Confessions of a Professional Developer

Sometimes when using ASP.NET MVC 3 / 4 with Entity Framework it can be difficult to see exactly which property is causing issues when db.SaveChanges() is called.

If you wrap the db.SaveChanges() in an appropriate try {} catch {} block whilst debugging (see below) each property in conflict will be written to your debug console which is much more helpful in finding and resolving the problem!

Don't forget to remove the try catch block after your debugging session though otherwise exceptions will be swallowed and disappear in a live environment which will then hinder further debugging efforts!

[Authorize(Roles = "SomeRole")]
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(string SomethingsName)
    if (ModelState.IsValid)
    {
        db.Something.Add(new Something()
        {
            Id = Guid.NewGuid()
            ,
            Name = SomethingsName
        });
        try
        {
            db.SaveChanges();
        }
        catch (DbEntityValidationException dbEx)
        {
            foreach (var validationErrors in dbEx.EntityValidationErrors)
            {
                foreach (var validationError in validationErrors.ValidationErrors)
                {
                    Debug.WriteLine("Property: {0} Error: {1}",
                               validationError.PropertyName,validationError.ErrorMessage);                 }
            }
        }
    }
    return RedirectToAction("Index");
} 





Generating routing links is extremely easy in MVC 3 using @Html.ActionLink(linkText,action,controller) when you're using Razor views this is great. However sometimes you need to generate the link within the controller - at which point you do not have direct access to the Html helper.

In these instances such as creating links for a wysiwyg editor or adding a link into an email it is preferable to have the system generate it with the appropriate protocol http/https and/or a port number if you're running locally. To this end I did some digging and put together the following little code snippet which does eactly that!

I thought I'd share it here to save me having to look it up again in the future!


            string absoluteAction = string.Format("{0}://{1}{2}",
                                                  Url.RequestContext.HttpContext.Request.Url.Scheme,
                                                  Url.RequestContext.HttpContext.Request.Url.Authority,
                                                  Url.Action("ActionName", "ControllerName", new {Id = "Data"}));

I've been tinkering with MVC 3 for a while now and I have to say I'm extremely impressed - it is a joy to work with as are its supporting technologies Entity Framework, ASP.NET Routing and Razor view engines to name a few.

However I've been working on WebForms for so long that I'm finding more than a few stumbling blocks as I grapple my way up the learning curve. One such hurdle was "How do I re-validate a model after its been posted back to the server". The scenario being I want a user to type a plain text password into a form which is required but not persisted - I used [NotMapped] DataAnnotation attribute in the model definition to get this bit done.

Following that on postback I need to create a Salt (required and persisted) and a PasswordHash (required and persisted). Trouble was, I originally had the Salt and Hash properties within my if (ModelState.IsValid) statement.

The Model was at this point invalid because no password hash or salt had been created yet. "Easy" I thought simply elevate the property assignments above the if condition. No luck (but along the right lines) as the properties were now filled but I needed to Re-Validate the model, no Page.Validate() to rely upon at this point so I did some digging. As it turns out you simply need to call two methods (below) and they are roughly equivalent to what a WebForms guy would consider to be Page.Validate().

p.Salt = CreateSalt(36);
p.PasswordHash = GenerateSaltedHash(UTF8.GetBytes(p.Password), p.Salt);
ModelState.Clear();
TryValidateModel(model);
if (ModelState.IsValid)
{
p.Id = Guid.NewGuid();
db.People.Add(p);
db.SaveChanges();
return RedirectToAction("Index");  
}
return View(person);

Hello again!

I've been following Microsoft development for years now and the advent of twitter gave me a brilliant insight into Microsoft developers thoughts and keeps me abreast of current feeling about technology by those developing it. For years i used Google Reader and added blogs and such forth to achieve the same result but it was must less immediate and much more in-depth.

This week has been a great week on twitter for me keeping up with what's going on at the MVP Conference (still not quite made it to MVP myself but that's all part of my life time goals plan ... ). OK so here a really obvious tip that only just occurred to m,e (stupid) if I hit the #mvp12 link in twitter and then hit the people link - presto a complete list of everyone who was at MVP and who is also on twitter - amazing - all the people i need to follow in one place:

https://twitter.com/#!/search/users/%23mvp12

I went through and more than quadrupled the amount of people I followed BUT hopefully this will give me an excellent view into what's happening going forward!

The same technique should work for any industry and any conference so if you're not sure who to follow and who's making noise in your industry target a conference and away you go!

Just a quick one today! This has probably been around for a while now but yesterday I had good cause to use this handy piece of functionality!

The location tag within the web config file of your asp.net 4 website allows you to specify a location tag with a path attribute and set "web.config" style setting for just that single location! This is particularly handy if you need to set request upload limits or request validation settings for a particular page that handles file uploads or downloads.

Here is an example which allows for the upload of very large files and allows a URL Encoded filename (with some very odd characters) to be downloaded





This location section should be placed within the <configuration> tags!

Whilst working on a simple data access layer using Sql Ce 4, POCO C# and using the Repository Pattern it occurred to me that when implementing a SaveChanges method that there was no real effective way to prevent a subsequent developer coming along and instantiating a new instasnce of some entity, directly setting the Id property and calling SaveChanges! I thought about nesting the entity within the repository and changing access levels on classes and properties but nothing really worked.

At this point I figured that there are much smarter people out there that have already solved this problem - I'll just have a look and see how they did it (A good view when standing on the shoulders of giants!).

I fired up visual studio, hit nuget for EF 4.3 updated everything, wrote a very contrived example waited for an exception at which point I'd delve into the code and possibly with a little reflection work out what was going on.

Sadly that's not what happened. I discovered that if you instantiate an instance of an entity manually populate its Id and call save changes it simply quietly adds it to the db with the next available identity and carries on!

Although this may well never actually happen in the real world I thought it was interesting none the less.

If I'm being a complete idiot here please do let me know!

- Class1.cs

namespace FactoryPatternSandbox.Core
{
    public class TestContext : DbContext
    {
        public TestContext()
            : base("name=conn")
        {
 
        }
 
        public DbSet<ExampleItem> ExampleItemSet {get; set;}
        
    }
 
    public class ExampleItem
    {
        public int Id { get; set; }
        public string Text { get; set; }
    }
}

Default.aspx
    public partial class Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            using (Core.TestContext context = new Core.TestContext())
            {
                Core.ExampleItem example = new Core.ExampleItem();
                // Set Id to a random hard coded int
                example.Id = 1234;
                // Set arbitrary text value
                example.Text = DateTime.Now.ToString();
                // Add to context with Id 1234
                context.ExampleItemSet.Add(example);
                // output Id to Literal (Output = 1234)
                something.Text = example.Id.ToString();
                context.SaveChanges();
// At this point the Id *should* have been added to the DB as 1234
// or thrown an exception e.g. CannotAssignIdToNewEntityException()
// However checking the DB the item has been added with the next
// available Id as per a normal INSERT INTO with an IDENTITY column specification
// But its not actually told us (via an exception) that the Id value
// has indeed changed so when we call for our random hard coded int
// it throws an exception saying there are no items in the collection.
Core.ExampleItem exampleFromDb = context.ExampleItemSet.Where(l => l.Id == 1234).Single();
 
            }
        }
    }

I'd like to share this little technique I've been using for quite a while, especially to receive feedback and validation on whether or not this is a good idea!

I've used this technique with great success in the past in production systems which require a a "grid" of check-boxes and a single "update" button. This kind of thing usually occurs when you have any X can be related to any Y in a many to many kind of relationship. It comes in especially handy when mapping Users to Roles or that kind of thing. Though it can easily be adapted to manage multiple updates of anything in ONE database hit.

Traditionally this kind of code ends up hitting the database either once per cell in the grid or once per row in the grid because SQL Server doesn't allow arrays of things to be sent to a stored procedure. Database hits are expensive and generally less is better.

My technique leverage's SQL Servers ability to access XML data using the OPENXML keyword. When the grid of check-boxes is submitted we gather together the form collection elements (those check-boxes that have been ticked) and create an XML snippet of the results. This is then passed to SQL Server as a single input representing a set of information. OPENXML is then used inside the stored procedure to convert the XML into a temporary table which is then interrogated and used to update the relationship information that the check box represents.

Below is a link to a visual studio 2010 project that you can download , it contains all the source code for the project please feel free to download and try it for yourself - if you find it useful or have an idea of how it could be improved please leave a comment at the bottom of this page.

I have used MVC 3 and SQL Server as a simple container for the project but the technique is equally valid for any type of project Classic ASP, ASP.NET Web-forms included, so long as the RDBMS supports XML the technique will be valid.

I will refrain from a long explanation here as the code is simply one model, controller and view and the database contains just three tables and two stored procedures. If you'd like some more detail please leave a comment at the bottom of the page and Ill update as soon as possible. If I get a lot of feedback then I will flesh out the method some more in a series of posts.

I do hope you find this useful and would love to hear from you!

Project files can be downloaded here  and unpacked using   7zip

Having not made a new years resolution at the time I have decided that it should be "use my blog more often". I'm doing quite well this year so far but to be honest its quite tricky fitting it in "out of hours" what with the twins, learning guitar and Skyrim being released but we can but try!

This post centres around the ease with which I managed to sign up for and integrate Disqus comments into this very blog. It turns out that to replace the (fairly basic) standard Blogger comments with Disqus is REALLY straightforward. Simply a case of signing up to Disqus pointing it at your blog and clicking the appropriate options.

Disqus accounts are free (though there are paid for versions) and it adds a social edge and more integrated experience if you're a Blogger or a commenter. I original was looking to integrate LiveFyre but it didn't seem to offer the kind of seamless integration and ease for which I was looking (I may be wrong but Disqus just made it so easy!).

Anyway if you're looking for "comments on social steroids) I would definitely recommend it if you're serious about building communities around your content!

http://disqus.com

http://www.livefyre.com/
One last word on LiveFyre if you're looking for something a bit different it works just like other comments managers however it also include live chat as a first-class feature which, when you see it, really is quite impressive!

Kodak ESP 5250 All-in-One Colour Ink-jet - Printer / copier / scanner:

'via Blog this'

Website of the day on Pocket-lint today - what a fantastic idea, keep up to date with the big stories in the press day by day with direct links to all the papers. Also spans multiple countries too!
UK Newspaper Front Pages @ Front Pages Today:

'via Blog this'

An extremely useful extension that should improve the frequency with which I update my blog. I usually post links through my twitter account ( @bUKaneer ) but will endeavour to post to my blog using this tool too!
One-click Blogging with BlogThis! Chrome Extension | Blogger Buzz:

'via Blog this'

NuGet: http://nuget.org/

This is a system for “installing” components into your web application quickly and easily. So lets say your doing a data driven website using SQL CE 4, you’re going to be using jQuery and CSS control adapters. Simply create your new website as per normal fire up NuGet, do a search for jQuery and hit install, do a search for CSSFriendly double click and install. At this point it will have put copies of jQuery and CSS Friendly control adapters straight into your project! Brilliant! Theres LOADS of stuff available ousing NuGet these are only two VERY small example – check it out!

SQL CE 4: http://weblogs.asp.net/scottgu/archive/2011/01/11/vs-2010-sp1-and-sql-ce.aspx

This is an “in site” file based database and needs no server components to run just some webspace supporting .NET 4 – it replaces using MS Access SQLite or PostgresSQL. In order to use it you simply need Visual Studio 2010 sp1 and the SQL CE 4 tooling support installed which can be downloaded from here http://www.microsoft.com/download/en/details.aspx?id=23691 and here http://go.microsoft.com/fwlink/?LinkId=212219 . Then when you right click App_Data select New Item a new option will appear call SQL Server CE 4 – double click it and it will create for you a new database which you can use as per you would access.

SQL CE 4 Membership Provider: http://www.hanselman.com/blog/IntroducingSystemWebProvidersASPNETUniversalProvidersForSessionMembershipRolesAndUserProfileOnSQLCompactAndSQLAzure.aspx

Righty this little gem (provided via NuGet) is a way to use the Membership provider system built into .NET with SQL CE 4 – this is actually really easy to implement in about three step and takes about 5 minutes (I know because I did it yesterday). Once the steps are completed you will be able to use all the Membership functions directly from your new SQL CE 4 database saving you the time and effort of implementing this on small websites each time.

Google and Microsoft CDN

If you’re wanting to include framework such as jQuery jQuery UI and jQuery Validate then consider using a CDN (Content Delivery Network) version. This is basically an include to a file or files stored in the cloud. The advantages are tht you do not have to keep local copies of the files in your project and also that when a request is made when the page loads the file will be delivered from the nearest server to your user which should in theory speed up download times. The google CDN and Microsoft CDNS can be used in tandem so you could include jQuery and jQuery UI files from Google and Validate from Microsoft (I've done this and it works fine) – it’s a good way to keep your file footprint down on small sites:

http://code.google.com/apis/libraries/devguide.html#jquery (Shows links to .js files) for the CSS to be included from CDN also please read the following http://blog.jqueryui.com/2009/03/jquery-ui-17/ (Both CSS and Javascript files are hosted on the Google CDN but only the js files are listed – bit silly however the previous link shows how to include the CSS files as well!)

Microsofts version can be foud here: http://www.asp.net/ajaxlibrary/cdn.ashx (Webpage currently not working!)

This has probably been done a million times before but i thought I would record my home-brew effort for posterity. The point of the following Javascript is to change the sequence in which Table Rows display using Javascript - this could be extended via AJAX calls to write back the new sequence to the data store but is beyond the scope of what I'm currently trying to achieve!

Tips & Tricks for ASP.NET, IIS, and Visual Web Developer : Tip#102: Did you know… How to specify tag specific formatting: "Tip#102: Did you know… How to specify tag specific formatting"

Microsoft/Amazon Deal: Nothing to See Here | The Linux Foundation

Recently I was trying to implement a web service call for a client who had another firm implementing a very secure web service using client certificates (Ill blog about how to get that working sometime soon). However once Id got the security sorted I was getting a Method not allowed 403 error in order to diagnose the problem I needed ot get at the raw data travelling across the wire. as it happens dot net has a brilliant diagnostics suite which is really simple to implement. Simply add the following into your web.config file underneath the system.web node and presto youll get a trace.log file will all that lovely low level info in!

response.Write("<hr/>")