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  • How should I build a simple database package for my python application?

    - by Carson Myers
    I'm building a database library for my application using sqlite3 as the base. I want to structure it like so: db/ __init__.py users.py blah.py etc.py So I would do this in Python: import db db.users.create('username', 'password') I'm suffering analysis paralysis (oh no!) about how to handle the database connection. I don't really want to use classes in these modules, it doesn't really seem appropriate to be able to create a bunch of "users" objects that can all manipulate the same database in the same ways -- so inheriting a connection is a no-go. Should I have one global connection to the database that all the modules use, and then put this in each module: #users.py from db_stuff import connection Or should I create a new connection for each module and keep that alive? Or should I create a new connection for every transaction? How are these database connections supposed to be used? The same goes for cursor objects: Do I create a new cursor for each transaction? Create just one for each database connection?

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  • How to deal with callback to your UIController after your UIController unloads?

    - by erotsppa
    Suppose your controller is a table view and one of the cells you are going off to do a length task (say download a thumbnail) to be viewed in the cell. Typically you would have the network call do a callback to your controller when it is done downloading. The callback can then reload the table or do some other form of UI update (hides a spinner etc). However, what if the controller is unloaded? Say the user navigated away from this controller and it got released? What happens? Will the callback still work despite the controller now not in memory? Also, if the callback operates on some objects (say the UITableView) what happens when the controller is deallocated? I suppose the controller can release all the objects and the callback would just be calling methods on nil to prevent crash. But is this the convention?

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  • Entity Framework 4 - Delete Object

    - by GibboK
    I have 3 Tables in my DataBase CmsMasterPages CmsMasterPagesAdvSlots (Pure Juction Table) CmsAdvSlots Here a Picture of my EDM: I need find out all objects CmsAdvSlot connected with a CmsMasterPage (it is working in my code posted belove), and DELETE the result (CmsAdvSlot) from the DataBase. My Problem is I am not able to DELETE this Objects when I found theme. Error: The object cannot be deleted because it was not found in the ObjectStateManager. int findMasterPageId = Convert.ToInt32(uxMasterPagesListSelector.SelectedValue); CmsMasterPage myMasterPage = context.CmsMasterPages.FirstOrDefault(x => x.MasterPageId == findMasterPageId); var resultAdvSlots = myMasterPage.CmsAdvSlots; // It is working until here foreach (var toDeleteAdv in resultAdvSlots) { context.DeleteObject(myMasterPage.CmsAdvSlots.Any()); // ERORR HERE!! context.SaveChanges(); } Any idea how to solve it? Thanks for your time! :-)

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  • Teacher confused about MVC?

    - by Gideon
    I have an assignment to create a game in java using MVC as a pattern. The thing is that stuff I read about MVC aren't really what the teacher is telling me. What I read is that the Model are the information objects, they are manipulated by the controllers. So in a game the controller mutates the placement of the objects and check if there is any collision etc. What my teacher told me is that I should put everything that is universal to the platform in the models and the controllers should only tell the model which input is given. That means the game loop will be in a model class, but also collision checks etc. So what I get from his story is that the View is the screen, the Controller is the unput handeler, and the Model is the rest. Can someone point me in the right direction?

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  • Many-to-one relationship in SQLAlchemy

    - by Arrieta
    This is a beginner-level question. I have a catalog of mtypes: mtype_id name 1 'mtype1' 2 'mtype2' [etc] and a catalog of Objects, which must have an associated mtype: obj_id mtype_id name 1 1 'obj1' 2 1 'obj2' 3 2 'obj3' [etc] I am trying to do this in SQLAlchemy by creating the following schemas: mtypes_table = Table('mtypes', metadata, Column('mtype_id', Integer, primary_key=True), Column('name', String(50), nullable=False, unique=True), ) objs_table = Table('objects', metadata, Column('obj_id', Integer, primary_key=True), Column('mtype_id', None, ForeignKey('mtypes.mtype_id')), Column('name', String(50), nullable=False, unique=True), ) mapper(MType, mtypes_table) mapper(MyObject, objs_table, properties={'mtype':Relationship(MType, backref='objs', cascade="all, delete-orphan")} ) When I try to add a simple element like: mtype1 = MType('mtype1') obj1 = MyObject('obj1') obj1.mtype=mtype1 session.add(obj1) I get the error: AttributeError: 'NoneType' object has no attribute 'cascade_iterator' Any ideas?

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  • Javascript: How to filter object array based on attributes?

    - by JGreig
    I have the following JavaScript JSON array of real estate home objects: var json = { 'homes' : [ { "home_id":"1", "price":"925", "sqft":"1100", "num_of_beds":"2", "num_of_baths":"2.0", }, { "home_id":"2", "price":"1425", "sqft":"1900", "num_of_beds":"4", "num_of_baths":"2.5", }, // ... (more homes) ... ]} var xmlhttp = eval('(' + json + ')'); homes = xmlhttp.homes; What I would like to do is be able to perform a filter on the object to return a subset of "home" objects. For example, I want to be able to filter based on: price, sqft, num_of_beds, and num_of_baths. Question: How can I perform something in javascript like the pseudo-code below: var newArray = homes.filter( price <= 1000 & sqft >= 500 & num_of_beds >=2 & num_of_baths >= 2.5); Note, the syntax does not have to be exactly like above. This is just an example.

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  • Does allocation speed depend on the garbage collector being used?

    - by jkff
    My app is allocating a ton of objects (1mln per second; most objects are byte arrays of size ~80-100 and strings of the same size) and I think it might be the source of its poor performance. The app's working set is only tens of megabytes. Profiling the app shows that GC time is negligibly small. However, I suspect that perhaps the allocation procedure depends on which GC is being used, and some settings might make allocation faster or perhaps make a positive influence on cache hit rate, etc. Is that so? Or is allocation performance independent on GC settings under the assumption that garbage collection itself takes little time?

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  • PHP array of object(stdClass) fusion/intersect?

    - by Gremo
    $arr1 is an associative array of anonymus objects: array 15898 => object(stdClass)[8] public 'date' => int $arr2 is another associative array with two (or more, it's not fixed) properties: array 15898 => object(stdClass)[10] public 'fruits' public 'drinks' I can't find any function for intersect and content fusion when dealing with objects. Basically i'd like to obtain: array 15898 => object(stdClass)[8] public 'date' => int public 'fruits' public 'drinks' Question is: is this even possible?

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  • Show a django relationship in a template

    - by kevin_82
    I have a django model as follows: class Person(models.Model): name = models.CharField(max_length=255) class Relationship(models.Model): parent = models.ForeignKey(Person) child = models.ForeignKey(Person) description = models.TextField(blank=True) In my view, I pass a certain person, and the relationships in which he/she is parent: person = Person.objects.filter(name ='some name') descendant_relationships = Relationship.objects.filter(parent = person) An I want to show this person's descendants in a list in a template: <ul> {% for item in descendant_relationships%} <li> {{item.child.name}} - {{item.description}} </li> {% endfor %} </ul> But this template code will not show the children of children (i.e. grandchildren, great-grandchildren etc.). How can I get these lower level descendants to show up? I imagine recursion is necessary somewhere, but where?

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  • What is the accepted way to replace java.util.Date(year,month,day)

    - by dagw
    I'm trying to do something really simple, but starting to realize that dates in Java are a bit of minefield. All I want is to get passed groups of three ints ( a year, a month and a date) create some Date objects, do some simple test on them (along the lines of as date A before date B and after January 1 1990), convert them to java.sql.Date objects and pass them off to the database via JDBC. All very simple and works fine using the java.util.Date(int year,int month,int day) constructor. Of course that constructor is depreciated, and I'd like to avoid using depreciated calls in new code I'm writing. However all the other options to solve this simple problem seem stupidly complicated. Is there really no simple way to do what I want without using depreciated constructors? I know the standard answer to all Java date related questions is "use joda time", but I really don't want to start pulling in third party libraries for such a seemingly trivial problem.

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  • Storing an arbitrary R object onto HDD?

    - by Harokitty
    I understand that we can export data matrices to csv or xlsx files. What about complex objects like lm? For example, in my work I might have a list of length 1000, each with a single lm() object. Each time I load R I have to wait a long time to populate the 1000 length list with these lm objects with a for loop or a lapply. I would rather just save the list somewhere on my HDD at the end of a session and open it at the start of the next session.

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  • How can I remove a duplicate object from a MongoDB array?

    - by andrewrk
    My data looks like this: foo_list: [ { id: '98aa4987-d812-4aba-ac20-92d1079f87b2', name: 'Foo 1', slug: 'foo-1' }, { id: '98aa4987-d812-4aba-ac20-92d1079f87b2', name: 'Foo 1', slug: 'foo-1' } { id: '157569ec-abab-4bfb-b732-55e9c8f4a57d', name: 'Foo 3', slug: 'foo-3' } ] Where foo_list is a field in a model called Bar. Notice that the first and second objects in the array are complete duplicates. Aside from the obvious solution of switching to PostgresSQL, what MongoDB query can I run to remove duplicate entries from foo_list? Similar answers that do not quite cut it: http://stackoverflow.com/a/16907596/432 http://stackoverflow.com/a/18804460/432 These questions answer the question if the array had bare strings in it. However in my situation the array is filled with objects. I hope it is clear that I am not interested in a query; I want the duplicates to be gone from the database forever.

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  • Can using non primitive Integer/ Long datatypes too frequently in the application, hurt the performance??

    - by Marcos
    I am using Long/Integer data types very frequently in my application, to build Generic datatypes. I fear that using these wrapper objects instead of primitive data types may be harmful for performance since each time it needs to create objects which is an expensive operation. but also it seems that I have no other choice(when I have to use primtives with generics) rather than just using them. However, still it would be great if you can suggest if there is anything I could do to make it better. or any way if I could just avoid it ?? Also What may be the downsides of this ? Suggestions welcomed!

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  • Django model class and custom property

    - by dArignac
    Howdy - today a weird problem occured to me: I have a modle class in Django and added a custom property to it that shall not be saved into the database and therefore is not represent in the models structure: class Category(models.Model): groups = models.ManyToManyField(Group) title = defaultdict() Now, when I'm within the shell or writing a test and I do the following: c1 = Category.objects.create() c1.title['de'] = 'german title' print c1.title['de'] # prints "german title" c2 = Category.objects.create() print c2.title['de'] # prints "german title" <-- WTF? It seems that 'title' is kind of global. If I change title to a simple string it works as expected, so it has to do something with the dict? I also tried setting title as a property: title = property(_title) But that did not work, too. So, how can I solve this? Thank you in advance! enter code here

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  • Using my ISerializable implementation instead of DataContractSerializer

    - by mpm
    My WCF client and server exchange objects whose types are defined on a class library shared by both, the server and the client. These objects implement custom serialization via ISerializable. However, my custom serialization is not being used. DataContractSerializer is being used, instead. How do I force my custom serialization to be used? The reason why I need to use my own serialization is because I do trasfer some big object graphs and my serialization algorithm does a good job in compressing/speeding up things.

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  • Deleting Part of An Array in Java to Free Memory on Heap

    - by kate
    I am implementing a dynamic programming algorithm for the knapsack problem in Java. I declare the array and then initialize its size to be [number of objects][capacity of knapsack]. When my number of objects or my capacity gets too large, I get a memory error because I run out of space on the heap. My questions is: If I delete rows from my double array as I go along, will Java free the memory as I delete? Or does Java reserve that memory space for the size of the array I originally created? If it's the latter, is there a way to manually free the memory in Java? Thanks for your Help!

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  • C# Dataset usage necessary before passing to GridView datasource?

    - by Goober
    Scenario Lets say for example I have a series of events that fire continually every half second presenting me with an object containing some bits of information. There are always between 10 and 15 objects that are being updated constantly. Since these bits of information are changing continually I want to display them in a GridView. When I do so, I want the user to see the data displayed in the gridview and actually be updated as opposed to just a continually extending list being printed and incrementing (like writeline on the console). Question Is the best way to achieve this to map my objects to a dataset and have the dataset mapped to the gridview? Thoughts Will this allow the gridview to just be "UPDATED" as opposed to being added to? Any implementation suggestions would be greatly appreciated. EDIT: it MUST be windows forms (I use DevExpress too)

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  • iOS UITableViewCell UIImageView setting on different conditions

    - by chis54
    I have an app that has a UITableView and in my Cells I have UIImageViews and UILabels that change images/textColors for a day theme and a night theme (trying to be automatically set). My issue is that I set the images and colors when the table is populated with cellForRowAtIndexPath and its during the day "theme", then if I reopen the app hours later in the night "theme" and the app is still in the "background" and not needing to be reloaded (ie viewDidLoad doesn't fire), the day "theme" shows until I scroll the UITableView and then the night "theme" shows when new cells are brought into view by scrolling. How should I set the objects in my cells when changing around time of the day? I was thinking to use an NSTimer, but I'm not sure how to update the objects in my cells. I was also thinking about using the appropriate methods in the AppDelagate to set things in motion, but is there a way to force reloading the TableView? Any suggestions?

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  • C#, Generic Lists and Inheritance

    - by Andy
    I have a class called Foo that defines a list of objects of type A: class Foo { List<A> Items = new List<A>(); } I have a class called Bar that can save and load lists of objects of type B: class Bar { void Save(List<B> ComplexItems); List<B> Load(); } B is a child of A. Foo, Bar, A and B are in a library and the user can create children of any of the classes. What I would like to do is something like the following: Foo MyFoo = new Foo(); Bar MyBar = new Bar(); MyFoo.Items = MyBar.Load(); MyBar.Save(MyFoo.Items); Obviously this won't work. Is there a clever way to do this that avoids creating intermediate lists? thanks, Andy

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  • Xcode automatically converts the object to NSArray

    - by Farrukh Javeid
    I have been working on an app and during the development, I am facing a very strange problem. I have a NSMutableArray tempSortedArray, which is full of objects of Store types. All the objects are valid as I can see them in my GUI, the problem arises when I iterate through the array, at index 90, which can be generally anyone, the XCode converts the Store object to NSMutableArray object. Any idea, why this is happening. This is the code to check out what I am doing: NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"cashBack" ascending:NO]; NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor]; NSArray *sortedArray = [storesArray sortedArrayUsingDescriptors:sortDescriptors]; for (int i = 0; i < [tempSortedArray count]; i++) { Store *currentStore = [tempSortedArray objectAtIndex:i]; NSLog(@"store class: %@", [currentStore.class description]); if (currentStore.cashBackTypeString != (id)[NSNull null]) { //do whatever is required to do here }

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  • Information Modeling

    - by Betamoo
    The sensor module in my project consists of a rotating camera, that collects noisy information about moving objects in the surrounding environment. The information consists of distance, angle and relative change of the moving objects.. The limiting view range of the camera makes it essential to rotate the camera periodically to update environment information... I was looking for algorithms / ways to model these information, in order to be able to guess / predict / learn motion properties of these object.. My current proposed idea is to store last n snapshots of each object in a queue. I take weighted average of positions and velocities of moving object, but I think it is a poor method... Can you state some titles that suit this case? Thanks

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  • Download multiple files in background in Android

    - by Addev
    Basically I'm trying to make a little app for watching offline content. So there's a moment where the user selects to download the contents (and the app should download about 300 small files and images). I'd like to show the user how does the process go if he enters the proper activity. Showing a list of all the files, telling what has been already downloaded, in progress or waiting for download. My problem is that I really don't know what approach to take for achieve this. Since the download should last until finished I imagine the solution is an Service, but whats best? an IntentService, a Bound Service or an Standard Service calling a startService() for each download? And how can I keep my objects updated for displaying them later? should I use a database or objects in memory? Thanks

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  • How should flushing be handled in a doctrine EntityManager instance shared across different services in symfony2?

    - by Jbm
    I have defined several services in symfony 2 which persist changes to the database. These services have the doctrine instance as one of their dependencies: a.given.service: class: Acme\TestBundle\Service\AGivenService arguments: [@doctrine] If I have two different services and both of them persist objects through the EntityManager, which is obtained like this from the doctrine instance: $em = $doctrine->getEntityManager(); Would all services always share the same EntityManager? If so, how should I handle flushing if I wanted to handle all the changes in a single transaction? I have checked this: http://docs.doctrine-project.org/projects/doctrine-orm/en/2.0.x/reference/transactions-and-concurrency.html and it explains how to handle different transactions in a request, but I want to achieve the opposite, which is having different changes in different services handled as a single transaction. Is there a better approach to handle multiple changes in different services? For now my best bet is having a front-end service in charge of calling the other services and doing the flushing afterwards. Backend services would persist objects but would not do any flushing.

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