IEnumerable, why use it?

Okay, first off: I really love the IEnumerable<T> interface, and I use it excessively throughout my applications.

Almost any list or collection throughout the .NET framework implements this interface. It exposes only one method (GetEnumerator), but this method is your friend in almost any circumstance.

This method returns an Enumerator, which again exposes methods used to traverse (or loop through) the collection. This means you can make a method definition like this:

public void MyMethod(IEnumerable<string> someEnumerable)
{

}

I could call this method with any sort of collection, it could be string[], List<string>, IList<string>, IQueryable<string> or even a basic IEnumerable<string>. I don’t give a damn. I don’t care what the implementation is, I just want a collection to work with, nothin’ more.

This means I don’t need to force other developers who use my code, to pass an array or a List or some custom collection, they just pass whatever collection they have, and I will be able to work with it. That’s awesome!

But wait! How do you get an IEnumerable<T> in the first place? How can we make our own?

Well, in “ye olde times” one would make an abomination like this:

public List<string> MyMethod()
{
List<string> myResult = newList<string>();
for (int i = 0; i < dataSource.Length; i++)
{
// Do some work.
myResult.Add(dataSource[i].SomeProperty);
}
return myResult;
}

Can you see what’s wrong here?

There’s actually more than one thing that’s wrong with this snippet.

First off: When we return a specific implementation, in this case List<T>, we force our code to use this implementation. We kinda dictates the use of our result which is a major drawback on agile Development. What if the consumer don’t want or need a list?

Second: In line 3, we create an instance of an object we actually don’t need, so that we can return a list.

Third: We loop through a collection of an unknown size. This Collection could potentially contain a billion items.

Fourth: We have to wait until the loop has ended. Which could take forever. Think about what would happen to your app, when you loop though a billion items and only need the first five.

This is where .NET provides a concept of Enumerators. These are methods that only returns data when said data is ready to be returned on not when all data is ready to be returned. And it is actually the same method called from the GetEnumerator()-method.

To convert our method from above into an Enumerator, we must make some changes. First we need to return an IEnumerable<string> instead of a List. Second we need to remove the list-object. And finally rewrite the loop to use the keyword “yield”.

This is how our method would then look like:

public IEnumerable<string> MyMethod()
{
for (int i = 0; i < dataSource.Length; i++)
{
// Do some work.
yield return dataSource[i].SomeProperty;
}
yield break;
}

As you can see, the code looks way simpler. We don’t force our consumer to take a list. And the yield-keyword, changes the method into an Enumerator, which gives us a LOT of benefits:

The yield return, returns our data when the property Current is called on the Enumerator-instance. This property is usually called each time the MoveNext()-method is called. This Means you do not have to wait until all items are looped. You can stop at any moment. the yield-return is only called when you request the next item.

So if your consumer needs to loop through each of your items, you will only have to loop once, whereas the List-thingy above, would loop through the same items twice. That’s two billion items! Secondly the first example would always loop though each item, but the second one only loops through as many items as you want it to. Nothin more nothin less.

 

The essence of it all: Always use IEnumerable, only use lists where it cannot be done without it.

For performance reasons, always use Enumerators. They will save the day.

 

This is my first attempt on a “professional”-programming guide. Please provide feedback!

NMultiSelect – Et jQuery Plugin

NMultiSelect

UPDATE

This has become quite an old version, it’s good to get started, but to get the latest version, please take a look here: http://ndesoft.dk/category/web/js/nmultiselect-js/

Quick links

About NMultiSelect

Okay, I have been foolin’ around with javascripts again, i know, can’t help it. This time I have made me a jQuery plug-in. I chose jQuery because it’s so much easier to do cross browser compatible stuff with that framework, compared to time it will take for me to build it on my own.

The last 3/4 of a year, i have worked on and off with the Microsoft ASP.NET MVC framework, and found it quite likeable, in terms of development speed and possibilities in the markup and, in this case, JavaScript.

While working with the MVC framework, I have been looking for a nice, easy to implement method for a user to choose multiple values from a list. The good ol’ “hold ctrl while clicking”-method doesn’t quite do the job, so I decided to build my own control.

It’s, like most of the other stuff I’ve made, quite easy to use.

Seen from a user’s perspective, it’s simple, click or double click, select and click or what ever he or she feels like. For the developer, it’s also quite easy. A few lines of code, and you’re ready to go:

 

Getting started

First we need to include a few scripts:

<span class="kwrd">&lt;</span><span class="html">script</span> <span class="attr">type</span><span class="kwrd">="text/javascript"</span> <span class="attr">src</span><span class="kwrd">="https://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"</span><span class="kwrd">&gt;&lt;/</span><span class="html">script</span><span class="kwrd">&gt;</span>

<span class="kwrd"> </span><span class="kwrd">&lt;</span><span class="html">script</span> <span class="attr">type</span><span class="kwrd">="text/javascript"</span> <span class="attr">src</span><span class="kwrd">="http://code.jdempster.com/jQuery.DisableTextSelect/jquery.disable.text.select.pack.js"</span><span class="kwrd">&gt;&lt;/</span><span class="html">script</span><span class="kwrd">&gt;</span>

<span class="kwrd"> </span><span class="kwrd">&lt;</span><span class="html">script</span> <span class="attr">type</span><span class="kwrd">="text/javascript"</span> <span class="attr">src</span><span class="kwrd">="http://nmultiselect.ndesoft.dk/scripts/jquery.nmultiselect.min.js"</span><span class="kwrd">&gt;&lt;/</span><span class="html">script</span><span class="kwrd">&gt;</span>

Where you wan’t to place your box, you just put a div:

<span class="kwrd">&lt;</span><span class="html">div</span> <span class="attr">id</span><span class="kwrd">="EmptySelectContainer"</span><span class="kwrd">&gt;&lt;/</span><span class="html">div</span><span class="kwrd">&gt;</span>

We wan’t to remember this ID for later…

To transform the div, to a multi select box, we will have to write the following piece of code:

$(document).ready(
    <span class="kwrd">function</span> () {
        <span class="kwrd">var</span> m1 = $(<span class="str">"#EmptySelectContainer"</span>).NMultiSelect(<span class="str">"mySelection"</span>);
    }
);

What happens here is:

  1. $(document).ready – We will wait until the page is ready before doing anything.
  2. $(“#EmptySelectContainer”) – We select’s our div, using the ID from earlier. You can use any form of selectors here.
  3. NMultiSelect(“mySelection”) – Transform our div to a multi select box. The parameter (mySelection) is the name of the field getting posted to the server. In this case, we will be able to get our data using $_POST[“mySelection”] (using php, but more on that later.)

Now, we have transformed our div to a multi select box, but it’s a bit useless. Lets fill it with some values. To do so, use this function:

AddItemToList(value,text,selected).

The function AddItemToList, takes 3 parameters.

The first, is the value posted to the server. Usually an ID.

The second, is the text shown in the box.

The third, is a boolean value (not mandatory). If true, the item will be selected and visible in the right hand side box.

You can add as many items you want, Below is an example:

m1 = $(<span class="str">"#EmptySelectContainer"</span>).NMultiSelect(<span class="str">"mySelection"</span>);

m1.AddItemToList(<span class="str">"1-1"</span>,<span class="str">"Value 1"</span>,<span class="kwrd">false</span>);
m1.AddItemToList(<span class="str">"2-1"</span>,<span class="str">"Value 2"</span>,<span class="kwrd">false</span>);
m1.AddItemToList(<span class="str">"3-1"</span>,<span class="str">"Value 3"</span>,<span class="kwrd">true</span>);
m1.AddItemToList(<span class="str">"4-1"</span>,<span class="str">"Value 4"</span>,<span class="kwrd">true</span>);

Here we add 4 items to our box. Whereof the last two are pre-selected.

Now we have our items, it could be nice, to track how the user chooses, for statistics or calling AJAX methods or whatever. To do se, we can subscribe to the event:

SelectionChanged(code).

The parameter (code), is code that will be executed, when a user selects or deselects one or more items.

An example:

m1.SelectionChanged(<span class="kwrd">function</span>(data)
{
    <span class="rem">// Do stuff here.</span>
});

The function, or code, that is being executed, must take one parameter, (call it whatever you feel like, i would recommend “data”, because, that is what it is). This parameter contains two properties:

  • Items
    • Contains all elements we have added.
  • Selection
    • Contains all chosen elements.

The objects contained in the lists, has the following properties:

  • Text
  • Value
  • Selected

Full example

Bellow is a full example. You could also see nmultiselect live here.

<span class="kwrd">&lt;!</span><span class="html">DOCTYPE</span> <span class="attr">html</span> <span class="attr">PUBLIC</span> <span class="kwrd">"-//W3C//DTD XHTML 1.1//EN"</span> <span class="kwrd">"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"</span><span class="kwrd">&gt;</span>
<span class="kwrd">&lt;</span><span class="html">html</span> <span class="attr">xmlns</span><span class="kwrd">="http://www.w3.org/1999/xhtml"</span> <span class="attr">xml:lang</span><span class="kwrd">="da"</span><span class="kwrd">&gt;</span>
<span class="kwrd">&lt;</span><span class="html">head</span><span class="kwrd">&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">title</span><span class="kwrd">&gt;</span>NMultiselect<span class="kwrd">&lt;/</span><span class="html">title</span><span class="kwrd">&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">link</span> <span class="attr">rel</span><span class="kwrd">="stylesheet"</span> <span class="attr">type</span><span class="kwrd">="text/css"</span> <span class="attr">href</span><span class="kwrd">="/styles/style.css"</span><span class="kwrd">/&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">script</span> <span class="attr">type</span><span class="kwrd">="text/javascript"</span> <span class="attr">src</span><span class="kwrd">="https://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"</span><span class="kwrd">&gt;&lt;/</span><span class="html">script</span><span class="kwrd">&gt;</span>
    &lt;script type=<span class="str">"text/javascript"</span> src=<span class="str">"/scripts/jquery.nmultiselect.min.js"</span>&gt;&lt;/script&gt;
    &lt;script&gt;
        <span class="kwrd">var</span> m1;
        <span class="kwrd">var</span> m2;

        $(document).ready(
            <span class="kwrd">function</span> () {
                m1 = $(<span class="str">"#EmptySelectContainer"</span>).NMultiSelect(<span class="str">"mySelection",<span class="kwrd">true</span></span>);

                m1.AddItemToList(<span class="str">"1-1"</span>,<span class="str">"Value 1"</span>,<span class="kwrd">false</span>);
                m1.AddItemToList(<span class="str">"2-1"</span>,<span class="str">"Value 2"</span>,<span class="kwrd">false</span>);
                m1.AddItemToList(<span class="str">"3-1"</span>,<span class="str">"Value 3"</span>,<span class="kwrd">true</span>);
                m1.AddItemToList(<span class="str">"4-1"</span>,<span class="str">"Value 4"</span>,<span class="kwrd">true</span>);

                m1.SelectionChanged(<span class="kwrd">function</span>(data)
                {
                    console.log(<span class="str">'List 1, selected values: '</span>+(data.Selection.length));
                });

                m2 = $(<span class="str">"#EmptySelectContainer2"</span>).NMultiSelect(<span class="str">"mySelection2"</span>);
                m2.AddItemToList(<span class="str">"1-2"</span>,<span class="str">"Value 1"</span>,<span class="kwrd">true</span>);
                m2.AddItemToList(<span class="str">"2-2"</span>,<span class="str">"Value 2"</span>,<span class="kwrd">false</span>);
                m2.AddItemToList(<span class="str">"3-2"</span>,<span class="str">"Value 3"</span>,<span class="kwrd">false</span>);
                m2.AddItemToList(<span class="str">"4-2"</span>,<span class="str">"Value 4"</span>,<span class="kwrd">true</span>);
                m2.AddItemToList(<span class="str">"5-2"</span>,<span class="str">"Value 5"</span>,<span class="kwrd">true</span>);
                m2.AddItemToList(<span class="str">"6-2"</span>,<span class="str">"Value 6"</span>,<span class="kwrd">true</span>);
                m2.AddItemToList(<span class="str">"7-2"</span>,<span class="str">"Value 7"</span>,<span class="kwrd">false</span>);
                m2.AddItemToList(<span class="str">"8-2"</span>,<span class="str">"Value 8"</span>,<span class="kwrd">false</span>);

                m2.SelectionChanged(<span class="kwrd">function</span>(data)
                {
                    console.log(<span class="str">'List 2, selected values: '</span>+(data.Selection.length));
                });
            }
        );
    <span class="kwrd">&lt;/</span><span class="html">script</span><span class="kwrd">&gt;</span>

<span class="kwrd">&lt;/</span><span class="html">head</span><span class="kwrd">&gt;</span>
<span class="kwrd">&lt;</span><span class="html">body</span><span class="kwrd">&gt;</span>
<span class="kwrd">&lt;</span><span class="html">form</span> <span class="attr">method</span><span class="kwrd">="get"</span><span class="kwrd">&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">div</span> <span class="attr">id</span><span class="kwrd">="EmptySelectContainer"</span><span class="kwrd">&gt;&lt;/</span><span class="html">div</span><span class="kwrd">&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">p</span><span class="kwrd">&gt;</span>hejsa<span class="kwrd">&lt;/</span><span class="html">p</span><span class="kwrd">&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">div</span> <span class="attr">id</span><span class="kwrd">="EmptySelectContainer2"</span><span class="kwrd">&gt;</span>

    <span class="kwrd">&lt;/</span><span class="html">div</span><span class="kwrd">&gt;</span>
    <span class="kwrd">&lt;</span><span class="html">input</span> <span class="attr">type</span><span class="kwrd">="submit"</span> <span class="attr">value</span><span class="kwrd">="submit"</span><span class="kwrd">/&gt;</span>
    <span class="kwrd">&lt;/</span><span class="html">form</span><span class="kwrd">&gt;</span>
<span class="kwrd">&lt;/</span><span class="html">body</span><span class="kwrd">&gt;</span>
<span class="kwrd">&lt;/</span><span class="html">html</span><span class="kwrd">&gt;</span>

 

Serverside

So, what to do on the serverside to get the data?

Well, the name you apply in the NMultiSelect function above, is the name of the field getting posted to the server.

If we say, you use the ASP.NET MVC framework, your backend would look somewhat like this:

[HttpPost]
<span class="kwrd">public</span> <span class="kwrd">void</span> GiveMeData(<span class="kwrd">string</span> mySelection)
{
    <span class="rem">// Først splittes værdierne:</span>
    <span class="rem">// Ja, vi splitter på komma, i en fremtidig version kan dette ændres!</span>
    <span class="kwrd">string</span>[] mySelectionItems = mySelection.Split(<span class="str">','</span>);

    <span class="rem">// Gennemløb værdierne:</span>
    <span class="kwrd">foreach</span>(<span class="kwrd">string</span> itemId <span class="kwrd">in</span> mySelectionItems)
    {
        <span class="rem">// Du kan her behandle værdierne som du ønsker.</span>
    }
}

PHP

&lt;?php
    <span class="rem"># Få fat i værdierne:</span>
    $selection = $_POST[<span class="str">"mySelection"</span>];

    <span class="rem"># Split værdierne:</span>
    $values = explode(<span class="str">","</span>, $selection);

    <span class="rem"># Gennemløb værdierne:</span>
    <span class="kwrd">foreach</span> ($values as &amp;$value) {
            <span class="rem"># Gør med dataene hvad du vil.</span>
    }

    <span class="rem"># Husk at ryde op:</span>
    unset($value);

?&gt;

Reference

Heres a short reference of all the functions available:

NMultiSelect(name,[move]) Creates a new instance of the NMultiSelect-box on the first item in the applied jQuery object. See exampe above.Name: Name of the field that is posted to the server.

move: Not mandatory! If true, the items will be moved between the boxes, instead of just being copied to the right hand side box. Default is false.

AddSelection() Chooses all selected items in the left hand box.
AddAll() Chooses all items in the left hand box.
RemoveSelection() Removes selected items from the right hand side box.
RemoveAll() Removes all items from the right hand side box.
AddItemToList(value,text,[selected]) Adds an item to the box.value: Value the item should have.

text: Text of the item.

selected: Not mandatory, if true, the item is pre-selected.

SelectionChanged(code) Event you can subscribe. Is called each time a change in the chosen items occur.code: Code to be executed, when the event is fired. The code, must have a parameter, that accepts the same objects as data(‘values’) returns.
data(‘values’) Returns all added items, and all chosen items.More details about data(‘values’) below.

data(‘values’)

If you call data(‘values’), (it’s importent to include the ‘values’ part. This is a jQuery thingy!), you will get an object with two properties:

  • Items
  • Selection

Each of these properties contains a list of objects. Items – A list of all items we’ve added, and selection – A list of all chosen items. Each of these objects has the following properties:

  • Value
  • Text
  • Selected

In the Items-list, all values will be the ones, the item was created with.

In the Selection-list, the only difference would be, that the selected-property will be true.

Download

You can grap the code and an example here:

Download NMultiSelect 1.0

DBTesting

Efter lang tids stilhed kommer her en lille opdatering på hvad jeg har gang i for tiden.

Jeg arbejder på et database-testnings system, DBTesting, til at oprette og køre automatiserede tests af en database under udvikling, så man sikre sig, at de data man får ud, er præcis som de skal være og ikke bliver ændret på nogen måder.

Jeg vil ikke gå så meget i dybden her, men du kan læse mere på hjemmesiden:

http://dbtesting.ndesoft.dk

NMapper v2.0

NMapper Logo

NMapper Logo

Så er jeg i gang med version 2 af min NMapper.

NMapper v2.0 kommer til at have følgende features:

  • Alt fra de foregående versioner.
  • Forbedret cache system.
  • Nyt DB Manager system.
    • Ansvaret flyttes fra managerne til NMapperen.
  • Mulighed for at lave instanser af datamapperen så man kan bruge flere DB managere.
  • Helt ny indre struktur.
  • Forbedret ydelse.
  • Flere generelle og automatiserede metoder.
  • Mulighed for at få taget tid på SQL kaldene.
  • Og meget mere.

Håber at blive færdig om 2-3 måneder. Hvis du har idéer eller ønsker til yderligere funktionalitet så må du gerne smide en kommentar herunder.

XML DBManager

commentxml1[1]Så er min XML Manager til NMapperen, ved at være godt moden. Jeg bruger den på mit arbejde, sammen med NMapperen, selvfølgelig, og har i den forbindelse fundet en hel del svagheder i den. I den seneste version er de fleste af de svagheder blevet helbredt.

Et af mine problemer opstod da jeg ville indsætte 9445 rækker i en tabel (xml fil) navigate to these guys. Den insisterede på at gemme filen for hver indsættelse. Det tog evigheder, sad i en halv time og ventede.

Så slog det mig. Indsæt en buffer, der indeholder alle XML-filer fra de oprettes eller indlæses, og så lade en tråd gemme de filer en gang i mellem.

På den måde skal der faktisk kun læses een gang fra harddisken og kun skrives til disken samtidig med at cachen renser sig selv.

NModules

Til den seneste version af NMapper’en har jeg haft brug for en modul styrings komponent. Det er der kommet NModules ud af.

I NModules kan du registrere flere interfaces. NModules gennemsøger så en mappe for dll’er og finder alle de klasser der implementere et registreret interface. Ud af de klasser kan NModules så lave instanser som kan bruges som var de hårdkodet i systemet.

NCache

Til den seneste version af NMapper’en, har jeg lavet et par nye komponenter. Det ene er NCache.

NCache bruges til cache håndtering. Man kan smide hvad som helst i den og få det frem igen. Som standard gemmer den de cachede objekter i 10 minutter, hvorefter den fjerner dem. Men den fjerner kun de objekter der er ældre end 10 min. så alle objekter er cachede lige lang tid.

Man kan selvfølgelig selv ændre hvor lang tid cachen skal gemmes.

Du kan læse mere om NCache her.

NMapper 1.0

Endelig! Efter utrolig lang tid, er det endelig lykkedes mig at få tid til at færdiggøre NMapper 1.0.

Der er kommet en masse nye features.

NMapper skal bl.a. ikke længere kende alle mulige og umulige versioner og udgaver af database systemer. NMapper er nemlig blevet modul baseret, så man selv kan lave en database manager der passer til den database man bruger. NMapperen skal nok selv finde og registrere manageren.

Ud over at have lavet database managere, har jeg også lavet cache styrring, så der skæres ned på trafikken til og fra databasen, samtidig med at svar tiden bliver hurtigere.

Det eneste jeg mangler nu er bare at skrive en masse dokumentation, men indtil den er færdig, kan du jo skrive herunder hvis der skulle blive problemer.

Læs mere her.

NLog v0.3

Så er der blevet tilføjet endnu en funktion til NLog.

Denne gang er der lagt en backup funktion i.

Denne funktion kopiere samtlige logs ud i en backup-mappe med url’en:

/Backup/[date]/[time]/Logs.xml

Oprettelsen af logs og entries er ikke ændret fra v0.2.

Kodeeksempler

NLogs.BackupLogs() // Tag backup af alle logs, fjerner alle entries i den originale og returnere true hvis backupen lykkedes og false hvis ikke.