MongoDB – getting better for .NET

by DotNetNerd 6. March 2010 16:24

Since my last post Rob Connery has joined the team working on MongoDB, and he recently blogged about the latest additions he has made on github. I couldn’t resist taking a look at the latest changes, and even though there is still some way to go it is nice to see the improvements to the drivers for .NET.

My last sample is already depricated, so Ill shamelessly steal his sample, and modify it slightly just to see the new bits running with entities that I worked with last. So Ill recommend looking at the sample from the blogpost, since I’ll be using his session class.

First thing to notice from Robs sample is that I don’t have to think much about mapping classes to documents any longer. One thing that is already depricated even from Robs own sample is that it is now a requitement that the class has an identifier. So going with the simplest thing possible I added an ID integer.

using (var session=new Session()){
   session.Add(new Actor { ID = 1, Name = "Hans", Age = 40, Gender = Gender.Male });
   session.Add(new Actor { ID = 2, Name = "Eva", Age = 22, Gender = Gender.Female });
}

So comparing to Db4o, we are now closer to a similar experience. One of the things I’ll wait to look at, but I see as fairly importait is how either will handle Lazy<T> properties and other kinds of more advanced scenarios.

With the above objects saved the data can be accessed using a Linq query like so:

using (var session=new Session())
{
   var actors = session.Actors;
   foreach (var actor in actors.Where(a => a.Gender == Gender.Male))
   {
       Console.Write(actor.Name);
   }
}

The LINQ provider is still not too far along so I’ll leave it alone for now, but it is also one of the places where it will be interesting to compare e.g. db4o and MongoDB in the future.

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Ayende - the relational dragonslayer

by DotNetNerd 23. February 2010 18:31

Ayende, who most know to be one of the Guru's when talking about ORM's and by extention working with relationel databases came to a very interesting conclusion a couple of days ago when he received a phonecall. To parafrase his point in "Slaying relational dragons" in a few words, a very real and complex problem had one very simple and elegant solution - do not use a relational database. This acknowledgement is as a see it a strong incentive to take a look at what NOSQL solutions like document and object based databases has to offer. And his blogpost is something I would definitely recomment reading...

 

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Db4o – first look

by DotNetNerd 21. February 2010 13:12

As the next step in my recent adventures into NoSQL country I decided to take a look at db4o. Shortly put I hope it will give me more than the document based databases, like Mongo that I have also been taking out for a spin.

My interest in NoSQL has been kindled further than it already was because of blog posts from Rob Connery, who looked into practical approaches and posts on CodeBetter provokingly entitled Using an ORM is like kissing your sister. Basically what they are all saying is that it is very limiting that we always start out with a relational database without even considering this very very important architectural decision.

Object vs Document

Similar to the document based database, the big win is that there is no schema, and no need to map between objects and a relational model. Actually with document based databases you do map to key/value pairs, so it’s not the whole truth, but still simpler than mapping to a relational model.

Mapping can be expensive in two ways – because it takes time to write the code, and it does warrant a certain overhead. On top of that db4o as an object oriented database has a concept of relations between objects. This means that rich querying capabilities are build in and that it performs really well.

When comparing to MongoDB the big thing missing is that it basically works on a flat file out of the box. So you need something to handle concurrency and stuff like that. Rob Connery posted a nice sample of how this could be done, and its really quite straight forward, because db4o does provide all you need to do it.

The basic stuff

In the interest of simplicity I’ll just sample how to work with db4o directly. Also this will illustrate just how straight forward it really is. The first thing that brought a smile to my face was how little I had to do to save and query a bunch of objects.

using (IObjectContainer context = Db4oEmbedded.OpenFile(Server.MapPath("myDatabase.yap")))
{
    var empolyeeToSave = new Employee() { Name = "John", Card = new TaxCard() { Number = "12345678" } };
    context.Store(empolyeeToSave);

    IList<Employee> retrievedEmployees =
        context.Query<Employee>(employee => employee.Card.Number == "12345678");
}

 

As you can see it’s very straightforward stuff. Besides this type fo querying which takes a predicate, there is also a QueryByExample, which works as one would expect. Another nice thing is that all calls to the Store method make up a transaction, so there is a Rollback method available. When the context is disposed the convention is that Commit is called for you, so when you don’t need rollbacks you don’t have to think about it.

Indexing is also possible with db4o, and it is also very simple to do, so if for instance I would like to apply an index for the name property on my Employee I could do this.

Db4oFactory.Configure().ObjectClass(typeof(Employee)).ObjectField("Name").Indexed(true);

Moving along

Some of the first things that I have heard people think about when I say object/document based database is how to handle versioning and querying. With querying in this case I mean how to enable a scenario similar to opening SQL Manager and writing some queries to take a look at the actual data.

The versioning part may take a little work, but there are methods to help with e.g. renaming directly baked in - and besides, it takes work no matter what kind of database your using. On top of that my thought is that both of these issues can be addressed with a dynamic language. My plan is to take a look at this at some point, and that it will fit nicely because my copy of IronRuby Unleashed should be on it’s way :)

b_DBA

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My Ajaxy JavaScript stack

by DotNetNerd 24. January 2010 12:12

I have been working primarily with ASP.NET MVC for a little over a year now, and this has prompted me to do quite a bit more Ajaxy functionality. So while doing this I have been looking at quite a few Ajax/Javascript libraries.

As most other developers I have been swept away by JQuery, which by far is the most important component when I am doing Ajax and manipulating the html DOM - see cheatsheet. Besides making a lot of these things easier, it also provides a wide variety of plugins that enable all sorts of shiny fancy features without much work. One of the very usefull ones that I find myself using on all kinds of projects is tablesorter- that makes clientside table sorting almost free.

Working in the Microsoft domain I have of course also been working with Microsofts ASP.NET Ajax Librarywhich also brings quite a few cool things to the table. Most basically it enriches the javascript experience by providing namespaces, intellisence and a bunch of extentions to the basic javascript type system. On top of that there are a lot of extenders to work with accordions, watermarks, listsearch etc. were most projects will find something that is useful to provide a better UI experience. The latest addition, that I am already very fond of even though it is still just in the beta version is templates. This gives us a easy way to do databinding on the client - one-way/two-way livebindings, and ways to do this both declaratively and imperatively. In other words it provides a rich templating experience and no more clumbsy string manipulation!

Next thing that is important when working with Ajax is having some solid libraries to do JSon serialization. Here I will strongly recommend JSON2for the client because eval is evil. Also a small but important thing to know is that data must be serialized and provided as a string when using JQuery to call a WCF service. On the serverside, I recommend Json.NET or maybe Json for the compact framework if you need something that is easier and more extendable than the .NET build in DataContractSerializer.

Finally something that might also be worth looking at to get better performance is using a content delivery network to reference the different scripting librarys. Here I will recommend looking at either Microsoft Ajax Content Delivery Networkor Google AJAX Libraries. Both seem very reliable and will give what you need, so its mostly a matter of personal preference.

18okt04_ajax_logo_150_rgb

ajax_logo2

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MongoDB – how to get started

by DotNetNerd 3. January 2010 11:17

Even though I have been pretty disconnected during the holydays I couldn’t help read that Rob Conery wrote quite a bit on his blog about his thoughts on Ayendes “EF vs NHibernate” discussion. Rob Conery argues that he is tired of these discussions and that we need to look at the NOSQL movement and instead focus on alternatives to relational databases.

I found this pretty interesting and decided that it was finally time for me to take a look at one of the document based databases out there. As Rob mentioned MongoDB I thought this was a good a place to start as any. Based on my experiences I then decided to do this post on what I learned about getting MongoDB up and running. So first of all, the steps to get a MongoDB server running are:

  1. Download and unpack from: http://www.mongodb.org/display/DOCS/Downloads
  2. Create folder C:\data\db and make sure the server has read and write access
  3. Run the server from cmd. Go to dir where you unpacked (eg: "c:\MongoDB\bin") and run "mongod"

You can now work with the database from the commandline, but to start writing some code you need to get a driver that suits you. In my case I went with a driver so I can write my code in C#. This driver along with a early edition of a LINQ library can be downloaded from http://github.com/samus/mongodb-csharp/downloads 

This is all you need to get going, so just create a new project and start coding!

A good sample can be found here http://blog.dynamicprogrammer.com/2009/11/10/UsingMongoDBFromC.aspx and if your into F# this might be interesting http://gist.github.com/218388

The first sample focuses on two ways to handle converting objects into documents.

  1. Serialize object(hierarchy) into JSon using JSonConverter - which was the sample I focused on.
  2. Make entities implement the IMongoEntity interface – which basically just makes your entity expose a Document property which then contains the state for the entity.

Of course I wont cheat you from seeing the bit of code I started out with, which is heavily inspired by the before mentioned blog posts.

//Connect to the database
var mongo = new Mongo();
mongo.Connect();
var db = mongo.getDB("movieReviews");

//Access the collection that you wish to work with
var movies = db.GetCollection("movies");

//Add a document
var movie = new Document();
movie["title"] = "Star Wars";
movie["leadActor"] = JsonConvert.SerializeObject(
 new Actor() {Name = "Mark Hamill", Age = 26, Gender = Gender.Male});
movie["releaseDate"] = new DateTime(1977, 5, 25);
movies.Insert(movie);

//Do a query
var result = from mov in movies.AsQueryable()
             where (string)mov["title"] == "Star Wars"
             select mov;

//Write out info from document
foreach (var document in result)
 foreach (string key in document.Keys) Console.WriteLine(document[key]);

//Deserialize and write name
Console.WriteLine(JsonConvert.DeserializeObject<Actor>((string)result.First()["leadActor"]).Name);

//Disconnect from database
mongo.Disconnect();

 

You'll also need this simple class for the sample:

public class Actor
{
 public string Name { get; set; }
 public int Age { get; set; }
 public Gender Gender { get; set; }
}

public enum Gender
{
 None = 0,
 Male = 1,
 Female = 2
}

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PS3 media server - abracadabra go away foolish limitations

by DotNetNerd 27. December 2009 15:48

During the hollidays I was visiting some friends for a round of junkfood and movies. As one of my friends was showing off his new tv I noticed how his menues looked a lot like what I get when accessing my PS3 over the network. I know however that he does not own a PS3. so I got curious. It turnes out that he had installed a PS3 media server on his PC.

I had never heard about the PS3 media server before, so I looked into what it has to offer. It turnes out that it is a free application that makes it possible to allow access to any folder on your network through the PS3. This was a limitation that had annoyed me immensely when using the PS3 to access media on my LAN (my Synology NAS box actually was the one giving me a hard time), so I quickly downloaded and installed the media server on my own box. It worked without any questions asked, and solved the one thing that I was not happy with when using my PS3 to play movies and music. So I can only give it my clear recommendation.

 

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Javascript - weak on getting week

by DotNetNerd 23. December 2009 08:42

Well this is one of those posts that start out being as a reminder for myself, since I had to do a script that I don't want to waste my time having to write again later on. Basically I ran into a customer who wanted week numbers added to a calendar. This seemed basic enough, but apparently getting a weeknumber is not a native thing in javascript.

First I picked up a script to add a getWeek method to the Date prototype, and I was a happy man. Sadly not customer not quite as much. It turns out that we do not follow the ISO 8601 standard for defining weeknumbers here in Denmark. According to my projectmanager the rule of thumb is that the first thursday always falls in week 1. This made me add a little extention so I now have a getIsoWeek and a getWeek method on my Date objects and this is how it was done.

/**
* Get the ISO 8601 week date week number
*/
Date.prototype.getIsoWeek = function() {
    // Create a copy of this date object 
    var target = new Date(this.valueOf());

    // ISO week date weeks start on monday 
    // so correct the day number 
    var dayNr = (this.getDay() + 6) % 7;

    // Set the target to the thursday of this week so the 
    // target date is in the right year 
    target.setDate(target.getDate() - dayNr + 3);

    // ISO 8601 states that week 1 is the week 
    // with january 4th in it 
    var jan4 = new Date(target.getFullYear(), 0, 4);

    // Number of days between target date and january 4th 
    var dayDiff = (target - jan4) / 86400000;

    // Calculate week number: Week 1 (january 4th) plus the  
    // number of weeks between target date and january 4th  
    var weekNr = 1 + Math.ceil(dayDiff / 7);

    return weekNr;
}

/**
* Get danish weeknumber.
* According to danish weeknumbers the first thursday always falls in week 1
*/
Date.prototype.getWeek = function() {
    var weekNr = this.getIsoWeek();

    var firstThursday = new Date(this.getFullYear(), 0, 1)
    while (firstThursday.getDay() != 4) firstThursday.setDate(firstThursday.getDate() + 1);

    if (firstThursday.getIsoWeek() == 2) weekNr--;

    if (weekNr == 0) weekNr = 1;

    return weekNr;
}

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Ajax Minifier - come and get your low hanging fruit

by DotNetNerd 21. December 2009 16:43

Not too long ago Microsoft released the Ajax Minifier, which can be downloaded from codeplex. It's basically just another javascript minifier, but the good thing about is it that the download includes both a commandline tool, an MS Build task and an assembly, so you can do your minification any way you like. Either way you wait to use it is very simple and it is explainted in the chm file which is included in the installation.

Today I finally got around to using it, for a HttpHandler that I wrote to serve some javascripts that I wanted to aggregate into one file and have them minified. It really took no time at all, and reduced my site from needing 13 files to 1 that was reduced in size by a little over 30%. All it required was about 10 lines of code in the HttpHandler (including handling caching). So basically what I am saying is that there is no excuse not to get this performance boost, since it is really low hanging fruit ripe for the plucking.

 

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.less is more

by DotNetNerd 8. December 2009 16:48

A little while ago I read about a nice little library called .less, which is a port from ruby less, that lets you write css, but with the added features of enabeling variables, operations, mixins and nesting. Today I decided to try it out, and I definately want to give it my recommendation.

Using variables makes stylesheets a lot more maintainable because it allows you to avoid having colorcodes scattered all around the stylesheet simply by writing:

@listbackground_color: #E3EFFF;

Nesting just makes it more maintainable and gives the stylesheet a better sence of structure like this:

table.MapsList
{
  background-color: @listbackground_color;       
  tr th
  {
    width: 300px;
    background-color: @listbackgroundheader_color;
  }
}

Finally mixins makes it possible to keep the stylesheets more DRY (don't repeat yourself) like so:

.rightBackground { background-repeat:no-repeat;background-position:right; }
th.headerSortUp { .rightBackground; background-image: url(desc.gif); }
th.headerSortDown { .rightBackground; background-image: url(asc.gif); }

An added bonus is that you can toggle caching and minimizing from your web.config.

 

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IronPython – add scripting to you application

by DotNetNerd 5. December 2009 16:43

Last time I looked at how IronPython is integrated with .NET which makes it possible to use all of the good stuff that we know and love from .NET. The obvious next thing to look at is doing the inverse and see how it is possible to run IronPython code from within a .NET app written in this case in C#.

The main scenario for this is to allow advanced users to write their own scripts that can extend the behavior of the application, or allow them to express complex logic. An example that comes to mind for me is a system I am working on at work, where we are doing payroll processing for any kind of company. Here a viable option could be to allow the rules for the processing to be expressed with scripts – since the tax laws have a tendency to change frequently it would be a valuable extensibility point.

The most basic way to run IronPython code from C# is to do like this:

var engine = new PythonEngine();
engine.ExecuteToConsole(@"print ""Sweet dude!""");

As you can see it is pretty simple to get code to run in the first place. It is not of much use however if it is not possible to pass in variables to the context in which the IronPython code is run. This is accomplished by passing in a module and a dictionary of variables like so:

engine.ExecuteToConsole(@"print ""Cool: "" + str(2+val)",
    engine.DefaultModule, new Dictionary<string, object>() { { "val", 6 } });

Again, this is pretty straight forward. Besides passing variables it would also be nice to be able to define global variables that can be used and accessed again after the script is run. This example shows how to do just that:

engine.DefaultModule.Globals["val"] = 6;
engine.ExecuteToConsole(@"val = ""Cool: "" + str(2+val+2)",    engine.DefaultModule, null);
string modifiedValue = (string)engine.DefaultModule.Globals["val"];

One thing to note here is that i set the global variable to a value of 6 which is an integer but I end up getting a string back. This is because IronPython is a dynamic language which allows the type to be changed which is done in the script because it is added with a string.

Now my guess is you might be thinking that there must be other ways to run scripts than to execute them to a console. Well of course there is. The PythonEngine has several overloads and alternate methods that can be used to run scripts. I wont go over them all but I’ll finish up with a sample that I think will probably be one of the ways I will end up using most often. In this case I simply evaluate a script that returns a value. This way a script could be used to define some logic and simply return the kind of result I need:

string myResult = engine.EvaluateAs<string>(@"str(2+2)");

Mainly there are two groups of methods to run IronPython code – you can either execute or evaluate the code, with the difference being that evaluating it returnes a value. There are also methods to execute code from a file, which might be convenient.

280px-python_logo_2

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Who am I?

My name is Christian Holm Diget, and I work as an independent consultant, in Denmark, where I write code, give advice on architecture and help with training. On the side I get to do a bit of speaking and help with miscellaneous community events.

Some of my primary focus areas are code quality, programming languages and using new technologies to provide value.

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