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  • Django QuerySet ordering by expression

    - by Andrew
    How can i use order_by like order_by('field1'*'field2') For example i have items with price listed in different currencies, so to order items - i have to make currency conversion. class Currency(models.Model): code = models.CharField(max_length=3, primary_key=True) rateToUSD = models.DecimalField(max_digits=20,decimal_places=10) class Item(models.Model): priceRT = models.DecimalField(max_digits=15, decimal_places=2, default=0) cur = models.ForeignKey(Currency) I would like to have something like: Item.objects.all().order_by(F('priceRT')*F('cur__rateToUSD')) But unfortunately it doesnt work, i also faild with annotate. How can i permorm QuerySet ordering by result of value multiplication of 2 model's fields.

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  • Sqlite3 Database versus populating Arrays

    - by Kenoy
    hi, I am working on a program that requires me to input values for 12 objects, each with 4 arrays, each with 100 values. (4800) values. The 4 arrays represent possible outcomes based on 2 boolean values... i.e. YY, YN, NN, NY and the 100 values to the array are what I want to extract based on another inputted variable. I previously have all possible outcomes in a csv file, and have imported these into sqlite where I can query then for the value using sql. However, It has been suggested to me that sqlite database is not the way to go, and instead I should populate using arrays hardcoded. Which would be better during run time and for memory management?

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  • .Remove(object) on a List<T> returned from LINQ to SQL compiled query won't delete the Object right

    - by soldieraman
    I am returning two lists from the database using LINQ to SQL compiled query. While looping the first list I remove duplicates from the second list as I dont want to process already existing objects again. eg. //oldCustomers is a List returned by my Compiled Linq to SQL Statmenet that I have added a .ToList() at the end to //Same goes for newCustomers for (Customer oC in oldCustomers) { //Do some processing newCustomers.Remove(newCusomters.Find(nC=> nC.CustomerID == oC.CusomterID)); } for (Cusomter nC in newCustomers) { //Do some processing } DataContext.SubmitChanges() I expect this to only save the changes that have been made to the customers in my processing and not Remove or Delete any of my customers from the database. Correct? I have tried it and it works fine - but I am trying to know if there is any rare case it might actually get removed

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  • WCF RIA Services v1.0 Timeouts

    - by Dan Wray
    I have a RIA service methods which return quite a large amount of (binary) data to my silverlight application. The methods themselves (database access etc) complete quickly, but since I upgraded to v1.0 from the RC2 I've been experiencing timeouts, even when I limit the data returned to the smallest objects. Debug shows the method returning, then 20-30 seconds later the silverlight "method complete" event will fire. There is not enough data to cause that much lag. Could anyone suggest why this might be? I've been unable to find any breaking changes documentation specific to the RC2 = 1.0 upgrade. Trying to eliminate any other possible causes also, but this is literally a case of worked before the install, doesn't work now! (also upgraded silverlight 4 tools for vs).

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  • Java/JAXB: Unmarshall Xml to specific subclass based on an attribute

    - by Frothy
    Is it possible to use JAXB to unmarshall xml to a specific Java class based on an attribute of the xml? <shapes> <shape type="square" points="4" square-specific-attribute="foo" /> <shape type="triangle" points="3" triangle-specific-attribute="bar" /> </shapes> I would like to have a List of Shape objects containing a triangle and a square, each with their own shape-specific attribute. IE: abstract class Shape { int points; //...etc } class Square extends Shape { String square-specific-attribute; //...etc } class Triangle extends Shape { String triangle-specific-attribute; //...etc } I'm currently just putting all attributes in one big "Shape" class and it's less than ideal. I could get this to work if the shapes were properly named xml elements, but unfortunately I don't have control of the xml I'm retrieving. Thanks!

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  • Accessing the Identity object in a MVC repository

    - by Rod
    Hi, I have a pretty generic repository that does basic CRUD for many of my business entities. The entities enherit form a generic object that has a few fields I maintain for all objects. eg. ModifiedBy, CreatedBy, CreatedDate, ModifiedDate. These fields ModifiedBy and CreatedBy will always be set before any update/save. My questions is: Is there any way to gain access to the Identity object from my MVC web application in my repositories? I was hoping to set the modifiedby to the identity user for any update in one shot?? Best Regard, Rod

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  • JDO in Google App Engine: order of keys in unowned one-to-many relationship

    - by Kel
    I'm implementing web application with JDO in Google App Engine. According to documentation, in owned one-to-many relationships, order of elements in "owner" object collection is determined either by automatically created index field, or by information given in explicit ordering clause. For example: @PersistenceCapable public class Person { // ... @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="country asc, city asc")) private List<ContactInfo> contacts = new List<ContactInfo>(); In unowned relationships, "owner" object contains collection of keys of "nested" objects, for example: @PersistenceCapable public class Author { // ... @Persistent private List<Key> books; Is order of keys preserved, if I use List<Key> collection in "owner" object for storing keys of "nested" elements? I could not find answer neither in JDO relationships article, nor in Data Classes article :(

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  • DB4o Linq query - How to check for null strings

    - by Dave
    Hey there - simple query: var q = (from SomeObject o in container where o.SomeInt > 8 && o.SomeString != null //Null Ref here select o; I always get a null reference exception. If I use String.IsNullOrEmpty(o.SomeString) the query takes about 100 times as long, as if I use && o.SomeString != "" (which is way faster, but obviously not correct). I'm guessing because DB4o needs to activate the objects, in order to pass them in to the IsNullOrEmpty call, and can't use the indexes. My question is, what's a better way to check for nulls in this situation? Is there something like: mystring != Db4o.DBNull.Value, or something? Cheers, Dave

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  • AsyncTask and onDestroy...

    - by stormin986
    I have an activity initiate a few AsyncTask downloads. After two of the three finish, it issues an Intent to load the next activity while still finishing up the last download. Obviously in onDestroy() i will call cancel() on all AsyncTask objects. If the OS tries to destroy my activity after the next activity starts, it will call and begin executing onDestroy in the apps UI thread, right? It won't wait for that AsyncTask to complete, correct? In all cases it will ultimately call onDestroy(), in turn canceling all AsyncTasks?

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  • javascript filter nested object based on key value

    - by murray3
    I wish to filter a nested javascript object by the value of the "step" key: var data = { "name": "Root", "step": 1, "id": "0.0", "children": [ { "name": "first level child 1", "id": "0.1", "step":2, "children": [ { "name": "second level child 1", "id": "0.1.1", "step": 3, "children": [ { "name": "third level child 1", "id": "0.1.1.1", "step": 4, "children": []}, { "name": "third level child 2", "id": "0.1.1.2", "step": 5, "children": []} ]}, ]} ] }; var subdata = data.children.filter(function (d) { return (d.step <= 2)}); This just returns the unmodified nested object, even if I put value of filter to 1. does .filter work on nested objects or do I need to roll my own function here, advise and correct code appreciated. cjm

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  • Creating a method that is simultaneously an instance and class method

    - by Mike Axiak
    In Python, I'd like to be able to create a function that behaves both as a class function and an instance method, but with the ability to change behaviors. The use case for this is for a set of serializable objects and types. As an example: >>> class Thing(object): #... >>> Thing.to_json() 'A' >>> Thing().to_json() 'B' I know that given the definition of classmethod() in funcobject.c in the Python source, this looks like it'd be simple with a C module. Is there a way to do this from within python? Thanks!

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  • python json_encode throws KeyError exception

    - by MattM
    In a unit test case that I am running, I get a KeyError exception on the 4th json object in the json text below. I went through the sub-objects and found that it was the "cpuid" object that is the offending object, but I am completely at a loss as to what is wrong with the formatting. response = self.app.post( '/machinestats', params=dict(record=self.json_encode([ {"type": "crash", "instance_id": "xxx", "version": "0.2.0", "build_id": "unknown", "crash_text": "Gah!"}, {"type": "machine_info", "machine_info": "I'm awesome.", "version": "0.2.0", "build_id": "unknown", "instance_id": "yyy"}, {"machine_info": "Soup", "crash_text": "boom!", "version": "0.2.0", "build_id": "unknown", "instance_id": "zzz", "type": "crash"}, {"build_id" : "unknown", "cpu_brand" : "intel", "cpu_count" : 4, "cpuid": { "00000000": {"eax" :123,"ebx" :456, "ecx" :789,"edx" :321}, "00000001": {"eax" :123,"ebx" :456, "ecx" :789,"edx" :321}}, "driver_installed" : True, "instance_id" : "yyy", "version" : "0.2.0", "machine_info" : "I'm awesome.", "os_version" : "linux", "physical_memory_mib" : 1024, "product_loaded" : True, "type" : "machine_info", "virtualization_advertised" : True} ])))

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  • Most efficient algorithm for mesh-level, optimal occlusion culling?

    - by Fredriku73
    I am new to culling. On a first glance, it seems that most occlusion culling algorithms are object-level, not examining single meshes, which would be practical for game rendering. What I am looking for is an algorithm that culls all meshes within a single object that are occluded for a given viewpoint, with high accuracy. It needs to be at least O(n log n), a naive mesh-by-mesh comparison (O(n^2)) is too slow. I notice that the Blender GUI identifies the occluded meshes for you in real-time, even if you work with large objects of 10,000+ meshes. What algorithm is used there, pray tell?

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  • A Simulator for a non-deterministic Push-Down Automaton

    - by shake
    Well, i need to make simulator for non-deterministic Push-Down Automaton. Everything is okey, i know i need to do recursion or something similar. But i do not know how to make that function which would simulate automaton. I got everything else under control, automaton generator, stack ... I am doing it in java, so this is maybe only issue that man can bump on, and i did it. So if anyone have done something similar, i could use advices. This is my current organisation of code: C lasses: class transit: list -contains non deterministic transitions state input sign stack sign class generator it generate automaton from file clas NPA public boolean start() - this function i am having trouble with Of course problem of separate stacks, and input for every branch. I tried to solve it with collection of objects NPA and try to start every object, but it doesn work :((..

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  • Arrays & Pointers

    - by Thomas
    Hi, Looking for some help with arrays and pointers and explanation of what I am trying to do. I want to create a new array on the heap of type Foo* so that I may later assign objects that have been created else where to this array. I am having troubles understanding what I am creating exactly when I do something like the following. Foo *(*f) = new Foo*[10]; Also once I have created my array how do I access each element for example. (f + 9)->fooMember(); ?????? Thanks in advance.

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  • Shortcut for adding to List in a HashMap

    - by Damo
    I often have a need to take a list of objects and group them into a Map based on a value contained in the object. Eg. take a list of Users and group by Country. My code for this usually looks like: Map<String, List<User>> usersByCountry = new HashMap<String, List<User>>(); for(User user : listOfUsers) { if(usersByCountry.containsKey(user.getCountry())) { //Add to existing list usersByCountry.get(user.getCountry()).add(user); } else { //Create new list List<User> users = new ArrayList<User>(1); users.add(user); usersByCountry.put(user.getCountry(), users); } } However I can't help thinking that this is awkward and some guru has a better approach. The closest I can see so far is the MultiMap from Google Collections. Are there any standard approaches? Thanks!

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  • How to get unique URL identifier after inserting item in Google Base with Zend Gdata API?

    - by msumme
    I need to get the unique URL identifier for the product that is created after inserting an item into Google Base using the Zend_Gdata_Gbase library. I can't seem to do this. I am finding a startling lack of documentation online about manipulating the objects used in these applications. The url that I add to the object does not work to retrieve the base item later, which is why I need to get the one that google generates upon submission. I am writing a program that will need to be able to delete content at a later date, and thus will need to store that information in order to keep the website synced with the Google Base feed. Thanks in advance for any help.

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  • Does std::multiset guarntee insertion order?

    - by Naveen
    I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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  • GUI system architecture?

    - by topright
    I'm designing GUI (graphical user interface) system for a game engine (C++). Idea is to create a heirarchy of GUI controllers like Focusable, Hoverable, Dragable etc. Every GUI component can attach multiple controllers, they modify component's behaviour. I think it gives flexible system and protects from code duplication. Different instances of the same GUI class can have different complex behaviours (may be, even change it dynamically), so this approach looks practical. The other choice is to add focused, hovered, dragged etc. flags in the base GUI component class. It looks like overhead and not that flexible. Another solution is to use Decorator pattern and wrap objects with FocusDecorator, HoverDecorator etc. Maintaining such system looks a bit harder. Question: What are pitfalls in my solution? May be you have seen a better approaches in GUI systems? What are the best ways of implementing such flexible complex system?

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  • Using C# Type as generic

    - by I Clark
    I'm trying to create a generic list from a specific Type that is retrieved from elsewhere: Type listType; // Passed in to function, could be anything var list = _service.GetAll<listType>(); However I get a build error of: The type or namespace name 'listType' could not be found (are you missing a using directive or an assembly reference?) Is this even possible or am I setting foot onto C# 4 Dynamic territory? As a background: I want to automatically load all lists with data from the repository. The code below get's passed a Form Model whose properties are iterated for any IEnum (where T inherits from DomainEntity). I want to fill the list with objects of the Type the list made of from the repository. public void LoadLists(object model) { foreach (var property in model.GetType() .GetProperties(BindingFlags.Public | BindingFlags.Instance | BindingFlags.SetProperty)) { if (IsEnumerableOfNssEntities(property.PropertyType)) { var listType = property.PropertyType.GetGenericArguments()[0]; var list = _repository.Query<listType>().ToList(); property.SetValue(model, list, null); } } }

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  • Generic unboxing of boxed value types

    - by slurmomatic
    I have a generic function that is constrained to struct. My inputs are boxed ("objects"). Is it possible to unbox the value at runtime to avoid having to check for each possible type and do the casts manually? See the above example: public struct MyStruct { public int Value; } public void Foo<T>(T test) where T : struct { // do stuff } public void TestFunc() { object o = new MyStruct() { Value = 100 }; // o is always a value type Foo(o); } In the example, I know that o must be a struct (however, it does not need to be MyStruct ...). Is there a way to call Foo without tons of boilerplate code to check for every possible struct type? Thank you.

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  • GUI designers! - got suggestions for a GUI modelling diagram language?

    - by naugtur
    Refering to this question I asked a while ago: UI functionality modeling languages It looks like there is no good-enough solution. I decided to develop one. (and prepare a set of elements for DIA or something) I'm sure it will require a good insight in peoples' experiences and problems in designing functionally complicated GUIs. I've got some ideas already, but I'd like to hear from You what You'd expect from a GUI functionality modelling language. Clarification: It's functionality modelling, so it's not about where I put a button. It's about objects that have some events binded, and the interface behaviour logic. If You think (just as I do) that UML is far from useful for such purposes - feel free to put Your expectations here. I'll try to meet them. ( not necessarily in person;) ) Remember - there is no such thing as a wrong answer to this question

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  • Returning references while using shared_ptrs

    - by Goose Bumper
    Suppose I have a rather large class Matrix, and I've overloaded operator== to check for equality like so: bool operator==(Matrix &a, Matrix &b); Of course I'm passing the Matrix objects by reference because they are so large. Now i have a method Matrix::inverse() that returns a new Matrix object. Now I want to use the inverse directly in a comparison, like so: if (a.inverse()==b) { ... }` The problem is, this means the inverse method needs to return a reference to a Matrix object. Two questions: Since I'm just using that reference in this once comparison, is this a memory leak? What happens if the object-to-be-returned in the inverse() method belongs to a boost::shared_ptr? As soon as the method exits, the shared_ptr is destroyed and the object is no longer valid. Is there a way to return a reference to an object that belongs to a shared_ptr?

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  • Why are only some of my attributes shown in the response xml of jaxws?

    - by Andreas
    I created a jaxws webservice, but it returns only some of the attributes of my objects in the response xml. E.g. public class MyObject { private String attribute1; private String attribute2; //getter and setter } But the returned XML only contains <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <ns2:getVariantsResponse xmlns:ns2="mynamespace"> <myObject> <attribute1>stringcontent</attribute1> </myObject> ....

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  • Application_End() cannot access cache through HttpContext.Current.Cache[key]

    - by Carl J.
    I want to be able to maintain certain objects between application restarts. To do that, I want to write specific cached items out to disk in Global.asax Application_End() function and re-load them back on Application_Start(). I currently have a cache helper class, which uses the following method to return the cached value: return HttpContext.Current.Cache[key]; Problem: during Application_End(), HttpContext.Current is null since there is no web request (it's an automated cleanup procedure) - therefore, I cannot access .Cache[] to retrieve any of the items to save to disk. Question: how can I access the cache items during Application_End()?

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