dandy cheat sheet, visit the Windows Experience Blog . IE 10 Want to get the most out of IE10, then How-To Geek’s The Best Tips and Tricks for Getting the Most out of Internet Explorer 10 is exactly what you need. There’s also Internet Explorer 10 Shortcut Keys In Windows 8 which has some Windows 8 stuff also.
Read more

Get Asp.Net Profile properties from Sql

-
Image
Ever wanted to include the profile information from an Asp.Net profile in a query? It’s not that hard once you understand the structure. I’ve written a little function that does all the work. Note: I’m using Sql Server as my repository. First we need to understand how the profile data is stored. Looking at the aspnet_Profile table, we can see that it stores the information in two columns: PropertyNames and PropertyValuesString. Looking at PropertyNames we can see that it has a basic structure of Property Name, Data Type, Starting Position and Length. For example, in the string “FirstName:S:0:4:Phone:S:4:10:LastName:S:14:5:” we can see that FirstName is of type string, starts at position 0 and has a length of 4. Notice the zero base for the starting position, we need to correct for that in our function. This means in the PropertyValuesString “John2175551212Smith”, we would start with the first position and proceed 4 characters to get the name.
Read more