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• Good way to identify similar images?

  - by Nick

  I've developed a simple and fast algorithm in PHP to compare images for similarity. Its fast (~40 per second for 800x600 images) to hash and a unoptimised search algorithm can go through 3,000 images in 22 mins comparing each one against the others (3/sec). The basic overview is you get a image, rescale it to 8x8 and then convert those pixels for HSV. The Hue, Saturation and Value are then truncated to 4 bits and it becomes one big hex string. Comparing images basically walks along two strings, and then adds the differences it finds. If the total number is below 64 then its the same image. Different images are usually around 600 - 800. Below 20 and extremely similar. Are there any improvements upon this model I can use? I havent looked at how relevant the different components (hue, saturation and value) are to the comparison. Hue is probably quite important but the others? To speed up searches I could probably split the 4 bits from each part in half, and put the most significant bits first so if they fail the check then the lsb doesnt need to be checked at all. I dont know a efficient way to store bits like that yet still allow them to be searched and compared easily. I've been using a dataset of 3,000 photos (mostly unique) and there havent been any false positives. Its completely immune to resizes and fairly resistant to brightness and contrast changes.

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• Rails - any fancy ways to handle 404s?

  - by jyoseph

  I have a rails app I built for an old site I converted from another cms (in a non-rails language, hehe). Most of the old pages are mapped to the new pages using routes.rb. But there are still a few 404s. I am a rails newb so I'm asking if there are any advanced ways to handle 404s. For example, if I was programming in my old language I'd do this: Get the URL (script_name) that was being accessed and parse it. Do a lookup in the database for any keywords, ids, etc found in the new URL. If found, redirect to the page (or if multiple records are found, show them all on a results page and let user choose). With rails I'd probably want to do :status = :moved_permanently I'm guessing? If not found, show a 404. Are there any gems/plugins or tutorials you know of that would handle such a thing, if it's even possible. Or can you explain on a high level how that can be done? I don't need a full code sample, just a push in the right direction. PS. It's a simple rails 3 app that uses a single Content model.

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• What's an effective way to move data from one open browser tab to another?

  - by slk

  I am looking for a quick way to grab some data off of one Web page and throw it into another. I don't have access to the query string in the URL of the second page, so passing the data that way is not an option. Right now, I am using a Greasemonkey user script in tandem with a JS bookmarklet trigger: javascript:doIt(); // ==UserScript== // @include public_site // @include internal_site // ==/UserScript== if (document.location.host.match(internal_site)) { var datum1 = GM_getValue("d1"); var datum2 = GM_getValue("d2"); } unsafeWindow.doIt = function() { if(document.location.host.match(public_site)) { var d1 = innerHTML of page element 1; var d2 = innerHTML of page element 2; //Next two lines use setTimeout to bypass GM_setValue restriction window.setTimeout(function() {GM_setValue("d1", d1);}, 0); window.setTimeout(function() {GM_setValue("d2", d2);}, 0); } else if(document.location.host.match(internal_site)) { document.getElementById("field1").value = datum1; document.getElementById("field2").value = datum2; } } While I am open to another method, I would prefer to stay with this basic model if possible, as this is just a small fraction of the code in doIt() which is used on several other pages, mostly to automate date-based form fills; people really like their "magic button." The above code works, but there's an interruption to the workflow: In order for the user to know which page on the public site to grab data from, the internal page has to be opened first. Then, once the GM cookie is set from the public page, the internal page has to be reloaded to get the proper information into the internal page variables. I'm wondering if there's any way to GM_getValue() at bookmarklet-clicktime to prevent the need for a refresh. Thanks!

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• What makes an effective UI for displaying versioning of structured hierarchical data

  - by Fadrian Sudaman

  Traditional version control system are displaying versioning information by grouping Projects-Folders-Files with Tree view on the left and details view on the right, then you will click on each item to look at revision history for that configuration history. Assuming that I have all the historical versioning information available for a project from Object-oriented model perspective (e.g. classes - methods - parameters and etc), what do you think will be the most effective way to present such information in UI so that you can easily navigate and access the snapshot view of the project and also the historical versioning information? Put yourself in the position that you are using a tool like this everyday in your job like you are currently using SVN, SS, Perforce or any VCS system, what will contribute to the usability, productivity and effectiveness of the tool. I personally find the classical way for display folders and files like above are very restrictive and less effective for displaying deep nested logical models. Assuming that this is a greenfield project and not restricted by specific technology, how do you think I should best approach this? I am looking for idea and input here to add values to my research project. Feel free to make any suggestions that you think is valuable. Thanks again for anyone that shares their thoughts.

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• Why is Routes.rb not loading the IPs from cache?

  - by Christian Fazzini

  I am testing this in local. My ip is 127.0.0.1. The ip_permissions table, is empty. When I browse the site, everything works as expected. Now, I want to simulate browsing the site with a banned IP. So I add the IP into the ip_permissions table via: IpPermission.create!(:ip => '127.0.0.1', :note => 'foobar', :category => 'blacklist') In Rails console, I clear the cache via; Rails.cache.clear. I browse the site. I don't get sent to pages#blacklist. If I restart the server. And browse the site, then I get sent to pages#blacklist. Why do I need to restart the server every time the ip_permissions table is updated? Shouldn't it fetch it based on cache? Routes look like: class BlacklistConstraint def initialize @blacklist = IpPermission.blacklist end def matches?(request) @blacklist.map { |b| b.ip }.include? request.remote_ip end end Foobar::Application.routes.draw do match '/(*path)' => 'pages#blacklist', :constraints => BlacklistConstraint.new .... end My model looks like: class IpPermission < ActiveRecord::Base validates_presence_of :ip, :note, :category validates_uniqueness_of :ip, :scope => [:category] validates :category, :inclusion => { :in => ['whitelist', 'blacklist'] } def self.whitelist Rails.cache.fetch('whitelist', :expires_in => 1.month) { self.where(:category => 'whitelist').all } end def self.blacklist Rails.cache.fetch('blacklist', :expires_in => 1.month) { self.where(:category => 'blacklist').all } end end

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• .save puts NULL in id field in Rails

  - by mathee

  Here's the model file: class ProfileTag < ActiveRecord::Base def self.create_or_update(options = {}) id = options.delete(:id) record = find_by_id(id) || new record.id = id record.attributes = options puts "record.profile_id is" puts record.profile_id record.save! record end end This gives me the correct print out in my log. But it also says that there's a call to UPDATE that sets profile_id to NULL. Here's some of the output in the log file: Processing ProfilesController#update (for 127.0.0.1 at 2010-05-28 18:20:54) [PUT] Parameter: {"commit"=>"Save", ...} ?[4;36;1mProfileTag Create (0.0ms)?[0m ?[0;1mINSERT INTO `profile_tags` (`reputation_value`, `updated_at`, `tag_id`, `id`, `profile_id`, `created_at`) VALUES(0, '2010-05-29 01:20:54', 1, NULL, 4, '2010-05-29 01:20:54')?[0m ?[4;35;1mSQL (2.0ms)?[0m ?[0mCOMMIT?[0m ?[4;36;1mSQL (0.0ms)?[0m ?[0;1mBEGIN?[0m ?[4;35;1mSQL (0.0ms)?[0m ?[0mCOMMIT?[0m ?[4;36;1mProfileTag Load (0.0ms)?[0m ?[0;1mSELECT * FROM `profile_tags` WHERE (`profile_tags`.profile_id = 4) ?[0m ?[4;35;1mSQL (1.0ms)?[0m ?[0mBEGIN?[0m ?[4;36;1mProfileTag Update (0.0ms)?[0m ?[0;1mUPDATE `profile_tags` SET profile_id = NULL WHERE (profile_id = 4 AND id IN (35)) ?[0m I'm not sure I understand why the INSERT puts the value into profile_id properly, but then it sets it to NULL on an UPDATE. If you need more specifics, please let me know. I'm thinking that the save functionality does many things other than INSERTs into the database, but I don't know what I need to specify so that it will properly set profile_id.

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• How to check for a null object reference when validating forms in MVC

  - by quakkels

  Hello SO, I'm experimenting with validating forms in the asp.net MVC framework. I'm focusing on server side validation for the time being. I've come across an error that I'm not sure how to rectify. System.NullReferenceException: Object reference not set to an instance of an object. The code that throws the error is: [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create([Bind(Exclude="ID")] MembersCreate mc ) { mc.Modules = ModuleListDataContext.GetModuleList(); ViewData.Model = mc; //Validation using ModelState // // //line below errors when form field is empty // if ((string)mc.Member.Username.Trim() == "") ModelState.AddModelError("Member.Username", "Username is required."); if (!ModelState.IsValid) return View(); try { // TODO: Add insert logic here return RedirectToAction("Index","Home"); } catch { return View(); } } When I put spaces in the field it performs exactly as i want, but if I leave the field blank and press submit I get the error. What's the best way to avoid this error and still validate blank form fields? Thanks all -

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• XForms relation of 'constraint' and 'required' properties

  - by Danny

  As a reference, the most similar question already asked is: http://stackoverflow.com/questions/8667849/making-xforms-enforce-the-constraint-and-type-model-item-properties-only-when-fi The difference is that I cannot use the relevant properties since I do want the field to be visible and accessible. I'm attempting to make a XForms form that has the following properties: It displays a text field named 'information'. (for the example) This field must not be required, since it may not be necessary to enter data. (Or this data will be entered at a later time.) However, if data is entered in this field, it must adhere to the specified constraint. I cannot mark the field as not relevant since this would hide the field and some data may need to be entered in it. The trouble now is that even though the field has no data in it, the constraint is still enforced (i.e. even though it is not marked as 'required'). I have taken a look at the XForms 1.1 specification, however it does not seem to describe how the properties 'required' and 'constraint' should interact. The only option I see, is to add a part to the constraint such that an empty value is allowed. e.g.: . = '' or <actual-constraint However, I don't like this. It feels like a workaround to add this to every such field. Is there any other way to express that non-required fields should not need to match the constraint for that field? (Am I missing something?)

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• Using IAM for user authentication

  - by mdavis6890

  I've read lots and lots of posts that touch on what I think should be a very common use case - but without finding exactly what I want, or a simple reason why it can't be done. I have some files on S3. I want to be able to grant certain users access to certain files, via a front end that I build. So far, I've made it work this way: I built the front end in Django, using it's built-in Users and Groups I have a model for Buckets, in which I mirror my S3 buckets. I have a m2m relationship from groups to buckets representing the S3 permissions. The user logs in and authenticates against Django's users. I grab from Django the list of buckets that the user is allowed to see I use boto to grab a list of links to files from those buckets and display to user. This works, but isn't ideal, and also just doesn't feel right. I've got to keep a mirror of the buckets, and I also have to maintain my own list of user/passwords and permissions, when AWS already has all that built in. What I really want is to simply create the users in IAM and use group permissions in IAM to control access to the S3 buckets. No duplication of data or function. My app would request a UN/PW from the user and use that to connect to IAM/S3 to pull the list of buckets and files, then display links to the user. Simple. How can I, or why can't I? Am I looking at this the wrong way? What's the "right" way to address this (I assume) very common use case?

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• android: consume key press, bypassing framework processing

  - by user360024

  What I want android to do: when user presses a single key, have the view respond, but do so without opening a text area and displaying the character associated with the key that was pressed, and without requiring that the Enter key be pressed, and without requiring that the user press Esc to make the text area go away. For example, when user presses "u" (and doesn't press Enter), that means "undo the last action", so the controller and model immediately undo the last action, then the view does an invalidate() and user sees that their last action has been undone. In other words the "u" key press should be silently processed, such that the only visual result is that user's last action has been undone. I've implemented OnKeyListener and provided an onKey() method: the class: public class MyGameView extends View implements OnKeyListener{ in the constructor: //2010jun06, phj: With onKey(), helps let this View consume key presses // before the framework gets a chance to consume the key press. setOnKeyListener((View.OnKeyListener)this); the onKey() method: public boolean onKey(View v, int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_R) { Log.d("BWA", "In onKey received keycode associated with R."); } return true; // meaning the event (key press) has been consumed, so // the framework should not handle this event. } but when user presses "u" key on the emulator keypad, a textarea is opened at the bottom of the screen, the "u" charater is displayed there, and the onKey() method doesn't execute until user presses the Enter key. Is there a way to make android do what I want? Thanks,

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• Is it possible to replace values in a queryset before sending it to your template?

  - by Issy

  Hi Guys, Wondering if it's possible to change a value returned from a queryset before sending it off to the template. Say for example you have a bunch of records Date | Time | Description 10/05/2010 | 13:30 | Testing... etc... However, based on the day of the week the time may change. However this is static. For example on a monday the time is ALWAYS 15:00. Now you could add another table to configure special cases but to me it seems overkill, as this is a rule. How would you replace that value before sending it to the template? I thought about using the new if tags (if day=1), but this is more of business logic rather then presentation. Tested this in a custom template tag def render(self, context): result = self.model._default_manager.filter(from_date__lte=self.now).filter(to_date__gte=self.now) if self.day == 4: result = result.exclude(type__exact=2).order_by('time') else: result = result.order_by('type') result[0].time = '23:23:23' context[self.varname] = result return '' However it still displays the results from the DB, is this some how related to 'lazy' evaluation of templates? Thanks! Update Responding to comments below: It's not stored wrong in the DB, its stored Correctly However there is a small side case where the value needs to change. So for example I have a From Date & To date, my query checks if todays date is between those. Now with this they could setup a from date - to date for an entire year, and the special cases (like mondays as an example) is taken care off. However if you want to store in the DB you would have to capture several more records to cater for the side case. I.e you would be capturing the same information just to cater for that 1 day when the time changes. (And the time always changes on the same day, and is always the same)

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• Building out a well-structured service layer

  - by Chris Stewart

  First, I want to say that it has been awhile since I've gotten into the kind of detail I am at currently. Lately, I've been very much in the SharePoint world and my entire thought process was focused there for quite some time. I'm very glad to be creating databases again, writing "lower level" code to deal with data access, and so forth. I'm working on a very simple web application and taking the opportunity to reacquaint myself with the way I used to structure my projects and various layers of code. For instance, I might have created something like this the last time I went about building something basic from scratch: - MyProject/ -- Domain/ --- Impl/ ---- Person -- Model/ --- IPersonRepository --- Impl/ ---- PersonRepository : IPersonRepository -- Services --- IPersonService --- Impl/ ---- PersonService : IPersonService That would have been the project I did the real work in, and then referenced in the ASP.NET project. My approach was very much inspired by what I saw from the CodeCampServer project as at that time ASP.NET MVC was still very new and it was the only open project I could find actively being developed, and by solid people at that. What ways are you going about structuring your projects and code, when it comes to a general problem you're working on? Certainly various problems can put constraints on this, but assume it's a basic problem without specific needs that affect the structure and layout of your code.

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• Enum exeeding the 65535 bytes limit of static initializer... what's best to do?

  - by Daniel Bleisteiner

  I've started a rather large Enum of so called Descriptors that I've wanted to use as a reference list in my model. But now I've come across a compiler/VM limit the first time and so I'm looking for the best solution to handle this. Here is my error : The code for the static initializer is exceeding the 65535 bytes limit It is clear where this comes from - my Enum simply has far to much elements. But I need those elements - there is no way to reduce that set. Initialy I've planed to use a single Enum because I want to make sure that all elements within the Enum are unique. It is used in a Hibernate persistence context where the reference to the Enum is stored as String value in the database. So this must be unique! The content of my Enum can be devided into several groups of elements belonging together. But splitting the Enum would remove the unique safety I get during compile time. Or can this be achieved with multiple Enums in some way? My only current idea is to define some Interface called Descriptor and code several Enums implementing it. This way I hope to be able to use the Hibernate Enum mapping as if it were a single Enum. But I'm not even sure if this will work. And I loose unique safety. Any ideas how to handle that case?

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• Spring MVC: should service layer be returning operation specific DTO's ?

  - by arrages

  In my Spring MVC application I am using DTO in the presentation layer in order to encapsulate the domain model in the service layer. The DTO's are being used as the spring form backing objects. hence my services look something like this: userService.storeUser(NewUserRequestDTO req); The service layer will translate DTO - Domain object and do the rest of the work. Now my problem is that when I want to retrieve a DTO from the service to perform say an Update or Display I can't seem to find a better way to do it then to have multiple methods for the lookup that return different DTO's like... EditUserRequestDTO userService.loadUserForEdit(int id); DisplayUserDTO userService.loadUserForDisplay(int id); but something does not feel right about this approach. The reason do have separate DTO's is that DisplayUserDTO is strongly typed to be read only and also there are many properties of user that are entities from a lookup table in the db (like city and state) so the DisplayUserDTO would have the string description of the properties while the EditUserRequestDTO will have the id's that will back the select drop down lists in the forms. What do you think? thanks

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• Retrieving models from form with ModelMultipleChoiceField

  - by colinjameswebb

  I am having difficulties with forms, specifically ModelMultipleChoiceField. I've pieced together this code from various examples, but it sadly doesn't work. I would like to be able to: Search for some Works on work_search.html Display the results of the search, with checkboxes next to each result Select the Works I want, via the checkboxes After pressing Add, display which works were selected. I believe everything is okay except the last part. The page simply displays "works" :( Here is the code - sorry about the length. Models.py class Work(models.Model): title = models.CharField(max_length=200) artist = models.CharField(max_length=200) writers = models.CharField(max_length=200) def __unicode__(self): return self.title + ' - ' + self.artist forms.py class WorkSelectForm(forms.Form): def __init__(self, queryset, *args, **kwargs): super(WorkSelectForm, self).__init__(*args, **kwargs) self.fields['works'] = forms.ModelMultipleChoiceField(queryset=queryset, widget=forms.CheckboxSelectMultiple()) views.py def work_search(request): query = request.GET.get('q', '') if query: qset = ( Q(title__icontains=query) | Q(artist__icontains=query) | Q(writers__icontains=query) ) results = Work.objects.filter(qset).distinct() form = WorkSelectForm(results) return render_to_response("work_search.html", {"form": form, "query": query }) else: results = [] return render_to_response("work_search.html", {"query": query }) def add_works(request): #if request.method == POST: form = WorkSelectForm(request.POST) #if form.isvalid(): items = form.fields['works'].queryset return render_to_response("add_works.html", {"items":items}) work_search.html {% extends "base.html" %} {% block content %} <h1>Search</h1> <form action="." method="GET"> <label for="q">Search: </label> <input type="text" name="q" value="{{ query|escape }}"> <input type="submit" value="Search"> </form> {% if query %} <h2>Results for "{{ query|escape }}":</h2> <form action="add_works" method="post"> <ul> {% if form %} {{ form.as_ul }} {% endif %} </ul> <input type="submit" value="Add"> </form> {% endif %} {% endblock %} add_works.html {% extends "base.html" %} {% block content %} {% if items %} {% for item in items %} {{ item }} {% endfor %} {% else %} <p>Nothing selected</p> {% endif %} {% endblock %}

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• getting data from dynamic schema

  - by coure2011

  I am using mongoose/nodejs to get data as json from mongodb. For using mongoose I need to define schema first like this var mongoose = require('mongoose'); var Schema = mongoose.Schema; var GPSDataSchema = new Schema({ createdAt: { type: Date, default: Date.now } ,speed: {type: String, trim: true} ,battery: { type: String, trim: true } }); var GPSData = mongoose.model('GPSData', GPSDataSchema); mongoose.connect('mongodb://localhost/gpsdatabase'); var db = mongoose.connection; db.on('open', function() { console.log('DB Started'); }); then in code I can get data from db like GPSData.find({"createdAt" : { $gte : dateStr, $lte: nextDate }}, function(err, data) { res.writeHead(200, { "Content-Type": "application/json", "Access-Control-Allow-Origin": "*" }); var body = JSON.stringify(data); res.end(body); }); How to define scheme for a complex data like this, you can see that subSection can go to any deeper level. [ { 'title': 'Some Title', 'subSection': [{ 'title': 'Inner1', 'subSection': [ {'titile': 'test', 'url': 'ab/cd'} ] }] }, .. ]

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• Spring MVC 3.0 Rest problem

  - by Gidogeek

  Hi Guys, I'm trying out Spring MVC 3.0 for the first time and like to make it RESTfull. This is my controller: @Controller @RequestMapping(value = "/product") @SessionAttributes("product") public class ProductController { @Autowired private ProductService productService; public void setProductValidator(ProductValidator productValidator, ProductService productService) { this.productService = productService; } @RequestMapping(method = RequestMethod.GET) public Product create() { //model.addAttribute(new Product()); return new Product(); } @RequestMapping(method = RequestMethod.POST) public String create(@Valid Product product, BindingResult result) { if (result.hasErrors()) { return "product/create"; } productService.add(product); return "redirect:/product/show/" + product.getId(); } @RequestMapping(value = "/show/{id}", method = RequestMethod.GET) public Product show(@PathVariable int id) { Product product = productService.getProductWithID(id); if (product == null) { //throw new ResourceNotFoundException(id); } return product; } @RequestMapping(method = RequestMethod.GET) public List<Product> list() { return productService.getProducts(); } } I have 2 questions about this. I'm a believer in Convention over Configuration and therefor my views are in jsp/product/ folder and are called create.jsp , list.jsp and show.jsp this works relatively well until I add the @PathVariable attribute. When I hit root/product/show/1 I get the following error: ../jsp/product/show/1.jsp" not found how do I tell this method to use the show.jsp view ? If I don't add the RequestMapping on class level my show method will be mapped to root/show instead of root/owner/show how do I solve this ? I'd like to avoid using the class level RequestMapping.

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• Why doesn't the Java Collections API include a Graph implementation?

  - by dvanaria

  I’m currently learning the Java Collections API and feel I have a good understanding of the basics, but I’ve never understood why this standard API doesn’t include a Graph implementation. The three base classes are easily understandable (List, Set, and Map) and all their implementations in the API are mostly straightforward and consistent. Considering how often graphs come up as a potential way to model a given problem, this just doesn’t make sense to me (it’s possible it does exist in the API and I’m not looking in the right place of course). Steve Yegge suggests in one of his blog posts that a programmer should consider graphs first when attacking a problem, and if the problem domain doesn’t fit naturally into this data structure, only then consider the alternative structures. My first guess is that there is no universal way to represent graphs, or that their interfaces may not be generic enough for an API implementation to be useful? But if you strip down a graph to its basic components (vertices and a set of edges that connect some or all of the vertices) and consider the ways that graphs are commonly constructed (methods like addVertex(v) and insertEdge(v1, v2)) it seems that a generic Graph implementation would be possible and useful. Thanks for helping me understand this better.

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• Why is BorderLayout calling setSize() and setBounds()?

  - by ags

  I'm trying to get my head around proper use of the different LayoutManagers to make my GUI design skills more efficient and effective. For me, that usually requires a detailed understanding of what is going on under the hood. I've found some good discussion of the interaction and consequences of a Container using BorderLayout containing a Container using FlowLayout. I understand it for the most part, but wanted to confirm my mental model and to do so I am looking at the code for BorderLayout. In the code snippet below taken from BorderLayout.layoutContainer(), note the calls to the child Component's setSize() method followed by setBounds(). Looking at the source for these methods of Component, setSize() actually calls setBounds() with the current values for Component.x and Component.y. Why is this done (and not entirely redudant?) Doesn't the setBounds() call completely overwrite the results of the setSize() call? if ((c=getChild(NORTH,ltr)) != null) { c.setSize(right - left, c.height); Dimension d = c.getPreferredSize(); c.setBounds(left, top, right - left, d.height); top += d.height + vgap; } I'm also tring to understand where/when the child Component's size is initially set (before the LayoutManager.layoutContainer() method is called). Finally, this post itself raises a "meta-question": in a situation like this, where the source is available elsewhere, is the accepteed protocol to include the entire method? Or some other way to make it easier for folks to participate in the thread? Thanks.

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• Non-normalized association with legacy tables in Rails and ActiveRecord

  - by Thomas Holmström

  I am building a Rails application accessing a legacy system. The data model contains Customers which can have one or more Subscriptions. A Subscription always belong to one and only one Customer. Though not needed, this association is represented through a join table "subscribes", which do not have an id column: Column | Type | Modifiers -----------------+---------+----------- customer_id | integer | not null subscription_id | integer | not null I have this coded as a has_and_belongs_to_many declarations in both Customer and Subscription class Customer < Activerecord::Base has_and_belongs_to_many :subscriptions, :join_table => "subscribes", :foreign_key => "customer_id", :association_foreign_key => "subscription_id" end class Subscription < Activerecord::Base has_and_belongs_to_many :customers, :join_table => "subscribes", :foreign_key => "subscription_id", :association_foreign_key => "customer_id" end The problem I have is that there can only ever be one customer for each subscription, not many, and the join table will always contain at most one row with a certain customer_id. And thus, I don't want the association "customers" on a Subscription which returns an array of (at most one) Customer, I really do want the relation "customer" which returns the Customer associated. Is there any way to force ActiveRecord to make this a 1-to-N relation even though the join table itself seems to make it an N-to-M relation? --Thomas

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• nullable bool is being passed to the controller null all the time regardless of the value

  - by user1807954

  I'm trying to pass a nullable bool to my controller. But when I pass the bool value from my view to the controller, it's being passed null all the time regardless of the value it has in my view. Here is my view: @model Cars.Models.Car @using (Html.BeginForm("Index", "Home", FormMethod.Post, new { id = "CategoryFormID"})) { <label>Convertible:</label> <input type="checkbox" id="ConvertibleID" name="convertible"/> <button type="submit" name="submit" value="search" id="SubmitID">Search</button> } And my controller: [HttpPost] public ActionResult Index(bool? convertible){ var cars = from d in db.Car select d; if (convertible.HasValue) { cars = cars.Where(x => x.Convertible == convertible); } return View("SearchResult", cars); } I also have other fields such as drop down lists and text fields, but they're being passed flawless. Any help would be really appreciated. Update: Thank you for your fast responds. However, I did try giving it a value="True" as you guys suggested. There is only 2 options now: null and true. But my intention is to use nullable bool to have three options: null (when user doesn't touch the checkbox), true(checked) and false(unchecked). I know it sounds not smart and silly, but I'm just trying to figure out how nullable bool is working, and what is the intention of having such a thing in C# (I'm new with C#). I was wondering if it is possible to do so with just checkbox and without the use of dropdownlist or radio buttons.

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• 2-Way databinding with Entity Framework and WPF DataGrid , is Possible ?

  - by Panindra

  i am working on POS application using SQL CE , WPF , Entity framework 3.5sp2 and iam trying to use data grid as my Order Entry Control for User to enter Products Order . Iam plannning to bind this to enitiy frmae work model , abd looking for 2 way updating ? private void button1_Click(object sender, RoutedEventArgs e) { using (MasterEntities nwEntities = new MasterEntities()) { var users = from d in nwEntities.Companies select new { d.CompanyId, d.CompanyName, d.Place }; listBox1.DataContext = users; dataGrid1.DataContext = users; // foreach (String c in customers) // { // MessageBox.Show(c.ToString()); // } } } When try to double clikc on the datagrid it through s a error with Caption " Invalid Operation Execption was unhandled " and Message " A TwoWay or OneWayToSource binding cannot work on the read-only property 'CompanyId' of type '<f__AnonymousType0`3[System.Int32,System.String,System.String]'. whats wrong here and my xaml coding goes like this <Grid> <ListBox Name="listBox1" ItemsSource="{Binding}" /> <Button Content="Show " Name="button1" Click="button1_Click" /> <DataGrid AutoGenerateColumns="False" Name="dataGrid1" ItemsSource="{Binding}" > <DataGrid.Columns> <DataGridTextColumn Header=" ID" Binding="{Binding CompanyId}"/> <DataGridTextColumn Header="Company Name" Binding="{Binding CompanyName}"/> <DataGridTextColumn Header="Place" Binding="{Binding Place}" /> </DataGrid.Columns> </DataGrid> </Grid> EDITED : i made the changes shown by @vorrtex, But, then i added another button to save the chages and in button click event i added follwing code , butit showing Updating error private void button2_Click(object sender, RoutedEventArgs e) { nwEntities.SaveChanges(); }

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• How to properly implement the Strategy pattern in a web MVC framework?

  - by jboxer

  In my Django app, I have a model (lets call it Foo) with a field called "type". I'd like to use Foo.type to indicate what type the specific instance of Foo is (possible choices are "Number", "Date", "Single Line of Text", "Multiple Lines of Text", and a few others). There are two things I'd like the "type" field to end up affecting; the way a value is converted from its normal type to text (for example, in "Date", it may be str(the_date.isoformat())), and the way a value is converted from text to the specified type (in "Date", it may be datetime.date.fromtimestamp(the_text)). To me, this seems like the Strategy pattern (I may be completely wrong, and feel free to correct me if I am). My question is, what's the proper way to code this in a web MVC framework? In a client-side app, I'd create a Type class with abstract methods "serialize()" and "unserialize()", override those methods in subclasses of Type (such as NumberType and DateType), and dynamically set the "type" field of a newly-instantiated Foo to the appropriate Type subclass at runtime. In a web framework, it's not quite as straightforward for me. Right now, the way that makes the most sense is to define Foo.type as a Small Integer field and define a limited set of choices (0 = "Number", 1 = "Date", 2 = "Single Line of Text", etc.) in the code. Then, when a Foo object is instantiated, use a Factory method to look at the value of the instance's "type" field and plug in the correct Type subclass (as described in the paragraph above). Foo would also have serialize() and unserialize() methods, which would delegate directly to the plugged-in Type subclass. How does this design sound? I've never run into this issue before, so I'd really like to know if other people have, and how they've solved it.

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• undefined method `key?' for nil:NilClass when using MongoMapper

  - by Radek Slupik

  I set up a new Rails application by following these instructions. I generated a new controller and added resources :tickets to the routes file. Hexapoda::Application.routes.draw do resources :tickets end This is the controller (`/app/controllers/tickets_controller.rb'). class TicketsController < ApplicationController def index @tickets = Ticket.all end end I then added a new model Ticket in /app/models/ticket.rb. class Ticket include MongoMapper::Document key :summary, String, :required => true end Here's the view (/app/views/index.html.erb): <h1>Tickets#index</h1> <p>Find me in app/views/tickets/index.html.erb</p> Now when I go to /tickets in my browser, I get an error message. NoMethodError in TicketsController#index undefined method `key?' for nil:NilClass I have no idea what's going on. What could be the problem? I'm using Rails 3.2.5 and MongoMapper 0.11.1.

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• Foreign key relationships in Entity Framework

  - by Anders Svensson

  I'm trying to add an object created from Entity Data Model classes. I have a table called Users, which has turned into a User EDM class. And I also have a table Pages, which has become a Page EDM class. These tables have a foreign key relationship, so that each page is associated with many users. Now I want to be able to add a page, but I can't get how to do it. I get a nullreference exception on Users below. I'm still rather confused by all this, so I'm sure it's a simple error, but I just can't see how to do it. Also, by the way, the compiler requires that I set PageID in the object initializer, even though this field is set to be an automatic id in the table. Am I doing it right just setting it to 0, expecting it to be updated automatically in the table when saved, or how should I do that? Any help appreciated! The method in question: private Page GetPage(User currentUser) { string url = _request.ServerVariables["url"].ToLower(); var userPages = from p in _context.PageSet where p.Users.UserID == currentUser.UserID select p; var existingPage = userPages.FirstOrDefault(e => e.Url == url); //Could be combined with above, but hard to read? if (existingPage != null) return existingPage; Page page = new Page() { Count = 0, Url = _request.ServerVariables["url"].ToLower(), PageID = 0, //Only initial value, changed later? }; _context.AddToPageSet(page); page.Users.UserID = currentUser.UserID; //Here's the problem... return page; }

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