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• Entity Attribute Value Database vs. strict Relational Model Ecommerce question

  - by Dr. Zim

  It is safe to say that the EAV/CR database model is bad. That said, Question: What database model, technique, or pattern should be used to deal with "classes" of attributes describing e-commerce products which can be changed at run time? In a good E-commerce database, you will store classes of options (like TV resolution then have a resolution for each TV, but the next product may not be a TV and not have "TV resolution"). How do you store them, search efficiently, and allow your users to setup product types with variable fields describing their products? If the search engine finds that customers typically search for TVs based on console depth, you could add console depth to your fields, then add a single depth for each tv product type at run time. There is a nice common feature among good e-commerce apps where they show a set of products, then have "drill down" side menus where you can see "TV Resolution" as a header, and the top five most common TV Resolutions for the found set. You click one and it only shows TVs of that resolution, allowing you to further drill down by selecting other categories on the side menu. These options would be the dynamic product attributes added at run time. Further discussion: So long story short, are there any links out on the Internet or model descriptions that could "academically" fix the following setup? I thank Noel Kennedy for suggesting a category table, but the need may be greater than that. I describe it a different way below, trying to highlight the significance. I may need a viewpoint correction to solve the problem, or I may need to go deeper in to the EAV/CR. Love the positive response to the EAV/CR model. My fellow developers all say what Jeffrey Kemp touched on below: "new entities must be modeled and designed by a professional" (taken out of context, read his response below). The problem is: entities add and remove attributes weekly (search keywords dictate future attributes) new entities arrive weekly (products are assembled from parts) old entities go away weekly (archived, less popular, seasonal) The customer wants to add attributes to the products for two reasons: department / keyword search / comparison chart between like products consumer product configuration before checkout The attributes must have significance, not just a keyword search. If they want to compare all cakes that have a "whipped cream frosting", they can click cakes, click birthday theme, click whipped cream frosting, then check all cakes that are interesting knowing they all have whipped cream frosting. This is not specific to cakes, just an example.

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• Unity and Object Creation

  - by William

  I am using unity as my IoC container. I am trying to implement a type of IProviderRepository. The concrete implementation has a constructor that accepts a type of IRepository. When I remove the constructor parameter from the concrete implementation everything works fine. I am sure the container is wired correctly. When I try to create the concrete object with the constructor I receive the following error: "The current build operation (build key Build Key[EMRGen.Infrastructure.Data.IRepository1[EMRGen.Model.Provider.Provider], null]) failed: The current type, EMRGen.Infrastructure.Data.IRepository1[EMRGen.Model.Provider.Provider], is an interface and cannot be constructed. Are you missing a type mapping? (Strategy type BuildPlanStrategy, index 3)". Is it possible to achieve the above mention functionality with Unity? Namely have Unity infer a concrete type from the Interface and also inject the constructor of the concrete type with the appropriate concrete object based on constructor parameters. Below is sample of my types defined in Unity and a skeleton class listing for what I want to achieve. IProviderRepository is implemented by ProviderRepository which has a constructor that expects a type of IRepository. <typeAlias alias="ProviderRepositoryInterface" type="EMRGen.Model.Provider.IProviderRepository, EMRGen.Model" /> <typeAlias alias="ProviderRepositoryConcrete" type="EMRGen.Infrastructure.Repositories.Providers.ProviderRepository, EMRGen.Infrastructure.Repositories" /> <typeAlias alias="ProviderGenericRepositoryInterface" type="EMRGen.Infrastructure.Data.IRepository`1[[EMRGen.Model.Provider.IProvider, EMRGen.Model]], EMRGen.Infrastructure" /> <typeAlias alias="ProviderGenericRepositoryConcrete" type="EMRGen.Infrastructure.Repositories.EntityFramework.ApplicationRepository`1[[EMRGen.Model.Provider.Provider, EMRGen.Model]], EMRGen.Infrastructure.Repositories" /> <!-- Provider Mapping--> <typeAlias alias="ProviderInterface" type="EMRGen.Model.Provider.IProvider, EMRGen.Model" /> <typeAlias alias="ProviderConcrete" type="EMRGen.Model.Provider.Doctor, EMRGen.Model" /> //Illustrate the call being made inside my class public class PrescriptionService { PrescriptionService() { IUnityContainer uc = UnitySingleton.Instance.Container; UnityServiceLocator unityServiceLocator = new UnityServiceLocator(uc); ServiceLocator.SetLocatorProvider(() => unityServiceLocator); IProviderRepository pRepository = ServiceLocator.Current.GetInstance<IProviderRepository>(); } } public class GenericRepository<IProvider> : IRepository<IProvider> { } public class ProviderRepository : IProviderRepository { private IRepository<IProvider> _genericProviderRepository; //Explict public default constructor public ProviderRepository(IRepository<IProvider> genericProviderRepository) { _genericProviderRepository = genericProviderRepository; } }

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• iPhone Core Data how to update the NSManagedObjects .h & .m after making changes to the data model

  - by jamone

  I have made a data model, and now I've made a 2nd version. All of the generated NSManagedObjects mapped to that data model are all version 1. Is there some way to update them to v2 without deleting them and then saying having them generated again?

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• How to implement 3D model interaction like 3D max or other game editors?

  - by Rushi

  I am developing game editor.To detect mouse hit on 3D model I am using mouse picking concept. But I want to give interactive arrows functionality like other game editor with actual arrows at the center of model in three direction. How to achieve this..?

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• Calling SubmitChanges on DataContext does not update database.

  - by drasto

  In C# ASP.NET MVC application I use Link to SQL to provide data for my application. I have got simple database schema like this: In my controller class I reference this data context called Model (as you can see on the right side of picture in properties) like this: private Model model = new Model(); I've got a table (List) of Series rendered on my page. It renders properly and I was able to add delete functionality to delete Series like this: public ActionResult Delete(int id) { model.Series.DeleteOnSubmit(model.Series.SingleOrDefault(s => s.ID == id)); model.SubmitChanges(); return RedirectToAction("Index"); } Where appropriate action link looks like this: <%: Html.ActionLink("Delete", "Delete", new { id=item.ID })%> Also create (implemented in similar way) works fine. However edit does not work. My edit looks like this: public ActionResult Edit(int id) { return View(model.Series.SingleOrDefault(s => s.ID == id)); } [HttpPost] public ActionResult Edit(Series series) { if (ModelState.IsValid) { UpdateModel(series); series.Title = series.Title + " some string to ensure title has changed"; model.SubmitChanges(); return RedirectToAction("Index"); } I have controlled that my database has a primary key set up correctly. I debugged my application and found out that everything works as expected until the line with model.SubmitChanges();. This command does not apply the changes of Title property(or any other) against the database. Please help.

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• Passing viewmodel to actionresult creates new viewmodel

  - by Jonas Bohez

  I am using a viewmodel, which i then when to send to an actionresult to use (the modified viewmodel) But in the controller, i lose the list and objects in my viewmodel. This is my view: @using PigeonFancier.Models @model PigeonFancier.Models.InschrijvingModel @using (Html.BeginForm("UpdateInschrijvingen","Melker",Model)) { <div> <fieldset> <table> @foreach (var item in Model.inschrijvingLijst) { <tr> <td>@Html.DisplayFor(model => item.Duif.Naam)</td> <td> @Html.CheckBoxFor(model => item.isGeselecteerd)</td> </tr> } </table> <input type="submit" value="Wijzigen"/> </fieldset> </div> } This is my controller, which does nothing at the moment until i can get the full viewmodel back from the view. public ActionResult UpdateInschrijvingen(InschrijvingModel inschrijvingsModel) { // inschrijvingsModel is not null, but it creates a new model before it comes here with //Use the model for some updates return RedirectToAction("Inschrijven", new { vluchtId = inschrijvingsModel.vlucht.VluchtId }); } This is the model with the List and some other objects who become null because it creates a new model when it comes back from the view to the actionresult public class InschrijvingModel { public Vlucht vlucht; public Duivenmelker duivenmelker; public List<CheckBoxModel> inschrijvingLijst { get; set; } public InschrijvingModel() { // Without this i get, No parameterless constructor defined exception. // So it uses this when it comes back from the view to make a new model } public InschrijvingModel(Duivenmelker m, Vlucht vl) { inschrijvingLijst = new List<CheckBoxModel>(); vlucht = vl; duivenmelker = m; foreach (var i in m.Duiven) { inschrijvingLijst.Add(new CheckBoxModel(){Duif = i, isGeselecteerd = i.IsIngeschrevenOpVlucht(vl)}); } } What is going wrong and how should i fix this problem please? Thanks

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• How to programmatically bind to a Core Data model?

  - by Dave Gallagher

  Hello. I have a Core Data model, and was wondering if you know how to create a binding to an Entity, programmatically? Normally you use bind:toObject:withKeyPath:options: to create a binding. But I'm having a little difficulty getting this to work with Core Data, and couldn't find anything in Apple's docs regarding doing this programmatically. The Core Data model is simple: An Entity called Book An Attribute of Book called author (NSString) I have an object called BookController. It looks like so: @interface BookController : NSObject { NSString *anAuthor; } @property (nonatomic, retain) NSString *anAuthor; // @synthesize anAuthor; inside @implementation I'd like to bind anAuthor inside BookController, to author inside a Book entity. This is how I'm attempting to wrongly do it (it partially works): // A custom class I made, providing an interface to the Core Data database CoreData *db = [[CoreData alloc] init]; // Creating a Book entity, saving it [db addMocObject:@"Book"]; [db saveMoc]; // Fetching the Book entity we just created NSArray *books = [db fetchObjectsForEntity:@"Book" withPredicate:nil withSortDescriptors:nil]; NSManagedObject *book = [books objectAtIndex:0]; // Creating the binding BookController *bookController = [[BookController alloc] init]; [bookController bind:@"anAuthor" toObject:book withKeyPath:@"author" options:nil]; // Manipulating the binding [bookController setAnAuthor:@"Bill Gates"]; Now, when updating from the perspective of bookController, things don't work quite right: // Testing the binding from the bookController's perspective [bookController setAnAuthor:@"Bill Gates"]; // Prints: "bookController's anAuthor: Bill Gates" NSLog(@"bookController's anAuthor: %@", [bookController anAuthor]); // OK! // ERROR HERE - Prints: "bookController's anAuthor: (null)" NSLog(@"Book's author: %@", [book valueForKey:@"author"]); // DOES NOT WORK! :( When updating from the perspective of the Book entity, things work fine: // ------------------------------ // Testing the binding from the Book's (Entity) perspective (this works perfect) [book setValue:@"Steve Jobs" forKey:@"author"]; // Prints: "bookController's anAuthor: Steve Jobs" NSLog(@"bookController's anAuthor: %@", [bookController anAuthor]); // OK! // Prints: "bookController's anAuthor: Steve Jobs" NSLog(@"Book's author: %@", [book valueForKey:@"author"]); // OK! It appears that the binding is partially working. I can update it on the side of the Model and it propagates up to the Controller via KVO, but if I update it on the side of the Controller, it doesn't trickle down to the Model via KVC. Any idea on what I'm doing wrong? Thanks so much for looking! :)

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• How can I add dynamic field in the model in django ?

  - by Wu Jie

  Hello, I'm using django to create a application download site. I try to write a model, that the admin can add the different download content dynamically in the admin page. For example I have a software named foobar, it have 3 different version: 1.1, 1.2, 1.3. I would like the user can admin the model by using an add button to add the download link with a download version. But I don't know how to do this in django.

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• In MVVM should the ViewModel or Model implement INotifyPropertyChanged?

  - by Edward Tanguay

  Most MVVM examples I have worked through have had the Model implement INotifyPropertyChanged, but in Josh Smith's CommandSink example the ViewModel implements INotifyPropertyChanged. I'm still cognitively putting together the MVVM concepts, so I don't know if: you have to put the INotifyPropertyChanged in the ViewModel to get CommandSink to work this is just an aberration of the norm and it doesn't really matter you should always have the Model implement INotifyPropertyChanged and this is just a mistake which would be corrected if this were developed from a code example to an application What have been others' experiences on MVVM projects you have worked on?

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• Ruby on Rails: Find records based on a method in the model?

  - by sjsc

  I'm looking to use named_scope to find records based on a method in the model. Right now I have in my Order.rb model: def self.paid collect { |order| order if order.paid? } end # the method def paid order.payments.total >= order.total_price end That works, but I can't chain it if I have a shipped named_scope: named_scope :shipped, :conditions => "shipped is true" And I wanted to do: Order.paid.shipped which doesn't work. Any ideas?

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• Microsoft Solver Foundation constraint

  - by emaster70

  Hello, I'm trying to use Microsoft Solver Foundation 2 to solve a fairly complicated situation, however I'm stuck with an UnsupportedModelException even when I dumb down the model as much as possible. Does anyone have an idea of what I'm doing wrong? Following is the least example required to reproduce the problematic behavior. var ctx = SolverContext.GetContext(); var model = ctx.CreateModel(); var someConstant = 1337.0; var decisionA = new Decision(Domain.Real, "decisionA"); var decisionB = new Decision(Domain.Real, "decisionB"); var decisionC = new Decision(Domain.Real, "decisionC"); model.AddConstraint("ca", decisionA <= someConstant); model.AddConstraint("cb", decisionB <= someConstant); model.AddConstraint("cc", decisionC <= someConstant); model.AddConstraint("mainConstraint", Model.Equal(Model.Sum(decisionA, decisionB, decisionC), someConstant)) model.AddGoal("myComplicatedGoal", GoalKind.Minimize, decisionC); var solution = ctx.Solve(); solution.GetReport().WriteTo(Console.Out); Console.ReadKey(); Please consider that my actual model should include, once complete, a few constraints in the form of a*a+b*a <= someValue, so if what I'm willing to do ultimately isn't supported, please let me know in advance. If that's the case I'd also appreciate a suggestion of some other solver with a .NET friendly interface that I could use (only well-known commercial packages, please). Thanks in advance

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• Is it possible to dynamically discover tables in an Entity Framework model ?

  - by Scott Davies

  Hi, I have co-workers working on an Entity Framework model that changes structure (entities), over time as software development progresses. I've written some utilities that interact with the tables within the model, but I'd like to have the code dynamically discover the tables. Is there a way I can do this ? Perhaps with ADO.NET to get the table names and then store them in a collection ? Thanks, Scott

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• CakePHP: Can I ignore a field when reading the Model from the DB?

  - by Daniel Magliola

  In one of my models, I have a "LONGTEXT" field that has a big dump of a bunch of stuff that I never care to read, and it slows things down, since I'm moving much more data between the DB and the web app. Is there a way to specify in the model that I want CakePHP to simply ignore that field, and never read it or do anything with it? I really want to avoid the hassle of creating a separate table and a separate model, only for this field. Thanks! Daniel

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• Jena Effects of Different Entailment Regimes

  - by blueomega

  I am trying sparql and the use of entailment. As a example i used http://www.w3.org/TR/2010/WD-sparql11-entailment-20100126/#t112 i try to put them in jena. OntClass book1= model.createClass(NS+"book1"); OntClass book2=model.createClass(NS+"book2"); OntClass book3=model.createClass(NS+"book3"); OntClass publication=model.createClass(NS+"publication"); OntClass article=model.createClass(NS+"article"); OntClass mit=model.createClass(NS+"MIT"); ObjectProperty a = model.createObjectProperty(NS+"a"); ObjectProperty publishes = model.createObjectProperty(NS+"publishes"); book1.addProperty(a, publication); book2.addProperty(a, article); publication.addSubClass(article); publishes.addRange(publication); mit.addProperty(publishes, book3); where model is type OntModel. and i used the query similar to the problem "PREFIX table: "I have correct namespace here"+ "SELECT *"+ "WHERE"+ "{"+ " ?x ?y table:publication ."+ "}"; The model was created like this. Hope OntModelSpec is ok. OntModel m = ModelFactory.createOntologyModel(OntModelSpec.OWL_MEM_RDFS_INF, null); i get as results from query x y | http://www.example.com/ontologies/sample.owl#publishes | rdfs:range | | http://www.example.com/ontologies/sample.owl#article | rdfs:subClassOf | | http://www.example.com/ontologies/sample.owl#book1 | http://www.example.com/ontologies/sample.owl#a | | http://www.example.com/ontologies/sample.owl#publication | rdfs:subClassOf | | http://www.example.com/ontologies/sample.owl#book3 | rdf:type | Can anyone give me a example, with and without entailment, so a cant try code, can get the results right.

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• django models : How to have variable number of foreign keys in a model ?

  - by Rohit

  For instance, Model Resume contains variable number of Model Project 's, What should be my models and relationships between them to achieve this ? Thanks in advance.

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• What are the pros and cons of "include foreign key columns in the model" option in EF 4

  - by Ralph Shillington

  With EF4 comes a new feature "Include foreign key columns in the model". What was the motivation behind adding this feature, and are there any particular gotcha's with either leaving it off, or turning it on when generating a model from an exisiting database?

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• Crashes in Core Data's Inferred Mapping Model Creation (Lightweight Migration). Threading Issue?

  - by enchilada

  I'm getting random crashes when creating an inferred mapping model (with Core Data's lightweight migration) within my application. By the way, I have to do it programmatically in my application while it is running. This is how I create this model (after I have made proper currentModel and newModel objects, of course): NSMappingModel *mappingModel = [NSMappingModel inferredMappingModelForSourceModel:currentModel destinationModel:newModel error:&error]; The problem is this: This method is crashing randomly. When it works, it works just fine without issues. But when it crashes, it crashes my application (instead of returning nil to signify that the method failed, as it should). By randomly, I mean that sometimes it happens and sometimes not. It is unpredictable. Now, here is the deal: I'm running this method in another thread. More precisely, it is located inside a block that is passed via GCD to run on the global main queue. I need to do this for my UI to appear crisp to the user, i.e. so that I can display a progress indicator while the work is underway. The strange thing seems to be that if I remove the GCD stuff and just let it run on the main thread, it seems to be working fine and never crashing. Thus, could it be because I'm running this on a different thread that this is crashing? I somehow find that weird because I don't believe I'm breaking any Core Data rules regarding multi-threading. In particular, I'm not passing any managed objects around, and whenever I need access to the MOC, I create a new MOC, i.e. I'm not relying on any MOC (or for that matter: anything) that has been created earlier on the main thread. Besides the little MOC stuff that occurs, occurs after the mapping model creation method, i.e. after the point at which the app crashes, so it can't possibly be a cause of the crashes under consideration here. All I'm doing is taking two MOMs and asking for a mapping model between them. That can't be wrong even under threading, now can it? Any ideas on what could be going on?

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• Django admin breaking with non-default primary_key for model with a m2m relationship ?

  - by Gj

  I have a simple Post model with a m2m field to a Tag model. The Tag had for some reason to use a non default primary key. Inside the admin page for a Post, the labels for the multiple selection field for Tags appear, but not the input field itself. I also tried using the filter_horizontal for the tags, but still only the labels appear without the actual field. Any ideas why it breaks and/or workarounds? Thanks!

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• How to insert a large number of records quickly using ADO.Net Entity Model?

  - by esac

  I am using the ADO.Net Entity Model. Everytime I create a record, I am calling _entity.AddToTable(object); _entity.SaveChanges(); What is the fastest way of inserting the data? Is there any "batch" or "SqlBulkCopy" option for entity model?

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• Qt – How to add calculated column in QsqlRelationalTableModel ?

  - by user289175

  I have an table view showed part description, quantity, price And I have a Model/View using this code model = new QSqlRelationalTableModel(this); model->setTable("parts"); model->setRelation(3,QSqlRelation("part_tbl","part_id","part_desc")); model->select(); ui->tableView->setModel(model); I need to add a new column that shows quantity * price in the table view. It's important to know I'm using QsqlRelationalTableModel Help is appreciated, Thanks in advance

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• How can I set a jQuery tab number that's present in an ASP.NET MVC model?

  - by user314241

  Hi, I have an ASP.NET MVC view on which I've placed jQuery tabs. I'm loading the tabs using: function getContentTab(index) { var url='<% = Url.Content("~/Books/GetBookTab") %/' + index; ... } I have stored the user's default tab selection in the model associated with this view. My question is this, how can I set the tab number (index) with the number in my model data? Thanks, Arnold

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• ASP.NET MVC: Why can't I set ShowForEdit model metadata with an attribute?

  - by UpTheCreek

  Why can't I set ShowForEdit model metadata with an attribute? It seems that the only attribute provided to alter this is [ScaffoldColumn], which sets both ShowForEdit and ShowForDisplay, which is not what I want to do. I want to be able to annotate the two separately from on my model.

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• Is it safe to put reference to current user in User model in Rails?

  - by Art Shayderov

  You know, I think I have to check current user in the model callbacks (like before_update). Rather than rely solely on adding where ('something.user_id = ?', 'current_user.id') in the controllers. I need something like Thread.CurrentPrincipal in .NET Is it safe to put reference to current user in User model? I'm sorry I don't really understand how it works under the hood yet. Or how you do it The Rails way? Sorry if this a silly question.

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• Bad practice to have models made up of other models?

  - by mattruma

  I have a situation where I have Model A that has a variety of properties. I have discovered that some of the properties are similar across other models. My thought was I could create Model B and Model C and have Model A be a composite with a Model B property and a Model C property. Just trying to determine if this is the best way to handle this situation.

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• Spring 3 MVC - Form Failure Causes Exception When Reloading JSP

  - by jboyd

  Using Spring 3 MVC, please bear with the long code example, it's quite simple, but I want to make sure all relevant information is posted. Basically here is the use case: There is a registration page, a user can login, OR fill out a registration form. The login form is a simple HTML form, the registration form is a more complicated, Spring bound form that uses a RegistrationFormData bean. Here is the relevant code: UserController.java ... @RequestMapping(value = "/login", method = RequestMethod.GET) public String login(Model model) { model.addAttribute("registrationInfo", new ProfileAdminFormData()); return "login"; } ... @RequestMapping(value = "/login.do", method = RequestMethod.POST) public String doLogin( @RequestParam(value = "userName") String userName, @RequestParam(value = "password") String password, Model model) { logger.info("login.do : userName=" + userName + ", password=" + password); try { getUser().login(userName, password); } catch (UserNotFoundException ex) { logger.error(ex); model.addAttribute("loginError", ex.getWebViewableErrorMessage()); return "login"; } return "redirect:/"; } ... @RequestMapping(value = "/register.do") public String register( @ModelAttribute(value = "registrationInfo") ProfileAdminFormData profileAdminFormData, BindingResult result, Model model) { //todo: redirect if (new RegistrationValidator(profileAdminFormData, result).validate()) { try { User().register(profileAdminFormData); return "index"; } catch (UserException ex) { logger.error(ex); model.addAttribute("registrationErrorMessage", ex.getWebViewableErrorMessage()); return "login"; } } return "login"; } and the JSP: ... <form:form commandName="registrationInfo" action="register.do"> ... So the problem here is that when login fails I get an exception because there is no bean "registrationInfo" in the model attributes. What I need is that regardless of the path through this controller that the "registrationInfo" bean is not null, that way if login fails, as opposed to registration, that bean is still in the model. As you can see I create the registrationInfo object explicitly in my controller in the method bound to "/login", which is what I thought was going to be kind of a setup method" Something doesn't feel right about the "/login" method which sets up the page, but I needed to that in order to get the page to render at all without throwing an exception because there is no "registrationInfo" model attribute, as needed by the form in the JSP

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