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  • Cannot return view model after POST

    - by Interfector
    HI, I am trying to return a model after a POST but I receive the following error: Exception Details: System.InvalidOperationException: Operation is not valid due to the current state of the object. Line 29: public UsersModel getUser(Int32 id) { Line 30: return ( Line 31: from users in db.NUsers Line 32: join userSettings in db.NUsersSettings The code in the controller looks like this: [AcceptVerbs( HttpVerbs.Post )] public ActionResult Edit( NUsers user ) { //Other code that doesn't affect the error :) UsersModel userDetails = this.usersObj.getUser( user.UserID ); return View( userDetails ); } The getUser method looks like this: public UsersModel getUser(Int32 id) { return ( from users in db.NUsers join userSettings in db.NUsersSettings on users.UserID equals userSettings.UserID where users.UserID == id select new UsersModel { UserId = Convert.ToInt32( users.UserID ), Email = Convert.ToString( users.Email ), FirstName = Convert.ToString( users.FirstName ), LastName = Convert.ToString( users.LastName ), Language = Convert.ToString( userSettings.Language ), Phone = Convert.ToString( users.Phone ) } ).First(); } and finally the UsersModel if you think it is relevant: public class UsersModel { public int UserId; public string Email; public string FirstName; public string LastName; public string Language; public string Phone; public List<NLanguages> Languages; public UsersModel() { Models.Languages languagesObj = new Models.Languages(); Languages = languagesObj.getLanguages(); } } Any thoughts on what might be causing the error and what can I do to fix it? Thx

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  • SQL Stored Queries - use result of query as boolean based on existence of records

    - by Christian Mann
    Just getting into SQL stored queries right now... anyway, here's my database schema (simplified for YOUR convenience): member ------ id INT PK board ------ id INT PK officer ------ id INT PK If you're into OOP, Officer Inherits Board Inherits Member. In other words, if someone is listed on the officer table, s/he is listed on the board table and the member table. I want to find out the highest privilege level someone has. So far my SP looks like this: DELIMITER // CREATE PROCEDURE GetAuthLevel(IN targetID MEDIUMINT) BEGIN IF SELECT `id` FROM `member` WHERE `id` = targetID; THEN IF SELECT `id` FROM `board` WHERE `id` = targetID; THEN IF SELECT `id` FROM `officer` WHERE `id` = targetID; THEN RETURN 3; /*officer*/ ELSE RETURN 2; /*board member*/ ELSE RETURN 1; /*general member*/ ELSE RETURN 0; /*not a member*/ END // DELIMITER ; The exact text of the error is #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT id FROM member WHERE id = targetID; THEN IF SEL' at line 4 I suspect the issue is in the arguments for the IF blocks. What I want to do is return true if the result-set is at least one -- i.e. the id was found in the table. Do any of you guys see anything to do here, or should I reconsider my database design into this:? person ------ id INT PK level SMALLINT

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  • Magento resource model for table with compound primary key

    - by sdek
    I am creating a custom module for a Magento ecommerce site, and the module will center around a new (ie, custom) table that has a compound/composite primary key, or rather the table has two columns that make up the primary key. Does anybody know how to create your models/resource models based on a table with a compound key? To give a few more details, I have looked up several tutorials and also used the excellent moduleCreator script. But it seems like all the tutorials revolve around the table having a PK with just one column in it. Something like this: class <Namespace>_<Module>_Model_Mysql4_<Module> extends Mage_Core_Model_Mysql4_Abstract { public function _construct(){ $this->_init('<module_alias>/<table_alias>', '<table_primary_key_id>'); } } Also, I just noticed that looking at the database model almost all tables have a single primary key. I understand this has much to do with the EAV-style db structure, but still is it possible to use a table with a compound PK? I want to stick with the Magento framework/conventions if possible. Is it discouraged? Should I just change the structure of my custom table to have some dummy id column? I do have the ability to do that, but geez! (Another side note that I thought I would mention is that it looks like the Zend Framework provides a way to base a class on a table with compound primary key (see Example #20 on this page - about half-way down), so it seems that the Magento framework should also provide for it... I just don't see how.)

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  • Facade Design Patterns and Subclassing

    - by Code Sherpa
    Hi. I am using a facade design pattern for a C# program. The program basically looks like this... public class Api { #region Constants private const int version = 1; #endregion #region Private Data private XProfile _profile; private XMembership _membership; private XRoles _role; #endregion Private Data public Api() { _membership = new XMembership(); _profile = new XProfile(); _role = new XRoles(); } public int GetUserId(string name) { return _membership.GetIdByName(name); } } Now, as I would like subclass my methods into three categories: Role, Profile, and Member. This will be easier on the developers eye because both Profile and Membership expose a lot of methods that look similar (and a few by Role). For example, getting a user's ID would look like: int _id = Namespace.Api.Member.GetUserId("Henry222"); Can somebody "illustrate" how subclassing should work in this case to achieve the effect I am looking for? Thanks in advance.

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  • Fastest Method to Learn Web Design for a Developer

    - by hekevintran
    I am a Web developer and in my projects I have noticed that my weakest point is not being good at the front-end design. Relying on other designers can be annoying if they are not able to produce as quickly as I want. My perspective on HTML/CSS is that it is basically a big hack that amazingly works. There are too many CSS and browser specific bugs/quirks to learn and remember them all without spending extreme amounts of time trying to untangle everything. Is there a fast track route to getting CSS into my brain? I have looked at some CSS books, but to me they really read as long lists of how to render things correctly in IE6 and how to make corners rounded. (Seriously why does it require so many tricks to make a sharp corner round? On any platform but the Web this would be called a major oversight.) Does there exist something that does the analogous to CSS that jQuery does for JavaScript? Using jQuery you don't need to know JavaScript well to make things that work. I am not interested in learning why IE6 does things in weird ways because I don't care about supporting it at all. I am more interested in a method of learning how to use CSS to do what I want without spending hours and hours reading obscure blogs.

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  • Rails Polymorphic Association with multiple associations on the same model

    - by Matt Rogish
    My question is essentially the same as this one: http://stackoverflow.com/questions/1168047/polymorphic-association-with-multiple-associations-on-the-same-model However, the proposed/accepted solution does not work, as illustrated by a commenter later. I have a Photo class that is used all over my app. A post can have a single photo. However, I want to re-use the polymorphic relationship to add a secondary photo. Before: class Photo belongs_to :attachable, :polymorphic => true end class Post has_one :photo, :as => :attachable, :dependent => :destroy end Desired: class Photo belongs_to :attachable, :polymorphic => true end class Post has_one :photo, :as => :attachable, :dependent => :destroy has_one :secondary_photo, :as => :attachable, :dependent => :destroy end However, this fails as it cannot find the class "SecondaryPhoto". Based on what I could tell from that other thread, I'd want to do: has_one :secondary_photo, :as => :attachable, :class_name => "Photo", :dependent => :destroy Except calling Post#secondary_photo simply returns the same photo that is attached via the Photo association, e.g. Post#photo === Post#secondary_photo. Looking at the SQL, it does WHERE type = "Photo" instead of, say, "SecondaryPhoto" as I'd like... Thoughts? Thanks!

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  • Rails model relations depending on count of nested relations

    - by Lowgain
    I am putting together a messaging system for a rails app I am working on. I am building it in a similar fashion to facebook's system, so messages are grouped into threads, etc. My related models are: MsgThread - main container of a thread Message - each message/reply in thread Recipience - ties to user to define which users should subscribe to this thread Read - determines whether or not a user has read a specific message My relationships look like class User < ActiveRecord::Base #stuff... has_many :msg_threads, :foreign_key => 'originator_id' #threads the user has started has_many :recipiences has_many :subscribed_threads, :through => :recipiences, :source => :msg_thread #threads the user is subscribed to end class MsgThread < ActiveRecord::Base has_many :messages has_many :recipiences belongs_to :originator, :class_name => "User", :foreign_key => "originator_id" end class Recipience < ActiveRecord::Base belongs_to :user belongs_to :msg_thread end class Message < ActiveRecord::Base belongs_to :msg_thread belongs_to :author, :class_name => "User", :foreign_key => "author_id" end class Read < ActiveRecord::Base belongs_to :user belongs_to :message end I'd like to create a new selector in the user sort of like: has_many :updated_threads, :through => :recipiencies, :source => :msg_thread, :conditions => {THREAD CONTAINS MESSAGES WHICH ARE UNREAD (have no 'read' models tying a user to a message)} I was thinking of either writing a long condition with multiple joins, or possibly writing giving the model an updated_threads method to return this, but I'd like to see if there is an easier way first. Any ideas? Also, if there is something fundamentally wrong with my structure for this functionality let me know! Thanks!!

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  • Sweave/R - Automatically generating an appendix that contains all the model summaries/plots/data pro

    - by John Horton
    I like the idea of making research available at multiple levels of detail i.e., abstract for the casually curious, full text for the more interested, and finally the data and code for those working in the same area/trying to reproduce your results. In between the actual text and the data/code level, I'd like to insert another layer. Namely, I'd like to create a kind of automatically generated appendix that contains the full regression output, diagnostic plots, exploratory graphs data profiles etc. from the analysis, regardless of whether those plots/regressions etc. made it into the final paper. One idea I had was to write a script that would examine the .Rnw file and automatically: Profile all data sets that are loaded (sort of like the Hmisc(?) package) Summarize all regressions - i.e., run summary(model) for all models Present all plots (regardless of whether they made it in the final version) The idea is to make this kind of a low-effort, push-button sort of thing as opposed to a formal appendix written like the rest of a paper. What I'm looking for is some ideas on how to do this in R in a relatively simple way. My hunch is that there is some way of going through the namespace, figuring out what something is and then dumping into a PDF. Thoughts? Does something like this already exist?

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  • Mimic remote API or extend existing django model

    - by drozzy
    I am in a process of designing a client for a REST-ful web-service. What is the best way to go about representing the remote resource locally in my django application? For example if the API exposes resources such as: List of Cars Car Detail Car Search Dealership summary So far I have thought of two different approaches to take: Try to wrangle the django's models.Model to mimic the native feel of it. So I could try to get some class called Car to have methods like Car.objects.all() and such. This kind of breaks down on Car Search resources. Implement a Data Access Layer class, with custom methods like: Car.get_all() Car.get(id) CarSearch.search("blah") So I will be creating some custom looking classes. Has anyone encoutered a similar problem? Perhaps working with some external API's (i.e. twitter?) Any advice is welcome. PS: Please let me know if some part of question is confusing, as I had trouble putting it in precise terms.

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  • How would you design a question/answer view (iPhone SDK)

    - by Aurélien Vallée
    I'm new to iPhone development, and I have a question on how to create a view for my application. The view should display a problem (using formatted/syntax highlighted text), and multiple possible answers. The user should be able to click on an answer to validate it. Currently, I am trying to use a UITableView embedding UIWebView as contentView. That allows me to display formatted text easily. The problem is that it is a real pain to compute and adjust the height of the cells. I have to preload the webview, call sizeToFit, get its height, and update the cell accordingly. This process should be done for the problem and the answers (as they are HTML formatted text too). It's such a pain that I am planning to switch to something else. I thought using only a big UIWebView and design everything in HTML. But I looked at some articles describing how to communicate between the HTML page and the ObjectiveC code. This seems to involve some awful tricks too... So... that's it, I don't really know what I should do. I guess some of you dealt with such things before, and would provide some greatly appreciated tips :)

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  • MVC Localization of Default Model Binder

    - by Dai Bok
    Hi, I am currently trying to figure out how to localize the error messages generated by MVC. Let me use the default model binder as an example, so I can explain the problem. Assuming I have a form, where a user enters thier age. The user then enters "ten" in to the form, but instead of getting the expected error of "Age must be beween 18 and 25." the message "The value 'ten' is not valid for Age." is displayed. The entity's age property is defined below: [Range(18, 25, ErrorMessageResourceType = typeof (Errors), ErrorMessageResourceName = "Age", ErrorMessage = "Range_ErrorMessage")] public int Age { get; set; } After some digging, I notice that this error text comes from the System.Web.Mvc.Resources.DefaultModelBinder_ValueInvalid in the MvcResources.resx file. Now, how can create localized versions of this file? As A solution, for example, should I download MVC source and add MvcResources.en_GB.resx, MvcResources.fr_FR.resx, MvcResources.es_ES.resx and MvcResources.de_DE.resx, and then compile my own version of MVC.dll? But I don't like this idea. Any one else know a better way?

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  • NHibernate: how to handle entity-based validation using session-per-request pattern, without control

    - by Seth Petry-Johnson
    What is the best way to do entity-based validation (each entity class has an IsValid() method that validates its internal members) in ASP.NET MVC, with a "session-per-request" model, where the controller has zero (or limited) knowledge of the ISession? Here's the pattern I'm using: Get an entity by ID, using an IFooRepository that wraps the current NH session. This returns a connected entity instance. Load the entity with potentially invalid data, coming from the form post. Validate the entity by callings its IsValid() method. If valid, call IFooRepository.Save(entity). Otherwise, display error message. The session is currently opened when the request begins and flushed when the request ends. Since my entity is connected to a session, flushing the session attempts to save the changes even if the object is invalid. What's the best way to keep validation logic in the entity class, limit controller knowledge of NH, and avoid saving invalid changes at the end of a request? Option 1: Explicitly evict on validation failure, implicitly flush: if the validation fails, I could manually evict the invalid object in the action method. If successful, I do nothing and the session is automatically flushed. Con: error prone and counter-intuitive ("I didn't call .Save(), why are my invalid changes being saved anyways?") Option 2: Explicitly flush, do nothing by default: By default I can dispose of the session on request end, only flushing if the controller indicates success. I'd probably create a SaveChanges() method in my base controller that sets a flag indicating success, and then query this flag when closing the session at request end. Pro: More intuitive to troubleshoot if dev forgets this step [relative to option 1] Con: I have to call IRepository.Save(entity)' and SaveChanges(). Option 3: Always work with disconnected objects: I could modify my repositories to return disconnected/transient objects, and modify the Repo.Save() method to re-attach them. Pro: Most intuitive, given that controllers don't know about NH. Con: Does this defeat many of the benefits I'd get from NH?

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  • .Net Architecture challenge: The Change-prone Frankestein Model

    - by SDReyes
    Good Morning SO! We've been scratching our heads with with this interesting scenario at the office, and we're anxious to hear your ideas and approaches: We have a database, whose schema is prone to changes -lets call it Prony-. (is used to store configuration parameters for embedded devices. so if the embedded devices guy need a new table, property or relationship for the model, he should be able to adapt the schema in a easy way -happens so often- ). Prony needs a web interface to create/edit its data. We have another database containing data that also need to be loaded to the devices, after making some transformations - lets call this one Oddy- (this data it's generated by an already existent administrative web application). Finally we have Tracy, a server that communicates our DBs and our embedded devices. She should to auto-adapt herself, to our dbs schema changes and serialize the data to the devices. Nice puzzle, don't think so? : ) Our current candidates: Rady: The fast Lets create some views in Prony that make the data transformation from Oddy. then use DynamicData (or some RAD tool) to create/update a simple web interface for Prony (so he can even consult the transformated data from coming from Prony : ). About Tracy, she will need to be recompiled to update her DB schema (Entity framework should work) and use Reflection to explore recursively the schema and serialize data. Cons: We would have to recompile Tracy and the Prony's web interface. What do you think of the candidate(s)? What would you do?

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  • Applying policy based design question

    - by Arthur
    I've not read the Modern C++ Design book but have found the idea of behavior injection through templates interesting. I am now trying to apply it myself. I have a class that has a logger that I thought could be injected as a policy. The logger has a log() method which takes an std::string or std::wstring depending on its policy: // basic_logger.hpp template<class String> class basic_logger { public: typedef String string_type; void log(const string_type & s) { ... } }; typedef basic_logger<std::string> logger; typedef basic_logger<std::wstring> wlogger; // reader.hpp template<class Logger = logger> class reader { public: typedef Logger logger_type; void read() { _logger.log("Reading..."); } private: logger_type _logger; }; Now the questing is, should the reader take a Logger as an argument, like above, or should it take a String and then instantiate a basic_logger as an instance variable? Like so: template<class String> class reader { public: typedef String string_type; typedef basic_logger<string_type> logger_type; // ... private: logger_type _logger; }; What is the right way to go?

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  • Error while uploading file method in Client Object Model Sharepoint 2010

    - by user1481570
    Error while uploading file method in Client Object Model + Sharepoint 2010. Once the file got uploaded. After that though the code compiles with no error I get the error while executing "{"Value does not fall within the expected range."} {System.Collections.Generic.SynchronizedReadOnlyCollection} I have a method which takes care of functionality to upload files /////////////////////////////////////////////////////////////////////////////////////////// public void Upload_Click(string documentPath, byte[] documentStream) { String sharePointSite = "http://cvgwinbasd003:28838/sites/test04"; String documentLibraryUrl = sharePointSite +"/"+ documentPath.Replace('\\','/'); //////////////////////////////////////////////////////////////////// //Get Document List List documentsList = clientContext.Web.Lists.GetByTitle("Doc1"); var fileCreationInformation = new FileCreationInformation(); //Assign to content byte[] i.e. documentStream fileCreationInformation.Content = documentStream; //Allow owerwrite of document fileCreationInformation.Overwrite = true; //Upload URL fileCreationInformation.Url = documentLibraryUrl; Microsoft.SharePoint.Client.File uploadFile = documentsList.RootFolder.Files.Add( fileCreationInformation); //uploadFile.ListItemAllFields.Update(); clientContext.ExecuteQuery(); } ///////////////////////////////////////////////////////////////////////////////////////////////// In the MVC 3.0 application in the controller I have defined the following method to invoke the upload method. ////////////////////////////////////////////////////////////////////////////////////////////////// public ActionResult ProcessSubmit(IEnumerable<HttpPostedFileBase> attachments) { System.IO.Stream uploadFileStream=null; byte[] uploadFileBytes; int fileLength=0; foreach (HttpPostedFileBase fileUpload in attachments) { uploadFileStream = fileUpload.InputStream; fileLength=fileUpload.ContentLength; } uploadFileBytes= new byte[fileLength]; uploadFileStream.Read(uploadFileBytes, 0, fileLength); using (DocManagementService.DocMgmtClient doc = new DocMgmtClient()) { doc.Upload_Click("Doc1/Doc2/Doc2.1/", uploadFileBytes); } return RedirectToAction("SyncUploadResult"); } ////////////////////////////////////////////////////////////////////////////////////////////////// Please help me to locate the error

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  • How to design a RESTful collection resource?

    - by Suresh Kumar
    I am trying to design a "collection of items" resource. I need to support the following operations: Create the collection Remove the collection Add a single item to the collection Add multiple items to the collection Remove a single item from the collection Remove multiple items from the collection This is as far as I have gone: Create collection: ==> POST /service Host: www.myserver.com Content-Type: application/xml <collection name="items"> <item href="item1"/> <item href="item2"/> <item href="item3"/> </collection> <== 201 Created Location: http://myserver.com/service/items Content-Type: application/xml ... Remove collection: ==> DELETE /service/items <== 200 OK Removing a single item from the collection: ==> DELETE /service/items/item1 <== 200 OK However, I am finding supporting the other operations a bit tricky i.e. what methods can I use to: Add single or multiple items to the collection. (PUT doesn't seem to be right here as per HTTP 1.1 RFC Remove multiple items from the collection in one transaction. (DELETE doesn't seem to right here either)

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  • Need help with WCF design

    - by Jason
    I have been tasked with creating a set of web services. We are a Microsoft shop, so I will be using WCF for this project. There is an interesting design consideration that I haven't been able to figure out a solution for yet. I'll try to explain it with an example: My WCF service exposes a method named Foo(). 10 different users call Foo() at roughly the same time. I have 5 special resources called R1, R2, R3, R4, and R5. We don't really need to know what the resource is, other than the fact that a particular resource can only be in use by one caller at a time. Foo() is responsible to performing an action using one of these special resources. So, in a round-robin fashion, Foo() needs to find a resource that is not in use. If no resources are available, it must wait for one to be freed up. At first, this seems like an easy task. I could maybe create a singleton that keeps track of which resources are currently in use. The big problem is the fact that I need this solution to be viable in a web farm scenario. I'm sure there is a good solution to this problem, but I've just never run across this scenario before. I need some sort of resource tracker / provider that can be shared between multiple WCF hosts. Any ideas from the architects out there would be greatly appreciated!

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  • set a default saving data in a selection box in HABTM model

    - by vincent low
    here is my problem which in my system. my system allow user to add event, which include date, time, places. In the other hand, user are allow to choose the "Event sharing to" some of other user. So i successful to created and share to other user, when the user login which are being choose to share with the event, he is able to view for that particular event. But the problem is, when user add the event, he must choose for his own name also in the select box. If not he will be unable to read the event that he had created. So i need to save a default data to my model, which is whenever the user got choose the sharing event or not, it also will save the data to his user id. here is my code for select box, what can i edit and do to let it set a default saving value which is always save with the user own data?? input('User',array( 'label' = 'Select Related Potential', 'options' = $users, //'id'='user', 'style'='width:250px;height:100px', //'selected' = $ownUserId )); ? i try to solve by adding 1 more row to the add.ctp, but the permission just set to the own user who created it, the other user i choose is unable to read. $form-input('User',array( 'label' = 'Select Related Potential', 'options' = $users, //'id'='user', 'style'='width:250px;height:100px', 'selected' = $ownUserId )); $form-input('User',array('type'='hidden','value'=$ownUserId));

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  • Association and model data saving problem

    - by Zhlobopotam
    Developing with cakephp 1.3 (latest from github). There are 2 models bind with hasAndBelongsToMany: documents and tags. Document can have many tags in other words. I've add a new document submitting form there user can enter a list of tags separated with commas (new tag will be added, if not exist already). I looked at cakephp bakery 2.0 source code on github and found the solution. But it seems that something is wrong. class Document extends AppModel { public $hasAndBelongsToMany = array('Tag'); public function beforeSave($options = array()) { if (isset($this->data[$this->alias]['tags']) && !empty($this- >data[$this->alias]['tags'])) { $tagIds = $this->Tag->saveDocTags($this->data[$this->alias] ['tags']); unset($this->data[$this->alias]['tags']); $this->data[$this->Tag->alias][$this->Tag->alias] = $tagIds; } return true; } } class Tag extends AppModel { public $hasAndBelongsToMany = array ('Document'); public function saveDocTags($commalist = '') { if ($commalist == '') return null; $tags = explode(',',$commalist); if (empty($tags)) return null; $existing = $this->find('all', array( 'conditions' => array('title' => $tags) )); $return = Set::extract($existing,'/Tag/id'); if (sizeof($existing) == sizeof($tags)) { return $return; } $existing = Set::extract($existing,'/Tag/title'); foreach ($tags as $tag) { if (!in_array($tag, $existing)) { $this->create(array('title' => $tag)); $this->save(); $return[] = $this->id; } } return $return; } } So, new tags creation works well but document model can't save association data and tells: SQL Error: 1054: Unknown column 'Array' in 'field list' Query: INSERT INTO documents (title, content, shortnfo, date, status) VALUES ('Document with tags', '', '', Array, 1) Any ideas how to solve this problem?

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  • Problem with Railscast #197 - Nested Model Form Part 2

    - by sscirrus
    I'm trying to implement Ryan's Railscast #197 in a system with Questions, Answers, and (multiple choice) Options. http://railscasts.com/episodes/197-nested-model-form-part-2. I have successfully implemented the nesting among these forms/partials. The simpler 'check box' way to delete records works properly. The problem occurs when I try to add/delete records. I have copied the code exactly as it appears in his Railscast: #new.html.erb <%= javascript_include_tag :defaults, :cache => true %> <% f.fields_for :in_options do |builder| %> <%= render "option_fields", :f => builder %> <% end %> #_option_fields.html.erb partial <%= f.hidden_field :_destroy %> <%= link_to_function "remove", "remove_fields(this)" %> #application_helper.rb (exact same as #197) def link_to_remove_fields(name, f) f.hidden_field(:_destroy) + link_to_function(name, "remove_fields(this)") end def link_to_add_fields(name, f, association) new_object = f.object.class.reflect_on_association(association).klass.new fields = f.fields_for(association, new_object, :child_index => "new_#{association}") do |builder| render(association.to_s.singularize + "_fields", :f => builder) end link_to_function(name, h("add_fields(this, \"#{association}\", \"#{escape_javascript(fields)}\")")) end #application.js (exact same as #197. I have an Event.addbehavior below this code.) function remove_fields(link) { $(link).previous("input[type=hidden]").value = "1"; $(link).up(".fields").hide(); } function add_fields(link, association, content) { var new_id = new Date().getTime(); var regexp = new RegExp("new_" + association, "g") $(link).up().insert({ before: content.replace(regexp, new_id) }); } 2 problems: When I click on the 'remove' link it doesn't remove - it just shifts the page up or down. When I include link_to_add_fields "Add Answer", f, :answers, I get undefined method `klass' for nil:NilClass. Thanks everyone.

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  • Systems design question: DB connection management in load-balanced n-tier

    - by aoven
    I'm wondering about the best approach to designing a DB connection manager for a load-balanced n-tier system. Classic n-tier looks like this: Client -> BusinessServer -> DBServer A load-balancing solution as I see it would then look like this: +--> ... +--+ +--> BusinessServer +--+--> SessionServer --+ Client -> Gateway --+--> BusinessServer +--| +--> DBServer +--> BusinessServer +--+--------------------+ +--> ... +--+ As pictured, the business server component is being load-balanced via multiple instances, and a hardware gateway is distributing the load among them. Session server probably needs to be situated outside the load-balancing array, because it manages state, which mustn't be duplicated. Barring any major errors in design so far, what is the best way to implement DB connection management? I've come up with a couple of options, but there may be others I'm not aware of: Introduce a new Broker component between the DBServer and the other components and let it handle the DB connections. The upside is that all the connections can be managed from a single point, which is very convenient. The downside is that now there is an additional "single point of failure" in the system. Other components must go through it for every request that involves DB in some way, which also makes this a bottleneck. Move the DB connection management into BusinessServer and SessionServer components and let each handle its own DB connections. The upside is that there is no additional "single point of failure" or bottleneck components. The downside is that there is also no control over possible conflicts and deadlocks apart from what DBServer itself can provide. What else can be done? FWIW: Technology is .NET, but none of the vendor-specific stacks are used (e.g. no WCF, MSMQ or the like).

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  • Nested namespaces, correct static library design issues

    - by PeterK
    Hello all, I'm currently in the process of developing a fairly large static library which will be used by some tools when it's finished. Now since this project is somewhat larger than anything i've been involved in so far, I realized its time to think of a good structure for the project. Using namespaces is one of those logical steps. My current approach is to divide the library into parts (which are not standalone, but their purpose calls for such a separation). I have a 'core' part which now just holds some very common typedefs and constants (used by many different parts of the library). Other parts are for example some 'utils' (hash etc.), file i/o and so on. Each of these parts has its own namespace. I have nearly finished the 'utils' part and realized that my approach probably is not the best. The problem (if we want to call it so) is that in the 'utils' namespace i need something from the 'core' namespace which results in including the core header files and many using directives. So i began to think that this probably is not a good thing and should be changed somehow. My first idea is to use nested namespaces as to have something like core::utils. Since this will require some heavy refactoring i want to ask here first. What do you think? How would you handle this? Or more generally: How to correctly design a static library in terms of namespaces and code organization? If there are some guidelines or articles about it, please mentoin them too. Thanks. Note: i'm quite sure that there are more good approaches than just one. Feel free to post your ideas, suggestions etc. Since i'm designing this library i want it to be really good. The goal is to make it as clean and FAST as possible. The only problem is that i will have to integrate a LOT of existing code and refactor it, which will really be a painful process (sigh) - thats why good structure is so important)

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  • Are MEF's ComposableParts contracts instance-based?

    - by Dave
    I didn't really know how to phrase the title of my questions, so my apologies in advance. I read through parts of the MEF documentation to try to find the answer to my question, but couldn't find it. I'm using ImportMany to allow MEF to create multiple instances of a specific plugin. That plugin Imports several parts, and within calls to a specific instance, it wants these Imports to be singletons. However, what I don't want is for all instances of this plugin to use the same singleton. For example, let's say my application ImportManys Blender appliances. Every time I ask for one, I want a different Blender. However, each Blender Imports a ControlPanel. I want each Blender to have its own ControlPanel. To make things a little more interesting, each Blender can load BlendPrograms, which are also contained within their own assemblies, and MEF takes care of this loading. A BlendProgram might need to access the ControlPanel to get the speed, but I want to ensure that it is accessing the correct ControlPanel (i.e. the one that is associated with the Blender that is associated with the program!) This diagram might clear things up a little bit: As the note shows, I believe that the confusion could come from an inherently-poor design. The BlendProgram shouldn't touch the ControlPanel directly, and instead perhaps the BlendProgram should get the speed via the Blender, which will then delegate the request to its ControlPanel. If this is the case, then I assume the BlendProgram needs to have a reference to a specific Blender. In order to do this, is the right way to leverage MEF and use an ImportingConstructor for BlendProgram, i.e. [ImportingConstructor] public class BlendProgram : IBlendProgram { public BlendProgram( Blender blender) {} } And if this is the case, how do I know that MEF will use the intended Blender plugin?

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  • Active Record two belongs_to calls to the same model

    - by ethyreal
    In linking a sports event to two teams, at first this seemed to make since: events - id:integer - integer:home_team_id - integer:away_team_id teams - integer:id - string:name However I am troubled by how I would link that up in the active record model: class Event belongs_to :home_team, :class_name => 'Team', :foreign_key => "home_team_id" belongs_to :away_team, :class_name => 'Team', :foreign_key => "away_team_id" end Is that the best solution? In an answer to a similar question I was pointed to single table inheritance, and then later found polymorphic associations. Neither of which seemed to fit this association. Perhaps I am looking at this wrong, but I see no need to subclass a team into home and away teams since the distinction is only in where the game is played. I thought also about a has_many through association but that seems two much as I will only ever need two teams, but those two teams don't belong to any one event. event_teams - integer:event_id - integer:team_id - boolean:is_home Is there a cleaner more semantic way for making these associations in active record? Thanks

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  • Creating content for rails-based applications

    - by Matthias Hryniszak
    Hi, I'm facing a problem of cleaning up my application in Ruby on Rails. What I have is a pretty standard 3-panel, header and footer layout where different parts of the screen contain different functionality. By that I mean for example that the header contains (among others) a select that allows one to select parts of the application and a context-dependent menu. The main content area contains obviously the most interactive stuff whereas side panels contain quick-links with stuff like shopping-cart preview, list of potentially attractive products for the customer, a selector to narrow down the list of options... I was wondering how do I go about simplifying the design. Right now I have the stuff that provides data for the "common" stuff (as opposed to direct content that's placed in the center) called from all the actions (with a filter) but that doesn't feel right for me. I've read that "components" are also not the way to go for obvious performance reasons. Is there something that's more like component-oriented (other frameworks do have that kind of stuff - Grails: <ui:include ../>, ASP.NET MVC: <% Html.RenderAction() %>)? Best regards, Matthias.

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