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• How does Core Data determine if an NSObjects data can be dropped?

  - by Kevin

  In the app I am working on now I was storing about 500 images in Core Data. I have since pulled those images out and store them in the file system now, but in the process I found that the app would crash on the device if I had an array of 500 objects with image data in them. An array with 500 object ids with the image data in those objects worked fine. The 500 objects without the image data also worked fine. I found that I got the best performance with both an array of object ids and image data stored on the filesystem instead of in core data. The conclusion I came to was that if I had an object in an array that told Core Data I was "using" that object and Core Data would hold on to the data. Is this correct?

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• Implementing Transparent Persistence

  - by Jules

  Transparent persistence allows you to use regular objects instead of a database. The objects are automatically read from and written to disk. Examples of such systems are Gemstone and Rucksack (for common lisp). Simplified version of what they do: if you access foo.bar and bar is not in memory, it gets loaded from disk. If you do foo.bar = baz then the foo object gets updated on disk. Most systems also have some form of transactions, and they may have support for sharing objects across programs and even across a network. My question is what are the different techniques for implementing these kind of systems and what are the trade offs between these implementation approaches?

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• What to return as an iterator when there is no container?

  - by DaClown

  I have an inheritance structure of objects with begin() and end() as pure virtual member functions in the base class. From this objects I'm planning to build a composite structure. This inner objects have std::vector member the begin() and end() get their data from. But in a leaf class there is no vector. Now I try to find a return value for begin() and end() in the leaf classes. What would be a good way to do that? The easiest way would be to have a vector member in the leaf classes with no elements in it to fuel begin() and end(), but this just doesn't feel right.

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• Django: query spanning multiple many-to-many relationships

  - by Brant

  I've got some models set up like this: class AppGroup(models.Model): users = models.ManyToManyField(User) class Notification(models.Model): groups_to_notify = models.ManyToManyField(AppGroup) The User objects come from django's authentication system. Now, I am trying to get all the notifications pertaining to the groups that the current user is a part of. I have tried.. notifications = Notification.objects.filter(groups_to_notify=AppGroup.objects.filter(users=request.user)) But that gives an error: more than one row returned by a subquery used as an expression Which I suppose is because the groups_to_notify is checking against several groups. How can I grab all the notifications meant for the user based on the groups he is a part of?

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• windows control library in c sharp

  - by apals

  I have just added a textbox, button, label to validate ID of 12 characters. The library is called check_ID. It works fine. The only problem is i have to access the forecolor of label, backcolor of textbox , forecolor of button as per color scheme of the project. But it seems that none of the properties of the objects in check_ID are available for modification. I have even changed the modifier to public of all objects by repoening the check_ID project. Is there another way to access the properties of these objects that are created using windows control library?. A very big thanks in advance.

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• importing data using get or create - identity error 1062

  - by hamackey

  I am importing data from a mssql database into mysql. Works except when it encounters the id of a previous entry. id is unique. I need to get entries that already exist so that they can be placed in the work of the day. Error is IntegrityError: (1062, "Duplicate entry '001355338' for key 2") This entry is already in the database. I need it entered for that day, but can not have it added to the table. It is already there. def handle(self, *args, **options): 59 #patients_local = Patient.objects.all() 60 #attendings_local = Attending.objects.all() 61 connection = pyodbc.connect("XXXXXXXXXXX") 62 cursor = connection.cursor() 63 cursor.execute(COMMAND) 64 rows = cursor.fetchall() 65 for row in rows: 66 # get_or_create returns (object, boolean) 67 p, created = Patient.objects.get_or_create( 68 first_name = row.Firstname, 69 middle_name = '', 70 last_name = row.Lastname, 71 id = row.id, 72 )

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• What is the pythonic way to add type information to an object's attributes?

  - by Tikitu

  I'm building classes where I know the types of the attributes, but Python of course doesn't. While it's un-pythonic to want to tell it, supposing I do want to, is there an idiomatic way to do so? Why: I'm reading in serialised data (without type information) involving objects-nested-inside-objects. It's easy to put it into nested dictionaries, but I want it in objects of my class-types, to get the right behaviours as well as the data. For instance: suppose my class Book has an attribute isbn which I will fill with an ISBNumber object. My serialised data gives me the isbn as a string; I would like to be able to look at Book and say "That field should be filled by ISBNumber(theString)." Bonus glee for me if the solution can be applied to classes I get from someone else without editing their code.

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• MVC, how view should be accessed from controller?

  - by Kirzilla

  Hello, I'm just learning MVC so you could find my question rather strange... My Controller have access to different shared objects through Container object passed to Controller's constructor. To access shared objects I should do $this-container-db to access Database adapter or $this-container-memcache to access Memcached adapter. I want to know should I put View object into Container with shared objects or no? From one side it is really comfortable to take view from this container, but this way I couldn't create multiple Views instances (for example, every time I'm calling Controller's method from View I should have one more View instance). What is the solution? How should I pass View object into Controller and/or how should I create new View instances from Controller? Thank you!

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• How to add an additional field to a queryset?

  - by Mark

  I've got a list of affiliates (users who have referred someone to the site): affiliates = User.objects.annotate(referral_count=Count('referrals')).filter(referral_count__gt=0) And a count of the number of users each affiliate has referred within a time frame: new_users = User.objects.filter(date_joined__gt=sd, date_joined__lte=ed) new_referrals = User.objects.filter(referrals__user__in=new_users).annotate(referral_count=Count('referrals')) How can I do something like new_referrals['affiliate.username'].referral_count from within my template? Note that this is not just a syntax issue, I also need to index new_referrals somehow so that I'm able to do this. Either this, or if I can somehow add a new_referral_count to the first query, that'd work too.

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• How do I reload a Roo project without clearing the database?

  - by Omniwombat

  I've been learning how to build projects using Roo and am making good progress. I have the nucleus of a project which correctly displays my defined entities and allows me to create, edit, and delete the representative objects. I am using mysql at the database and I see that objects entered using the UI correctly appear in the mysql database. Per the Roo instructions, I am starting the webapp using "mvn tomcat:run". Unfortunately, I've discovered that whenever I restart Tomcat using Maven, it clears all of the existing objects out of the database. I'm left with empty tables. It seems to do this as the final step just prior to Tomcat stating that the server has started. I know this is just me being a n00b, but searches haven't been very helpful, none of the project's XML files seem relevant,

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• Reusing a vector in C++

  - by Bobby

  I have a vector declared as a global variable that I need to be able to reuse. For example, I am reading multiple files of data, parsing the data to create objects that are then stored in a vector. vector<Object> objVector(100); void main() { while(THERE_ARE_MORE_FILES_TO_READ) { // Pseudocode ReadFile(); ParseFileIntoVector(); ProcessObjectsInVector(); /* Here I want to 'reset' the vector to 100 empty objects again */ } } Can I reset the vector to be "vector objVector(100)" since it was initially allocated on the stack? If I do "objVector.clear()", it removes all 100 objects and I would have a vector with a size of 0. I need it to be a size of 100 at the start of every loop.

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• Fetch a Rails ActiveRecord 'datetime' attribute as a DateTime object.

  - by Tobias Cohen

  I have an attribute in one of my models that contains a Date/Time value, and is declared using t.datetime :ended_on in my migrations. When I fetch this value using myevent.ended_on, I get a Time object. The problem is that when I try to use this attribute as an axis in a Flotilla chart, it doesn't work properly because Flotilla only recognizes dates as Date or DateTime objects. I thought about writing a virtual attribute that will convert the existing Time value to a DateTime, but I'm wary of doing this, since I've heard that Time can't handle dates later than 2040, and I don't wish to risk creating a "2040 bug" to worry about later. Is there any way I can persuade ActiveRecord to return DateTime objects for this attribute instead of Time objects?

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• C# Container Class

  - by Jamie

  I'm building a game in c# which allows you to script your own level, although I have come across a bit of a thought. I have a base class called "World" as an object. This was made with a simple: class World { However, when the user is scripting their level, all of the game objects will be contained in the world object. I want them to be able to do something on the lines of: World.ParentObjectName.ParentObjectProperty = "abc"; I know that the System.Windows.Forms.Panel and other classes are like containers and can have objects in them and be accessed in that kind of way... my question is how can I make a class which is like a container in which I can add objects to, and then access them with a World.ObjectName I have tried class World : System.Collections.CollectionBase, but with this method, I have to keep typing World.Item("ObjectName") Can anyone help? Thanks!

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• ToList()-- Does it Create a New List?

  - by Ngu Soon Hui

  Let's say I have a class public class MyObject { public int SimpleInt{get;set;} } And I have a List<MyObject>, and I ToList() it and then change one of the SimpleInt, will my change be propagated back to the original list. In other words, what would be the output of the following method? public void RunChangeList() { var objs = new List<MyObject>(){new MyObject(){SimpleInt=0}}; var whatInt = ChangeToList(objs ); } public int ChangeToList(List<MyObject> objects) { var objectList = objects.ToList(); objectList[0].SimpleInt=5; return objects[0].SimpleInt; } Why? P/S: I'm sorry if it seems obvious to find out. But I don't have compiler with me now...

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• Design guide-lines for writing a Typed SQL Statement API ?

  - by this. __curious_geek

  Last night I came up to sometihng intersting while designing my new project that brought me to ask this qustion here. My project is supposed to follow Table Gateway pattern using tradional ADO.Net datasets for data access. I don't want to write plain queries in my data-access classes. So I came up with an idea of writing a parser kindaa api that exposes objects and methods to generate queries on the move based on my domain objects. Later I want this api to hook up to my Business objects and provide Typed SQL generator api right on the business object instances. Any idea or references how can I do this ? This seems very wide to start with that I'm compelled take your opinions here. Does there anything already exists that can do this ?

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• Why does my git push hang after successfully pushing?

  - by John

  On a newly set up ssh git repo, whenever I push, I get normal output like this: ? git push Counting objects: 15, done. Delta compression using up to 4 threads. Compressing objects: 100% (9/9), done. Writing objects: 100% (9/9), 989 bytes, done. Total 9 (delta 7), reused 0 (delta 0) It happens very quickly, and the changes are immediately available on the server repo. But the output hangs there for about a minute, and then finishes with: To [email protected]:baz.git c8c391c..1de5e80 branch_name -> branch_name If I control-c before it finishes, everything seems to continue to be normal and healthy, locally and remotely. What is it doing while hanging? Is something configured incorrectly on the server side?

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• Fluent mapping help

  - by Matt Thrower

  Hi, This is probably a very simple question but I'm new to nHibernate and I'm having trouble working this out. I have a Page object, which can have many Region objects. I also have a Workflow object. Page and Region objects both have a relationship to Workflow and it's this double association that I'm having trouble with. The PageMap has HasMany(Function(x) x.Regions).Cascade.All() And the RegionMap has: References(Function(x) x.Page) And this all seems to work. But how do I define the relationship between Workflow and these two objects?

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• How to handle injecting dependencies into rich domain models?

  - by Arne

  In a web server project with a rich domain model (application logic is in the model, not in the services) how do you handle injecting the dependencies into the model objects? What are your experiences? Do you use some form of AOP? Like Springs @Configurable annotation? Load time or build time weawing? Problems you encountered? Do you use manual injection? Then how do you handle different instantiation scenarios (creating of the objects through an library [like Hibernate], creating objects with "new" ...)? Or do you use some other way of injecting the dependencies?

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• Best way to reuse a Runnable

  - by Gandalf

  I have a class that implements Runnable and am currently using an Executor as my thread pool to run tasks (indexing documents into Lucene). executor.execute(new LuceneDocIndexer(doc, writer)); My issue is that my Runnable class creates many Lucene Field objects and I would rather reuse them then create new ones every call. What's the best way to reuse these objects (Field objects are not thread safe so I cannot simple make them static) - should I create my own ThreadFactory? I notice that after a while the program starts to degrade drastically and the only thing I can think of is it's GC overhead. I am currently trying to profile the project to be sure this is even an issue - but for now lets just assume it is.

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• IDisposable, does it really matter

  - by adrianm

  Coming from C/C++ a long time ago I still have a habit of ensuring that all resources are cleaned up correctly. I always ensure Dispose is called on IDisposable classes and implement Dispose patterns in my classes containing disposable objects. However, in my environment I'm more or less the only one doing this. Others just don't understand what I'm doing and think my code is more difficult to understand. They just create database connections, open streams etc without calling Close or Dispose. Sometimes they set a local or member variable to "Nothing" at the end of a method (guess their background). My problem is that their code works just as well as mine. Code that over time creates thousands of database connection objects just works. So, ignoring any arguments about code correctness, following guidelines etc, does IDiposable really matter? Has anyone actually ran out of resources from not Disposing objects?

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• Using JLists and ListModels

  - by devoured elysium

  I have defined a DirectoryListModel class that extends the AbstractListModel class from the Java Api. Internally, I have a list of File objects. I have defined the getElementAt(int index) method as: @Override public Object getElementAt(int index) { return directoryElements.get(index) } The problem is that when I try to run my JList with my DirectoryListModel, it is going to show up the full paths of files instead of just the filenames. I could change this code to: @Override public Object getElementAt(int index) { return directoryElements.get(index).getName(); } and it'd work wonders, but the problem is that in the onclick event I'll want to have the File objects so I can do some checking with them (check if they're directories, etc). If I make getElementAt() return a String, I'm losing that possibility, thus I'd like to konw if there is a way I can format my File objects before the JList shows them in my window. Thanks

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• Looking for an array (vs linked list) hashtable implementation in C

  - by kingusiu

  hi, I'm looking for a hashtable implementation in C that stores its objects in (twodimensional) arrays rather than linked lists. i.e. if a collision happens, the object that is causing the collision will be stored in the next free row index rather than pushed to the head and first element of a linked list. plus, the objects themselves must be copied to the hashtable, rather than referenced by pointers. (the objects do not live for the whole lifetime of the program but the table does). I know that such an implementation might have serious efficiency drawbacks and is not the "standard way of hashing" but as I work on a very special system-architecture i need those characteristics. thanks

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• Filtering across two ManyToMany fields

  - by KVISH

  I have a User model and an Event model. I have the following for both: class Event(models.Model): ... timestamp = models.DateTimeField() organization_map = models.ManyToManyField(Organization) class User(AuthUser): ... subscribed_orgs = models.ManyToManyField('Organization') I want to find all events that were created in a certain timeframe and find the users who are subscribed to those organizations. I know how to write SQL for this (it's very easy), but whats the pythonic way of doing this using Django ORM? I'm trying as per below: orgs = Organization.objects.all() events = Event.objects.filter(timestamp__gt=min_time) # Min time is the time I want to start from events = events.filter(organization_map__in=orgs) But from there, how do I map to users who have that organization as a subscription? I'm trying to map it like so: users = User.objects.filter(subscribed_orgs__in=...

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• new MyClass(); vs new MyClass;

  - by Bytecode Ninja

  In some JavaScript code snippets (e.g. http://mckoss.com/jscript/object.htm) I have seen objects being created in this way: var obj = new Foo; However, at least at MDC, it seems that the parentheses are not optional when creating an object: var obj = new Foo(); Is the former way of creating objects valid and defined in the ECMA standard? Are there any differences between the former way of creating objects and the later? Is one preferred over the other? Thanks in advance.

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• Global Import/using Aliasing in .NET

  - by Josh Stodola

  Using import aliasing in a single class, we can reference class library namespaces by assigning our own custom alias like this: ' VB Imports Db = Company.Lib.Data.Objects // C# using Db = Company.Lib.Data.Objects; And then we are able to reference the classes inside of Company.Lib.Data.Objects by using the Db alias that we assigned. Is it possible to do this at the global level so that the alias is applied to the entire solution instead of the given file? Currently, we are working with web applications, so I was hoping we could add something to web.config, but I am also interested in whether or not this is possible with windows forms, console apps, and/or class libraries.

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