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• Does anyone else think instance variables are problematic in database-backed applications?

  - by Ben Aston

  It occurs to me that state control in languages like C# is not well supported. By this, I mean, it is left upto the programmer to manage the state of in-memory objects. A common use-case is that instance variables in the domain-model are copies of information residing in persistent storage (i.e. the database). Clearly this violates the single point of authority principle, and "synchronisation" has to be managed by the developer. I envisage a system where instead of instance variables, we have simple public access/mutator methods marked with attributes that link them to the database, and where reads and writes are mediated by a framework that decides whether to hit the database. Does such a system exist? Am I completely missing the point, or is there some truth to this idea?

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• What does this Obj-C "unrecognized selector sent to instance" exception indicate?

  - by user128647

  What does this mean? * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[NSPathStore2 hidesBottomBarWhenPushed]: unrecognized selector sent to instance 0x1cd3d0'

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

  - by Jbm

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

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• Is it possible to create an enum whose instance can't be created but can be used for readonly purpos

  - by Shantanu Gupta

  I created an enum where I stored some table names. I want it to be used to get the name of the table like ds.Tables[BGuestInfo.TableName.L_GUEST_TYPE.ToString()]. public class a { public enum TableName : byte { L_GUEST_TYPE = 0 ,L_AGE_GROUP = 1 ,M_COMPANY = 2 ,L_COUNTRY = 3 ,L_EYE_COLOR = 4 ,L_GENDER = 5 ,L_HAIR_COLOR = 6 ,L_STATE_PROVINCE = 7 ,L_STATUS = 8 ,L_TITLE = 9 ,M_TOWER = 10 ,L_CITY = 11 ,L_REGISTER_TYPE = 12 } } class b { a.TableName x; //trying to restrict this ds.Tables[a.TableName.L_GUEST_TYPE] //accessible and can be used like this } This is my enum. Now I have not created any instance of this enum so that no one can use it for other than read only purpose. For this enum to be accessible in outer classes as well I have to make it public which means some outer class can create its object as well. So what can i do so as to restrict its instance creation.

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• Methods specific only to an instance? What are they called in Ruby?

  - by daremarkovic

  I know there are "instance methods", "class methods" but what are these types of methods called, for eg: s1 = "This is my STRING!" def s1.m1 downcase end p s1 # => "This is my STRING!" p s1.m1 # => "this is my string!" What type of method is the "m1" method called on the s1 "instance" of the "string" class? It's really weird because I didn't know this was possible at all if I try: s2 = "This is ANOTHER string" s2.m1 # => Won't work! Which kind of makes sense, but not sure why defining methods like m1 on instances on a class are useful at all.

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• can I debug my web project and wcf project on same vs 2008 instance ?

  - by dotnetcoder

  I have two projects in my solution   1- asp.net web project.   2- wcf serivce project.   3- other common projects between two listed above Current on the local dev machine I have to run two visual studio instance to run both projects in debug mode. That makes the system run out of resources as these projects share some other project in the soultion which are heavy in files. Is there a way i can hookup the wcf project on a sinlge visual stodio instance and also be able to debug my asp.net web project. ? I do not want to combine the web and wcf project in to one. Have already considred this option. thanks for sharing your thoughts in advance.

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• Are static members slower to access than instance members in AS3?

  - by Pup

  Are static members slower to access than instance members in AS3?

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• Declaring two classes that contain instance variables of each others' types.

  - by Benji XVI

  Let’s say you wish to have two classes like so, each declaring an instance variable that is of the other’s class. @interface A : NSObject { B *something; } @end @interface B : NSObject { A *something; } @end It seems to be impossible to declare these classes with these instance variables. In order for A to include an IV of class B, B must already be compiled, and so its @interface must come before A’s. But A’s must be put before B’s for the same reason. Putting the two class declarations in separate files, and #import-ing each other’s .h doesn’t work either, for obvious reasons. So, what is the solution? Or is this either (1) impossible or (2) indicative of a bad design anyway?

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• Checking for a session variable... returns (Object reference not set to an instance of an object.)

  - by Chocol8

  In the Session_Start i have Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs) Session("login") = False End Sub and in a custom .aspx page i included the following... Public ReadOnly Property GetLoginState() As Boolean Get If Current.Session("login") Is Nothing Then Current.Session("login") = False End If Return Current.Session("login") End Get End Property Why i am getting error the error Object reference not set to an instance of an object. at line If Current.Session("login") Is Nothing Then while checking for the login state as follows? If GetLogin = False Then 'Do something End if I mean i have already created the instance on the Session_Start... Haven't i? What am i doing wrong here?

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• why can not create instance from any class out side of constructor?

  - by Phsika

  why i generate instance outside of class. i give inheritance snifC to sinifD i need to create instance sinifC sinifc= new sinifC() in SinifD out side of constructor? public class sinifC { public void method3() { Console.WriteLine("Deneme3"); } } public class sinifD : sinifC { void method4() { Console.WriteLine("Deneme4"); } public sinifD() { sinifC sinifc = new sinifC(); sinifc.method3(); } } i want to make it below: public class sinifC { public void method3() { Console.WriteLine("Deneme3"); } } public class sinifD : sinifC { void method4() { Console.WriteLine("Deneme4"); } sinifC sinifc = new sinifC(); sinifc.method3(); } Error: Invalid token '(' in class, struct, or interface member declaration

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• Are static members of a generic class tied to the specific instance?

  - by mafutrct

  This is more of a documentation than a real question. I noticed the principle it is not described on SO yet (did I miss it?), so here goes: Imagine a generic class that contains a static member: class Foo<T> { public static int member; } Is there a new instance of the member for each specific class, or is there only a single instance for all Foo-type classes? It can easily be verified by code like this: Foo<int>.member = 1; Foo<string>.member = 2; Console.WriteLine (Foo<int>.member); What is the result, and where is this behavior documented?

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• Simple Backup Strategy for Amazon EC2 instances / volumes?

  - by minerj

  You have entered Introductory Backups for Amazon EC2 EBS-backed Windows Images 010... I have been browsing my brains out to find a simple backup strategy for our single windows 2008 server running SharePoint Services. This is an EBS-backed image of one server with one data volume. I don’t need anything exotic. I only need a “daily” backup (losing a day’s worth of data is not catastrophic). We have created and saved an EBS backed AMI image (Windows 2008) we are comfortable using. We started off making backups by simply creating a new EBS AMI image. This is really simple, but the running server is put offline during the first 10 – 15 minutes of creating the image – not ideal. The standard way of creating backups would seem to be creating snapshots of volumes attached to a running instance. Again it’s pretty simple and the server remains usable during the snapshot generation. The apparent Catch-22 is that you can’t simply launch a new instance directly from a snapshot. I know how to bundle a running instance to S3 storage and then register the AMI from the S3 bucket. This does allow me to capture a backup of a running instance and, if the running instance is lost, register the AMI from the S3 bucket and launch the new AMI to recover the instance, but this seems really convoluted and it seems ridiculous to have to juggle back and forth between the AWS Console and the S3 Organizer plug-in for Firefox to get this accomplished. (Please don't mention the command line approach, this is an 010 level course). From playing around with EBS-backed images, the following approach appears to work for me (all done within the AWS Console): 1.For your backups, simply snapshot the system volume (/dev/sda1) as needed. 2.If you lose your running instance, do the following: a.Create a new volume from your last snapshot backup b.Launch another instance of your starting AMI (must be EBS-backed) c.Stop this instance. d.Detach the existing system volume from the new stopped instance and discard. e.Attach the newly created volume as system volume (/dev/sda1) to the stopped instance. f.Re-start the new instance. I have tested this out a couple of times and it seems to work for me. Question: Is there anything wrong with this approach?

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• How to figure out how much RAM each prefork thread requires for maximum Wordpress performance on an EC2 small instance

  - by two7s_clash

  Just read Making WordPress Stable on EC2-Micro In the "Tuning Apache" section, I can't quite figure out how he comes up with his numbers for his prefork config. He explains how to get the numbers for an average process, which I get. But then: Or roughly 53MB per process...In this case, ten threads should be safe. This means that if we receive more than ten simultaneous requests, the other requests will be queued until a worker thread is available. In order to maximize performance, we will also configure the system to have this number of threads available all of the time. From 53MB per process, with 613MB of RAM, he somehow gets this config, which I don't get: <IfModule prefork.c> StartServers 10 MinSpareServers 10 MaxSpareServers 10 MaxClients 10 MaxRequestsPerChild 4000 </IfModule> How exactly does he get this from 53MB per process, with 613MB limit? Bonus question From the below, on a small instance (1.7 GB memory), what would good settings be? bitnami@ip-10-203-39-166:~$ ps xav |grep httpd 1411 ? Ss 0:00 2 0 114928 15436 0.8 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1415 ? S 0:06 10 0 125860 55900 3.1 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1426 ? S 0:08 19 0 127000 62996 3.5 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1446 ? S 0:05 48 0 131932 72792 4.1 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1513 ? S 0:05 7 0 125672 54840 3.1 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1516 ? S 0:02 2 0 125228 48680 2.7 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1517 ? S 0:06 2 0 127004 55796 3.1 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1518 ? S 0:03 1 0 127196 54208 3.0 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf 1531 ? R 0:04 0 0 127500 54236 3.0 /opt/bitnami/apache2/bin/httpd -f /opt/bitnami/apache2/conf/httpd.conf

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• Can't install NPM after installing Node on EC2 Linux instance?

  - by frequent

  I'm trying my first attempt on getting a node server set up on an amazon ec2 linux instance. I think I made it quite far. First problem I ran into was when trying to make Node the connection timed out after a while, so I need three attempts until I got this: LINK(target) /home/ec2-user/node/out/Release/node: Finished touch /home/ec2-user/node/out/Release/obj.target/node_dtrace_header.stamp touch /home/ec2-user/node/out/Release/obj.target/node_dtrace_provider.stamp touch /home/ec2-user/node/out/Release/obj.target/node_dtrace_ustack.stamp touch /home/ec2-user/node/out/Release/obj.target/node_etw.stamp make[1]: Leaving directory `/home/ec2-user/node/out' ln -fs out/Release/node node Which tells me, "Node is done", although I'm not sure it is also working as it should. Following this,this and this tutorial, I'm now stuck at installing npm. I think I first cloned into the wrong folder, which always gave me error 127, but even if I'm doing this: cd ~ git clone git://github.com/isaacs/npm.git cd npm sudo -s PATH=/usr/local/bin:$PATH make install I'm still getting this: #after cloning# make[1]: Entering directory `/root/npm' node cli.js install bash: node: command not found make[1]: *** [node_modules/.bin/ronn] Error 127 make[1]: Leaving directory `/root/npm' make: *** [man/man3/start.3] Error 2 Question:: Since I'm pretty much a newby at everything I'm trying here, can someone please tell me what I'm doing wrong and how to get npm to install? Also, in case I cloned into the wrong folder, is there a way to remove the "false clone" or is this not written to disk until I call make install and I don't need to worry? Thanks for helping out!

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• Best VNC client for remote desktop assistance?

  - by e.m.fields

  Poll on best VNC / remote desktop software for assisting others on Windows/Mac machines from Ubuntu? I've heard good things about TeamViewer and Fog Creek Copilot, but I'm wondering if the included GNOME Vinaigre VNC client is good enough for this. To specify, I'm looking for best option based on: SIMPLEST ease-of-use for client to download/use on their end. See #1. Works cross-platform I am able to control client's mouse and/or keyboard from remote machine.

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• How should I share variables between instances/classes?

  - by tesselode

  I'm making a game using LOVE, so everything is programmed in Lua. I've been experimenting with using classes and object orientation recently. I've found out that a nice system to use is having most of the game's code in different classes, and having a table of instances with all of the instances of any class in it. This way, I can go through every instance of every class and update and draw it by calling the same function. There is a problem, though. Let's say I have an instance of a player with variables for health and recharge time of a weapon. I also have a master instance which is responsible for drawing the HUD. How can I tell the master instance what the player's health is? Bad solutions: Assuming that the player instance will always have the same position in the table - that can be easily changed. Using global variables. Global variables are evil. Have the master instance outside of the instances table, and have the player set variables inside the master instance, which it then uses for HUD drawing. This is really bad because now I have to make a duplicate of every variable the master instance needs. What is the proper, standard way of sharing variables between instances? Do I need to change the way I keep track of instances?

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• Auto-hydrate your objects with ADO.NET

  - by Jake Rutherford

  Recently while writing the monotonous code for pulling data out of a DataReader to hydrate some objects in an application I suddenly wondered "is this really necessary?" You've probably asked yourself the same question, and many of you have: - Used a code generator - Used a ORM such as Entity Framework - Wrote the code anyway because you like busy work     In most of the cases I've dealt with when making a call to a stored procedure the column names match up with the properties of the object I am hydrating. Sure that isn't always the case, but most of the time it's 1 to 1 mapping.  Given that fact I whipped up the following method of hydrating my objects without having write all of the code. First I'll show the code, and then explain what it is doing.      /// <summary>     /// Abstract base class for all Shared objects.     /// </summary>     /// <typeparam name="T"></typeparam>     [Serializable, DataContract(Name = "{0}SharedBase")]     public abstract class SharedBase<T> where T : SharedBase<T>     {         private static List<PropertyInfo> cachedProperties;         /// <summary>         /// Hydrates derived class with values from record.         /// </summary>         /// <param name="dataRecord"></param>         /// <param name="instance"></param>         public static void Hydrate(IDataRecord dataRecord, T instance)         {             var instanceType = instance.GetType();                         //Caching properties to avoid repeated calls to GetProperties.             //Noticable performance gains when processing same types repeatedly.             if (cachedProperties == null)             {                 cachedProperties = instanceType.GetProperties().ToList();             }                         foreach (var property in cachedProperties)             {                 if (!dataRecord.ColumnExists(property.Name)) continue;                 var ordinal = dataRecord.GetOrdinal(property.Name);                 var isNullable = property.PropertyType.IsGenericType &&                                  property.PropertyType.GetGenericTypeDefinition() == typeof (Nullable<>);                 var isNull = dataRecord.IsDBNull(ordinal);                 var propertyType = property.PropertyType;                 if (isNullable)                 {                     if (!string.IsNullOrEmpty(propertyType.FullName))                     {                         var nullableType = Type.GetType(propertyType.FullName);                         propertyType = nullableType != null ? nullableType.GetGenericArguments()[0] : propertyType;                     }                 }                 switch (Type.GetTypeCode(propertyType))                 {                     case TypeCode.Int32:                         property.SetValue(instance,                                           (isNullable && isNull) ? (int?) null : dataRecord.GetInt32(ordinal), null);                         break;                     case TypeCode.Double:                         property.SetValue(instance,                                           (isNullable && isNull) ? (double?) null : dataRecord.GetDouble(ordinal),                                           null);                         break;                     case TypeCode.Boolean:                         property.SetValue(instance,                                           (isNullable && isNull) ? (bool?) null : dataRecord.GetBoolean(ordinal),                                           null);                         break;                     case TypeCode.String:                         property.SetValue(instance, (isNullable && isNull) ? null : isNull ? null : dataRecord.GetString(ordinal),                                           null);                         break;                     case TypeCode.Int16:                         property.SetValue(instance,                                           (isNullable && isNull) ? (int?) null : dataRecord.GetInt16(ordinal), null);                         break;                     case TypeCode.DateTime:                         property.SetValue(instance,                                           (isNullable && isNull)                                               ? (DateTime?) null                                               : dataRecord.GetDateTime(ordinal), null);                         break;                 }             }         }     }   Here is a class which utilizes the above: [Serializable] [DataContract] public class foo : SharedBase<foo> {     [DataMember]     public int? ID { get; set; }     [DataMember]     public string Name { get; set; }     [DataMember]     public string Description { get; set; }     [DataMember]     public string Subject { get; set; }     [DataMember]     public string Body { get; set; }            public foo(IDataRecord record)     {         Hydrate(record, this);                }     public foo() {} }   Explanation: - Class foo inherits from SharedBase specifying itself as the type. (NOTE SharedBase is abstract here in the event we want to provide additional methods which could be overridden by the instance class) public class foo : SharedBase<foo> - One of the foo class constructors accepts a data record which then calls the Hydrate method on SharedBase passing in the record and itself. public foo(IDataRecord record) {      Hydrate(record, this); } - Hydrate method on SharedBase will use reflection on the object passed in to determine its properties. At the same time, it will effectively cache these properties to avoid repeated expensive reflection calls public static void Hydrate(IDataRecord dataRecord, T instance) {      var instanceType = instance.GetType();      //Caching properties to avoid repeated calls to GetProperties.      //Noticable performance gains when processing same types repeatedly.      if (cachedProperties == null)      {           cachedProperties = instanceType.GetProperties().ToList();      } . . . - Hydrate method on SharedBase will iterate each property on the object and determine if a column with matching name exists in data record foreach (var property in cachedProperties) {      if (!dataRecord.ColumnExists(property.Name)) continue;      var ordinal = dataRecord.GetOrdinal(property.Name); . . . NOTE: ColumnExists is an extension method I put on IDataRecord which I’ll include at the end of this post. - Hydrate method will determine if the property is nullable and whether the value in the corresponding column of the data record has a null value var isNullable = property.PropertyType.IsGenericType && property.PropertyType.GetGenericTypeDefinition() == typeof (Nullable<>); var isNull = dataRecord.IsDBNull(ordinal); var propertyType = property.PropertyType; . . .  - If Hydrate method determines the property is nullable it will determine the underlying type and set propertyType accordingly - Hydrate method will set the value of the property based upon the propertyType   That’s it!!!   The magic here is in a few places. First, you may have noticed the following: public abstract class SharedBase<T> where T : SharedBase<T> This says that SharedBase can be created with any type and that for each type it will have it’s own instance. This is important because of the static members within SharedBase. We want this behavior because we are caching the properties for each type. If we did not handle things in this way only 1 type could be cached at a time, or, we’d need to create a collection that allows us to cache the properties for each type = not very elegant.   Second, in the constructor for foo you may have noticed this (literally): public foo(IDataRecord record) {      Hydrate(record, this); } I wanted the code for auto-hydrating to be as simple as possible. At first I wasn’t quite sure how I could call Hydrate on SharedBase within an instance of the class and pass in the instance itself. Fortunately simply passing in “this” does the trick. I wasn’t sure it would work until I tried it out, and fortunately it did.   So, to actually use this feature when utilizing ADO.NET you’d do something like the following:        public List<foo> GetFoo(int? fooId)         {             List<foo> fooList;             const string uspName = "usp_GetFoo";             using (var conn = new SqlConnection(_dbConnection))             using (var cmd = new SqlCommand(uspName, conn))             {                 cmd.CommandType = CommandType.StoredProcedure;                 cmd.Parameters.Add(new SqlParameter("@FooID", SqlDbType.Int)                                        {Direction = ParameterDirection.Input, Value = fooId});                 conn.Open();                 using (var dr = cmd.ExecuteReader())                 {                     fooList= (from row in dr.Cast<DbDataRecord>()                                             select                                                 new foo(row)                                            ).ToList();                 }             }             return fooList;         }   Nice! Instead of having line after line manually assigning values from data record to an object you simply create a new instance and pass in the data record. Note that there are certainly instances where columns returned from stored procedure do not always match up with property names. In this scenario you can still use the above method and simply do your manual assignments afterward.

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• How to reduce memory consumption an AWS EC2 t1.micro instance (free tier) ubuntu server 14.04 LTS EBS

  - by CMPSoares

  Hi I'm working on my bachelor thesis and for that I need to host a node.js web application on AWS, in order to avoid costs I'm using a t1.micro instance with 30GB disk space (from what I know it's the maximum I get in the free tier) which is barely used. But instead I have problems with memory consumption, it's using all of it. I tried the approach of creating a virtual swap area as mentioned at Why don't EC2 ubuntu images have swap? with these commands: sudo dd if=/dev/zero of=/var/swapfile bs=1M count=2048 && sudo chmod 600 /var/swapfile && sudo mkswap /var/swapfile && echo /var/swapfile none swap defaults 0 0 | sudo tee -a /etc/fstab && sudo swapon -a But this swap area isn't used somehow. Is something missing in this approach or is there another process of reducing the memory consumption in these type of AWS instances? Bottom-line: This originates server freezes and crashes and that's what I want to stop either by using the swap, reducing memory usage or both.

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• How to add dynamic profile fields in Invision Power Board?

  - by user361908

  I run a game server and want to link the persons in game character name and stats to Invision Power Board. I've setup IPB so players currently login with their in game login. That means their username on the forum is the same as their username for the game. They can have multiple characters on 1 account so ideally I'd like to allow them to choose a main character and display an actual image of that character and allow them to display other characters if they are online. Currently I'm doing something like this by hacking profileFields.php but it's messy and not very efficient on the user or server end. My code currently uses 2 custom fields which the player can enter their character names in. To display only their main character they enter the name in the first field. To also display other characters if they are online they enter the same name into the second field. To resolve the IDs I have to run a lot of queries. I know PHP but I am not familiar with IPBs code at all. I just need pointed in a direction where I can combine the 2 fields into 1 field. tl;dr: Here is my setup: Invision Power Board 3 Data is stored in MySQL on the same server the forum is hosted on. Usernames on the forum are identical to usernames in the game Here is a breakdown of what I'd like to do: In the edit profile section I need to resolve the forum username to the games account id then: Display a list of characters and allow them to choose which characters they want to display if they are online as well as a default character that will be displayed if none are online. In the posts user info pane: Display the online character or the default if none are online. Here is what I need to know: How to generate a list of characters in the profile edit form and allow selection (checkbox) of each character to display as well as the selection of a default character (radio or dropdown?) How to fetch the data and place it in the posts user info pane

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• JSF 2.0: Validate equality of 2 InputSecret Fields (confirm password) without writing Code?

  - by yournamehere

  I'm developing a pure JavaEE6 application with JSF 2.0 and Glassfish. My JSF implementation is Primefaces (beside Mojarra provided by Glassfish). I want to verify if the values of 2 password fields in a JSF form are equal. With Seam, there is the neat component <s:validateEquality for="pw1"/>. I want do to the same without Seam, just using JSF (or maybe a component of a JSF library). Until now i only saw examples which validate the form with a custom validator. But i would like to compare the fields without writing Java code or Javascript code. Is that possible? This what it looks like with Seam: ... <h:inputSecret id="passwort" value="#{personHome.instance.password}" redisplay="true" required="true"> <f:validateLength minimum="8"/> <a:support event="onblur" reRender="passwortField" bypassUpdates="true" ajaxSingle="true" /> </h:inputSecret> ... <h:inputSecret id="passwort2" required="true" redisplay="true"> <!-- find the JSF2.0-equivalent to this tag: --> <s:validateEquality for="passwort"/> <a:support event="onblur" reRender="passwort2Field" bypassUpdates="true" ajaxSingle="true" /> </h:inputSecret> ... Any help is appreciated. Thanks!

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• How to delete duplicate records in MySQL by retaining those fields with data in the duplicate item b

  - by NJTechGuy

  I have few thousands of records with few 100 fields in a MySQL Table. Some records are duplicates and are marked as such. Now while I can simply delete the dupes, I want to retain any other possible valuable non-null data which is not present in the original version of the record. Hope I made sense. For instance : a b c d e f key dupe -------------------- 1 d c f k l 1 x 2 g h j 1 3 i h u u 2 4 u r t 2 x From the above sample table, the desired output is : a b c d e f key dupe -------------------- 2 g c h k j 1 3 i r h u u 2 If you look at it closely, the duplicate is determined by using the key (it is the same for 2 records, so the one that has an 'x' for dupe field is the one to be deleted by retaining some of the fields from the dupe (like c, e values for key 1). Please let me know if you need more info about this puzzling problem. Thanks a tonne! p.s : If it is not possible using MySQL, a PERL/Python script sample would be awesome! Thanks!

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• Java extends classes - Share the extended class fields within the super class.

  - by Bastan

  Straight to the point... I have a class public class P_Gen{ protected String s; protected Object oP_Gen; public P_Gen(String str){ s = str; oP_Gen = new Myclass(this); } } Extended class: public class P extends P_Gen{ protected Object oP; public P(String str){ oP = new aClass(str); super(str); } } MyClass: public class MyClass{ protected Object oMC; public MyClass(P extendedObject){ oMc = oP.getSomething(); } } I came to realize that MyClass can only be instantiated with (P_Gen thisObject) as opposed to (P extendedObject). The situation is that I have code generated a bunch of classes like P_Gen. For each of them I have generated a class P which would contains my P specific custom methods and fields. When I'll regenerate my code in the future, P would not be overwritten as P_Gen would. ** So what happened in my case???!!!... I realized that MyClass would beneficiate from the info stored in P in addition to only P_Gen. Would that possible? I know it's not JAVA "realistic" since another class that extends P_Gen might not have the same fields... BY DESIGN, P_Gen will not be extended by anything but P.... And that's where it kinda make sens. :-) at least in other programming language ;-) In other programming language, it seems like P_Gen.this === P.this, in other word, "this" becomes a combination of P and P_Gen. Is there a way to achieve this knowing that P_Gen won't be extended by anything than P?

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• How to define default values optional fields in play framework forms?

  - by natalinobusa

  I am implementing a web api using the scala 2.0.2 play framework. I would like to extract and validate a number of get parameters. And for this I am using a play "form" which allows me to define optional fields. Problem: For those optional fields, I need to define a default value if the parameter is not passed. The code is intended to parse correctly these three use cases: /test?top=abc (error, abc is not an integer) /test?top=123 (valid, top is 123) /test (valid, top is 42 (default value)) I have come up with the following code: def test = Action { implicit request => case class CData(top:Int) val p = Form( mapping( "top" -> optional(number) )((top) => CData($top.getOrElse(42))) ((cdata:CData) => Some(Some(cdata.top))) ).bindFromRequest() Ok("all done.") } The code works, but it's definitely not elegant. There is a lot of boiler plate going on just to set up a default value for a missing request parameter. Can anyone suggest a cleaner and more coincise solution?

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• Better code for accessing fields in a matlab structure array?

  - by John

  I have a matlab structure array Modles1 of size (1x180) that has fields a, b, c, ..., z. I want to understand how many distinct values there are in each of the fields. i.e. max(grp2idx([foo(:).a])) The above works if the field a is a double. {foo(:).a} needs to be used in the case where the field a is a string/char. Here's my current code for doing this. I hate having to use the eval, and what is essentially a switch statement. Is there a better way? names = fieldnames(Models1); for ix = 1 : numel(names) className = eval(['class(Models1(1).',names{ix},')']); if strcmp('double', className) || strcmp('logical',className) eval([' values = [Models1(:).',names{ix},'];']); elseif strcmp('char', className) eval([' values = {Models1(:).',names{ix},'};']); else disp(['Unrecognized class: ', className]); end % this line requires the statistics toolbox. [g, gn, gl] = grp2idx(values); fprintf('%30s : %4d\n',names{ix},max(g)); end

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• How to enforce jsf to create new instance of bean instead of throwing NullPointerException?

  - by Roman

  I'm almost sure that I do something wrong and thus the question's title is a bit incorrect. I have a form with several fields for creating a new User-objects (fields like login, password, birthday etc). And I have 2 buttons - Cancel and Create. I didn't finish Create yet :) , but when I press Cancel I see NullPointerException. Here is simplified code: <f:view> <h:form> <h:panelGroup layout="block"> <h:inputText id="add_login" value="#{userSupport.user.login}"/> <h:inputSecret id="add_password" value="#{userSupport.user.password}"/> <h:inputText id="add_name" value="#{userSupport.user.name}"/> <h:inputText id="add_surname" value="#{userSupport.user.surname}"/> <h:commandButton value="Cancel" action="cancel"/> </h:panelGroup> </h:form> </f:view> UserSupport class has field user with getter and setter and some other methods. It's a Spring bean with Session scope. When I press cancel, I see NPE because jsf tries to save values from inputs in user-object, but user-object is null. What is the correct way of doing this?

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