Web Development

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.

.NET Charts (Pleasing clients by giving them a graph to look at)

Irrespective of if your working on some kind of company extranet or the admin side of a public facing site, one thing that will make you're clients go ooooooo and love your work is the inclusion of a funky looking chart. It may not serve any amazing purpose, but as there looking through all the boring text area's and buttons that actually make up the functionality of the site, the inclusion of nice looking chart is going to make them go "oooo that's nice" and like you even more. For those of us working in .NET, thanks' to an update from Microsoft at the end of 2008 it's also something that've very quick an easy to do. Better yet the update was free so the only cost is the time you take to implement it. 

First off if you want to use the chart's and you haven't downloaded them then that's what you need to do. The chart's shipped after .NET 3.5 so there a separate install, .NET 4 however has them included by default. 

Using the Chart Control

Like I said adding a chart to a page is a quick and easy thing to do. Once you have the Visual Studio add on installed you can also drag and drop everything into place. However I'm going to go into a bit more detail. 

To start your going to need a data source. In this example I'm using a SQL Data Source object for ease of use, in a production environment I heavily recommend against using them as there going to make your code a completely unmanageable mess, instead I would use something like a Entity Data Source. My chart is going to be showing a graph of mobile phone handset popularity so my SQL is simply just returning a table of phone names and how many people use them. 

Code so far: 

1<asp:SqlDataSource ID="ChartDB" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" SelectCommand="SELECT [Name], [People] FROM [PhonePopularity]">
2</asp:SqlDataSource> 

Next we need to add a chart, the easiest way to do this is to just drag a chart object onto the page from the toolbox, however if you do want to type it yourself it's not particularly complex. 

First you will need to register the assembly on the page.. 

1 <%@ Register assembly="System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" namespace="System.Web.UI.DataVisualization.Charting" tagprefix="asp" %> 

And then add the chart like so...

1<asp:Chart ID="Chart1" runat="server" DataSourceID="ChartDB" Height="400px" Width="400px">
2 </asp:Chart>

Now we're ready to start customizing what type of chart we're going to have and what data it should show from our data source.

To actually show a chart there's two bits of information you have to describe, area's and series'. The first area's is used to define an area for a chart to appear, one interesting thing about the chart control is you aren't limited to just one area. In fact in this example I'm going to have to chart's one showing a pie chart of phone popularity that will quickly show what kind of share each phone has, and then a second bar chart making it more clear the actual numbers people have of each phone. Area's also let you set properties on what the chart is actually going to look like as well. In this instance I'm going to set for both charts to be 3D.

The second bit of information is the Series. This is where you're actually specifying what data is going to be shown in which area and what kind of chart it is (e.g. Pie, Column, Donut etc). My completed code then looks like this...

1<asp:Chart ID="Chart1" runat="server" DataSourceID="ChartDB" Height="400px" Width="400px">
2

3<series>
4

5<asp:Series ChartArea="ChartArea1" ChartType="Pie" Name="Series1" XValueMember="Name" YValueMembers="People">
6</asp:Series>
7<asp:Series ChartArea="ChartArea2" Name="Series2" XValueMember="Name" YValueMembers="People">
8</asp:Series>
9

10</series>
11<chartareas>
12

13<asp:ChartArea AlignmentOrientation="Horizontal" Name="ChartArea1">
14

15<Area3DStyle Enable3D="True" />
16

17</asp:ChartArea>
18<asp:ChartArea Name="ChartArea2">
19

20<area3dstyle enable3d="True" />
21

22</asp:ChartArea>
23

24</chartareas>
25

26</asp:Chart>

Depending on your data this should give you something like this...

This is just a simple example of what you can do, but if you download the Chart Samples Project and have a look through there is no end to the possibilities with everything from different styles of charts to adding ajax functionality even with the ability to click of different parts of the carts to trigger events.

System.Lazy

Lazy loading isn't a new concept, it's a pattern that been around for a while to improve the performance of your apps by only loading objects when they are going to be used. For example if you have an object that contains a property of a list of customers then you only really need to populate it when you access the property not when the object was initially created, as it may never be used. At the same time though you don't want to be going off to the database every time access the property. So the simple solution is to have another private variable that stores if the customers property is populated or not and then check that in the property's get to determine if the data needs to be loaded or not.

Well now in .NET 4, lazy loading has been built into the framework with System.Lazy. Instead of the above all you need to do now is write something like this...

Lazy<Customers> _customers = new Lazy<Customers>();

What this will do is create you a customers object but only run the constructor when you actually access the objects Value property which will be of type Customers. e.g.

_customers.Value.CustomerData

It's that simple, but can get even better. The constructor may not be the only thing you want to run when you access the property the first time. In this case you would write something like...

_customers = new Lazy<Customers>(() =>
        {
            // Write any other initialization stuff in here
            return new Customers();
        });

I must point out though while as great as this is, it does have some limitations so you probably won't want to use it in all scenarios.

For more information check out the Lazy initialization page on MSDN