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• With NHibernate, how can I add a child object when updating a parent object?

  - by BMZ

  I have a simple Parent/Child relationship between a Person object and an Address object. The Person object exists in the DB. After doing a Get on the Person, I add a new Address object to the Address sub-object list of the parent, and do some other updates to the Person object. Finally, I do an Update on the Person object. With a SQL trace window, I can see the update to the Person object to the Person table and the Insert of the Address record to the Address table. The issue is that, after the update is performed, the AddressId (primary key on the Address object) is still set to 0, which is what it defaults to when you first initialize the Address object. I have verified that when I do an Add, this value is set correctly. Is this a known issue when trying to add sub-objects as part of an NHibernate UPDATE? Sample code and mapping files are below Thanks <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"> <class name="BusinessEntities.Wellness.Person,BusinessEntities.Wellness" table="Person" lazy="true" dynamic-insert="true" dynamic-update="false"> <id name="Personid" column="PersonID" type="int"> <generator class="native" /> </id> <version type="binary" generated="always" name="RecordVersion" column="`RecordVersion`"/> <property type="int" not-null="true" name="Customerid" column="`CustomerID`" /> <property type="AnsiString" not-null="true" length="9" name="Ssn" column="`SSN`" /> <property type="AnsiString" not-null="true" length="30" name="FirstName" column="`FirstName`" /> <property type="AnsiString" not-null="true" length="35" name="LastName" column="`LastName`" /> <property type="AnsiString" length="1" name="MiddleInitial" column="`MiddleInitial`" /> <property type="DateTime" name="DateOfBirth" column="`DateOfBirth`" /> <bag name="PersonAddresses" inverse="true" lazy="true" cascade="all"> <key column="PersonID" /> <one-to-many class="BusinessEntities.Wellness.PersonAddress,BusinessEntities.Wellness" / </bag> </class> </hibernate-mapping> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"> <class name="BusinessEntities.Wellness.PersonAddress,BusinessEntities.Wellness" table="PersonAddress" lazy="true" dynamic-insert="true" dynamic-update="false"> <id name="PersonAddressId" column="PersonAddressID" type="int"> <generator class="native" /> </id> <version type="binary" generated="always" name="RecordVersion" column="`RecordVersion`" /> <property type="AnsiString" not-null="true" length="1" name="AddressTypeid" column="`AddressTypeID`" /> <property type="AnsiString" not-null="true" length="60" name="AddressLine1" column="`AddressLine1`" /> <property type="AnsiString" length="60" name="AddressLine2" column="`AddressLine2`" /> <property type="AnsiString" length="60" name="City" column="`City`" /> <property type="AnsiString" length="2" name="UsStateId" column="`USStateID`" /> <property type="AnsiString" length="5" name="UsPostalCodeId" column="`USPostalCodeID`" /> <many-to-one name="Person" cascade="none" column="PersonID" /> </class> </hibernate-mapping> Person newPerson = new Person(); newPerson.PersonName = "John Doe"; newPerson.SSN = "111111111"; newPerson.CreatedBy = "RJC"; newPerson.CreatedDate = DateTime.Today; personDao.AddPerson(newPerson); Person updatePerson = personDao.GetPerson(newPerson.PersonId); updatePerson.PersonAddresses = new List<PersonAddress>(); PersonAddress addr = new PersonAddress(); addr.AddressLine1 = "1 Main St"; addr.City = "Boston"; addr.State = "MA"; addr.Zip = "12345"; updatePerson.PersonAddresses.Add(addr); personDao.UpdatePerson(updatePerson); int addressID = updatePerson.PersonAddresses[0].AddressId;

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• Getting Segmentation Fault in C++, but why?

  - by Carlos

  I am getting segmentation fault in this code but i cant figure out why. I know a segmentation fault happens when a pointer is NULL, or when it points to a random memory address. #include <iostream> #include <fstream> #include <cmath> using namespace std; //**************************** CLASS ******************************* class Database { struct data{ string city; float latitude, longitude; data *link; }*p; public: Database(); void display(); void add(string cityName, float lat, float lon); private: string cityName; float lat, lon; }; //************************** CLASS METHODS ************************** Database::Database() { p = NULL; } void Database::add(string cityName, float lat, float lon){ data *q, *t; if(p == NULL){ p = new data; p -> city = cityName; p -> latitude = lat; p -> longitude = lon; p -> link = NULL; } else{ q = p; while(q -> link != NULL){ q = q -> link; } t = new data; t -> city = cityName; t -> latitude = lat; t -> longitude = lon; q -> link = t; } } void Database::display() { data *q; cout<<endl; for( q = p ; q != NULL ; q = q->link ) cout << endl << q -> city; } //***************************** MAIN ******************************* //*** INITIALIZATION *** Database D; void loadDatabase(); //****** VARIABLES ***** //******* PROGRAM ****** int main() { loadDatabase(); D.display(); } void loadDatabase() { int i = 0; string cityName; float lat, lon; fstream city; city.open("city.txt", ios::in); fstream latitude; latitude.open("lat.txt", ios::in); fstream longitude; longitude.open("lon.txt", ios::in); while(!city.eof()){ //************************************ city >> cityName; //* * latitude >> lat; //Here is where i think is the problem longitude >> lon; //* * D.add(cityName, lat, lon); //************************************ } city.close(); latitude.close(); longitude.close(); } This is the error am actually getting in console

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• Running code when all threads are finished processing.

  - by rich97

  Quick note: Java and Android noob here, I'm open to you telling me I'm stupid (as long as you tell me why.) I have an android application which requires me start multiple threads originating from various classes and only advance to the next activity once all threads have done their job. I also want to add a "failsafe" timeout in case one the the threads takes too long (HTTP request taking too long or something.) I searched Stack Overflow and found a post saying that I should create a class to keep a running total of open threads and then use a timer to poll for when all the threads are completed. I think I've created a working class to do this for me, it's untested as of yet but has no errors showing in eclipse. Is this a correct implementation? Are there any APIs that I should be made aware of (such as classes in the Java or Android APIs that could be used in place of the abstract classes at the bottom of the class?) package com.dmp.geofix.libs; import java.util.ArrayList; import java.util.Iterator; import java.util.Timer; import java.util.TimerTask; public class ThreadMonitor { private Timer timer = null; private TimerTask timerTask = null; private OnSuccess onSuccess = null; private OnError onError = null; private static ArrayList<Thread> threads; private final int POLL_OPEN_THREADS = 100; private final int TIMEOUT = 10000; public ThreadMonitor() { timerTask = new PollThreadsTask(); } public ThreadMonitor(OnSuccess s) { timerTask = new PollThreadsTask(); onSuccess = s; } public ThreadMonitor(OnError e) { timerTask = new PollThreadsTask(); onError = e; } public ThreadMonitor(OnSuccess s, OnError e) { timerTask = new PollThreadsTask(); onSuccess = s; onError = e; } public void start() { Iterator<Thread> i = threads.iterator(); while (i.hasNext()) { i.next().start(); } timer = new Timer(); timer.schedule(timerTask, 0, POLL_OPEN_THREADS); } public void finish() { Iterator<Thread> i = threads.iterator(); while (i.hasNext()) { i.next().interrupt(); } threads.clear(); timer.cancel(); } public void addThread(Thread t) { threads.add(t); } public void removeThread(Thread t) { threads.remove(t); t.interrupt(); } class PollThreadsTask extends TimerTask { private int timeElapsed = 0; @Override public void run() { timeElapsed += POLL_OPEN_THREADS; if (timeElapsed <= TIMEOUT) { if (threads.isEmpty() == false) { if (onSuccess != null) { onSuccess.run(); } } } else { if (onError != null) { onError.run(); } finish(); } } } public abstract class OnSuccess { public abstract void run(); } public abstract class OnError { public abstract void run(); } }

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• Android inserting into SQLite JSON object

  - by Nizmon

  I'm trying to insert the below json response from a server into my sqlite DB and then read from the DB. The problem I am getting is that when I run my code it compiles fine and runs with no errors. But when trying to read from the DB I just get back what seems like an empty string so I know that the table is being created. I have the correct permissions within the manifest. I have also reference all my classes within there. {"locations": [{"locations":"Newcastle","location_id":"1"},{"locations":"London","location_id":"2"},{"locations":"Sunderland","location_id":"3"}]} Below where I use: Log.v("one", one); Log.v("two", two); below It only prints out the first set within the JSON object so Newcastle and 1. I don't get any errors at all which is stumping me. When I call the method getName within the Location class I just seem to get a blank string back! // This class creates the table as well as inserts and returns data from the sqlite DB public class Location { private DatabaseHelper mDbHelper; private SQLiteDatabase mDb; private final Context mCtx; private static final String vd_location = ("CREATE TABLE " + TABLE_VD_LOCATION + " (" + LOCATION + " TEXT," + LOCATION_ID + " TEXT " +");"); private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(vd_location); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { } } public Location(Context ctx) { this.mCtx = ctx; } public Location open() throws SQLException { this.mDbHelper = new DatabaseHelper(this.mCtx); this.mDb = this.mDbHelper.getWritableDatabase(); return this; } public void close() { this.mDbHelper.close(); } public void addOffer (JSONObject json){ try{ JSONArray earthquakes = json.getJSONArray("offers"); for(int i=0;i<earthquakes.length();i++){ open(); JSONObject e = earthquakes.getJSONObject(i); String one = e.getString("locations"); String two = e.getString("location_id"); Log.v("one", one); Log.v("two", two); mDb.execSQL("INSERT INTO " + TABLE_VD_LOCATION + " ( locations, location_id ) " + "VALUES (?, ?)", new Object [] { e.getString("locations"), e.getString("location_id")}); close(); } }catch(Exception e){ }finally{ close(); } } public String getName(long l) throws SQLException{ String[] columns = new String[]{ LOCATION, LOCATION_ID}; Cursor c = mDb.query(TABLE_VD_LOCATION, columns, null, null, null, null, null); String result = ""; int iRow = c.getColumnIndex(LOCATION); int iName = c.getColumnIndex(LOCATION_ID); for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){ result = result + c.getString(iRow) + " " + c.getString(iName) + " " + "\n"; } return result; } } // This code reads from the DB, this is just some very hacked together code so excuse it, it also works when used on other tables public void getData(){ boolean didItWork = true; try { Location loc = new Location(this); loc.open(); String data = loc.getName(0); loc.close(); Dialog t = new Dialog(this); t.setTitle("get" + data); t.show(); } catch (Exception e) { didItWork = false; String error = e.toString(); Dialog d = new Dialog(this); d.setTitle("Dang it!"); TextView tv = new TextView(this); tv.setText(error); d.setContentView(tv); d.show(); } finally { if (didItWork) { Dialog d = new Dialog(this); d.setTitle("Heck Yea!"); TextView tv = new TextView(this); tv.setText("Success"); d.setContentView(tv); d.show(); //entry.close(); } } }

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• How to get the value of an item from database and set it as the spinner value

  - by kulPrins

  I have a database and the database populates a listview. when i long press a list item from the listview i get a context menu where i have the option to edit. When the edit option is clicked i open an activity and get all the values of the respective fields from the database. Now, here I want to get a value from the database and show it in the spinner. the spinner already has these values and is getting populated from the database... I have tried the following, but i get an error saying I can't cast a SimpleCursorAdapter to an ArrayAdapter.. String osub = cursor.getString(Database.INDEX_SUBJECT); Cursor cs = mDBS.querySub(osub); String subs = cs.getString(DatabaseSub.INDEX_SSUBJECT); if(cs!=null){ ArrayAdapter<String> myAdap = (ArrayAdapter<String>) subSpinner.getAdapter(); //cast to an ArrayAdapter int spinnerPosition = myAdap.getPosition(subs); //set the default according to value subSpinner.setSelection(spinnerPosition); Please tell me how to do this.. Thank you.. I am relatively new so please let me know if I am overlooking something. Thanks.. EDIT querySub method public Cursor querySub(String sub) throws SQLException { Cursor cursor = mDatabase.query(true, DATABASE_TABLE, sAllColumns, "ssub like " + "'" + sub + "'", null, null, null, null, null); if (cursor.moveToNext()) { return cursor; } cursor.moveToFirst(); return cursor; } Error Log 06-05 12:11:14.144: E/AndroidRuntime(775): FATAL EXCEPTION: main 06-05 12:11:14.144: E/AndroidRuntime(775): java.lang.RuntimeException: Unable to start activity ComponentInfo{an.droid.kit/an.droid.kit.DetailsActivity}: java.lang.ClassCastException: android.widget.SimpleCursorAdapter cannot be cast to android.widget.ArrayAdapter 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.ActivityThread.access$600(ActivityThread.java:123) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.os.Handler.dispatchMessage(Handler.java:99) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.os.Looper.loop(Looper.java:137) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.ActivityThread.main(ActivityThread.java:4424) 06-05 12:11:14.144: E/AndroidRuntime(775): at java.lang.reflect.Method.invokeNative(Native Method) 06-05 12:11:14.144: E/AndroidRuntime(775): at java.lang.reflect.Method.invoke(Method.java:511) 06-05 12:11:14.144: E/AndroidRuntime(775): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 06-05 12:11:14.144: E/AndroidRuntime(775): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 06-05 12:11:14.144: E/AndroidRuntime(775): at dalvik.system.NativeStart.main(Native Method) 06-05 12:11:14.144: E/AndroidRuntime(775): Caused by: java.lang.ClassCastException: android.widget.SimpleCursorAdapter cannot be cast to android.widget.ArrayAdapter 06-05 12:11:14.144: E/AndroidRuntime(775): at an.droid.kit.DetailsActivity.dbToUI(DetailsActivity.java:217) 06-05 12:11:14.144: E/AndroidRuntime(775): at an.droid.kit.DetailsActivity.onCreate(DetailsActivity.java:104) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.Activity.performCreate(Activity.java:4465) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 06-05 12:11:14.144: E/AndroidRuntime(775): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 06-05 12:11:14.144: E/AndroidRuntime(775): ... 11 more

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• Javascript and Twitter API rate limitation? (Changing variable values in a loop)

  - by Pablo

  Hello, I have adapted an script from an example of http://github.com/remy/twitterlib. It´s a script that makes one query each 10 seconds to my Twitter timeline, to get only the messages that begin with a musical notation. It´s already working, but I don´t know it is the better way to do this... The Twitter API has a rate limit of 150 IP access per hour (queries from the same user). At this time, my Twitter API is blocked at 25 minutes because the 10 seconds frecuency between posts. If I set up a frecuency of 25 seconds between post, I am below the rate limit per hour, but the first 10 posts are shown so slowly. I think this way I can guarantee to be below the Twitter API rate limit and show the first 10 posts at normal speed: For the first 10 posts, I would like to set a frecuency of 5 seconds between queries. For the rest of the posts, I would like to set a frecuency of 25 seconds between queries. I think if making somewhere in the code a loop with the previous sentences, setting the "frecuency" value from 5000 to 25000 after the 10th query (or after 50 seconds, it´s the same), that´s it... Can you help me on modify this code below to make it work? Thank you in advance. var Queue = function (delay, callback) { var q = [], timer = null, processed = {}, empty = null, ignoreRT = twitterlib.filter.format('-"RT @"'); function process() { var item = null; if (q.length) { callback(q.shift()); } else { this.stop(); setTimeout(empty, 5000); } return this; } return { push: function (item) { var green = [], i; if (!(item instanceof Array)) { item = [item]; } if (timer == null && q.length == 0) { this.start(); } for (i = 0; i < item.length; i++) { if (!processed[item[i].id] && twitterlib.filter.match(item[i], ignoreRT)) { processed[item[i].id] = true; q.push(item[i]); } } q = q.sort(function (a, b) { return a.id > b.id; }); return this; }, start: function () { if (timer == null) { timer = setInterval(process, delay); } return this; }, stop: function () { clearInterval(timer); timer = null; return this; }, empty: function (fn) { empty = fn; return this; }, q: q, next: process }; }; $.extend($.expr[':'], { below: function (a, i, m) { var y = m[3]; return $(a).offset().top y; } }); function renderTweet(data) { var html = ''; html += ''; html += twitterlib.ify.clean(data.text); html += ''; since_id = data.id; return html; } function passToQueue(data) { if (data.length) { twitterQueue.push(data.reverse()); } } var frecuency = 10000; // The lapse between each new Queue var since_id = 1; var run = function () { twitterlib .timeline('twitteruser', { filter : "'?'", limit: 10 }, passToQueue) }; var twitterQueue = new Queue(frecuency, function (item) { var tweet = $(renderTweet(item)); var tweetClone = tweet.clone().hide().css({ visibility: 'hidden' }).prependTo('#tweets').slideDown(1000); tweet.css({ top: -200, position: 'absolute' }).prependTo('#tweets').animate({ top: 0 }, 1000, function () { tweetClone.css({ visibility: 'visible' }); $(this).remove(); }); $('#tweets p:below(' + window.innerHeight + ')').remove(); }).empty(run); run();

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• One to many in nhibernate mapping problem

  - by chobo2

  Hi I have this using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Demo.Framework.Domain { public class UserEntity { public virtual Guid UserId { get; protected set; } } } using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace TDemo.Framework.Domain { public class Users : UserEntity { public virtual string OpenIdIdentifier { get; set; } public virtual string Email { get; set; } public virtual IList<Movie> Movies { get; set; } } } using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Demo.Framework.Domain { public class Movie { public virtual int MovieId { get; set; } public virtual Guid UserId { get; set; } // not sure if I should inherit UserEntity public virtual string Title { get; set; } public virtual DateTime ReleaseDate { get; set; } // in my ms sql 2008 database I want this to be just a Date type. Not sure how to do that. public virtual int Upc { get; set; } } } <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Demo.Framework" namespace="Demo.Framework.Domain"> <class name="Users"> <id name="UserId"> <generator class="guid.comb" /> </id> <property name="OpenIdIdentifier" not-null="true" /> <property name="Email" not-null="true" /> </class> <subclass name="Movie"> <list name="Movies" cascade="all-delete-orphan"> <key column="MovieId" /> <index column="MovieIndex" /> // not sure what index column is really. <one-to-many class="Movie"/> </list> </subclass> </hibernate-mapping> <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Demo.Framework" namespace="Demo.Framework.Domain"> <class name="Movie"> <id name="MovieId"> <generator class="native" /> </id> <property name="Title" not-null="true" /> <property name="ReleaseDate" not-null="true" type="Date" /> <property name="Upc" not-null="true" /> <property name="UserId" not-null="true" type="Guid"/> </class> </hibernate-mapping> I get this error 'extends' attribute is not found or is empty. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: NHibernate.MappingException: 'extends' attribute is not found or is empty. Source Error: Line 17: { Line 18: Line 19: var nhConfig = new Configuration().Configure(); Line 20: var sessionFactory = nhConfig.BuildSessionFactory(); Line 21:

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• Do I need to manually create indexes for a DBIx::Class belongs_to relationship

  - by Dancrumb

  I'm using the DBIx::Class modules for an ORM approach to an application I have. I'm having some problems with my relationships. I have the following package MySchema::Result::ClusterIP; use strict; use warnings; use base qw/DBIx::Class::Core/; our $VERSION = '1.0'; __PACKAGE__->load_components(qw/InflateColumn::Object::Enum Core/); __PACKAGE__->table('cluster_ip'); __PACKAGE__->add_columns( # Columns here ); __PACKAGE__->set_primary_key('objkey'); __PACKAGE__->belongs_to( 'configuration' => 'MySchema::Result::Configuration', 'config_key'); __PACKAGE__->belongs_to( 'cluster' => 'MySchema::Result::Cluster', { 'foreign.config_key' => 'self.config_key', 'foreign.id' => 'self.cluster_id' } ); As well as package MySchema::Result::Cluster; use strict; use warnings; use base qw/DBIx::Class::Core/; our $VERSION = '1.0'; __PACKAGE__->load_components(qw/InflateColumn::Object::Enum Core/); __PACKAGE__->table('cluster'); __PACKAGE__->add_columns( # Columns here ); __PACKAGE__->set_primary_key('objkey'); __PACKAGE__->belongs_to( 'configuration' => 'MySchema::Result::Configuration', 'config_key'); __PACKAGE__->has_many('cluster_ip' => 'MySchema::Result::ClusterIP', { 'foreign.config_key' => 'self.config_key', 'foreign.cluster_id' => 'self.id' }); There are a couple of other modules, but I don't believe that they are relevant. When I attempt to deploy this schema, I get the following error: DBIx::Class::Schema::deploy(): DBI Exception: DBD::mysql::db do failed: Can't create table 'test.cluster_ip' (errno: 150) [ for Statement "CREATE TABLE `cluster_ip` ( `objkey` smallint(5) unsigned NOT NULL auto_increment, `config_key` smallint(5) unsigned NOT NULL, `cluster_id` char(16) NOT NULL, INDEX `cluster_ip_idx_config_key_cluster_id` (`config_key`, `cluster_id`), INDEX `cluster_ip_idx_config_key` (`config_key`), PRIMARY KEY (`objkey`), CONSTRAINT `cluster_ip_fk_config_key_cluster_id` FOREIGN KEY (`config_key`, `cluster_id`) REFERENCES `cluster` (`config_key`, `id`) ON DELETE CASCADE ON UPDATE CASCADE, CONSTRAINT `cluster_ip_fk_config_key` FOREIGN KEY (`config_key`) REFERENCES `configuration` (`config_key`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB"] at test_deploy.pl line 18 (running "CREATE TABLE `cluster_ip` ( `objkey` smallint(5) unsigned NOT NULL auto_increment, `config_key` smallint(5) unsigned NOT NULL, `cluster_id` char(16) NOT NULL, INDEX `cluster_ip_idx_config_key_cluster_id` (`config_key`, `cluster_id`), INDEX `cluster_ip_idx_config_key` (`config_key`), PRIMARY KEY (`objkey`), CONSTRAINT `cluster_ip_fk_config_key_cluster_id` FOREIGN KEY (`config_key`, `cluster_id`) REFERENC ES `cluster` (`config_key`, `id`) ON DELETE CASCADE ON UPDATE CASCADE, CONSTRAINT `cluster_ip_fk_config_key` FOREIGN KEY (`config_key`) REFERENCES `configuration` (`conf ig_key`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB") at test_deploy.pl line 18 From what I can tell, MySQL is complaining about the FOREIGN KEY constraint, in particular, the REFERENCE to (config_key, id) in the cluster table. From my reading of the MySQL documentation, this seems like a reasonable complaint, especially in regards to the third bullet point on this doc page. Here's my question. Am I missing something in the DBIx::Class module? I realize that I could explicitly create the necessary index to match up with this foreign key constraint, but that seems to be repetitive work. Is there something I should be doing to make this occur implicitly?

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• Keeping video viewing statistics breakdown by video time in a database

  - by Septagram

  I need to keep a number of statistics about the videos being watched, and one of them is what parts of the video are being watched most. The design I came up with is to split the video into 256 intervals and keep the floating-point number of views for each of them. I receive the data as a number of intervals the user watched continuously. The problem is how to store them. There are two solutions I see. Row per every video segment Let's have a database table like this: CREATE TABLE `video_heatmap` ( `id` int(11) NOT NULL AUTO_INCREMENT, `video_id` int(11) NOT NULL, `position` tinyint(3) unsigned NOT NULL, `views` float NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `idx_lookup` (`video_id`,`position`) ) ENGINE=MyISAM Then, whenever we have to process a number of views, make sure there are the respective database rows and add appropriate values to the views column. I found out it's a lot faster if the existence of rows is taken care of first (SELECT COUNT(*) of rows for a given video and INSERT IGNORE if they are lacking), and then a number of update queries is used like this: UPDATE video_heatmap SET views = views + ? WHERE video_id = ? AND position >= ? AND position < ? This seems, however, a little bloated. The other solution I came up with is Row per video, update in transactions A table will look (sort of) like this: CREATE TABLE video ( id INT NOT NULL AUTO_INCREMENT, heatmap BINARY (4 * 256) NOT NULL, ... ) ENGINE=InnoDB Then, upon every time a view needs to be stored, it will be done in a transaction with consistent snapshot, in a sequence like this: If the video doesn't exist in the database, it is created. A row is retrieved, heatmap, an array of floats stored in the binary form, is converted into a form more friendly for processing (in PHP). Values in the array are increased appropriately and the array is converted back. Row is changed via UPDATE query. So far the advantages can be summed up like this: First approach Stores data as floats, not as some magical binary array. Doesn't require transaction support, so doesn't require InnoDB, and we're using MyISAM for everything at the moment, so there won't be any need to mix storage engines. (only applies in my specific situation) Doesn't require a transaction WITH CONSISTENT SNAPSHOT. I don't know what are the performance penalties of those. I already implemented it and it works. (only applies in my specific situation) Second approach Is using a lot less storage space (the first approach is storing video ID 256 times and stores position for every segment of the video, not to mention primary key). Should scale better, because of InnoDB's per-row locking as opposed to MyISAM's table locking. Might generally work faster because there are a lot less requests being made. Easier to implement in code (although the other one is already implemented). So, what should I do? If it wasn't for the rest of our system using MyISAM consistently, I'd go with the second approach, but currently I'm leaning to the first one. But maybe there are some reasons to favour one approach or another?

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• Java: how to avoid circual references when dumping object information with reflection?

  - by Tom

  I've modified an object dumping method to avoid circual references causing a StackOverflow error. This is what I ended up with: //returns all fields of the given object in a string public static String dumpFields(Object o, int callCount, ArrayList excludeList) { //add this object to the exclude list to avoid circual references in the future if (excludeList == null) excludeList = new ArrayList(); excludeList.add(o); callCount++; StringBuffer tabs = new StringBuffer(); for (int k = 0; k < callCount; k++) { tabs.append("\t"); } StringBuffer buffer = new StringBuffer(); Class oClass = o.getClass(); if (oClass.isArray()) { buffer.append("\n"); buffer.append(tabs.toString()); buffer.append("["); for (int i = 0; i < Array.getLength(o); i++) { if (i < 0) buffer.append(","); Object value = Array.get(o, i); if (value != null) { if (excludeList.contains(value)) { buffer.append("circular reference"); } else if (value.getClass().isPrimitive() || value.getClass() == java.lang.Long.class || value.getClass() == java.lang.String.class || value.getClass() == java.lang.Integer.class || value.getClass() == java.lang.Boolean.class) { buffer.append(value); } else { buffer.append(dumpFields(value, callCount, excludeList)); } } } buffer.append(tabs.toString()); buffer.append("]\n"); } else { buffer.append("\n"); buffer.append(tabs.toString()); buffer.append("{\n"); while (oClass != null) { Field[] fields = oClass.getDeclaredFields(); for (int i = 0; i < fields.length; i++) { if (fields[i] == null) continue; buffer.append(tabs.toString()); fields[i].setAccessible(true); buffer.append(fields[i].getName()); buffer.append("="); try { Object value = fields[i].get(o); if (value != null) { if (excludeList.contains(value)) { buffer.append("circular reference"); } else if ((value.getClass().isPrimitive()) || (value.getClass() == java.lang.Long.class) || (value.getClass() == java.lang.String.class) || (value.getClass() == java.lang.Integer.class) || (value.getClass() == java.lang.Boolean.class)) { buffer.append(value); } else { buffer.append(dumpFields(value, callCount, excludeList)); } } } catch (IllegalAccessException e) { System.out.println("IllegalAccessException: " + e.getMessage()); } buffer.append("\n"); } oClass = oClass.getSuperclass(); } buffer.append(tabs.toString()); buffer.append("}\n"); } return buffer.toString(); } The method is initially called like this: System.out.println(dumpFields(obj, 0, null); So, basically I added an excludeList which contains all the previousely checked objects. Now, if an object contains another object and that object links back to the original object, it should not follow that object further down the chain. However, my logic seems to have a flaw as I still get stuck in an infinite loop. Does anyone know why this is happening?

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• How to mix C++ Qt objects and Qt Jambi objects

  - by Dan

  Hi, I'm trying to combine some existing Qt code written in C++ with some code written in Java using Qt Jambi, but I'm not quite sure how to do it. I'm basically trying to acieve two things: Pass a QObject from C++ to Java using JNI Pass a Qt Jambi QObject from Java to C++ It looks like I can pass the pointer directly and then wrap it in QNativePointer on the Java side, but I can't figure out how to turn a QNativePointer back into the original object, wrapped by Qt Jambi. Eg: I can pass a QWidget* as a long to Java and then create a QNativePointer in Java, but how can I then construct a QWidget out of this? QJambiObject and QObject dont seem to have a "setNativePointer" method and I'm not sure how to convert it. In C++: QWidget* widget = ... jclass cls = env->FindClass("Test"); jmethodID mid = env->GetStaticMethodID(cls, "test", "(I)V"); env->CallStaticVoidMethod(cls, mid, int(widget)); In Java: public class Test { public static void test (int ptr) { QNativePointer pointer = new QNativePointer(QNativePointer.Type.Int); pointer.setIntValue(ptr); QWidget widget = ... Thanks!

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• maintaining a large list in python

  - by Oren

  I need to maintain a large list of python pickleable objects that will quickly execute the following algorithm: The list will have 4 pointers and can: Read\Write each of the 4 pointed nodes Insert new nodes before the pointed nodes Increase a pointer by 1 Pop nodes from the beginning of the list (without overlapping the pointers) Add nodes at the end of the list The list can be very large (300-400 MB), so it shouldnt be contained in the RAM. The nodes are small (100-200 bytes) but can contain various types of data. The most efficient way it can be done, in my opinion, is to implement some paging-mechanism. On the harddrive there will be some database of a linked-list of pages where in every moment up to 5 of them are loaded in the memory. On insertion, if some max-page-size was reached, the page will be splitted to 2 small pages, and on pointer increment, if a pointer is increased beyond its loaded page, the following page will be loaded instead. This is a good solution, but I don't have the time to write it, especially if I want to make it generic and implement all the python-list features. Using a SQL tables is not good either, since I'll need to implement a complex index-key mechanism. I tried ZODB and zc.blist, which implement a BTree based list that can be stored in a ZODB database file, but I don't know how to configure it so the above features will run in reasonable time. I don't need all the multi-threading\transactioning features. No one else will touch the database-file except for my single-thread program. Can anyone explain me how to configure the ZODB\zc.blist so the above features will run fast, or show me a different large-list implementation?

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• Delegates in .NET: how are they constructed ?

  - by Saulius

  While inspecting delegates in C# and .NET in general, I noticed some interesting facts: Creating a delegate in C# creates a class derived from MulticastDelegate with a constructor: .method public hidebysig specialname rtspecialname instance void .ctor(object 'object', native int 'method') runtime managed { } Meaning that it expects the instance and a pointer to the method. Yet the syntax of constructing a delegate in C# suggests that it has a constructor new MyDelegate(int () target) where I can recognise int () as a function instance (int *target() would be a function pointer in C++). So obviously the C# compiler picks out the correct method from the method group defined by the function name and constructs the delegate. So the first question would be, where does the C# compiler (or Visual Studio, to be precise) pick this constructor signature from ? I did not notice any special attributes or something that would make a distinction. Is this some sort of compiler/visualstudio magic ? If not, is the T (args) target construction valid in C# ? I did not manage to get anything with it to compile, e.g.: int () target = MyMethod; is invalid, so is doing anything with MyMetod, e.g. calling .ToString() on it (well this does make some sense, since that is technically a method group, but I imagine it should be possible to explicitly pick out a method by casting, e.g. (int())MyFunction. So is all of this purely compiler magic ? Looking at the construction through reflector reveals yet another syntax: Func CS$1$0000 = new Func(null, (IntPtr) Foo); This is consistent with the disassembled constructor signature, yet this does not compile! One final interesting note is that the classes Delegate and MulticastDelegate have yet another sets of constructors: .method family hidebysig specialname rtspecialname instance void .ctor(class System.Type target, string 'method') cil managed Where does the transition from an instance and method pointer to a type and a string method name occur ? Can this be explained by the runtime managed keywords in the custom delegate constructor signature, i.e. does the runtime do it's job here ?

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• Why so much stack space used for each recursion?

  - by Harvey

  I have a simple recursive function RCompare() that calls a more complex function Compare() which returns before the recursive call. Each recursion level uses 248 bytes of stack space which seems like way more than it should. Here is the recursive function: void CMList::RCompare(MP n1) // RECURSIVE and Looping compare function { auto MP ne=n1->mf; while(StkAvl() && Compare(n1=ne->mb)) RCompare(n1); // Recursive call ! } StkAvl() is a simple stack space check function that compares the address of an auto variable to the value of an address near the end of the stack stored in a static variable. It seems to me that the only things added to the stack in each recursion are two pointer variables (MP is a pointer to a structure) and the stuff that one function call stores, a few saved registers, base pointer, return address, etc., all 32-bit (4 byte) values. There's no way that is 248 bytes is it? I don't no how to actually look at the stack in a meaningful way in Visual Studio 2008. Thanks

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• Accessing Firefox tab element in nsIWebProgressListener::OnStateChange using C++

  - by Vaibhav Gade

  Hi All, I am developing extension for Firefox 3.0-3.5 versions using VS2008. I want to set attribute to a tab once the document load request completes within that tab window. So in OnStateChange method, I am checking for document load. I have used STATE_STOP & STATE_IS_DOCUMENT for it. I want to determine which tab window has been associated with particular document request. I have valid DOM Document pointer got from nsIWebProgress *aWebProgress which is 1st input parameter of OnStateChange. if ((aStateFlags & STATE_STOP) && (aStateFlags & STATE_IS_DOCUMENT)) { nsCOMPtr<nsIDOMWindow> domwin; nsCOMPtr<nsIDOMDocument> domDoc; aWebProgress->GetDOMWindow(getter_AddRefs(domwin)); domwin->GetDocument(getter_AddRefs(domDoc)); } I have tried to get nsIDOMDocumentXBL pointer by QIing nsIDOMDocument pointer(domDoc in my example) but it fails with Error code 0x80004002 (2147500034) i.e.NS_ERROR_NO_INTERFACE. How do I get the tab element corresponding to document load request. Could any one please help me? Thanks in Advance, Vaibhav D. Gade.

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• c - strncpy issue

  - by Joe

  Hi there, I am getting segmentation fault when using strncpy and (pointer-to-struct)-(member) notation: I have simplified my code. I initialise a struct and set all of it's tokens to an empty string. Then a declare a pointer to a struct and assign the address of the struct to it. I pass the pointer to a function. I can print out the contents of the struct at the beginning of the function, but if I try to use the tp - mnemonic in a strncpy function, I get seg fault. Can anyone tell me what I am doing wrong? typedef struct tok { char* label; char* mnem; char* operand; }Tokens; Tokens* tokenise(Tokens* tp, char* line) { // This prints fine printf("Print this - %s\n", tp -> mnem); // This function gives me segmentation fault strncpy(tp -> mnem, line, 4); return tp; } int main() { char* line = "This is a line"; Tokens tokens; tokens.label = ""; tokens.mnem = "load"; tokens.operand = ""; Tokens* tp = &tokens; tp = tokenise(tp, line); return 0; } I have used printf statements to confirm that the code definitely stops executing at the strncpy function. Can anyone tell me where I am going wrong? Many thanks Joe

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• Why does std::cout convert volatile pointers to bool?

  - by Joseph Garvin

  If you try to cout a volatile pointer, even a volatile char pointer where you would normally expect cout to print the string, you will instead simply get '1' (assuming the pointer is not null I think). I assume output stream operator<< is template specialized for volatile pointers, but my question is, why? What use case motivates this behavior? Example code: #include <iostream> #include <cstring> int main() { char x[500]; std::strcpy(x, "Hello world"); int y; int *z = &y; std::cout << x << std::endl; std::cout << (char volatile*)x << std::endl; std::cout << z << std::endl; std::cout << (int volatile*)z << std::endl; return 0; } Output: Hello world 1 0x8046b6c 1

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• How to get rid of void-pointers.

  - by Patrick

  I inherited a big application that was originally written in C (but in the mean time a lot of C++ was also added to it). Because of historical reasons, the application contains a lot of void-pointers. Before you start to choke, let me explain why this was done. The application contains many different data structures, but they are stored in 'generic' containers. Nowadays I would use templated STL containers for it, or I would give all data structures a common base class, so that the container can store pointers to the base class, but in the [good?] old C days, the only solution was to cast the struct-pointer to a void-pointer. Additionally, there is a lot of code that works on these void-pointers, and uses very strange C constructions to emulate polymorphism in C. I am now reworking the application, and trying to get rid of the void-pointers. Adding a common base-class to all the data structures isn't that hard (few days of work), but the problem is that the code is full of constructions like shown below. This is an example of how data is stored: void storeData (int datatype, void *data); // function prototype ... Customer *myCustomer = ...; storeData (TYPE_CUSTOMER, myCustomer); This is an example of how data is fetched again: Customer *myCustomer = (Customer *) fetchData (int datatype, char *key); I actually want to replace all the void-pointers with some smart-pointer (reference-counted), but I can't find a trick to automate (or at least) help me to get rid of all the casts to and from void-pointers. Any tips on how to find, replace, or interact in any possible way with these conversions?

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• should std::auto_ptr<>::operator = reset / deallocate its existing pointee ?

  - by afriza

  I read here about std::auto_ptr<::operator= Notice however that the left-hand side object is not automatically deallocated when it already points to some object. You can explicitly do this by calling member function reset before assigning it a new value. However, when I read the source code for header file C:\Program Files\Microsoft Visual Studio 8\VC\ce\include\memory template<class _Other> auto_ptr<_Ty>& operator=(auto_ptr<_Other>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr<_Ty>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr_ref<_Ty> _Right) _THROW0() { // assign compatible _Right._Ref (assume pointer) _Ty **_Pptr = (_Ty **)_Right._Ref; _Ty *_Ptr = *_Pptr; *_Pptr = 0; // release old reset(_Ptr); // set new return (*this); } What is the correct/standard behavior? How do other STL implementations behave?

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• What's correct way to remove a boost::shared_ptr from a list?

  - by Catskul

  I have a std::list of boost::shared_ptr<T> and I want to remove an item from it but I only have a pointer of type T* which matches one of the items in the list. However I cant use myList.remove( tPtr ) I'm guessing because shared_ptr does not implement == for its template argument type. My immediate thought was to try myList.remove( shared_ptr<T>(tPtr) ) which is syntactically correct but it will crash from a double delete since the temporary shared_ptr has a separate use_count. std::list< boost::shared_ptr<T> > myList; T* tThisPtr = new T(); // This is wrong; only done for example code. // stand-in for actual code in T using // T's actual "this" pointer from within T { boost::shared_ptr<T> toAdd( tThisPtr ); // typically would be new T() myList.push_back( toAdd ); } { //T has pointer to myList so that upon a certain action, // it will remove itself romt the list //myList.remove( tThisPtr); //doesn't compile myList.remove( boost::shared_ptr<T>(tThisPtr) ); // compiles, but causes // double delete } The only options I see remaining are to use std::find with a custom compare, or to loop through the list brute force and find it myself, but it seems there should be a better way. Am I missing something obvious, or is this just too non-standard a use to be doing a remove the clean/normal way?

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• What is the correct JNA mapping for UniChar on Mac OS X?

  - by Trejkaz

  I have a C struct like this: struct HFSUniStr255 { UInt16 length; UniChar unicode[255]; }; I have mapped this in the expected way: public class HFSUniStr255 extends Structure { public UInt16 length; // UInt16 is just an IntegerType with length 2 for convenience. public /*UniChar*/ char[] unicode = new char[255]; //public /*UniChar*/ byte[] unicode = new byte[255*2]; //public /*UniChar*/ UInt16[] unicode = new UInt16[255]; public HFSUniStr255() { } public HFSUniStr255(Pointer pointer) { super(pointer); } } If I use this version, I get every second character of the string into my char[] ("aits D" for "Macintosh HD".) I am assuming that this is something to do with being on a 64-bit platform and JNA mapping the value to a 32-bit wchar_t but then chopping off the high 16 bits on each wchar_t on copying them back. If I use the byte[] version, I get data which decodes correctly using the UTF-16LE charset. If I use the UInt16[] version, I get the right code point for each character but it is then inconvenient to convert them back into a string. Is there some way I can define my type as char[], and yet have it convert correctly?

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• COM-Objects containing maps / content error(0)

  - by Florian Berzsenyi

  I'm writing a small wrapper to get familiar with some important topics in C++ (WinAPI, COM, STL,OOP). For now, my class shall be able to create a (child) window. Mainly, this window is connected to a global message loop that distribute messages to a local loop of the right instance (global is static, local is virtual). Obviously, there are surely better ways to do that but I'm using std::maps to store HWND and their instance pointer in pairs (the Global loop looks for the pointer with the HWND-parameter, gets itself the pointer from the map and calls then the local loop). Now, it appears that the map does not accept any values because of a unknown reason. It seems to allocate enough space but something went wrong anyway [ (error) 0 is displayed instead of the entries in visual C++). I've looked that up in google as well and found out that maps cause some trouble when used in classes AND DLLs. May this be the reason and is there any solution?? Protected scope of class: static std::map<HWND,MAP_BASE_OBJECT*> m_LoopBuf Implementation in .cpp-file: std::map<HWND,MAP_BASE_OBJECT*> HWindow::m_LoopBuf;

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• Qt/C++, Problems with large QImage

  - by David Günzel

  I'm pretty new to C++/Qt and I'm trying to create an application with Visual Studio C++ and Qt (4.8.3). The application displays images using a QGraphicsView, I need to change the images at pixel level. The basic code is (simplified): QImage* img = new QImage(img_width,img_height,QImage::Format_RGB32); while(do_some_stuff) { img->setPixel(x,y,color); } QGraphicsPixmapItem* pm = new QGraphicsPixmapItem(QPixmap::fromImage(*img)); QGraphicsScene* sc = new QGraphicsScene; sc->setSceneRect(0,0,img->width(),img->height()); sc->addItem(pm); ui.graphicsView->setScene(sc); This works well for images up to around 12000x6000 pixel. The weird thing happens beyond this size. When I set img_width=16000 and img_height=8000, for example, the line img = new QImage(...) returns a null image. The image data should be around 512,000,000 bytes, so it shouldn't be too large, even on a 32 bit system. Also, my machine (Win 7 64bit, 8 GB RAM) should be capable of holding the data. I've also tried this version: uchar* imgbuf = (uchar*) malloc(img_width*img_height*4); QImage* img = new QImage(imgbuf,img_width,img_height,QImage::Format_RGB32); At first, this works. The img pointer is valid and calling img-width() for example returns the correct image width (instead of 0, in case the image pointer is null). But as soon as I call img-setPixel(), the pointer becomes null and img-width() returns 0. So what am I doing wrong? Or is there a better way of modifying large images on pixel level? Regards, David

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• Defining an implementation independent version of the global object in JavaScript

  - by Aadit M Shah

  I'm trying to define the global object in JavaScript in a single line as follows: var global = this.global || this; The above statement is in the global scope. Hence in browsers the this pointer is an alias for the window object. Assuming that it's the first line of JavaScript to be executed in the context of the current web page, the value of global will always be the same as that of the this pointer or the window object. In CommonJS implementations, such as RingoJS and node.js the this pointer points to the current ModuleScope. However, we can access the global object through the property global defined on the ModuleScope. Hence we can access it via the this.global property. Hence this code snippet works in all browsers and in at least RingoJS and node.js, but I have not tested other CommomJS implementations. Thus I would like to know if this code will not yield correct results when run on any other CommonJS implementation, and if so how I may fix it. Eventually, I intend to use it in a lambda expression for my implementation independent JavaScript framework as follows (idea from jQuery): (function (global) { // javascript framework })(this.global || this);

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• Common lisp, CFFI, and instantiating c structs

  - by andrew

  Hi, I've been on google for about, oh, 3 hours looking for a solution to this "problem." I'm trying to figure out how to instantiate a C structure in lisp using CFFI. I have a struct in c: struct cpVect{cpFloat x,y;} Simple right? I have auto-generated CFFI bindings (swig, I think) to this struct: (cffi:defcstruct #.(chipmunk-lispify "cpVect" 'classname) (#.(chipmunk-lispify "x" 'slotname) :double) (#.(chipmunk-lispify "y" 'slotname) :double)) This generates a struct "VECT" with slots :X and :Y, which foreign-slot-names confirms (please note that I neither generated the bindings or programmed the C library (chipmunk physics), but the actual functions are being called from lisp just fine). I've searched far and wide, and maybe I've seen it 100 times and glossed over it, but I cannot figure out how to create a instance of cpVect in lisp to use in other functions. Note the function: cpShape *cpPolyShapeNew(cpBody *body, int numVerts, cpVect *verts, cpVect offset) Takes not only a cpVect, but also a pointer to a set of cpVects, which brings me to my second question: how do I create a pointer to a set of structs? I've been to http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html and tried the code, but get "Error: Unbound variable: PTR" (I'm in Clozure CL), not to mention that looks to only return a pointer, not an instance. I'm new to lisp, been going pretty strong so far, but this is the first real problem I've hit that I can't figure out. Thanks!

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