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  • Zend_Form and Liskov Substitution Principle

    - by blockhead
    A very common pattern I see (I'm picking on Zend Framework, only because I was dealing with it at the moment of this question), is something like this: class My_Form extends Zend_Form { public function init() { $this->addElement(); } } Zend_Form is not an abstract class, but is perfectly usable on its own. This seems to be "recommended" as place to "encapsulate" your forms into a nice class. Does this violate the Liskov Substitution Principle? Each subclass of Zend_Form will have a wildy different behavior than the base class. Would it be better to use composition for this, or am I totally misunderstanding this principle?

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  • NameValueCollection Issue In Proxy Generation

    - by N W. annor-adjei
    I have a proxy generation problem I am building my own customised XMLMembershipProvider in WCF. The code runs well in ASP.Net and am consuming the same code in WCF for silverlight, My class inherits the Membership provider hence have implemented all the MembershipProvider methods. Now, consumung this methods in WCF requires also the Initialize Method having NameValueCollection as passin parameter, which is the cause of the problem because WCF does not supporteCollection serialization. when the initialize method is marked as OperationContract, Proxy class does not get generated. I could have use Dictionary but that is impossible here bacause the base class's initialize method accepts two parameter one of which should be a NameValueCollection. If i don't mark the Initialize as OperationContract, the proxy class is generated with all the methods but i realized i still need the Initialize marked as Operation contract to start the provider. Has any one got any idea about the use of NameValueCollection in WCF and the work around this problem Thank you. Nicholas

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  • Ads in whole app iPhone problem

    - by lars
    I am using mobclix together with admob. The code is to big to add it in all classes. So i created a new class: Ads Everytime i want an ad in a view, i have to send the view to the ad class: - (void)initAd:(UIView *) pView { NSLog(@"ads init"); self.loadedView = pView; ..... To create an ad in a class: Ad* ad = [Ads new]; [ad initAd:self.view]; I dont know if thats the right way. I have to create a new Ads object everytime i change a view (or class). Is there a way to always have an Ads instance running, or is there another better way? Thanks alot!!

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  • javascript hide/show tabs using JQuery

    - by JohnMerlino
    Hey all, I have a quick question of how I can use jquery tabs (you click on link button to display/hide certain divs). The div id matches the href of the link: HTML links: <table class='layout tabs'> <tr> <td><a href="#site">Site</a></td> <td><a href="#siteno">Number</a></td> </tr> <tr> <td><a href="#student">Student</a></td> <td><a href="#school">School</a></td> </tr> </table> </div> div that needs to display/hide: <div id="site"> <table class='explore'> <thead class='ui-widget-header'> <tr> <th class=' sortable'> Site </th> <th class=' sortable'> Number </th> </tr> </thead> </table> </div> Thanks for any response.

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  • Why is C# statically typed?

    - by terrani
    I am a PHP web programmer who is trying to learn C#. I would like to know why C# requires me to specify the data type when creating a variable. Class classInstance = new Class(); Why do we need to know the data type before a class instance?

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  • Dynamic Operator Overloading on dict classes in Python

    - by Ishpeck
    I have a class that dynamically overloads basic arithmetic operators like so... import operator class IshyNum: def __init__(self, n): self.num=n self.buildArith() def arithmetic(self, other, o): return o(self.num, other) def buildArith(self): map(lambda o: setattr(self, "__%s__"%o,lambda f: self.arithmetic(f, getattr(operator, o))), ["add", "sub", "mul", "div"]) if __name__=="__main__": number=IshyNum(5) print number+5 print number/2 print number*3 print number-3 But if I change the class to inherit from the dictionary (class IshyNum(dict):) it doesn't work. I need to explicitly def __add__(self, other) or whatever in order for this to work. Why?

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  • Filename of script that instantiates an object

    - by Calvin L
    In PHP, is it possible to get the file name of the script that instantiated an object? For example I have a script called file.php that creates a new instance of class Class. The class has an Error object that, when triggered, returns some error information. I would like to show that file.php triggered the error.

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  • Hibernate does not allow an embedded object with an int field to be null?

    - by Jason Novak
    Hibernate does not allow me to persist an object that contains an null embedded object with an integer field. For example, if I have a class called Thing that looks like this @Entity public class Thing { @Id public String id; public Part part; } where Part is an embeddable class that looks like this @Embeddable public class Part { public String a; public int b; } then trying to persist a Thing object with a null Part causes Hibernate to throw an Exception. In particular, this code Thing th = new Thing(); th.id = "thing.1"; th.part = null; session.saveOrUpdate(th); causes Hibernate to throw this Exception org.hibernate.PropertyValueException: not-null property references a null or transient value: com.ace.moab.api.jobs.Thing.part My guess is that this is happening because Part is an embedded class and so Part.a and Part.b are simply columns in the Thing database table. Since the Thing.part is null Hibernate wants to set the Part.a and Part.b column values to null for the row for thing.1. However, Part.b is an integer and Hibernate will not allow integer columns in the database to be null. This is what causes the Exception, right? So I am looking for workarounds for this problem. I noticed making Part.b an Integer instead of an int seems to work, but for reasons I won't bore you with this is not a good option for us. Thanks!

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  • What is Ruby's double-colon (::) all about?

    - by Meltemi
    I'd probably be able to answer this for myself if "::" wasn't so hard to Google. Didn't see anything on SO so thought I'd try my luck. What is this double-colon :: all about? I see it everywhere in Rails: class User < ActiveRecord::Base or… ActionController::Routing::Routes.draw do |map| I found a definition from this guy: The :: is a unary operator that allows: constants, instance methods and class methods defined within a class or module, to be accessed from anywhere outside the class or module. but that just leads to more questions. What good is scope (private, protected) if you can just use :: to expose anything?

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  • Make dynamic changing background with last FM api

    - by user1854225
    I make some class. This class search some artist and return picture. After than I go to my class with player , where I create an instance of class and call the method and is passed artist. After i go to my tableview with audio So its doesn't work. Background still not changed and my app crashed. I don't know how I can fix that. http://pastebin.com/hUxqAuAh on this link my source code. Error like this ( 2012-11-27 17:00:57.846 VKMusic[4959:c07] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'data parameter is nil' ) I want make like http://rghost.net/41831486.view on this picture. upd: I found first problem. I must do like this NSString *encodedText = [artist stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

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  • NoClassDefFoundError with new eclipse bundle

    - by djmedic
    I am informed by a customer that they are receiving an error. On the report they filed it is continuosly coming up with NoClassDefFoundError. It appears none of my other customers are having this issue. I'm not having this issue running the app on my Motorola Droid Maxx. The customer is running the app on a rooted Droid Bionic. Everything was working fine on my version at 2.3 but when I updated it to 2.4, this issue arose. I also replaced my computer with a new and now I am running windows 8 and installed the adt bundle. The only change I made to the file in question in changing a -90 to -85. Below is the code...I have also included below the code the error report. This is only happening on phone. import android.app.Activity; import android.content.Context; import android.content.Intent; import android.net.ConnectivityManager; import android.net.NetworkInfo; import android.os.Bundle; import android.telephony.PhoneStateListener; import android.telephony.SignalStrength; import android.telephony.TelephonyManager; public class ConnectivityCheck extends Activity { TelephonyManager Tel; MyPhoneStateListener MyListener; boolean isGsm; boolean cellAvailable; int strengthAmplitudeGSM; int strengthAmplitudeCDMA; @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); ConnectivityManager connec = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE); if (connec.getNetworkInfo(0) != null) { cellAvailable = true; } if (cellAvailable) { /* Update the listener, and start it */ MyListener = new MyPhoneStateListener(); Tel = ( TelephonyManager )getSystemService(Context.TELEPHONY_SERVICE); Tel.listen(MyListener ,PhoneStateListener.LISTEN_SIGNAL_STRENGTHS); } if (connec.getNetworkInfo(1).getState() == NetworkInfo.State.CONNECTED) { startActivity(new Intent(ConnectivityCheck.this, LicenseCheck.class)); if (cellAvailable) { Tel.listen(MyListener, PhoneStateListener.LISTEN_NONE); } finish(); } else if (cellAvailable) { if (connec.getNetworkInfo(0).getState() == NetworkInfo.State.CONNECTED && strengthAmplitudeCDMA >= -90) { startActivity(new Intent(ConnectivityCheck.this, LicenseCheck.class)); Tel.listen(MyListener, PhoneStateListener.LISTEN_NONE); finish(); } else if (connec.getNetworkInfo(0).getState() == NetworkInfo.State.CONNECTED && isGsm && strengthAmplitudeGSM >= 10 && strengthAmplitudeGSM <= 31) { startActivity(new Intent(ConnectivityCheck.this, LicenseCheck.class)); Tel.listen(MyListener, PhoneStateListener.LISTEN_NONE); finish(); } else { startActivity(new Intent(ConnectivityCheck.this, ProtocolsMMenuActivity.class)); Tel.listen(MyListener, PhoneStateListener.LISTEN_NONE); finish(); } } else { startActivity(new Intent(ConnectivityCheck.this, ProtocolsMMenuActivity.class)); if (cellAvailable) { Tel.listen(MyListener, PhoneStateListener.LISTEN_NONE); } finish(); } } /* Called when the application is minimized */ @Override protected void onPause() { super.onPause(); if (cellAvailable) { Tel.listen(MyListener, PhoneStateListener.LISTEN_NONE); } } /* Called when the application resumes */ @Override protected void onResume() { super.onResume(); if (cellAvailable) { Tel.listen(MyListener, PhoneStateListener.LISTEN_SIGNAL_STRENGTHS); } } /* Start the PhoneState listener */ private class MyPhoneStateListener extends PhoneStateListener { /* Get the Signal strength from the provider, each tiome there is an update */ @Override public void onSignalStrengthsChanged(SignalStrength signalStrength) { isGsm = signalStrength.isGsm(); strengthAmplitudeGSM = signalStrength.getGsmSignalStrength(); strengthAmplitudeCDMA = signalStrength.getCdmaDbm(); super.onSignalStrengthsChanged(signalStrength); } };/* End of private Class */ } Here is the error report java.lang.NoClassDefFoundError: com.emsprotocols.njalsprotocolspaidac.ConnectivityCheck at com.emsprotocols.njalsprotocolspaidac.ProtocolsSplashActivity$1.onAnimationEnd (ProtocolsSplashActivity.java:144) at android.view.animation.AnimationSet.getTransformation(AnimationSet.java:411) at android.view.animation.Animation.getTransformation(Animation.java:920) at android.view.ViewGroup.drawChild(ViewGroup.java:2657) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2489) at android.view.ViewGroup.drawChild(ViewGroup.java:2885) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2489) at android.view.ViewGroup.drawChild(ViewGroup.java:2885) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2489) at android.view.View.draw(View.java:11009) at android.widget.FrameLayout.draw(FrameLayout.java:450) at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2154) at android.view.ViewRootImpl.draw(ViewRootImpl.java:2096) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1679) at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2558) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4722) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554) at dalvik.system.NativeStart.main(Native Method)

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  • Qthread - trouble shutting down threads

    - by Bryan Greenway
    For the last few days, I've been trying out the new preferred approach for using QThreads without subclassing QThread. The trouble I'm having is when I try to shutdown a set of threads that I created. I regularly get a "Destroyed while thread is still running" message (if I'm running in Debug mode, I also get a Segmentation Fault dialog). My code is very simple, and I've tried to follow the examples that I've been able to find on the internet. My basic setup is as follows: I've a simple class that I want to run in a separate thread; in fact, I want to run 5 instances of this class, each in a separate thread. I have a simple dialog with a button to start each thread, and a button to stop each thread (10 buttons). When I click one of the "start" buttons, a new instance of the test class is created, a new QThread is created, a movetothread is called to get the test class object to the thread...also, since I have a couple of other members in the test class that need to move to the thread, I call movetothread a few additional times with these other items. Note that one of these items is a QUdpSocket, and although this may not make sense, I wanted to make sure that sockets could be moved to a separate thread in this fashion...I haven't tested the use of the socket in the thread at this point. Starting of the threads all seem to work fine. When I use the linux top command to see if the threads are created and running, they show up as expected. The problem occurs when I begin stopping the threads. I randomly (or it appears to be random) get the error described above. Class that is to run in separate thread: // Declaration class TestClass : public QObject { Q_OBJECT public: explicit TestClass(QObject *parent = 0); QTimer m_workTimer; QUdpSocket m_socket; Q_SIGNALS: void finished(); public Q_SLOTS: void start(); void stop(); void doWork(); }; // Implementation TestClass::TestClass(QObject *parent) : QObject(parent) { } void TestClass::start() { connect(&m_workTimer, SIGNAL(timeout()),this,SLOT(doWork())); m_workTimer.start(50); } void TestClass::stop() { m_workTimer.stop(); emit finished(); } void TestClass::doWork() { int j; for(int i = 0; i<10000; i++) { j = i; } } Inside my main app, code called to start the first thread (similar code exists for each of the other threads): mp_thread1 = new QThread(); mp_testClass1 = new TestClass(); mp_testClass1->moveToThread(mp_thread1); mp_testClass1->m_socket.moveToThread(mp_thread1); mp_testClass1->m_workTimer.moveToThread(mp_thread1); connect(mp_thread1, SIGNAL(started()), mp_testClass1, SLOT(start())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(quit())); connect(mp_testClass1, SIGNAL(finished()), mp_testClass1, SLOT(deleteLater())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(deleteLater())); connect(this,SIGNAL(stop1()),mp_testClass1,SLOT(stop())); mp_thread1->start(); Also inside my main app, this code is called when a stop button is clicked for a specific thread (in this case thread 1): emit stop1(); Sometimes it appears that threads are stopped and destroyed without issue. Other times, I get the error described above. Any guidance would be greatly appreciated. Thanks, Bryan

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  • how can I get instance from the property.

    - by viky
    In my application I have a class which has properties of user-defined types like this: class MyType { public A MyProperty { get; set; } } class A { .....some methods and proeprties } for some operations that I need to perform from my main program, I create a List of MyProperty whenever creating object of MyType and pass it to my main program and there I perform different operation on these properties which reflects in there instances also. Is there any way by which I could get the object instance for any particular MyProperty from that property in the list.

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  • Why is String final in Java?

    - by Alex
    From when I learned that the class java.lang.String is declared as final in Java, I was wondering why is that? I didn't find any answer back then, but this post: How to create a replica of String class in Java? reminded me of my query. Sure, String provides all the functionality I ever needed, and never thought of any operation that would require an extension of class String, but still you'll never know what someone might need! So, does anyone know what was the intent of the designers when they decided to make it final? See also: Why is String a sealed class in C#?

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  • Error in connection in ruby.

    - by piemesons
    require 'rubygems' require 'mysql' db = Mysql.connect('localhost', 'root', '', 'mohit') //db.rb:4: undefined method `connect' for Mysql:Class (NoMethodError) //undefined method `real_connect' for Mysql:Class (NoMethodError) db.query("CREATE TABLE people ( id integer primary key, name varchar(50), age integer)") db.query("INSERT INTO people (name, age) VALUES('Chris', 25)") begin query = db.query('SELECT * FROM people') puts "There were #{query.num_rows} rows returned" query.each_hash do |h| puts h.inspect end rescue puts db.errno puts db.error end error i am geting is: undefined method `connect' for Mysql:Class (NoMethodError) OR undefined method `real_connect' for Mysql:Class (NoMethodError) EDIT return value of Mysql.methods ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "object_id", "__send__", "method_defined?", "instance_variable_defined?", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "instance_method", "hash", "autoload?", "dup", "to_enum", "instance_methods", "public_method_defined?", "instance_variables", "class_variable_defined?", "eql?", "constants", "id", "instance_eval", "singleton_methods", "module_exec", "const_missing", "taint", "instance_variable_get", "frozen?", "enum_for", "private_method_defined?", "public_instance_methods", "display", "instance_of?", "superclass", "method", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "public_class_method", "to_s", "<=", "const_set", "allocate", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "autoload", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"] return value of Mysql.methods(false) is []... blank array

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  • Is a many-to-many relationship with extra fields the right tool for my job?

    - by whichhand
    Previously had a go at asking a more specific version of this question, but had trouble articulating what my question was. On reflection that made me doubt if my chosen solution was correct for the problem, so this time I will explain the problem and ask if a) I am on the right track and b) if there is a way around my current brick wall. I am currently building a web interface to enable an existing database to be interrogated by (a small number of) users. Sticking with the analogy from the docs, I have models that look something like this: class Musician(models.Model): first_name = models.CharField(max_length=50) last_name = models.CharField(max_length=50) dob = models.DateField() class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) class Instrument(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) Where I have one central table (Musician) and several tables of associated data that are related by either ForeignKey or OneToOneFields. Users interact with the database by creating filtering criteria to select a subset of Musicians based on data the data on the main or related tables. Likewise, the users can then select what piece of data is used to rank results that are presented to them. The results are then viewed initially as a 2 dimensional table with a single row per Musician with selected data fields (or aggregates) in each column. To give you some idea of scale, the database has ~5,000 Musicians with around 20 fields of related data. Up to here is fine and I have a working implementation. However, it is important that I have the ability for a given user to upload there own annotation data sets (more than one) and then filter and order on these in the same way they can with the existing data. The way I had tried to do this was to add the models: class UserDataSets(models.Model): user = models.ForeignKey(User) name = models.CharField(max_length=100) description = models.CharField(max_length=64) results = models.ManyToManyField(Musician, through='UserData') class UserData(models.Model): artist = models.ForeignKey(Musician) dataset = models.ForeignKey(UserDataSets) score = models.IntegerField() class Meta: unique_together = (("artist", "dataset"),) I have a simple upload mechanism enabling users to upload a data set file that consists of 1 to 1 relationship between a Musician and their "score". Within a given user dataset each artist will be unique, but different datasets are independent from each other and will often contain entries for the same musician. This worked fine for displaying the data, starting from a given artist I can do something like this: artist = Musician.objects.get(pk=1) dataset = UserDataSets.objects.get(pk=5) print artist.userdata_set.get(dataset=dataset.pk) However, this approach fell over when I came to implement the filtering and ordering of query set of musicians based on the data contained in a single user data set. For example, I could easily order the query set based on all of the data in the UserData table like this: artists = Musician.objects.all().order_by(userdata__score) But that does not help me order by the results of a given single user dataset. Likewise I need to be able to filter the query set based on the "scores" from different user data sets (eg find all musicians with a score 5 in dataset1 and < 2 in dataset2). Is there a way of doing this, or am I going about the whole thing wrong?

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  • Python hash() can't handle long integer?

    - by Xie
    I defined a class: class A: ''' hash test class a = A(9, 1196833379, 1, 1773396906) hash(a) -340004569 This is weird, 12544897317L expected. ''' def __init__(self, a, b, c, d): self.a = a self.b = b self.c = c self.d = d def __hash__(self): return self.a * self.b + self.c * self.d Why, in the doctest, hash() function gives a negative integer?

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  • Using group_by with fields_for and accepts_nested_attributes_for

    - by Derek
    I have a the following rails models: class Release < ActiveRecord::Base has_many :release_questionnaires, :dependent => :destroy accepts_nested_attributes_for :release_questionnaires ... end class class ReleaseQuestionnaire < ActiveRecord::Base belongs_to :release belongs_to :milestone ... end class In my view code, I have the following form. <% form_for @release, ... do |f| %> ... <table class="questionnaires"> <% f.fields_for :release_questionnaires, @release.release_questionnaires.sort_by{|ra| ra.questionnaire.name} do |builder| %> ... <% end %> </table> <% end %> This works and allows me to view and edit the questionnaires as desired. However, I have an additional requirement to break the questionnaires out into their own tables grouped by the milestone they are associated to, rather than in a single table. It appears as though the group_by method is design to accomplish this, but I cannot get it to work as desired inside the tag. It may be that I'm missing something obvious, as I am a beginner... Any help is appreciated.

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  • callbacks via objective-c selectors

    - by codemonkey
    I have a "BSjax" class that I wrote that lets me make async calls to our server to get json result sets, etc using the ASIHTTPRequest class. I set it up so that the BSjax class parses my server's json response, then passes control back to the calling view controller via this call: [[self delegate] performSelectorOnMainThread:@selector(bsRequestFinished:) withObject:self waitUntilDone:YES]; ... where "bsRequestFinished" is the callback method in the calling view controller. This all worked fine and well until I realized that some pages are going to need to make different types of requests... i.e. I'll want to do different types of things in that callback function depending on which type of request was made. To me it seems like being able to pass different callback function names to my BSjax class would be the cleanest fix... but I'm having trouble (and am not even sure if it's possible) to pass in a variable that holds the callback function name and then replace the call above with something like this: [[self delegate] performSelectorOnMainThread:@selector(self.variableCallbackFunctionName) withObject:self waitUntilDone:YES]; ... where "self.variableCallbackFunctionName" is set by the calling view controller when it calls BSjax to make a new request. Is this even possible? If so, advisable? If not, alternatives? EDIT: Note that whatever fix I arrive at will need to take into account the reality that this class is making async requests... so I need to make sure that the callback function processing is correctly tied to the specific requests... as I can't rely on FIFO processing sequence.

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  • django admin site - filtering available objects for user

    - by JPG
    I have models that belong to some 'group' (Company class). I want to add users, who will also belong to a one group and should be able to edit/manage/add objects with membership in associated group. something like: class Company() class Something() company = ForeignKey(Company) user Microsoft_admin company = ForeignKey(Company) and this user should only see and edit objects belonging to associated Company in the Admin Interface. How to acomplish that?

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  • Replacing objects, handling clones, dealing with write logs

    - by Alix
    Hi everyone, I'm dealing with a problem I can't figure out how to solve, and I'd love to hear some suggestions. [NOTE: I realise I'm asking several questions; however, answers need to take into account all of the issues, so I cannot split this into several questions] Here's the deal: I'm implementing a system that underlies user applications and that protect shared objects from concurrent accesses. The application programmer (whose application will run on top of my system) defines such shared objects like this: public class MyAtomicObject { // These are just examples of fields you may want to have in your class. public virtual int x { get; set; } public virtual List<int> list { get; set; } public virtual MyClassA objA { get; set; } public virtual MyClassB objB { get; set; } } As you can see they declare the fields of their class as auto-generated properties (auto-generated means they don't need to implement get and set). This is so that I can go in and extend their class and implement each get and set myself in order to handle possible concurrent accesses, etc. This is all well and good, but now it starts to get ugly: the application threads run transactions, like this: The thread signals it's starting a transaction. This means we now need to monitor its accesses to the fields of the atomic objects. The thread runs its code, possibly accessing fields for reading or writing. If there are accesses for writing, we'll hide them from the other transactions (other threads), and only make them visible in step 3. This is because the transaction may fail and have to roll back (undo) its updates, and in that case we don't want other threads to see its "dirty" data. The thread signals it wants to commit the transaction. If the commit is successful, the updates it made will now become visible to everyone else. Otherwise, the transaction will abort, the updates will remain invisible, and no one will ever know the transaction was there. So basically the concept of transaction is a series of accesses that appear to have happened atomically, that is, all at the same time, in the same instant, which would be the moment of successful commit. (This is as opposed to its updates becoming visible as it makes them) In order to hide the write accesses in step 2, I clone the accessed field (let's say it's the field list) and put it in the transaction's write log. After that, any time the transaction accesses list, it will actually be accessing the clone in its write log, and not the global copy everyone else sees. Like this, any changes it makes will be done to the (invisible) clone, not to the global copy. If in step 3 the commit is successful, the transaction should replace the global copy with the updated list it has in its write log, and then the changes become visible for everyone else at once. It would be something like this: myAtomicObject.list = updatedCloneOfListInTheWriteLog; Problem #1: possible references to the list. Let's say someone puts a reference to the global list in a dictionary. When I do... myAtomicObject.list = updatedCloneOfListInTheWriteLog; ...I'm just replacing the reference in the field list, but not the real object (I'm not overwriting the data), so in the dictionary we'll still have a reference to the old version of the list. A possible solution would be to overwrite the data (in the case of a list, empty the global list and add all the elements of the clone). More generically, I would need to copy the fields of one list to the other. I can do this with reflection, but that's not very pretty. Is there any other way to do it? Problem #2: even if problem #1 is solved, I still have a similar problem with the clone: the application programmer doesn't know I'm giving him a clone and not the global copy. What if he puts the clone in a dictionary? Then at commit there will be some references to the global copy and some to the clone, when in truth they should all point to the same object. I thought about providing a wrapper object that contains both the cloned list and a pointer to the global copy, but the programmer doesn't know about this wrapper, so they're not going to use the pointer at all. The wrapper would be like this: public class Wrapper<T> : T { // This would be the pointer to the global copy. The local data is contained in whatever fields the wrapper inherits from T. private T thisPtr; } I do need this wrapper for comparisons: if I have a dictionary that has an entry with the global copy as key, if I look it up with the clone, like this: dictionary[updatedCloneOfListInTheWriteLog] I need it to return the entry, that is, to think that updatedCloneOfListInTheWriteLog and the global copy are the same thing. For this, I can just override Equals, GetHashCode, operator== and operator!=, no problem. However I still don't know how to solve the case in which the programmer unknowingly inserts a reference to the clone in a dictionary. Problem #3: the wrapper must extend the class of the object it wraps (if it's wrapping MyClassA, it must extend MyClassA) so that it's accepted wherever an object of that class (MyClass) would be accepted. However, that class (MyClassA) may be final. This is pretty horrible :$. Any suggestions? I don't need to use a wrapper, anything you can think of is fine. What I cannot change is the write log (I need to have a write log) and the fact that the programmer doesn't know about the clone. I hope I've made some sense. Feel free to ask for more info if something needs some clearing up. Thanks so much!

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  • Generic <T> how cast ?

    - by Kris-I
    Hi, I have a "Product" base class, some other classes "ProductBookDetail","ProductDVDDetail" inherit from this class. I use a ProductService class to make operation on these classes. But, I have to do some check depending of the type (ISBN for Book, languages for DVD). I'd like to know the best way to cast "productDetail" value, I receive in SaveOrupdate. I tried GetType() and cast with (ProductBookDetail)productDetail but that's not work. Thanks, var productDetail = new ProductDetailBook() { .... }; var service = IoC.Resolve<IProductServiceGeneric<ProductDetailBook>>(); service.SaveOrUpdate(productDetail); var productDetail = new ProductDetailDVD() { .... }; var service = IoC.Resolve<IProductServiceGeneric<ProductDetailDVD>>(); service.SaveOrUpdate(productDetail); public class ProductServiceGeneric<T> : IProductServiceGeneric<T> { private readonly ISession _session; private readonly IProductRepoGeneric<T> _repo; public ProductServiceGeneric() { _session = UnitOfWork.CurrentSession; _repo = IoC.Resolve<IProductRepoGeneric<T>>(); } public void SaveOrUpdate(T productDetail) { using (ITransaction tx = _session.BeginTransaction()) { //here i'd like ot know the type and access properties depending of the class _repo.SaveOrUpdate(productDetail); tx.Commit(); } } }

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  • C++, function pointer to the template function pointer

    - by Ian
    I am having a pointer to the common static method class MyClass { private: static double ( *pfunction ) ( const Object *, const Object *); ... }; pointing to the static method class SomeClass { public: static double getA ( const Object *o1, const Object *o2); ... }; Initialization: double ( *MyClass::pfunction ) ( const Object *o1, const Object *o2 ) = &SomeClass::getA; I would like to convert this pointer to the static template function pointer: template <class T> static T ( *pfunction ) ( const Object <T> *, const Object <T> *); //Compile error where: class SomeClass { public: template <class T> static double getA ( const Object <T> *o1, const Object <T> *o2); ... }; But there is some error... Thanks for your help...

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  • django model relation definition

    - by Laurent Luce
    Hello, Let say I have 3 models: A, B and C with the following relations. A can have many B and many C. B can have many C Is the following correct: class A(models.Model): ... class B(models.Model): ... a = ForeignKey(A) class C(models.Model): ... a = ForeignKey(A) b = ForeignKey(B)

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