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• Picture Box and Form Transparency

  - by Qu1nncunxIV

  Maybe I am missing something, but is it the case that when you set a pictureboxes background to transparent, all it really does is set it to the same color as the forms background? What I am trying to do is draw an animation for the benefit of this, a bouncing ball - which I paint on the form, then overlay that with a picture frame. End result should be a bouncing ball in a picture frame, I should mention that the picture frame does not have a straight edge, so it is not possible to arrange 4 picture boxes in a frame. The ball needs to vanish behind the frame to change color and then magically bounce back out. I have tried: 1.Setting the picture box background to pink and then key out the same pink, this basically cuts away everything, including that which is behind the picture box 2.Setting the picture box to transparent, this just displays the picture box background as the same color as the forms background. 3.I have tried painting the image in a rectangle, this had the same effect as drawing it in a picture box. I am not sure what I am doing wrong, I am wondering if there is any other ways I could try or if someone has made a custom control or library that supports transparency?

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• Rails how to return a list of answers with a specific question_id

  - by mytwocentsisworthtwocents

  Let's say I have two Models, Answers and Questions (there are others, but irrelevant to the question). The models are as follows: Answer.rb class Answer < ActiveRecord::Base attr_accessible :description, :question_id has_one :question, :through => :user, :dependent => :destroy validates :description, :presence => true end Question.rb class Question < ActiveRecord::Base attr_accessible :budget, :description, :headline, :user_id, :updated_at, :created_at belongs_to :user has_many :answers validates :headline, :description, :user_id, :presence => true end I'd like to display on a page a list of all answers associated with a question, and only those questions. I got this far. I believe this variable finds all the questions in the database by the question_id (foreign key): @findanswers = Answer.all(params[:question_id]) And this one grabs the the id of the current question (this code will reside as an ERB on the page where the current question is located): @questionshow = Question.find(params[:id]) And now I'm stuck. How do I put the two together so that I list all the answers with the current question id?

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• Validating a phone number in Android PreferenceScreen

  - by djechelon

  I have a PreferenceScreen in which the user is capable, if system can't autodetect it, to enter the device's phone number. I'm still learning this part of Android but I managed to understand a bit of PreferenceScreens by examples provided by Android SDK itself and a few tutorials. What I want is that the user can save the phone number only if null or valid, where by "valid" I mean running a generic validation logic (ie. an anonymous method that returns true or false, that can be reused in any possible situation*) or better, just to simplify things, ^(\+39)?3[0-9]{9}$ For now I have the following XML snip <EditTextPreference android:inputType="phone" android:key="@string/preference_phoneNo" android:selectAllOnFocus="true" android:singleLine="true" android:summary="@string/pref_phoneNumber_description" android:title="@string/pref_phoneNumber" /> and following code by courtesy of Eclipse New Activity wizard: private void setupSimplePreferencesScreen() { if (!isSimplePreferences(this)) { return; } addPreferencesFromResource(R.xml.pref_general); bindPreferenceSummaryToValue(findPreference(getString(R.string.preference_phoneNo))); } addPreferenceFromResource is supposed to load the XML node and add the preference to the screen, while binPreferenceSummaryToValue is supposed to make description text change when preference is updated. Just for sake of completeness for those who don't like code courtesy of the IDE, the second method is provided by Eclipse who also provides a private class in the code file that is /** * A preference value change listener that updates the preference's summary * to reflect its new value. */ In the general case, what should I do to perform validation logic before the preference gets saved when I click OK on the preference editor? Where is the validation logic to be put in a PreferenceScreen? *Aren't we all here to learn?

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• JDBC with JSP fails to insert

  - by StrykeR

  I am having some issues right now with JDBC in JSP. I am trying to insert username/pass ext into my MySQL DB. I am not getting any error or exception, however nothing is being inserted into my DB either. Below is my code, any help would be greatly appreciated. <% String uname=request.getParameter("userName"); String pword=request.getParameter("passWord"); String fname=request.getParameter("firstName"); String lname=request.getParameter("lastName"); String email=request.getParameter("emailAddress"); %> <% try{ String dbURL = "jdbc:mysql:localhost:3306/assi1"; String user = "root"; String pwd = "password"; String driver = "com.mysql.jdbc.Driver"; String query = "USE Users"+"INSERT INTO User (UserName, UserPass, FirstName, LastName, EmailAddress) " + "VALUES ('"+uname+"','"+pword+"','"+fname+"','"+lname+"','"+email+"')"; Class.forName(driver); Connection conn = DriverManager.getConnection(dbURL, user, pwd); Statement statement = conn.createStatement(); statement.executeUpdate(query); out.println("Data is successfully inserted!"); } catch(SQLException e){ for (Throwable t : e) t.printStackTrace(); } %> DB script here: CREATE DATABASE Users; use Users; CREATE TABLE User ( UserID INT NOT NULL AUTO_INCREMENT, UserName VARCHAR(20), UserPass VARCHAR(20), FirstName VARCHAR(30), LastName VARCHAR(35), EmailAddress VARCHAR(50), PRIMARY KEY (UserID) );

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• How can I get sessions to work if I'm using Google App Engine + Django 1.1?

  - by user341642

  Is there a way for me to get sessions working? I know Django has built in session management, and GAE has some tools for it if you're using their watered down version of Django 0.96, but is there a way to get sessions to work if you're trying to use GAE w/ Django 1.1 (i.e. use_library() call). I assume using a db-backed session doesn't work, and a file system backed one won't work b/c we don't have access to the filesystem if we deploy to the Google production servers. This kinda worked (as in didn't crap out) when I used SessionMiddleware backed by a local-memory backed cache and a non-persistent cache (i.e. setting SESSION_ENGINE to django.contrib.sessions.backends.cache). But the session never seems to persist in this case, no matter how I set the timeouts. A new session key is generated on every page reload. Maybe this is b/c the GAE assumes complete statelessness with each request and blows away my local cache? Apologies in advance, I'm pretty new to Python. Any suggestions would be greatly appreciated.

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• Speeding up a group by date query on a big table in postgres

  - by zaius

  I've got a table with around 20 million rows. For arguments sake, lets say there are two columns in the table - an id and a timestamp. I'm trying to get a count of the number of items per day. Here's what I have at the moment. SELECT DATE(timestamp) AS day, COUNT(*) FROM actions WHERE DATE(timestamp) >= '20100101' AND DATE(timestamp) < '20110101' GROUP BY day; Without any indices, this takes about a 30s to run on my machine. Here's the explain analyze output: GroupAggregate (cost=675462.78..676813.42 rows=46532 width=8) (actual time=24467.404..32417.643 rows=346 loops=1) -> Sort (cost=675462.78..675680.34 rows=87021 width=8) (actual time=24466.730..29071.438 rows=17321121 loops=1) Sort Key: (date("timestamp")) Sort Method: external merge Disk: 372496kB -> Seq Scan on actions (cost=0.00..667133.11 rows=87021 width=8) (actual time=1.981..12368.186 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 32447.762 ms Since I'm seeing a sequential scan, I tried to index on the date aggregate CREATE INDEX ON actions (DATE(timestamp)); Which cuts the speed by about 50%. HashAggregate (cost=796710.64..796716.19 rows=370 width=8) (actual time=17038.503..17038.590 rows=346 loops=1) -> Seq Scan on actions (cost=0.00..710202.27 rows=17301674 width=8) (actual time=1.745..12080.877 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 17038.663 ms I'm new to this whole query-optimization business, and I have no idea what to do next. Any clues how I could get this query running faster?

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• android: error on SQLiteDatabase rawQuery (fetching data)

  - by Jin

  So I have a SQliteDatabase mDb. It only has one column, and its data are Strings for previously saved inputs. I'm trying to populate all the data from mDb into a String[] for AutoCompleteTextView (so that the autocomplete is based on previous inputs), and here's my code to get all of the String. public String[] fetchAllSearch() { ArrayList<String> allSearch = new ArrayList<String>(); Cursor c = mDb.rawQuery("select * from " + DATABASE_TABLE, null); c.moveToFirst(); if (c.getCount() > 0) { do { allSearch.add(c.getString(c.getColumnIndex("KEY"))); } while (c.moveToNext()); } String[] foo = (String[]) allSearch.toArray(); if (foo == null) { foo = new String[] {""}; } return foo; } my CREATE_TABLE command is private static final String DATABASE_CREATE = "create table " + DATABASE_TABLE; .. public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); } But for some reason the line mDb.rawQuery(...) is giving me "no such table found" exception, and for the life of me I can't figure out why. Any pointers?

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• ref and out parameters in C# and cannot be marked as variant.

  - by Water Cooler v2

  What does the statement mean? From here ref and out parameters in C# and cannot be marked as variant. 1) Does it mean that the following can not be done. public class SomeClass<R, A>: IVariant<R, A> { public virtual R DoSomething( ref A args ) { return null; } } 2) Or does it mean I cannot have the following. public delegate R Reader<out R, in A>(A arg, string s); public static void AssignReadFromPeonMethodToDelegate(ref Reader<object, Peon> pReader) { pReader = ReadFromPeon; } static object ReadFromPeon(Peon p, string propertyName) { return p.GetType().GetField(propertyName).GetValue(p); } static Reader<object, Peon> pReader; static void Main(string[] args) { AssignReadFromPeonMethodToDelegate(ref pReader); bCanReadWrite = (bool)pReader(peon, "CanReadWrite"); Console.WriteLine("Press any key to quit..."); Console.ReadKey(); } I tried (2) and it worked.

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• Entityframework duplicate record on second insert

  - by Delysid

  I am building an application for recipe/meal planning, and i have come across a problem i cant seem to figure out. i have a table for units of measure, where i keep the used units in, i only want unique units in here (for grocery list calculation and so forth) but if i use a unit from the table on a recipe, the first time it is okay, nothing is inserted in units of measure, but the second time i get a "duplicate". i suspect it has something to do with entitykey, because the primary key is identity column on the sql server (2008 r2) for some reason it works to change the objectstate on some objects (courses, see code) and that does not generate a duplicate, but that does not work on the unit of measure my insert methods looks like this : public recipe Create(recipe recipe) { using (RecipeDataContext ctx = new RecipeDataContext()) { foreach (recipe_ingredient rec_ing in recipe.recipe_ingredient) { if (rec_ing.ingredient.ingredient_id == 0) { ingredient ing = (from _ing in ctx.ingredients where _ing.name == rec_ing.ingredient.name select _ing).FirstOrDefault(); if (ing != null) { rec_ing.ingredient_id = ing.ingredient_id; rec_ing.ingredient = null; } } if (rec_ing.unit_of_measure.unit_of_measure_id == 0) { unit_of_measure _uom = (from dbUom in ctx.unit_of_measure where dbUom.unit == rec_ing.unit_of_measure.unit select dbUom).FirstOrDefault(); if (_uom != null) { rec_ing.unit_of_measure_id = _uom.unit_of_measure_id; rec_ing.unit_of_measure = null; } } ctx.Recipes.AddObject(recipe); //for some reason it works to change object state of this, and not generate a duplicate ctx.ObjectStateManager.ChangeObjectState(recipe.courses[0], EntityState.Unchanged); } ctx.SaveChanges(); } return recipe; } My datamodel looks like this : http://i.imgur.com/NMwZv.png

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• Some ASP.NET and Access

  - by Fazleh

  Good Day all, I have a big problem but i think its minor for you guys in Stackoverflow. I am creating a web application that has two main parts. The Payment part and Requisition part. It backbone is using access and the script is in ASP.NET. I managed to sort out most of the application. But I have been having a few problems. I have pasted the link to the project in http://www.mediafire.com/download/p09fefreifidud3/Inyatsi.rar so it will be easy for someone to see what I am blabbing about. Now for my problems: The AddRequisition.aspx/AddPayment.aspx: both have a reference number. I wanted it to be unique number(but not a primary key). I wanted it to be in the following format: DDMMYY(TransactionNo)(UserID) eg: 24061101PK. I have tried and tried but have not been able to sort it out. The AmountINWords gets the value from Amount. It converts the Amount into words. Thats not all. It picks what currncy was picked in the CurrencyPaidIn and pust the respective currency inside. eg. 123.45 USD becomes One Hundred and twenty three dollars and forty five cents. I tried using queries but as you will see that went all wrong. Those are the only two things that I cant seem to get my head around. I do know that there are some things that are not conventional ASP.NET and some text boxes are not the right size. I was thinking of sorting out those after I get those two fixed because they are simple to do. I really need some help with this application please. If someone can just have a look at the code and add a few things here and there. Thanks in advance. Faz

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• Good C string libary

  - by chamakits

  Hello all. I recently got inspired to start up a project I've been wanting to code for a while. I want to do it in C, because memory handling is key this application. I was searching around for a good implementation of strings in C, since I know me doing it myself could lead to some messy buffer overflows, and I expect to be dealing with a fairly big amount of strings. I found this article which gives details on each, but they each seem like they have a good amount of cons going for them (don't get me wrong, this article is EXTREMELY helpful, but it still worries me that even if I were to choose one of those, I wouldn't be using the best I can get). I also don't know how up to date the article is, hence my current plea. What I'm looking for is something that may hold a large amount of characters, and simplifies the process of searching through the string. If it allows me to tokenize the string in any way, even better. Also, it should have some pretty good I/O performance. Printing, and formatted printing isn't quite a top priority. I know I shouldn't expect a library to do all the work for me, but was just wandering if there was a well documented string function out there that could save me some time and some work. Any help is greatly appreciated. Thanks in advance! EDIT: I was asked about the license I prefer. Any sort of open source license will do, but preferably GPL (v2 or v3). EDIt2: I found betterString (bstring) library and it looks pretty good. Good documentation, small yet versatile amount of functions, and easy to mix with c strings. Anyone have any good or bad stories about it? The only downside I've read about it is that it lacks Unicode (again, read about this, haven't seen it face to face just yet), but everything else seems pretty good. EDIT3: Also, preferable that its pure C.

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• Hibernate OneToMany and ManyToOne confusion! Null List!

  - by squizz

  I have two tables... For example - Company and Employee (let's keep this real simple) Company( id, name ); Employee( id, company_id ); Employee.company_id is a foreign key. My entity model looks like this... Employee @ManyToOne(cascade = CascadeType.PERSIST) @JoinColumn(name = "company_id") Company company; Company @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) @JoinColumn(name = "company_id") List<Employee> employeeList = new ArrayList<Employee>(); So, yeah I want a list of employees for a company. When I do the following... Employee e = new Employee(); e.setCompany(c); //c is an Company that is already in the database. DAO.insertEmployee(e); //this works fine! If I then get my Company object it's list is empty! Ive tried endless different ways from the Hibernate documentation! Obviously not tried the correct one yet! I just want the list to be populated for me or find out a sensible alternative. Help would be greatly appreciated, thanks!

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• WPF: Trying to add a class to Window.Resources Again

  - by user3952846

  I did exactly the same thing, but still the same error is occurring: "The tag 'CenterToolTipConverter' does not exist in XML namespace 'clr-namespace:WpfApplication1;assembly=WpfApplication1'. Line 12 Position 10." CenterToolTipConverter.cs namespace WpfApplication1 { public class CenterToolTipConverter : IMultiValueConverter { public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) { if (values.FirstOrDefault(v => v == DependencyProperty.UnsetValue) != null) { return double.NaN; } double placementTargetWidth = (double)values[0]; double toolTipWidth = (double)values[1]; return (placementTargetWidth / 2.0) - (toolTipWidth / 2.0); } public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) { throw new NotSupportedException(); } } } MainWindow.xaml <Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:WpfApplication1;assembly=WpfApplication1" Title="MainWindow" Height="350" Width="525"> <Window.Resources> <local:CenterToolTipConverter x:Key="myCenterToolTipConverter"/> </Window.Resources> </Window> What am I doing wrong? Thanks in advance!!!

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• What is the best way to create a running integer id on the AppEngine data storage?

  - by Freed

  For various reasons, I need a unique running integer id for my entities stored on the Google AppEngine. The automatically generated key sort of has this behaviour, but it doesn't start from 1 (or 0) and doesn't guarantee that the generated integer part will come from a continuous sequence. What would be the best way to efficiently implement this on AppEngine? Is there any support from the storage system? To add to the complexity, I might need to do this over entities from different entity groups, meaning I can't just get the highest id right now and save an entity with the next id in a transaction. Might memcache be the way to go..? Edit: I havn't yet implemented this, but to clarify on the memcache idea. I know memcache is unreliable, but in practice it probably won't lose data "too often" to hurt performance. Basically, I would have a memcache entry for the last used id, update it (somehow atomically) whenever I create a new entity and use that id. In the case of memcache not having a value for this entry, I'd get the highest id so far by doing a query on my entities sorted by the id and update memcache (unless someone else had already done so). The only problem I can see with this right now would be atomicity of the operation as a whole if the save of my new entity was also part of a transaction. Thoughts..?

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• Merging rows with uniqueness constraints

  - by Flambino

  I've got a little time-tracking web app (implemented in Rails 3.2.8 & MySQL). The app has several users who add their time to specific tasks, on a given date. The system is set up so a user can only have 1 time entry (i.e. row) per task per date. I.e. if you add time twice on the same task and date, it'll add time to the existing row, rather than create a new one. Now I'm looking to merge 2 tasks. In the simplest terms, merging task ID 2 into task ID 1 would take this time | user_id | task_id | date ------+----------+----------+----------- 10 | 1 | 1 | 2012-10-29 15 | 2 | 1 | 2012-10-29 10 | 1 | 2 | 2012-10-29 5 | 3 | 2 | 2012-10-29 and change it into this time | user_id | task_id | date ------+----------+----------+----------- 20 | 1 | 1 | 2012-10-29 <-- time values merged (summed) 15 | 2 | 1 | 2012-10-29 <-- no change 5 | 3 | 1 | 2012-10-29 <-- task_id changed (no merging necessary) I.e. merge by summing the time values, where the given user_id/date/task combo would conflict. I figure I can use a unique constraint to do a ON DUPLICATE KEY UPDATE ... if I do an insert for every task_id=2 entry. But that seems pretty inelegant. I've also tried to figure a way to first update all the rows in task 1 with the summed-up times, but I can't quite figure that one out. Any ideas?

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• NHibernate Native SQL multiple joins

  - by Chris

  Hi all, I"m having some problems with Nhibernate and native sql. I've got an entity with alot of collections and I am doing an SQL Fulltext search on it. So when returning 100 or so entities, I dont want all collections be lazy loaded. For this I changed my SQL query: SELECT Query.* FROM (SELECT {spr.*}, {adr.*}, {adrt.*}, {cty.*}, {com.*}, {comt.*}, spft.[Rank] AS [Rak], Row_number() OVER(ORDER BY spft.[Rank] DESC) AS rownum FROM customer spr INNER JOIN CONTAINSTABLE ( customerfulltext , computedfulltextindex , '" + parsedSearchTerm + @"' ) AS spft ON spr.customerid = spft.[Key] LEFT JOIN [Address] adr ON adr.customerid = spr.customerid INNER JOIN [AddressType] adrt ON adrt.addresstypeid = adr.addresstypeid INNER JOIN [City] cty ON cty.cityid = adr.cityid LEFT JOIN [Communication] com ON com.customerid = spr.customerid INNER JOIN [CommunicationType] comt ON comt.communicationtypeid = com.communicationtypeid) as Query ORDER BY Query.[Rank] DESC This is how I setup the query: var items = GetCurrentSession() .CreateSQLQuery(query) .AddEntity("spr", typeof(Customer)) .AddJoin("adr", "spr.addresses") .AddJoin("adrt", "adr.Type") .AddJoin("cty", "adr.City") .AddJoin("com", "spr.communicationItems") .AddJoin("comt", "com.Type") .List<Customer>(); What happens now is, that the query returns customers twice (or more), I assume this is because of the joins since for each customer address, communicationItem (e.g. phone, email), a new sql row is returned. In this case I thought I could use the DistinctRootEntityResultTransformer. var items = GetCurrentSession() .CreateSQLQuery(query) .AddEntity("spr", typeof(Customer)) .AddJoin("adr", "spr.addresses") .AddJoin("adrt", "adr.Type") .AddJoin("cty", "adr.City") .AddJoin("com", "spr.communicationItems") .AddJoin("comt", "com.Type") .SetResultTransformer(new DistinctRootEntityResultTransformer()) .List<Customer>(); Doing so an exception is thrown. This is because I try to list customers .List<Customer>() but the transformer returns only entities of the last join added. E.g. in the case above, the entity with alias "comt" is returned when doing .List() instead of .List(). If I would switch last join with the join alias "cty", then the transformer returns a list of cities only... Anyone knows how I can return a clean list of customers in this case?

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• InputStreamBody in HttpMime 4.0.3 settings for content-length

  - by Ram

  I am trying to send a multi part formdata post through my java code. Can someone tell me how to set Content Length in the following?? There seem to be headers involved when we use InputStreamBody which implements the ContentDescriptor interface. Doing a getContentLength on the InputStreamBody gives me -1 after i add the content. I subclassed it to give contentLength the length of my byte array but am not sure if other headers required by ContentDescriptor will be set for a proper POST. HttpClient httpclient = new DefaultHttpClient(); HttpPost httpPost = new HttpPost(myURL); ContentBody cb = new InputStreamBody(new ByteArrayInputStream(bytearray), myMimeType, filename); //ContentBody cb = new ByteArrayBody(bytearray, myMimeType, filename); MultipartEntity mpentity = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE); mpentity.addPart("key", new StringBody("SOME_KEY")); mpentity.addPart("output", new StringBody("SOME_NAME")); mpentity.addPart("content", cb); httpPost.setEntity(mpentity); HttpResponse response = httpclient.execute(httpPost); HttpEntity resEntity = response.getEntity();

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• Automatically Persisting a Complex Java Object

  - by VeeArr

  For a project I am working on, I need to persist a number of POJOs to a database. The POJOs class definitions are sometimes highly nested, but they should flatten okay, as the nesting is tree-like and contains no cycles (and the base elements are eventually primitives/Strings). It is preferred that the solution used create one table per data type and that the tables will have one field per primitive member in the POJO. Subclassing and similar problems are not issues for this particular project. Does anybody know of any existing solutions that can: Automatically generate a CREATE TABLE definition from the class definition Automatically generate a query to persist an object to the database, given an instance of the object Automatically generate a query to retrieve an object from the database and return it as a POJO, given a key. Solutions that can do this with minimum modifications/annotions to the class files and minimum external configuration are preferred. Example: Java classes //Class to be persisted class TypeA { String guid; long timestamp; TypeB data1; TypeC data2; } class TypeB { int id; int someData; } class TypeC { int id; int otherData; } Could map to CREATE TABLE TypeA ( guid CHAR(255), timestamp BIGINT, data1_id INT, data1_someData INT, data2_id INt, data2_otherData INT ); Or something similar.

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• Create an index only on certain rows in mysql

  - by dhruvbird

  So, I have this funny requirement of creating an index on a table only on a certain set of rows. This is what my table looks like: USER: userid, friendid, created, blah0, blah1, ..., blahN Now, I'd like to create an index on: (userid, friendid, created) but only on those rows where userid = friendid. The reason being that this index is only going to be used to satisfy queries where the WHERE clause contains "userid = friendid". There will be many rows where this is NOT the case, and I really don't want to waste all that extra space on the index. Another option would be to create a table (query table) which is populated on insert/update of this table and create a trigger to do so, but again I am guessing an index on that table would mean that the data would be stored twice. How does mysql store Primary Keys? I mean is the table ordered on the Primary Key or is it ordered by insert order and the PK is like a normal unique index? I checked up on clustered indexes (http://dev.mysql.com/doc/refman/5.0/en/innodb-index-types.html), but it seems only InnoDB supports them. I am using MyISAM (I mention this because then I could have created a clustered index on these 3 fields in the query table). I am basically looking for something like this: ALTER TABLE USERS ADD INDEX (userid, friendid, created) WHERE userid=friendid

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• What is the mean of @ModelAttribute annotation at method argument level?

  - by beemaster

  Spring 3 reference teaches us: When you place it on a method parameter, @ModelAttribute maps a model attribute to the specific, annotated method parameter I don't understand this magic spell, because i sure that model object's alias (key value if using ModelMap as return type) passed to the View after executing of the request handler method. Therefore when request handler method executes the model object's name can't be mapped to the method parameter. To solve this contradiction i went to stackoverflow and found this detailed example. The author of example said: // The "personAttribute" model has been passed to the controller from the JSP It seems, he is charmed by Spring reference... To dispel the charms i deployed his sample app in my environment and cruelly cut @ModelAttribute annotation from method MainController.saveEdit. As result the application works without any changes! So i conclude: the @ModelAttribute annotation is not needed to pass web form's field values to the argument's fields. Then i stuck to the question: what is the mean of @ModelAttribute annotation? If the only mean is to set alias for model object in View, then why this way better than explicitly adding of object to ModelMap?

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• Cryptography for P2P card game

  - by zephyr

  I'm considering writing a computer adaptation of a semi-popular card game. I'd like to make it function without a central server, and I'm trying to come up with a scheme that will make cheating impossible without having to trust the client. The basic problem as I see it is that each player has a several piles of cards (draw deck, current hand and discard deck). It must be impossible for either player to alter the composition of these piles except when allowed by the game rules (ie drawing or discarding cards), nor should players be able to know what is in their or their oppponent's piles. I feel like there should be some way to use something like public-key cryptography to accomplish this, but I keep finding holes in my schemes. Can anyone suggest a protocol or point me to some resources on this topic? [Edit] Ok, so I've been thinking about this a bit more, and here's an idea I've come up with. If you can poke any holes in it please let me know. At shuffle time, a player has a stack of cards whose value is known to them. They take these values, concatenate a random salt to each, then hash them. They record the salts, and pass the hashes to their opponent. The opponent concatenates a salt of their own, hashes again, then shuffles the hashes and passes the deck back to the original player. I believe at this point, the deck has been randomized and neither player can have any knowledge of the values. However, when a card is drawn, the opponent can reveal their salt, allowing the first player to determine what the original value is, and when the card is played the player reveals their own salt, allowing the opponent to verify the card value.

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• How to break an object into chunks based on some property?

  - by CurlyFro

  public class InvestorMailing { public string To { get; set; } public IEnumerable<string> Attachments { get; set; } public int AttachmentCount { get; set; } public long AttachmentSize { get; set; } } i have an IList<InvestorMailing> mailingList. if the attachment size is greater than x, then i need to split my object into chunks. is there an easy linq-y way to do this? Edited: this is how i'm generating my mailings: var groupedMailings = mailingList.GroupBy(g => g.GroupBy); var investorMailings = groupedMailings.Select( g => new DistinctInvestorMailing { Id = g.Select(x => x.Id).FirstOrDefault(), To = g.Key.Trim(), From = g.Select(x => x.From).FirstOrDefault(), FromName = g.Select(x => x.FromName).FirstOrDefault(), Bcc = g.Select(x => x.Bcc).FirstOrDefault(), DeliveryCode = g.Select(x => x.DeliveryCode).FirstOrDefault(), Subject = g.Select(x => x.Subject).FirstOrDefault(), Body = g.Select(x => x.Body).FirstOrDefault(), CommentsOnStatus = g.Select(x => x.CommentsOnStatus).FirstOrDefault(), Attachments = g.Select(x => x.AttachmentPath), AttachmentCount = g.Select(x => x.AttachmentPath).Count(), AttachmentSize = g.Sum(x => x.AttachmentSize), MailType = g.Select(x => x.MessageType).FirstOrDefault() } ).ToList();

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• What guarantees are there on the run-time complexity (Big-O) of LINQ methods?

  - by tzaman

  I've recently started using LINQ quite a bit, and I haven't really seen any mention of run-time complexity for any of the LINQ methods. Obviously, there are many factors at play here, so let's restrict the discussion to the plain IEnumerable LINQ-to-Objects provider. Further, let's assume that any Func passed in as a selector / mutator / etc. is a cheap O(1) operation. It seems obvious that all the single-pass operations (Select, Where, Count, Take/Skip, Any/All, etc.) will be O(n), since they only need to walk the sequence once; although even this is subject to laziness. Things are murkier for the more complex operations; the set-like operators (Union, Distinct, Except, etc.) work using GetHashCode by default (afaik), so it seems reasonable to assume they're using a hash-table internally, making these operations O(n) as well, in general. What about the versions that use an IEqualityComparer? OrderBy would need a sort, so most likely we're looking at O(n log n). What if it's already sorted? How about if I say OrderBy().ThenBy() and provide the same key to both? I could see GroupBy (and Join) using either sorting, or hashing. Which is it? Contains would be O(n) on a List, but O(1) on a HashSet - does LINQ check the underlying container to see if it can speed things up? And the real question - so far, I've been taking it on faith that the operations are performant. However, can I bank on that? STL containers, for example, clearly specify the complexity of every operation. Are there any similar guarantees on LINQ performance in the .NET library specification?

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• Blit SDL_Surface onto another SDL_Surface and apply a colorkey

  - by NordCoder

  I want to load an SDL_Surface into an OpenGL texture with padding (so that NPOT-POT) and apply a color key on the surface afterwards. I either end up colorkeying all pixels, regardless of their color, or not colorkey anything at all. I have tried a lot of different things, but none of them seem to work. Here's the working snippet of my code. I use a custom color class for the colorkey (range [0-1]): // Create an empty surface with the same settings as the original image SDL_Surface* paddedImage = SDL_CreateRGBSurface(image->flags, width, height, image->format->BitsPerPixel, #if SDL_BYTEORDER == SDL_BIG_ENDIAN 0xff000000, 0x00ff0000, 0x0000ff00, 0x000000ff #else 0x000000ff, 0x0000ff00, 0x00ff0000, 0xff000000 #endif ); // Map RGBA color to pixel format value Uint32 colorKeyPixelFormat = SDL_MapRGBA(paddedImage->format, static_cast<Uint8>(colorKey.R * 255), static_cast<Uint8>(colorKey.G * 255), static_cast<Uint8>(colorKey.B * 255), static_cast<Uint8>(colorKey.A * 255)); SDL_FillRect(paddedImage, NULL, colorKeyPixelFormat); // Blit the image onto the padded image SDL_BlitSurface(image, NULL, paddedImage, NULL); SDL_SetColorKey(paddedImage, SDL_SRCCOLORKEY, colorKeyPixelFormat); Afterwards, I generate an OpenGL texture from paddedImage using similar code to the SDL+OpenGL texture loading code found online (I'll post if necessary). This code works if I just want the texture with or without padding, and is likely not the problem. I realize that I set all pixels in paddedImage to have alpha zero which causes the first problem I mentioned, but I can't seem to figure out how to do this. Should I just loop over the pixels and set the appropriate colors to have alpha zero?

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• Recomendations for Creating a Picture Slide Show with Super-Smooth Transitions (For Live Presentaito

  - by Nick

  Hi everyone, I'm doing a theatrical performance, and I need a program that can read images from a folder and display them full screen on one of the computer's VGA outputs, in a predetermined order. All it needs to do is start with the first image, and when a key is pressed (space bar, right arrow), smoothly cross-fade to the next image. Sounds just like power-point right? The only reason why I can use power-point/open-office is because the "fade smoothly" transition isn't smooth enough, or configurable enough. It tends to be fast and choppy, where I would like to see a perfectly smooth fade over, say, 30 seconds. So the question is what is the best (cheap and fast) way to accomplish this? Is there a program that already does this well (for cheap or free)? OR should I try to hack at open-office's transition code? Or would it be easier to create this from scratch? Are there frameworks that might make it easier? I have web programming experience (php), but not desktop or real-time rendering. Any suggestions are appreciated!

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