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• parse a special xml in python

  - by zhaojing

  I have s special xml file like below: <alarm-dictionary source="DDD" type="ProxyComponent"> <alarm code="402" severity="Alarm" name="DDM_Alarm_402"> <message>Database memory usage low threshold crossed</message> <description>dnKinds = database type = quality_of_service perceived_severity = minor probable_cause = thresholdCrossed additional_text = Database memory usage low threshold crossed </description> </alarm> ... </alarm-dictionary> I know in python, I can get the "alarm code", "severity" in tag alarm by: for alarm_tag in dom.getElementsByTagName('alarm'): if alarm_tag.hasAttribute('code'): alarmcode = str(alarm_tag.getAttribute('code')) And I can get the text in tag message like below: for messages_tag in dom.getElementsByTagName('message'): messages = "" for message_tag in messages_tag.childNodes: if message_tag.nodeType in (message_tag.TEXT_NODE, message_tag.CDATA_SECTION_NODE): messages += message_tag.data But I also want to get the value like dnkind(database), type(quality_of_service), perceived_severity(thresholdCrossed) and probable_cause(Database memory usage low threshold crossed ) in tag description. That is, I also want to parse the content in the tag in xml. Could anyone help me with this? Thanks a lot!

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• JAR files, don't they just bloat and slow Java down?

  - by Josamoto

  Okay, the question might seem dumb, but I'm asking it anyways. After struggling for hours to get a Spring + BlazeDS project up and running, I discovered that I was having problems with my project as a result of not including the right dependencies for Spring etc. There were .jars missing from my WEB-INF/lib folder, yes, silly me. After a while, I managed to get all the .jar files where they belong, and it comes at a whopping 12.5MB at that, and there's more than 30 of them! Which concerns me, but it probably and hopefully shouldn't be concerned. How does Java operate in terms of these JAR files, they do take up quite a bit of hard drive space, taking into account that it's compressed and compiled source code. So that can really quickly populate a lot of RAM and in an instant. My questions are: Does Java load an entire .jar file into memory when say for instance a class in that .jar is instantiated? What about stuff that's in the .jar that never gets used. Do .jars get cached somehow, for optimized application performance? When a single .jar is loaded, I understand that the thing sits in memory and is available across multiple HTTP requests (i.e. for the lifetime of the server instance running), unlike PHP where objects are created on the fly with each request, is this assumption correct? When using Spring, I'm thinking, I had to include all those fiddly .jars, wouldn't I just be better off just using native Java, with say at least and ORM solution like Hibernate? So far, Spring just took extra time configuring, extra hard drive space, extra memory, cpu consumption, so I'm concerned that the framework is going to cost too much application performance just to get for example, IoC implemented with my BlazeDS server. There still has to come ORM, a unit testing framework and bits and pieces here and there. It's just so easy to bloat up a project quickly and irresponsibly easily. Where do I draw the line?

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• Django ModelForm Imagefield Upload

  - by Wei Xu

  I am pretty new to Django and I met a problem in handling image upload using ModelForm. My model is as following: class Project(models.Model): name = models.CharField(max_length=100) description = models.CharField(max_length=2000) startDate = models.DateField(auto_now_add=True) photo = models.ImageField(upload_to="projectimg/", null=True, blank=True) And the modelform is as following: class AddProjectForm(ModelForm): class Meta: model = Project widgets = { 'description': Textarea(attrs={'cols': 80, 'rows': 50}), } fields = ['name', 'description', 'photo'] And the View function is: def addProject(request, template_name): if request.method == 'POST': addprojectform = AddProjectForm(request.POST,request.FILES) print addprojectform if addprojectform.is_valid(): newproject = addprojectform.save(commit=False) print newproject print request.FILES newproject.photo = request.FILES['photo'] newproject.save() print newproject.photo else: addprojectform = AddProjectForm() newProposalNum = projectProposal.objects.filter(solved=False).count() return render(request, template_name, {'addprojectform':addprojectform, 'newProposalNum':newProposalNum}) the template is: <form class="bs-example form-horizontal" method="post" action="">{% csrf_token %} <h2>Project Name</h2><br> {{ addprojectform.name }}<br> <h2>Project Description</h2> {{ addprojectform.description }}<br> <h2>Image Upload</h2><br> {{ addprojectform.photo }}<br> <input type="submit" class="btn btn-success" value="Add Project"> </form> Can anyone help me or could you give an example of image uploading? Thank you!

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• Code refactoring c# question around several if statements performing the same check

  - by James Radford

  I have a method that has a load of if statements that seems a bit silly although I'm not sure how to improve the code. Here's an example. This logic was inside the view which is now in the controller which is far better but is there something I'm missing, maybe a design pattern that stops me having to check against panelCount < NumberOfPanelsToShow and handling the panelCount every condition? Maybe not, just feels ugly! Many thanks if (model.Train && panelCount < NumberOfPanelsToShow) { panelTypeList.Add(TheType.Train); panelCount++; } if (model.Car && panelCount < NumberOfPanelsToShow) { panelTypeList.Add(TheType.Car); panelCount++; } if (model.Hotel && panelCount < NumberOfPanelsToShow) { panelTypeList.Add(TheType.Hotel); panelCount++; } ...

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• How to limit TCP writes to particular size and then block untlil the data is read

  - by ustulation

  {Qt 4.7.0 , VS 2010} I have a Server written in Qt and a 3rd party client executable. Qt based server uses QTcpServer and QTcpSocket facilities (non-blocking). Going through the articles on TCP I understand the following: the original implementation of TCP mentioned the negotiable window size to be a 16-bit value, thus maximum being 65535 bytes. But implementations often used the RFC window-scale-extension that allows the sliding window size to be scalable by bit-shifting to yield a maximum of 1 gigabyte. This is implementation defined. This could have resulted in majorly different window sizes on receiver and sender end as the server uses Qt facilities without hardcoding any window size limit. Client 1st asks for all information it can based on the previous messages from the server before handling the new (accumulating) incoming messages. So at some point Server receives a lot of messages each asking for data of several MB's. This the server processes and puts it into the sender buffer. Client however is unable to handle the messages at the same pace and it seems that client’s receiver buffer is far smaller (65535 bytes maybe) than sender’s transmit window size. The messages thus get accumulated at sender’s end until the sender’s buffer is full too after which the TCP writes on sender would block. This however does not happen as sender buffer is much larger. Hence this manifests as increase in memory consumption on the sender’s end. To prevent this from happening, I used Qt’s socket’s waitForBytesWritten() with timeout set to -1 for infinite waiting period. This as I see from the behaviour blocks the thread writing TCP data until the data has actually been sensed by the receiver’s window (which will happen when earlier messages have been processed by the client at application level). This has caused memory consumption at Server end to be almost negligible. is there a better alternative to this (in Qt) if i want to restrict the memory consumption at server end to say x MB's? Also please point out if any of my understandings is incorrect.

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• zend-framework doctrine, and mvc pattern: what should connect data between models and forms?

  - by Skirmantas

  I am learning Zend Framework and Doctrine. I am wondering what is the best practice to connect forms to models and vice versa. I don't know where I should put my code. I have seen in Zendcast video tutorials where author creates methods like mapFormToRecord and mapRecordToForm in form class. Well I guess it is very handy when form is sophisticated and uses many records. Is it a good practice? I somehow believe that form-class should not need to know about data-records. And sometimes we might have model which is used in many forms. So It would be handy to have few functions in that model which would help to prepare data for forms. For example to give an array of id=name pairs so that it might be used in Zend_Form_Element_Select. However I would like to have a consistency. So I don't want to put this code nor in model nor in form because on different situations I act different. So only controller is what is left to deal it. However this will result in code duplication if one form will be used more than in one controller. Moreover controller gets bloated if form is not from the simple ones. Or maybe there is a consistent pattern in those data conversions between forms and models? I think that there is. At least in my simple cases. So maybe a separate class could be a solution? Where should I put such class and how should I name it? Another question: Zend_Form has validators and filter. Doctrine has validators and filters too. Which do we use and when? What is your way of dealing the connections between forms and models? (Sorry if it was hard for you to read my text. I don't have enough knowledge of English language to express myself freely)

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• Django Many-to-Many Question

  - by DZ

  My questions seems like a common problem that when I have seen any questions on it is never really asked right or not answered. So Im going to try to get the question right, and maybe someone knows how to resolve the issue, or correct my understanding. The problem: When you have a many-to-many relation ship (related_name not through) and you are trying to use the admin interface you are required to input one of the rleationships even though it does not have to exsist for you to create the first entry. Meaning you have to assign a group to an event to create the group. Wow that sounds complicated. So I can see why the question is not getting answered. Lets try the non code explanation example... First and important versions: Django 1.1.1 Phython 2.6 So I have a model where I created a many-to-many realtionship and Im using the related_name Im creating an app that is an event organizer, for simplicty lets say events although they could be anytype). For this first post Im going to stay away from the code and just try to explain. A few keys: (explaining comment) ** - many-to-many So in the model we have 1) The Main Event (this is main model) 2) Groups (link to events and their can be many events for a group) a) Events** I have simplified this example a little becuase I recognize that what does it matter. Just create the event first... But there are specific varations where that will not work. What the many-to-many related_name does it created another table with the indecies of the two other tables. Nothing says that this extra table HAS to be populated. Becuase if I look in the database and work within myPHPadmin I can create a group with out registering an event, since the connection between the two is a seperate table the DB does not care. How do I make the admin interface this realize it? Ok I know thats a lot so I hope I have explained it clearly. Thank you anyone for your comments/thoughts/advice

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• Quickly accessing files in a 'project'

  - by bbbscarter

  Hi all. I'm looking for a way to quickly open files in my project's source tree. What I've been doing so far is adding files to the file-name-cache like so: (file-cache-add-directory-recursively (concat project-root "some/sub/folder") ".*\\.\\(py\\)$") after which I can use anything-for-files to access any file in the source tree with about 4 keystrokes. Unfortunately, this solution started falling over today. I've added another folder to the cache and emacs has started running out of memory. What's weird is that this folder contains less than 25% of files I'm adding, and yet emacs memory use goes up from 20mb to 400mb on adding just this folder. The total number of files is around 2000, so this memory use seems very high. Presumably I'm abusing the file cache. Anyway, what do other people do for this? I like this solution for its simplicity and speed; I've looked at some of the many, many project management packages for emacs and none of them really grabbed me... Thanks in advance! Simon

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• How can I improve this SQL to avoid several problems with its results?

  - by Josh Curren

  I am having some problems with trying to search. Currently this will only return results that have at least 1 row in the maintenance_parts table. I would like it to return results even if there are 0 parts rows. My second problem is that when you search for a vehicle and it should return multiple results (multiple maintenance rows) it will only return 1 result for that vehicle. Some Background Info: The user has 2 fields to fill out. The fields are vehicle and keywords. The vehicle field is meant to allow searching based on the make, model, VIN, truck number (often is 2 - 3 digits or a letter prefix followed by 2 digits), and a few other fields that belong to the truck table. The keywords are meant to search most fields in the maintenance and maintenance_parts tables (things like the description of the work, parts name, parts number). The maintenance_parts table can contain 0, 1, or more rows for each maintenance row. The truck table contains exactly 1 row for every maintenance row. A truck can have multiple maintenance records. "SELECT M.maintenance_id, M.some_id, M.type_code, M.service_date, M.mileage, M.mg_id, M.mg_type, M.comments, M.work_done, MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) + MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) + MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) AS score FROM maintenance M, maintenance_parts P, truck T WHERE M.maintenance_id = P.maintenance_id AND M.some_id = T.truck_id AND M.type_code = 'truck' AND ( (MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) OR T.truck_number LIKE '%$vehicle%') OR MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) OR MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) ) AND M.status = 'A' GROUP BY maintenance_id ORDER BY score DESC, maintenance_id DESC LIMIT 0, $limit"

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• Can I split a single SQL 2008 DB Table into multiple filegroups, based on a discriminator column?

  - by Pure.Krome

  Hi folks, I've got a SQL Server 2008 R2 database which has a number of tables. Two of these tables contains a lot of large data .. mainly because one of them is VARBINARY(MAX) and the sister table is GEOGRAPHY. (Why two tables? Read Below if you're interested***) The data in these tables are geospatial shapes, such as zipcode boundaries. Now, the first 70K odd rows are for DataType = 1 the rest 5mil rows are for DataType = 2 Now, is it possible to split the table data into two files? so all rows that are for DataType != 2 goes into File_A and DataType = 2 goes into File_B? This way, when I backup the DB, I can skip adding File_B so my download is waaaaay smaller? Is this possible? I guessing you might be thinking - why not keep them as TWO extra tables? Mainly because in the code, the data is conceptually the same .. it's just happens that I want to split the storage of this model data. It really messes up my model if I now how two aggregates in my model, instead of one. ***Entity Framework doesn't like Tables with GEOGRAPHY, so i have to create a new table which transforms the GEOGRAPHY to VARBINARY, and then drop that into EF.

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• breaking datetime into constituent parts ASP.NET MVC form

  - by nick

  hi guys, i have searched the web relentlessly for this and have not found anything - which is surprising because i would think it is such a common scenario! Basically, on my model i have a DateTime field which i wish the user to populate through a form. I am using the Html helper to render all other parts of the form (along with validation) So this question is in two parts... Html Helper Firstly, is there any way to use the Html helper to split the DateTime field to be rendered as the three constituent parts of a date: day, month, year (since i do not care about the time part). This could be rendered as text boxes, drop down lists or a combination of both. Model Binding And then when the form is posted, what is the best approach for binding back up to the model? I have seen Scott Hanselmann's solution to this, but it seems a little bloated for what i need - i was hoping for a slightly more elegant solution. Is it recommended to extend DefaultModelBinder and set that as default binder (since all dates would be handled in this way) or write a class that implements IModelBionder and set it as the default binder for the DateTime type? Thanks for all the help in advance :-) i'm loving MVC but it's infuriating me that something so trivial is causing so much headaches!

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• Assigning Object to View, big MySQL resultset.

  - by A Finn

  Hello (Sorry for my bad English) Is it bad practice to assign object to view and call its methods in there? I use smarty as my template engine. In my controller I could do like this 1# $this->view->assign("name", $this->model->getName); and in my view <p>{$name}</p> OR 2# $this->view->assign("Object", $this->model); and in my view <p>{$Report->getName()}</p> Well my biggest problem is that I have to handle a big amount of data coming out from the MySQL and I thought that if I would made a method that would print out the data while looping mysql_fetch_row. Well at least I know that using html-tags in the model is a bad thing to do. So I would assign the object to the view to get the result to the right position on the page.. Reading a mysql-result to an array first may cause memory problems am I right? So what is the solution doing things MVC style.. And yes Im using a framework of my own.

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• Mixing has_one and has_and_belongs_to_many associations

  - by Thomas

  I'm trying to build a database of urls(links). I have a Category model that has and belongs to many Links. Here's the migration I ran: class CreateLinksCategories < ActiveRecord::Migration def self.up create_table :links_categories, :id => false do |t| t.references :link t.references :category end end def self.down drop_table :links_categories end end Here's the Link model: class Link < ActiveRecord::Base validates :path, :presence => true, :format => { :with => /^(#{URI::regexp(%w(http https))})$|^$/ } validates :name, :presence => true has_one :category end Here's the category model: class Category < ActiveRecord::Base has_and_belongs_to_many :links end And here's the error the console kicked back when I tried to associate the first link with the first category: >>link = Link.first => #<Link id: 1, path: "http://www.yahoo.com", created_at: "2011-01-10... >>category = Category.first => #<category id : 1, name: "News Site", created_at: "2011-01-11... >>link.category << category => ActiveRecord::StatementInvalid: SQLite3::Exception: no such column : categories.link_id: Are my associations wrong or am I missing something in the database? I expected it to find the links_categories table. Any help is appreciated.

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• Roles Provider - AccountModel

  - by Jemes

  I'm adding the Roles provider to the built in AccountModel but having some problems adding GetAllRoles in my view using the Register View Model. View Model from AccountModel public class RegisterModel { UserName, Email Etc.... [Required] [DisplayName("AllRoles")] public SelectList AllRoles { get; set; } } Roles Service added to AccountModel public interface IRolesService { SelectList GetAllRoles(); } public class RolesService : IRolesService { public SelectList GetAllRoles() { var AllRoles = new SelectList(Roles.GetAllRoles()); return AllRoles; } } Register View Page Inherits RegisterModel Form... <div class="editor-label"> <%= Html.LabelFor(m => m.ConfirmPassword) %> </div> <div class="editor-field"> <%= Html.PasswordFor(m => m.ConfirmPassword) %> <%= Html.ValidationMessageFor(m => m.ConfirmPassword) %> </div> <%= Html.DropDownListFor(m => m.AllRoles)%> I'm not sure how to populate the DropDown list with all the Roles from the View Model. Any help would be really great!!

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• Split UInt32 (audio frame) into two SInt16s (left and right)?

  - by morgancodes

  Total noob to anything lower-level than Java, diving into iPhone audio, and realing from all of the casting/pointers/raw memory access. I'm working with some example code wich reads a WAV file from disc and returns stereo samples as single UInt32 values. If I understand correctly, this is just a convenient way to return the 32 bits of memory required to create two 16 bit samples. Eventually this data gets written to a buffer, and an audio unit picks it up down the road. Even though the data is written in UInt32-sized chunks, it eventually is interpreted as pairs of 16-bit samples. What I need help with is splitting these UInt32 frames into left and right samples. I'm assuming I'll want to convert each UInt32 into an SInt16, since an audio sample is a signed value. It seems to me that for efficiency's sake, I ought to be able to simply point to the same blocks in memory, and avoid any copying. So, in pseudo-code, it would be something like this: UInt32 myStereoFrame = getFramefromFilePlayer; SInt16* leftChannel = getFirst16Bits(myStereoFrame); SInt16* rightChannel = getSecond16Bits(myStereoFrame); Can anyone help me turn my pseudo into real code?

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• CodeIgniter -- unable to use an object

  - by Smandoli

  THE SUMMARY: When I call .../index.php/product, I receive: Fatal error: Call to a member function get_prod_single() on a non-object in /var/www/sparts/main/controllers/product.php on line 16 The offending Line 16 is: $data['pn_oem'] = $this->product_model->get_prod_single($product_id); Looks like I don't know how to make this a working object. Can you help me? THE CODE: In my /Models folder I have product_model.php: <?php class Product_model extends Model { function Product_model() { parent::Model(); } function get_prod_single($product_id) { //This will be a DB lookup ... return 'foo'; //stub to get going } } ?> In my /controllers folder I have product.php: <?php class Product extends Controller { function Product() { parent::Controller(); } function index() { $this->load->model('Product_model'); $product_id = 113; // will get this dynamically $data['product_id'] = $product_id; $data['pn_oem'] = $this->product_model->get_prod_single($product_id); $this->load->view('prod_single', $data); } } ?>

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• Kohana 3, problem with m2m data adding

  - by Marek

  Hello I posted this on official forum but with no result. I am getting :Undefined index: enrollment error when trying to save data. My pivot model: class Model_Enrollment extends ORM { protected $_belongs_to = array('page' => array(), 'menugroup' => array()); } Model_Page protected $_has_many = array('templates' => array(), 'menugroups' => array('through' => 'enrollment')); Model_Menugroup protected $_has_many = array('menuitems' => array(), 'pages' => array('through' => 'enrollment')); //Overriden save() method in Model_Menugroup: public function save() { if (empty($this->created)) { $this->created = time(); } parent::save(); $this->reload(); if (! $this->is_global) { if (! empty($this->groupOwnerPagesId) { $page = ORM::factory('page'); foreach($this->groupOwnerPagesId as $id) { $this->add('enrollment', $page->find($id)); } } } } I did: I corrected table names in pivot model by changing them to singular I even now using the same name for pivot table / model = enrollment. The same as in tutorial. Just in case So the pivot table has name 'enrollment' and has 2 columns: page_id , menugroup_id I tried to add pk in pivot table, but it changed nothing I tried to add/remove db relation between pages/menugroups and pivot table (InnoDB) but with no luck I tried save all data in controller, but with the same bad result:( I am still getting the same error: Undefined index: enrollment in ORM line: $columns = array($this-_has_many[$alias]['foreign_key'], $this-_has_many[$alias]['far_key']); Could somebody tell me, what can be else wrong? I have no other ideas:( Kind regards

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• ThickBox - update inside without redirect

  - by Alex Maslakov

  ASP.NET MVC and jQuery ThickBox. I show some content in ThickBox. It includes file upload form The view multi-media.apsx (it's strange, the this editor doesn't allow start the line with "<" in the code) form action="/upload/multi-media" method="post" enctype="multipart/form-data" label for="file"File name: input type="file" name="file" id="file" / input type="submit" value="Upload" / <% if (Model.Count > 0) { foreach (FileInfo mediaFile in Model) { <img width="100px" height="100px" src="<%: ResolveUrl("~/audio.png") %>" border="0" alt="<%: mediaFile.Name %>" / //................ After file upload I redirect to /upload/multi-media action and content shows in normal window, not in ThickBox. [ActionName("multi-media"), HttpPost] public ActionResult MultiMedia(HttpPostedFileBase file) { if (file.ContentLength > 0) { file.SaveAs(GenerateNewFileName(fullFileName)); return View("multi-media", model); } } How can I stay into ThickBox after file upload? I need show content in ThickBox all the time, even after the file upload.

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• Best tree/heap data structure for fixed set of nodes with changing values + need top 20 values?

  - by user350139

  I'm writing something like a game in C++ where I have a database table containing the current score for each user. I want to read that table into memory at the start of the game, quickly change each user's score while the game is being played in response to what each user does, and then when the game ends write the current scores back to the database. I also want to be able to find the 20 or so users with the highest scores. No users will be added or deleted during the short period when the game is being played. I haven't tried it yet, but updating the database might take too much time during the period when the game is being played. Fixed set of users (might be 10,000 to 50,000 users) Will map user IDs to their score and other user-specific information. User IDs will be auto_increment values. If the structure has a high memory overhead that's probably not an issue. If the program crashes during gameplay it can just be re-started. Quickly get a user's current score. Quickly add to a user's current score (and return their current score) Quickly get 20 users with highest score. No deletes. No inserts except when the structure is first created, and how long that takes isn't critical. Getting the top 20 users will only happen every five or ten seconds, but getting/adding will happen much more frequently. If not for the last, I could just create a memory block equal to sizeof(user) * max(user id) and put each user at user id * sizeof(user) for fast access. Should I do that plus some other structure for the Top 20 feature, or is there one structure that will handle all of this together?

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• Loading more than 10 images on iPhone??

  - by SeniorLee

  I'm trying to add more than 10 pictures on ScrollView. NSUInteger i; for (i = 1; i <= numberOfImage; i++) { NSString *imageName = [NSString stringWithFormat:@"d%dimage%d.png", imageSection, i]; UIImage *image = [UIImage imageNamed:imageName]; UIImageView *imageView = [[UIImageView alloc] initWithImage:image]; // setup each frame to a default height and width, it will be properly placed when we call "updateScrollList" CGRect rect = imageView.frame; rect.size.height = kScrollObjHeight; rect.size.width = kScrollObjWidth; imageView.frame = rect; imageView.tag = i; // tag our images for later use when we place them in serial fashion [scrollView addSubview:imageView]; [imageView release]; } This code is from Apple example and it works fine. But if the variable 'i' is bigger than 10, 'UIImage *image' is empty. The imageName seems to correct. But I don't know why it does not load image. Does anybody sees the problem?? And one more thing. If I do like that, does iOS controls memory automatically? I mean it's kind of wasting memory if all (more than 10) images are loaded on memory even they are not displayed. I've heard that iOS loads images only displayed on screen and free images those are not displayed. Is that right? Thanks for reading.

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• Handling large (object) datasets with PHP

  - by Aron Rotteveel

  I am currently working on a project that extensively relies on the EAV model. Both entities as their attributes are individually represented by a model, sometimes extending other models (or at least, base models). This has worked quite well so far since most areas of the application only rely on filtered sets of entities, and not the entire dataset. Now, however, I need to parse the entire dataset (IE: all entities and all their attributes) in order to provide a sorting/filtering algorithm based on the attributes. The application currently consists of aproximately 2200 entities, each with aproximately 100 attributes. Every entity is represented by a single model (for example Client_Model_Entity) and has a protected property called $_attributes, which is an array of Attribute objects. Each entity object is about 500KB, which results in an incredible load on the server. With 2000 entities, this means a single task would take 1GB of RAM (and a lot of CPU time) in order to work, which is unacceptable. Are there any patterns or common approaches to iterating over such large datasets? Paging is not really an option, since everything has to be taken into account in order to provide the sorting algorithm.

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• Generating all possible subsets of a given QuerySet in Django

  - by Glen

  This is just an example, but given the following model: class Foo(models.model): bar = models.IntegerField() def __str__(self): return str(self.bar) def __unicode__(self): return str(self.bar) And the following QuerySet object: foobar = Foo.objects.filter(bar__lt=20).distinct() (meaning, a set of unique Foo models with bar <= 20), how can I generate all possible subsets of foobar? Ideally, I'd like to further limit the subsets so that, for each subset x of foobar, the sum of all f.bar in x (where f is a model of type Foo) is between some maximum and minimum value. So, for example, given the following instance of foobar: >> print foobar [<Foo: 5>, <Foo: 10>, <Foo: 15>] And min=5, max=25, I'd like to build an object (preferably a QuerySet, but possibly a list) that looks like this: [[<Foo: 5>], [<Foo: 10>], [<Foo: 15>], [<Foo: 5>, <Foo: 10>], [<Foo: 5>, <Foo: 15>], [<Foo: 10>, <Foo: 15>]] I've experimented with itertools but it doesn't seem particularly well-suited to my needs. I think this could be accomplished with a complex QuerySet but I'm not sure how to start.

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• Storing large numbers of varying size objects on disk

  - by Foredecker

  I need to develop a system for storing large numbers (10's to 100's of thousands) of objects. Each object is email-like - there is a main text body, and several ancillary text fields of limited size. A body will be from a few bytes, to several KB in size. Each item will have a single unique ID (probably a GUID) that identifies it. The store will only be written to when an object is added to it. It will be read often. Deletions will be rare. The data is almost all human readable text so it will be readily compressible. A system that lets me issue the I/Os and mange the memory and caching would be ideal. I'm going to keep the indexes in memory, using it to map indexes to the single (and primary) key for the objects. Once I have the key, then I'll load it from disk, or the cache. The data management system needs to be part of my application - I do not want to depend on OS services. Or separately installed packages. Native (C++) would be best, but a manged (C#) thing would be ok. I believe that a database is an obvious choice, but this needs to be super-fast for look up and loading into memory of an object. I am not experienced with data base tech and I'm concerned that general relational systems will not handle all this variable sized data efficiently. (Note, this has nothing to do with my job - its a personal project.) In your experience, what are the viable alternatives to a traditional relational DB? Or would a DB work well for this?

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• A question of long-running and disruptive branches

  - by Matt Enright

  We are about to begin prototyping a new application that will share some existing infrastructure assemblies with an existing application, and also involve a significant subset of the existing domain model. Parts of the domain model will likely undergo some serious changes for this new application, and the endgame for all of this, once the new application has been fully specified and is launch-ready is that we would like to re-unify the models of the two applications (as well as share a database, link functionality, etc.), but for the duration of development, prototyping, etc, we will be using a separate database so that we can change things without worrying about impact to development or use of the existing application. Since it is a prototype, there will be a pretty long window during which serious changes or rearchitecturing can occur as product management experiments with different workflows, different customer bases are surveyed, and we try and keep up. We have already made a Subversion branch, so as to not impact concurrent development on the mature application, and are toying with 2 potential ways of moving forward with this: Use the svn branch as the sole mechanism of separation. Make our changes to the existing domain models, and evaluate their impact on the existing application (and make requisite changes to ProjectA) when we have established that our long-running side branch is stable enough for re-entry to trunk. "Fork" the shared code (temporarily): Copy ProjectA.Entities to NewProject.Entities, and treat all of the NewProject code as self-contained. When all of the perturbations around the model have died down and we feel satisfied, manually re-integrate the changes (as granular or sweeping as warranted) back into ProjectA.Entities, updating ProjectA to use the improved models at each step (this can take place either before or after the subversion merge has occurred). The subversion merge will then not handle recombination of any of the heavy changes here. Note: the "fork" method only applies to the code we see significant changes in store for, and whose modification will break ProjectA - shared infrastructure stuff for example, we would just modify in place (on our branch) and let the merge sort out. Development is hard, go shopping. Naturally, after not coming to an agreement, we're turning it over to the oracle of power that is SO. Any experience with any of these methods, pain points to watch out for, something new entirely?

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• C#: Determine Type for (De-)Serialization

  - by dbemerlin

  Hi, i have a little problem implementing some serialization/deserialization logic. I have several classes that each take a different type of Request object, all implementing a common interface and inheriting from a default implementation: This is how i think it should be: Requests interface IRequest { public String Action {get;set;} } class DefaultRequest : IRequest { public String Action {get;set;} } class LoginRequest : DefaultRequest { public String User {get;set;} public String Pass {get;set;} } Handlers interface IHandler<T> { public Type GetRequestType(); public IResponse HandleRequest(IModel model, T request); } class DefaultHandler<T> : IHandler<T> // Used as fallback if the handler cannot be determined { public Type GetRequestType() { return /* ....... how to get the Type of T? ((new T()).GetType()) ? .......... */ } public IResponse HandleRequest(IModel model, T request) { /* ... */ } } class LoginHandler : DefaultHandler<LoginRequest> { public IResponse HandleRequest(IModel mode, LoginRequest request) { } } Calling class Controller { public ProcessRequest(String action, String serializedRequest) { IHandler handler = GetHandlerForAction(action); IRequest request = serializer.Deserialize<handler.GetRequestType()>(serializedRequest); handler(this.Model, request); } } Is what i think of even possible? My current Solution is that each handler gets the serialized String and is itself responsible for deserialization. This is not a good solution as it contains duplicate code, the beginning of each HandleRequest method looks the same (FooRequest request = Deserialize(serializedRequest); + try/catch and other Error Handling on failed deserialization). Embedding type information into the serialized Data is not possible and not intended. Thanks for any Hints.

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