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• Good real-world uses of metaclasses (e.g. in Python)

  - by Carles Barrobés

  I'm learning about metaclasses in Python. I think it is a very powerful technique, and I'm looking for good uses for them. I'd like some feedback of good useful real-world examples of using metaclasses. I'm not looking for example code on how to write a metaclass (there are plenty examples of useless metaclasses out there), but real examples where you have applied the technique and it was really the appropriate solution. The rule is: no theoretical possibilities, but metaclasses at work in a real application. I'll start with the one example I know: Django models, for declarative programming, where the base class Model uses a metaclass to fill the model objects of useful ORM functionality from the attribute definitions. Looking forward to your contributions.

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• ASP.NET GridView throwing error: "Update is disabled for this control".

  - by NTDLS

  I have the absolutely most simple setup imaginable. A single table defined in an Entity model in ASP.net v4, the model is bound directly to a GridView with AutoGenerateEditButton enabled. However, each time I hit edit, then save, the page throws the error “Update is disabled for this control" for which I cannot find a solution. What is causing this error? What can do to resolve it? <% <asp:GridView ID="MenuItemsGrid" runat="server" DataSourceID="gridDataSource" AutoGenerateEditButton="true" AutoGenerateColumns="true"> </asp:GridView> <asp:EntityDataSource ID="gridDataSource" runat="server" ConnectionString="name=dataEntitiesModel" DefaultContainerName="dataEntities" EntitySetName="MenuItems" /> %>

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• ASPNET MVC what do you call this, a partial view? Or something else?

  - by JK

  I'm trying to google for info on a situation, but I dont know what it is called, so its hard to find results :) I have a model with say 10 fields. But only some of those are shown on a particular view, lets say 3 of them: id, name, date. What do you call this kind of view that does not display the whole model? A partial view? The problem is that because 7 fields are not sent to the view, when the Update action is called on the controller, those fields are null, and the DB gets updated with those 7 fields set to null.

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• Use CSS (and maybe JavaScript) to make an element be square (or maintain a specific aspect ratio)

  - by David Pfeffer

  I have a div that I want to have the following characteristics: Width = 50% of its parent element Height equal to whatever it needs to be in order to maintain a certain aspect ratio. I need to use percentages because the object will resize left-right when the browser is resized. I want the object to be resized top-bottom to ensure the object maintains the same aspect ratio. I don't think there's any way to use pure CSS to do this, but does anyone know of a way? Alternatively, is there an easy JavaScript way to do this? (JQuery is fine.)

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• What is dbReferenceProperty?

  - by user246114

  Hi, In the python app engine docs, I see something called dbReferenceProperty. I can't understand what it is, or how it's used. I'm using the java interface to app engine, so I'm not sure if there's an equivalent. I'm interested in it because it sounds like some sort of pseudo-join, where we can point a property of a class to some other object's value - something like if we had: class User { private String mPhotoUrl; private String mPhone; private String mState; private String mCountry; .. etc .. } class UserLite { @ReferenceProperty User.mPhotoUrl; private String mPhotoUrl; } then if we had to update a User object's mPhotoUrl value, the change would somehow propagate out to all UserLite instances referencing it, rather than having to update every UserLite object instance manually, Thanks

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• Any good class diagram editors out there for Java (not UML)

  - by user85116

  I'm looking for an editor that can create class diagrams, similar to the typical UML class diagram, but specifically for java (so using java terminology; instead of terms like "generalization, realization etc", we use the java equivalents "interface, abstract class, extends etc"). I've looked into UML several times, but each time I've been turned off by the shear amount of "stuff" that comes with UML. I just want to be able to model my java classes quickly and intuitively, without getting bogged down by all the cruft that comes with UML. Preferably, it would come with a source reader that can keep the diagram up to date, and with a few nice features like "show only public methods in this class" etc. As well, it would automatically "know" about the classes in the standard java library, and possibly even be able to read classes from jars. Performance is also a big thing for me, I don't like having to wait 2 seconds for a popup menu to appear, or watch the diagram jerk crazily while resizing an element in the model. What do you think, am I asking too much?

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• Backbone inheritance - deep copying

  - by Ed .

  I've seen this question regarding inheritance in Backbone: Backbone.js view inheritance. Useful but doesn't answer my question. The problem I'm experiencing is this: Say I have a class Panel (model in this example); var Panel = Backbone.Model.extend({ defaults : { name : 'my-panel' } }); And then an AdvancedPanel; var AdvancedPanel = Panel.extend({ defaults : { label : 'Click to edit' } }); The following doesn't work: var advancedPanel = new AdvancedPanel(); alert(advancedPanel.get('name')); // Undefined :( JSFiddle here: http://jsfiddle.net/hWmnb/ I guess I can see that I can achieve this myself through some custom extend function that creates a deep copy of the prototype, but this seems like a common thing that people might want from Backbone inheritance, is there a standard way of doing it?

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• is it safe to refactor my django models?

  - by Johnd

  My model is similar to this. Is this ok or should I make the common base class abstract? What are the differcenes between this or makeing it abstract and not having an extra table? It seems odd that there is only one primary key now that I have factored stuff out. class Input(models.Model): details = models.CharField(max_length=1000) user = models.ForeignKey(User) pub_date = models.DateTimeField('date published') rating = models.IntegerField() def __unicode__(self): return self.details class Case(Input): title = models.CharField(max_length=200) views = models.IntegerField() class Argument(Input): case = models.ForeignKey(Case) side = models.BooleanField() is this ok to factor stuff out intpu Input? I noticed Cases and Arguments share a primary Key. like this: CREATE TABLE "cases_input" ( "id" integer NOT NULL PRIMARY KEY, "details" varchar(1000) NOT NULL, "user_id" integer NOT NULL REFERENCES "auth_user" ("id"), "pub_date" datetime NOT NULL, "rating" integer NOT NULL ) ; CREATE TABLE "cases_case" ( "input_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "cases_input" ("id"), "title" varchar(200) NOT NULL, "views" integer NOT NULL ) ; CREATE TABLE "cases_argument" ( "input_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "cases_input" ("id"), "case_id" integer NOT NULL REFERENCES "cases_case" ("input_ptr_id"), "side" bool NOT NULL )

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• How decide whether a e-mail was newly sent, replied or forwarded?

  - by user572783

  I use Visual Studio 2010 to create an Outlook 2007 Addin. Now i want to know whether a e-mail was newly sent, replied or forwarded. Is there any property for this? using Outlook = Microsoft.Office.Interop.Outlook; namespace _Outlook2k7_Add_In { public partial class ThisAddIn { private void ThisAddIn_Startup(object sender, System.EventArgs e) { } private void ThisAddIn_Shutdown(object sender, System.EventArgs e) { } void Application_ItemSend(object Item, ref bool Cancel) { Outlook.MailItem mail = Item as Outlook.MailItem; if (mail == null) return; // Magic? } #region VSTO generated code /// <summary> /// Required method for Designer support - do not modify /// the contents of this method with the code editor. /// </summary> private void InternalStartup() { this.Startup += new System.EventHandler(ThisAddIn_Startup); this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown); this.Application.ItemSend += new Outlook.ApplicationEvents_11_ItemSendEventHandler(Application_ItemSend); } #endregion } }

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• How can I traverse a reverse generic relation in a Django template?

  - by user569139

  I have the following class that I am using to bookmark items: class BookmarkedItem(models.Model): is_bookmarked = models.BooleanField(default=False) user = models.ForeignKey(User) content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey() And I am defining a reverse generic relationship as follows: class Link(models.Model): url = models.URLField() bookmarks = generic.GenericRelation(BookmarkedItem) In one of my views I generate a queryset of all links and add this to a context: links = Link.objects.all() context = { 'links': links } return render_to_response('links.html', context) The problem I am having is how to traverse the generic relationship in my template. For each link I want to be able to check the is_bookmarked attribute and change the add/remove bookmark button according to whether the user already has it bookmarked or not. Is this possible to do in the template? Or do I have to do some additional filtering in the view and pass another queryset?

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• How do I use SPMemember.ID property to get User or Group

  - by Jason

  I have to write a utility to enumerate and manage the owners of groups within a SharePoint site. I know I can use the Groups property of the SPWeb object to retrieve a collection of groups. And I know I can use the Owner property of the group to get back the owner. My problem is that I do not know what to do next. The SPGroup.Owner property returns a SPMember object. The member object has one property called ID that returns the unique ID (an integer) of the member. What I cannot seem to find information on is how to use that integer value to determine if the member is a User or a Group and how to get back additional details (say the name). Any ideas? Thanks.

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• How to coerce type of ActiveRecord attribute returned by :select phrase on joined table?

  - by tribalvibes

  Having trouble with AR 2.3.5, e.g.: users = User.all( :select => "u.id, c.user_id", :from => "users u, connections c", :conditions => ... ) Returns, e.g.: => [#<User id: 1000>] >> users.first.attributes => {"id"=>1000, "user_id"=>"1000"} Note that AR returns the id of the model searched as numeric but the selected user_id of the joined model as a String, although both are int(11) in the database schema. How could I better form this type of query to select columns of tables backing multiple models and retrieving their natural type rather than String ? Seems like AR is punting on this somewhere. How could I coerce the returned types at AR load time and not have to tack .to_i (etc.) onto every post-hoc access?

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• Accessing CoreData relationships

  - by georgeliquor

  I have the following core data model with two entities: entity "item" which holds name, date, description and a to many relationship "image". image is optional. entity "image" holds url, name and relationship to one item. I load the executed Fetchrequest into this NSArray "entityArray" This is what I do to display my data in a UITableView for example to display title in main cell: NSManagedObject *object = (NSManagedObject *)[entityArray objectAtIndex:indexPath.row]; cell.textLabel.text=[object valueForKey:@"title"]; Now I have no clue how to access my relationship image ([object valueForKey:@"image"]), because it contains more than just a string.

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• How to read the values returned by the Json?

  - by user281180

  I have the following code in my view: <% using (Ajax.BeginForm("JsonCreate", new AjaxOptions { OnComplete = "createCategoryComplete" })) { % Add new category <%=Html.TextBox("CategoryId")% <%=Html.TextBox("Test")% Name: <%= Html.TextBox("Name")% <%= Html.ValidationMessage("Name")% </p> <p> <input type="submit" value="Create" /> </p> </fieldset> </div> <% } % In the controller the code is as follows: [AcceptVerbs(HttpVerbs.Post)] public JsonResult JsonCreate(string Name) { if (ModelState.IsValid) { try { //Return a json object to the javascript return Json(new { CategoryId = 123, Test= "test successful" }); } catch { #region Log errors about the exception //Log error to administrator here #endregion } } //If we got this far, something failed, return an empty json object return Json(new { /* Empty object */ }); } What should be the code in the view for the following function to read the values returned by the Json and update the textboxes for CategoryId and Test? function createCategoryComplete() {....???}

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• Programming terms - field, member, properties (C#)

  - by Petr

  Hi, I was trying to find meaning of this terms but especially due to language barrier I was not able to understand what they are used for. I assume that "field" is variable (object too?) in the class while "property" is just an object that returns specific value and cannot contain methods etc. By "member" I understand any object that is declared on the class level. But these are just my assumptions based on commented code samples where some careful programmers used "property region" etc. I would really appreciate if someone could explain it to me.

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• filter queryset based on list, including None

  - by jujule

  Hi all I dont know if its a django bug or a feature but i have a strange ORM behaviour with MySQL. class Status(models.Model): name = models.CharField(max_length = 50) class Article(models.Model) status = models.ForeignKey(status, blank = True, null=True) filters = Q(status__in =[0, 1,2] ) | Q(status=None) items = Article.objects.filter(filters) this returns Article items but some have other status than requested [0,1,2,None] looking at the sql query : SELECT [..] FROM `app_article` LEFT OUTER JOIN `app_status` ON (`app_article`.`status_id` = `app_status`.`id`) WHERE (`app_article`.`status_id` IN (1, 2) OR `app_status`.`id` IS NULL) ORDER BY [...] the OR app_status.id IS NULL part seems to be the cause. if i change it to OR app_article.status_id IS NULL it works correctly. How to deal with this ? Thanx.

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• MVC: Structuring Feed Output

  - by Brian Wigginton

  The framework I'm using on my project follows the MVC Pattern. I"M building JSON feeds and need to structure them in a different way then what the system gives me by default from the ORM. Where should I be handling the task of mangling and shaping my data that I'll serve up, in the model, view or controller? Right now I'm doing it in my controller, then passing that data to the view. I can see this fitting better under the Model or the View but not sure which one.

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• Why I should use an N-Tier Approach When using an SqlDatasource is ALOT EASIER ?

  - by The_AlienCoder

  When it comes to web development I have always tried to work SMART not HARD. So for along time My Aproach to interacting with databases in my AspNet projects has been this : 1) Create my stored procedures 2) Drag an SQLDatasource control on my aspx page 3) Bind a DataList Control to my SQLDatasource 4) Insert, Update & Delete by using my Datalist or programmatically using built in SQLDatasource methods e.g MySqlDataSource.InsertParameters["author"].DefaultValue = TextBox1.Text; MySqlDataSource.Insert(); Recently however I got a relatively easy web project. So I decided to employ a 3-tier Model...But I got exhausted halfway and just didnt seem worth it ! It seemed like I was working too HARD for a project that could have been easily accomplished by a couple of SqlDataSource Controls. So Why Is the N-Tier Model better than my Approach? Has it anything to do with performance? What are the advantages of the ObjectDataSource control over the SqlDataSource Control?

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• get foreign key objects in a single query - Django

  - by John

  Hi I have 2 models in my django code: class ModelA(models.Model): name = models.CharField(max_length=255) description = models.CharField(max_length=255) created_by = models.ForeignKey(User) class ModelB(models.Model): category = models.CharField(max_length=255) modela_link = models.ForeignKey(ModelA, 'modelb_link') functions = models.CharField(max_length=255) created_by = models.ForeignKey(User) Say ModelA has 100 records, all of which may or may not have links to ModelB Now say I want to get a list of every ModelA record along with the data from ModelB I would do: list_a = ModelA.objects.all() Then to get the data for ModelB I would have to do for i in list_a: i.additional_data = i.modelb_link.all() However this runs a query on every instance of i. Thus making 101 queries to run. Is there any way of running this all in just 1 query. Or at least less than the 101 queries. I've tried putting in ModelA.objects.select_related().all() but this didn't seem to have any effect. Thanks

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• thread destructors in C++0x vs boost

  - by Abruzzo Forte e Gentile

  Hi All These days I am reading the pdf Designing MT programs . It explains that the user MUST explicitly call detach() on an object of class std::thread in C++0x before that object gets out of scope. If you don't call it std::terminate() will be called and the application will die. I usually use boost::thread for threading in C++. Correct me if I am wrong but a boost::thread object detaches automatically when it get out of scope. Is seems to me that the boost approach follow a RAII principle and the std doesn't. Do you know if there is some particular reason for this? Kind Regards AFG

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• how to force nhibernate to set the foreign key of the child item?

  - by npeBeg

  i have a collection in the mapping: <bag name="Values" cascade="all-delete-orphan" lazy="false" inverse="true"> <key column="[TemplateId]"/> <one-to-many class="MyNamespace.Value, MyLib"/> </bag> the Value object has a foreign key [TemplateId]. both entities has their generator set to "identity". when i call session.Save() for the parent Template object, the Value objects has their [TemplateId] (the foreign key) set to zero, so an SQL exception appears. how do i forse nhibernate to set the FK value for the child items to the value of the inserted parent object?

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• Rails Authlogic authentication method

  - by Rabbott

  Within Authlogic, is there a way that I can add conditions to the authentication method? I know by using the find_by_login_method I can specify another method to use, but when I use this I need to pass another parameter since the find_by_login_method method only passes the parameter that is deemed the 'login_field'. What I need to do is check something that is an association of the authentic model.. Here is the method I want to use # make sure that the user has access to the subdomain that they are # attempting to login to, subdomains are company names def self.find_by_email_and_company(email, company) user = User.find_by_email(email) companies = [] user.brands.each do |b| companies << b.company.id end user && companies.include?(company) end But this fails due to the fact that only one parameter is sent to the find_by_email_and_company method. The company is actually the subdomain, so in order to get it here I am just placing it in a hidden field in the form (only way I could think to get it to the model) Is there a method I can override somehow..?

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• How to ensure consistency of enums in Java serialization?

  - by Uri

  When I serialize an object, I can use the serialVersionUID mechanism at the class level to ensure the compatibility of the two types. However, what happens when I serialize fields of enum values? Is there a way to ensure that the enum type has not been manipulated between serialization and deserialization? Suppose that I have an enum like OperationResult {SUCCESS, FAIL}, and a field called "result" in an object that is being serialized. How do I ensure, when the object is deserialized, that result is still correct even if someone maliciously reversed the two? (Suppose the enum is declared elsewhere as a static enum) I am wondering out of curiosity - I use jar-level authentication to prevent manipulation.

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• What is an instance of a field called?

  - by waxwing

  This might be an odd question, but it has actually caused me some headache. In Object oriented programming, there are accepted names for key concepts. In our model, we have classes with methods and fields. Now, going to the data world: An instance of a class is called an object. An instance of a field is called... what? A value? Isn't the term value a little broad for this? I have been offered "property" as well, but isn't property also part of the model and not the data? (This is not purely academic, I am actually coding these concepts.)

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• ASP.NET MVC2 : DateTime modelbinding via HTTP GET

  - by mathieu

  I'm getting some trouble binding a date from QueryString : I have the following model public class QueryParms { public DateTime Date { get; set; } } And the following controller action : public ActionResult Search( QueryParms query ); I have a form, with a field where I can type my date. If the form is FormMethod.Post, everything is fine, my date is correctly bound to my model. If the form is FormMethod.Get, it is not working anymore. The date is left to the default value (01/01/0001) I think it is a culture issue : When i look into the value provider, the FormValueProvider has a culture property set for my date : {fr-FR}. The QueryStringValueProvider doesn't have the culture property set. Is there a way to set this property ?

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