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Custom Validator Error from Server Side

The built in ASP.NET validators are amazing as we all know. You just drag them on the page, tell them what control to validate, give them a summary control to list the errors and they do it. But what if there's something you need to add server side? Such as something that needs to check with the database before saving. You already have your validation summary control, so it would be nice to re-user that and have everything automatically looking the same. But it would appear there's no easy way of doing it built in, so here's an easy way of doing it... 

Creating a Custom Validation Error

First your going to need a class with some static class's that you can pass your error message to. Here I have two functions one for simply adding the error to the page and the other for adding the error to the page with a specific validation group. I am using a CustomValidator object to make this all work, another option is to implement IValidator but it's actually more effort than's needed. The other section to note is that I'm setting the Error.Text to a non breaking space (this is what would normally go next to the form field you're validating). This is because if you don't then it will default to the ErrorMessage which we only want to go into the summary. If you try setting it to a normal space it will still also default to the summary text.

1using System;
2using System.Collections.Generic;
3using System.Linq;
4using System.Web;
5using System.Web.UI;
6using System.Web.UI.WebControls;
7 
8/// <summary>
9/// Summary description for Validator
10/// </summary>
11public class ValidationError
12{
13 
14    public static void Display(string Message)
15    {
16        Display(Message, "");
17    }
18 
19public static void Display(string Message, string ValidationGroup)
20    {
21CustomValidator Error = new CustomValidator();
22        Error.IsValid = false;
23        Error.ErrorMessage = Message;
24        Error.ValidationGroup = ValidationGroup;
25        Error.Text = " ";
26 
27Page currentPage = HttpContext.Current.Handler as Page;
28        currentPage.Validators.Add(Error);
29    }
30}

Now to trigger the error you just need to called the function as below:

1ValidationError.Display("Useful error message", "ValidationGroupName");

LINQ to SQL Inserts and Deletes

Inserting and Deleting records in a database using LINQ to SQL is just as easy as selecting information. What's not so easy is actually finding out how to do it. There are lots of excellent blog posts around such as this one by Scott Guthrie http://weblogs.asp.net/scottgu/archive/2007/07/11/linq-to-sql-part-4-updating-our-database.aspx, however most of them we're all written for the Beta version of LINQ to SQL which let you do a .Add() or .Remove() on your table, which was  changed on the final release. 

So to insert do something like this: 

1DataClassesDataContext dataContext = new DataClassesDataContext(); 
2 
3//Create my new Movie record
4Movie movie = new Movie();
5movie.Name = "Tim's movie"; 
6 
7//Insert the movie into the data context
8dataContext.Movies.InsertOnSubmit(movie); 
9 
10//Submit the change to the database
11dataContext.SubmitChanges();

And to delete do something like this:

1DataClassesDataContext dataContext = new DataClassesDataContext();
2 
3var movies = from m in dataContext.Movies
4                  where m.Name == "Tim's movie"
5                  select m;
6 
7dataContext.Movies.DeleteAllOnSubmit(movies);
8 
9dataContext.SubmitChanges();

LINQ to SQL Connection Strings

LINQ to SQL is great but like all great things at some point it does something that you don't expect and gives you a headache. An example of this happened to me this week with the differences between how connection strings are handled when you LINQ to SQL model is in a class library rather than a Website or Web Application.

What makes this issue particularly annoying is that it only appears when you try and change the database server that your code is looking at which could end up being when it's going live or moving to a staging server.

So we all know about connection strings, their quite simple and you just store them in your web.config file, which is how LINQ to SQL works when your using them in a Website. But as soon as you move them to a class library things change. First your connection string name is no longer that simple name you gave it e.g. ConnectionString, now it is prefixed with the namespace which is annoying but not the end of the world. Second discovery though is no matter what you do, it just doesn't seem to pick up the connection string from the web.config file. Reason being your original connection string has now compiled itself in the class library's dll and that is what it is using.

The Solution

Depending when you discovered this the solution is not to bad as you either have a lot of code to change or only a small amount. You can always pass a connection string to the constructor when you are creating an instance of the data context e.g.

1DataClasses1DataContext da = new DataClasses1DataContext(connectionstring);

You can also set the connection string on your LINQ to SQL model to be blank, this will remove the default constructor and force you to pass a connection string. This way you web application has the choice of what connection string to use and you can keep re-using your class library in different projects.

Add keyboard shortcuts to your web app

Keyboard shortcuts are common place in desktop apps, to such an extent that you would probably be surprised if holding ctrl+s didn't save a document, or if holding ctrl+n didn't do some kind of new action. But with website's its a lot less common. The bigger email providers all now provide the support, but for the sites produced smaller companies out there it's still not the norm. Actually adding the support for it though is actually quite straight forward.

In this example I'm going to use jQuery but it's just as easy in everyday JavaScript.

1var isCtrl = false;
2 
3$(document).keyup(function (e) {
4    if(e.which == 17) isCtrl=false;
5}).keydown(function (e) {
6    if(e.which == 17) isCtrl=true;
7    if(e.which == 83 && isCtrl == true) {
8        alert("Hello World");
9        return false;
10    }
11});

What is happening here is relatively straight forward. When you hold a key down, JavaScript will pick up an event that says which key was pressed by it's number. However what it can't do is pick up a combination, so if you do a ctrl+s what you get is two events (one for the ctrl and one for the s). So on every keydown if it's a ctrl we set the variable isCtrl to true, then on the next keydown we know it's a combination. The keyup detects the end of the ctrl being held down and sets the variable back to false.

The return false, when we've detected a ctrl+s is also very important as what this will do is stop the browser from carrying out any shortcuts it may have had for that combination.

So there we have it, in around 10 lines of code you can add some functionality to your web app, that seems really advanced but is actually really really simple.