jarrod dixon - Page 3 - Developer IT

DataReader already open when using LINQ

- by Jamie Dixon

I've got a static class containing a static field which makes reference to a wrapper object of a DataContext. The DataContext is basically generated by Visual Studio when we created a dbml file & contains methods for each of the stored procedures we have in the DB. Our class basically has a bunch of static methods that fire off each of these stored proc methods & then returns an array based on a LINQ query. Example: public static TwoFieldBarData[] GetAgesReportData(string pct) { return DataContext .BreakdownOfUsersByAge(Constants.USER_MEDICAL_PROFILE_KEY, pct) .Select(x => new TwoFieldBarData(x.DisplayName, x.LeftValue, x.RightValue, x.TotalCount)) .ToArray(); } Every now and then, we get the following error: There is already an open DataReader associated with this Command which must be closed firs This is happening intermittently and I'm curious as to what is going on. My guess is that when there's some lag between one method executing and the next one firing, it's locking up the DataContext and throwing the error. Could this be a case for wrapping each of the DataContext LINQ calls in a lock(){} to obtain exclusivity to that type and ensure other requests are queued?

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Int[] Reverse - What does this actually do?

- by Jamie Dixon

I was just having a play around with some code in LINQPad and noticed that on an int array there is a Reverse method. Usually when I want to reverse an int array I'd do so with Array.Reverse(myIntArray); Which, given the array {1,2,3,4} would then return 4 as the value of myIntArray[0]. When I used the Reverse() method directly on my int array: myIntArray.Reverse(); I notice that myIntArray[0] still comes out as 1. What is the Reverse method actually doing here?

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How to embed cover art in an MP3 file so that the iPhone player displays it when downloaded

- by Paul Dixon

I want to be able to provide a URL to a music track, and when that track is played on an iPhone, to show the cover art. I've tried embedding the cover art as an ID3 v2.3 tag, and while desktop players like VLC and Windows Media Player can see it, it seems the iPhone doesn't. Is this possible? Does anyone know of a way to achieve this - preferably a method which can be automated? Edit: this may not be possible - even if I add cover art with iTunes, the resulting file will still not have the coverart displayed when played as a download :(

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Static field in class - Is it a re-instantiated for each static method call?

- by Jamie Dixon

If I have a static class with a static field such as: private static myField = new myObject(); I then have a bunch of static methods that use myField. Is myField re-instantiated for each method call? My guess is that it's instantiated the first time a method is called that uses it and it remains in memory until the GC clears it up? Cheers for any pointers :-)

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Eliminating static properties - What patterns do I have at my disposal?

- by Jamie Dixon

I currently have a type that I inject into my controllers that's used for getting and setting session data. I use this so that I can obtain relevant session information as _sessionData.Username rather than using Session["username"]. I'd like to use this session information across all of my views and would previously have done this by making the SessionData members static instead of injecting the SessionData class into my controller. I want to avoid using static members as well as having to pass the object to the view in each controller. What patterns best suit this type of scenario? What do you do to solve this same problem?

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Agile version control?

- by Paul Dixon

I'm trying to work out a good method to manage code changes on a large project with multiple teams. We use subversion at the moment, but I want more flexibility in building a new release than I seem to be able to get with subversion. Here's roughly I want: for each developer to create easily identifiable patches for the project. Each patch delivers a complete user story (a releasable feature or fix). It might encompass many changes to many files. developers are able to easily apply and remove their own and other patches to facilitate testing release manager selects the patches to be used in the next release into a new branch branch is tested, fixes merged in, and ultimately merged into live teams can then pull these changes back down into their sandboxes. I'm looking at stacked git as a way of achieving this, but what other tools or techniques can deliver this sort of workflow?

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Injecting a dependancy into a base class

- by Jamie Dixon

Hey everyone, I'm on a roll today with questions. I'm starting out with Dependency Injection and am having some trouble injecting a dependency into a base class. I have a BaseController controller which my other controllers inherit from. Inside of this base controller I do a number of checks such as determining if the user has the right privileges to view the current page, checking for the existence of some session variables etc. I have a dependency inside of this base controller that I'd like to inject using Ninject however when I set this up as I would for my other dependencies I'm told by the compiler that: Error 1 'MyProject.Controllers.BaseController' does not contain a constructor that takes 0 argument This makes sense but I'm just not sure how to inject this dependency. Should I be using this pattern of using a base controller at all or should I be doing this in a more efficient/correct way?

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Updating database row from model

- by Jamie Dixon

Hey everyone, I'm haing a few problems updating a row in my database using Linq2Sql. Inside of my model I have two methods for updating and saving from my controller, which in turn receives an updated model from my view. My model methods like like: public void Update(Activity activity) { _db.Activities.InsertOnSubmit(activity); } public void Save() { _db.SubmitChanges(); } and the code in my Controller likes like: [HttpPost] public ActionResult Edit(Activity activity) { if (ModelState.IsValid) { UpdateModel<Activity>(activity); _activitiesModel.Update(activity); _activitiesModel.Save(); } return View(activity); } The problem I'm having is that this code inserts a new entry into the database, even though the model item i'm inserting-on-submit contains a primary key field. I've also tried re-attaching the model object back to the data source but this throws an error because the item already exists. Any pointers in the right direction will be greatly appreciated. UPDATE: I'm using dependancy injection to instantiate my datacontext object as follows: IMyDataContext _db; public ActivitiesModel(IMyDataContext db) { _db = db; }

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Does it make sense to have a model with only static methods?

- by Jamie Dixon

Hey everyone, I have an ASP.NET MVC 2 project that I'm working on and I'm wondering where I should place some of my code. I currently have a UsersModel which consists of a bunch of static methods that operate against my data context. These methods include such things as: UserExistsInDatabase, UserIsRegisteredForActivity, GetUserIdFromFacebookId etc etc. Should these methods be inside a UsersModel class or would they be more suited to a user helper class outside of the models context? Cheers for any pointers.

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need to print 5 column list in alpha order, vertically

- by Brad

Have a webpage that will be viewed by mainly IE users, so CSS3 is out of the question. I want it to list like: A D G B E H C F I Here is the function that currently lists like: A B C D E F G H I function listPhoneExtensions($group,$group_title) { $adldap = new adLDAP(); $group_membership = $adldap->group_members(strtoupper($group),FALSE); sort($group_membership); print " <a name=\"".strtolower($group_title)."\"></a> <h2>".$group_title."</h2> <ul class=\"phone-extensions\">"; foreach ($group_membership as $i => $username) { $userinfo = $adldap->user_info($username, array("givenname","sn","telephonenumber")); $displayname = "".substr($userinfo[0]["sn"][0],0,9).", ".substr($userinfo[0]["givenname"][0],0,9)."".$userinfo[0]["telephonenumber"][0].""; if($userinfo[0]["sn"][0] != "" && $userinfo[0]["givenname"][0] != "" && $userinfo[0]["telephonenumber"][0] != "") { print "<li>".$displayname."</li>"; } } print "</ul><a href=\"#top\" class=\"link-to-top\">↑ top</a>"; } Example rendered html: <ul class="phone-extensions"> <li>Barry Bonds8281</li> <li>Gerald Clark8211</li> <li>Juan Dixon8282</li> <li>Omar Ebbs8252</li> <li>Freddie Flank2281</li> <li>Jerry Gilmore4231</li> <li>Kim Moore5767</li> <li>Barry Bonds8281</li> <li>Gerald Clark8211</li> <li>Juan Dixon8282</li> <li>Omar Ebbs8252</li> <li>Freddie Flank2281</li> <li>Jerry Gilmore4231</li> <li>Kim Moore5767</li> <li>Barry Bonds8281</li> <li>Gerald Clark8211</li> <li>Juan Dixon8282</li> <li>Omar Ebbs8252</li> <li>Freddie Flank2281</li> <li>Jerry Gilmore4231</li> <li>Kim Moore5767</li> </ul> Any help is appreciated to getting it to list alpha vertically.

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Can EC2 instances be set up to come from different IP ranges?

- by Joshua Frank

I need to run a web crawler and I want to do it from EC2 because I want the HTTP requests to come from different IP ranges so I don't get blocked. So I thought distributing this on EC2 instances might help, but I can't find any information about what the outbound IP range will be. I don't want to go to the trouble of figuring out the extra complexity of EC2 and distributed data, only to find that all the instances use the same address block and I get blocked by the server anyway. NOTE: This isn't for a DoS attack or anything. I'm trying to harvest data for a legitimate business purpose, I'm respecting robots.txt, and I'm only making one request per second, but the host is still shutting me down. Edit: Commenter Paul Dixon suggests that the act of blocking even my modest crawl indicates that the host doesn't want me to crawl them and therefore that I shouldn't do it (even assuming I can work around the blocking). Do people agree with this?

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Implementing Model-level caching

- by Byron

I was posting some comments in a related question about MVC caching and some questions about actual implementation came up. How does one implement a Model-level cache that works transparently without the developer needing to manually cache, yet still remains efficient? I would keep my caching responsibilities firmly within the model. It is none of the controller's or view's business where the model is getting data. All they care about is that when data is requested, data is provided - this is how the MVC paradigm is supposed to work. (Source: Post by Jarrod) The reason I am skeptical is because caching should usually not be done unless there is a real need, and shouldn't be done for things like search results. So somehow the Model itself has to know whether or not the SELECT statement being issued to it worthy of being cached. Wouldn't the Model have to be astronomically smart, and/or store statistics of what is being most often queried over a long period of time in order to accurately make a decision? And wouldn't the overhead of all this make the caching useless anyway? Also, how would you uniquely identify a query from another query (or more accurately, a resultset from another resultset)? What about if you're using prepared statements, with only the parameters changing according to user input? Another poster said this: I would suggest using the md5 hash of your query combined with a serialized version of your input arguments. This would require twice the number of serialization options. I was under the impression that serialization was quite expensive, and for large inputs this might be even worse than just re-querying. And is the minuscule chance of collision worth worrying about? Conceptually, caching in the Model seems like a good idea to me, but it seems in practicality the developer should have direct control over caching and write it into the controller. Thoughts/ideas? Edit: I'm using PHP and MySQL if that helps to narrow your focus.

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