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• Concurrency pattern of logger in multithreaded application

  - by Dipan Mehta

  The context: We are working on a multi-threaded (Linux-C) application that follows a pipeline model. Each module has a private thread and encapsulated objects which do processing of data; and each stage has a standard form of exchanging data with next unit. The application is free from memory leak and is threadsafe using locks at the point where they exchange data. Total number of threads is about 15- and each thread can have from 1 to 4 objects. Making about 25 - 30 odd objects which all have some critical logging to do. Most discussion I have seen about different levels as in Log4J and it's other translations. The real big questions is about how the overall logging should really happen? One approach is all local logging does fprintf to stderr. The stderr is redirected to some file. This approach is very bad when logs become too big. If all object instantiate their individual loggers - (about 30-40 of them) there will be too many files. And unlike above, one won't have the idea of true order of events. Timestamping is one possibility - but it is still a mess to collate. If there is a single global logger (singleton) pattern - it indirectly blocks so many threads while one is busy putting up logs. This is unacceptable when processing of the threads are heavy. So what should be the ideal way to structure the logging objects? What are some of the best practices in actual large scale applications? I would also love to learn from some of the real designs of large scale applications to get inspirations from!

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• What type of pattern would be used in this case

  - by Admiral Kunkka

  I want to know how to tackle this type of scenario. We are building a person's background, from scratch, and I want to know, conceptually, how to proceed with a secure object pattern in both design and execution... I've been reading on Factory patterns, Model-View-Controller types, Dependency injection, Singleton approaches... and I can't seem to grasp or 'fit' these types of designs decisions into what I'm trying to do.. First and foremost, I started with having a big jack-of-all-trades class, then I read some more, and some tips were to make sure your classes only have a single purpose.. which makes sense and I started breaking down certain things into other classes. Okay, cool. Now I'm looking at dependency injection and kind of didn't really know what's going on. Example/insight of what kind of heirarchy I need to accomplish... class Person needs to access and build from a multitude of different classes. class Culture needs to access a sub-class for culture benefits class Social needs to access class Culture, and other sub-classes class Birth needs to access Social, Culture, and other sub-classes class Childhood/Adolescence/Adulthood need to access everything. Also, depending on different rolls, this class heirarchy needs to create multiple people as well, such as Family, and their backgrounds using some, if not all, of these same classes. Think of it as a people generator, all random, with backgrounds and things that happen to them. Ageing, death of loved ones, military careers, e.t.c. Most of the generation is done randomly, making calls to a mt_rand function to pick from most of the selections inside the classes, guaranteeing the data to be absolutely random. I have most of the bulk-data down, and was looking for some insight from fellow programmers, what do you think?

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• Command Pattern refactor for input processing?

  - by Casey

  According to Game Coding Complete 4th. ed. processing input via the following is considered unmanagable and inflexible. But does not show an example. I've used the Command pattern to represent GUI button commands but could not figure out how to represent the input from the keyboard and/or mouse. if(g_keyboard->KeyDown(KEY_ESC)) { quit = true; return; } //Processing if(g_keyboard->KeyDown(KEY_T)) { g_show_test_gateway = !g_show_test_gateway; } if(g_mouse->ButtonDown(a2de::Mouse::BUTTON2)) { g_selected_part = GWPart::PART_NONE; SetMouseImageToPartImage(); } ResetButtonStates(); g_prevButton = g_curButton; g_curButton = GetButtonHovered(); if(g_curButton) { g_mouse->SetImageToDefault(); if(g_mouse->ButtonDown(a2de::Mouse::BUTTON1) || g_mouse->ButtonPress(a2de::Mouse::BUTTON1)) { ButtonPressCommand curCommand(g_curButton); curCommand.Execute(); } else if(g_mouse->ButtonUp(a2de::Mouse::BUTTON1)) { if(g_prevButton == g_curButton) { ButtonReleaseCommand curCommand(g_curButton); curCommand.Execute(); if(g_curButton->GetType() == "export") { ExportCommand curCommand(g_curButton, *g_gateway); curCommand.Execute(); } } else { ResetButtonStates(); } } else { ButtonHoverCommand curCommand(g_curButton); curCommand.Execute(); } } else { g_status_message.clear(); SetMouseImageToPartImage(); if(g_mouse->ButtonDown(a2de::Mouse::BUTTON1)) { CreatePartCommand curCommand(*g_gateway, g_selected_part, a2de::Vector2D(g_mouse->GetX(), g_mouse->GetY())); curCommand.Execute(); } }

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• What Pattern will solve this - fetching dependent record from database

  - by tunmise fasipe

  I have these classes class Match { int MatchID, int TeamID, //used to reference Team ... other fields } Note: Match actually have 2 teams which means 2 TeamID class Team { int TeamID, string TeamName } In my view I need to display List<Match> showing the TeamName. So I added another field class Match { int MatchID, int TeamID, //used to reference Team ... other fields string TeamName; } I can now do Match m = getMatch(id); m.TeamName = getTeamName(m.TeamId); //get name from database But for a List<Match>, getTeamName(TeamId) will go to the database to fetch TeamName for each TeamID. For a page of 10 Matches per page, that could be (10x2Teams)=20 trip to database. To avoid this, I had the idea of loading everything once, store it in memory and only lookup the TeamName in memory. This made me have a rethink that what if the records are 5000 or more. What pattern is used to solve this and how?

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• MVVM and service pattern

  - by alfa-alfa

  I'm building a WPF application using the MVVM pattern. Right now, my viewmodels calls the service layer to retrieve models (how is not relevant to the viewmodel) and convert them to viewmodels. I'm using constructor injection to pass the service required to the viewmodel. It's easily testable and works well for viewmodels with few dependencies, but as soon as I try to create viewModels for complex models, I have a constructor with a LOT of services injected in it (one to retrieve each dependencies and a list of all available values to bind to an itemsSource for example). I'm wondering how to handle multiple services like that and still have a viewmodel that I can unit test easily. I'm thinking of a few solutions: Creating a services singleton (IServices) containing all the available services as interfaces. Example: Services.Current.XXXService.Retrieve(), Services.Current.YYYService.Retrieve(). That way, I don't have a huge constructor with a ton of services parameters in them. Creating a facade for the services used by the viewModel and passing this object in the ctor of my viewmodel. But then, I'll have to create a facade for each of my complexe viewmodels, and it might be a bit much... What do you think is the "right" way to implement this kind of architecture ?

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• Squid 3 and Internet Explorer 11 with authentication

  - by StBlade

  Need some help. My college has up until now been running Squid 3 on Ubuntu 12.02 and now 14.04 successfully. That was till recently. Our WSUS server is dishing out updates to all our workstations of which Internet Explorer 11 is one of them. Now all of a sudden users do not need to authenticate via the squid proxy to be able to use the internet. This makes it rather difficult as I also use SARG to generate usage logs for all users each day. All our workstations also have Chrome on them, and Chrome authenticates fine via the Squid proxy. Doing a couple of Googles, I ran into and article, where someone made mention that Microsoft has deprecated digest and basic authentication from IE 11. Reason was given that Office 2013 was giving problems as it was not giving the popup screen for authentication when Office tries to download templates from the internet. I have run into this problem, but by setting those sites to not authenticate via squid fixed the problem. Has anyone else run into something similiar? Would changing to NTLM or Kereberos be a solution?

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• Say goodbye to System.Reflection.Emit (any dynamic proxy generation) in WinRT

  - by mbrit

  tl;dr - Forget any form of dynamic code emitting in Metro-style. It's not going to happen.Over the past week or so I've been trying to get Moq (the popular open source TDD mocking framework) to work on WinRT. Irritatingly, the day before Release Preview was released it was actually working on Consumer Preview. However in Release Preview (RP) the System.Reflection.Emit namespace is gone. Forget any form of dynamic code generation and/or MSIL injection.This kills off any project based on the popular Castle Project Dynamic Proxy component, of which Moq is one example. You can at this point in time not perform any form of mocking using dynamic injection in your Metro-style unit testing endeavours.So let me take you through my journey on this, so that other's don't have to...The headline fact is that you cannot load any assembly that you create at runtime. WinRT supports one Assembly.Load method, and that takes the name of an assembly. That has to be placed within the deployment folder of your app. You cannot give it a filename, or stream. The methods are there, but private. Try to invoke them using Reflection and you'll be met with a caspol exception.You can, in theory, use Rotor to replace SRE. It's all there, but again, you can't load anything you create.You can't write to your deployment folder from within your Metro-style app. But, can you use another service on the machine to move a file that you create into the deployment folder and load it? Not really.The networking stack in Metro-style is intentionally "damaged" to prevent socket communication from Metro-style to any end-point on the local machine. (It just times out.) This militates against an approach where your Metro-style app can signal a properly installed service on the machine to create proxies on its behalf. If you wanted to do this, you'd have to route the calls through a C&C server somewhere. The reason why Microsoft has done this is obvious - taking out SRE know means they don't have to do it in an emergency later. The collateral damage in removing SRE is that you can't do mocking in test mode, but you also can't do any form of injection in production mode. There are plenty of reasons why enterprise apps might want to do this last point particularly. At CP, the assumption was that their inspection tools would prevent SRE being used as a malware vector - it now seems they are less confident about that. (For clarity, the risk here is in allowing a nefarious program to download instructions from a C&C server and make up executable code on the fly to run, getting around the marketplace restrictions.)So, two things:- System.Reflection.Emit is gone in Metro-style/WinRT. Get over it - dynamic, on-the-fly code generation is not going to to happen.- I've more or less got a version of Moq working in Metro-style. This is based on the idea of "baking" the dynamic proxies before you use them. You can find more information here: https://github.com/mbrit/moqrt

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• Design pattern to handle queries using multiple models

  - by coderkane

  I am presented with a dilemma while trying to re-designing the class structure for my PHP/MySQL application to make it more elegant and conform it to the SOLID principle. The problem goes like this: Let as assume, there is an abstract class called person which has certain properties to define a generic person, such as name, age, date of birth etc. There are two classes, student, and teacher, that implements this abstract class. They add their own unique properties to it. I have designed all the three classes to include all the operational logic (details of which are not relevant in context of the question). Now, I need to create views/reports/data grids which contain details from multiple classes, for example, say, a list of all students doing projects in Chemistry mentored by a teacher whose name is the parameter to the query. This is just one example of a view, there are many different views in the application, which uses data from 3-4 tables, and each of them have multiple input parameters to generate them. Considering this particular example, I have written the relevant query using JOIN and the results are as expected and proper, now here is the dilemma: Keeping in mind the single responsibility principle, where should I keep this query? It does not belong to either Student class, or Teacher class or any other classes currently present. a) Should I create a new class, say dataView class, and design it as a MVC pattern and keep the query there? What about the other views? how do they fit in this architecture? b) Should I not keep the query in code at all, and make it DB View ? c) Am I completely wrong in the approach? If so what is the right approach? My considerations are as follows: a) should be easy to add new views later on if requirement comes, without having to copy-paste-modify code b) would like to make it as loosely coupled as possible so that if minor db structure changes happen, it does not break I did google searches on report design and OOP report generators, but all the result seem to focus on the visual design of the report rather than fetching the data. I have already taken care of the visual aspect of the report using MVC with html templates. I am sure this is a very fundamental problem with known solution, but I am somehow not able to find it (maybe searching with wrong keyword). Edit1: Modified the title to make it more relevant Edit2: The accepted answer got me thinking in the right direction and identify my design flaws, which eventually led me to find this question and the solution in Stack Overflow which gave me the detailed answer to clear the confusion.

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• Validation and Error Generation when using the Data Mapper Pattern

  - by AndyPerlitch

  I am working on saving state of an object to a database using the data mapper pattern, but I am looking for suggestions/guidance on the validation and error message generation step (step 4 below). Here are the general steps as I see them for doing this: (1) The data mapper is used to get current info (assoc array) about the object in db: +=====================================================+ | person_id | name | favorite_color | age | +=====================================================+ | 1 | Andy | Green | 24 | +-----------------------------------------------------+ mapper returns associative array, eg. Person_Mapper::getPersonById($id) : $person_row = array( 'person_id' => 1, 'name' => 'Andy', 'favorite_color' => 'Green', 'age' => '24', ); (2) the Person object constructor takes this array as an argument, populating its fields. class Person { protected $person_id; protected $name; protected $favorite_color; protected $age; function __construct(array $person_row) { $this->person_id = $person_row['person_id']; $this->name = $person_row['name']; $this->favorite_color = $person_row['favorite_color']; $this->age = $person_row['age']; } // getters and setters... public function toArray() { return array( 'person_id' => $this->person_id, 'name' => $this->name, 'favorite_color' => $this->favorite_color, 'age' => $this->age, ); } } (3a) (GET request) Inputs of an HTML form that is used to change info about the person is populated using Person::getters <form> <input type="text" name="name" value="<?=$person->getName()?>" /> <input type="text" name="favorite_color" value="<?=$person->getFavColor()?>" /> <input type="text" name="age" value="<?=$person->getAge()?>" /> </form> (3b) (POST request) Person object is altered with the POST data using Person::setters $person->setName($_POST['name']); $person->setFavColor($_POST['favorite_color']); $person->setAge($_POST['age']); *(4) Validation and error message generation on a per-field basis - Should this take place in the person object or the person mapper object? - Should data be validated BEFORE being placed into fields of the person object? (5) Data mapper saves the person object (updates row in the database): $person_mapper->savePerson($person); // the savePerson method uses $person->toArray() // to get data in a more digestible format for the // db gateway used by person_mapper Any guidance, suggestions, criticism, or name-calling would be greatly appreciated.

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• How pattern lock disbles screen lock in android

  - by CED

  Hi, In android 2.1, if we enable pattern lock, then the screen lock (slide to unlock) is not displayed and if pattern lock is disabled then screen lock is enabled again. Can someone point me out the java file in framework and the function where this happens. I mean when the screen is about to get locked, how does android decide that whether it will display pattern lock or screen lock and if pattern lock, how it prevents the screen lock from getting displayed.

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• Design pattern for adding / removing elements

  - by de3

  Wikipedia's definition for Iterator pattern design: the Iterator pattern is a design pattern in which iterators are used to access the elements of an aggregate object sequentially without exposing its underlying implementation. Iterator interface in java provides the following methods hasNext() next() remove() Is there a pattern design, or a java interface for inserting / deleting elements, and getting length of the aggregate object, in addition to iterating them? I know remove() is an optional method that can be used once per call to next(), but I am implementing a circular FIFO array and need a method delete() independent of iterator's next().

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• How do I use LDAP proxy user authentication from .net?

  - by DN

  I have a .net web application that uses simple bind to query the LDAP. The application uses integrated windows authentication. Do you have any recommendations on which option to use to authenticate against the LDAP: 1. simple LDAP bind using the logged in user's credentials 2. simple LDAP bind using a service account created for the application's use 3. LDAP proxy user authentication - I dont have enough info about this, so i'd be grateful if someone could explain it's benefit, recommended use and sample .net code to do the query.

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• WCF Rest services for use with the repository pattern?

  - by mark smith

  Hi there, I am considering moving my Service Layer and my data layer (repository pattern) to a WCF Rest service. So basically i would have my software installed locally (WPF client) which would call the Service Layer that exists via a Rest Service... The service layer would then call my data layer using a WCF Rest Service also OR maybe just call it via the DLL assembly I was hoping to understand what the performance would be like. Currently I have my datalayer and servicelayer installed locally via DLL Assemblies locally on the pc. Also i presume the WCF REST services won't support method overloading hance the same name but with a different signature?? I would really appreciate any feedback anyone can give. Thanks

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• What's the best way to implement a dynamic proxy in C#?

  - by gap

  Hi, I've got a need to create a dynamic proxy in C#. I want this class to wrap another class, and take on it's public interface, forwarding calls for those functions: class MyRootClass { public virtual void Foo() { Console.Out.WriteLine("Foo!"); } } interface ISecondaryInterface { void Bar(); } class Wrapper<T> : ISecondaryInterface where T: MyRootClass { public Wrapper(T otherObj) { } public void Bar() { Console.Out.WriteLine("Bar!"); } } Here's how I want to use it: Wrapper<MyRootClass> wrappedObj = new Wrapper<MyRootClass>(new MyRootClass()); wrappedObj.Bar(); wrappedObj.Foo(); to produce: Bar! Foo! Any ideas? What's the easiest way to do this? What's the best way to do this? Thanks so much.

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• How to avoid double construction of proxy with DynamicProxy::CreateClassProxyWithTarget?

  - by Belvasis

  I am decorating an existing object using the CreateClassProxyWithTarget method. However, the constructor and therefore, initialization code, is being called twice. I already have a "constructed" instance (the target). I understand why this happens, but is there a way to avoid it, other than using an empty constructor? Edit: Here is some code: First the proxy creation: public static T Create<T>(T i_pEntity) where T : class { object pResult = m_pGenerator.CreateClassProxyWithTarget(typeof(T), new[] { typeof(IEditableObject), typeof(INotifyPropertyChanged) , typeof(IMarkerInterface), typeof(IDataErrorInfo) }, i_pEntity, ProxyGenerationOptions.Default, new BindingEntityInterceptor<T>(i_pEntity)); return (T)pResult; } I use this for example with an object of the following class: public class KatalogBase : AuditableBaseEntity { public KatalogBase() { Values = new HashedSet<Values>(); Attributes = new HashedSet<Attributes>(); } ... } If i now call BindingFactory.Create(someKatalogBaseObject); the Values and Attributes properties are beeing initialized again.

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• Squid Proxy: url_regex acl is not working?

  - by bharathi

  I am using squid proxy 3.1 in ubuntu machine. I want to allow only urls matching our pattern through our proxy server. I configured acl like below. Acl for dstdomain is working fine. If i access any url besides .zmedia.com , I got proxy connection refused. But the url_regex is not working. What i am trying here is. Allow only request from ".zmedia.com" domain and the request url should be in "/blog" context. # # Recommended minimum configuration: # acl manager proto cache_object acl localhost src 127.0.0.1/32 ::1 acl to_localhost dst 127.0.0.0/8 ::1 acl urlwhitelist url_regex -i ^http(s)://([a-zA-Z]+).zmedia.com/blog/.*$ acl allowdomain dstdomain .zmedia.com acl Safe_ports port 80 8080 8500 7272 # Example rule allowing access from your local networks. # Adapt to list your (internal) IP networks from where browsing # should be allowed acl SSL_ports port 443 acl Safe_ports port 80 # http acl Safe_ports port 21 # ftp acl Safe_ports port 443 # https acl Safe_ports port 70 # gopher acl Safe_ports port 210 # wais acl Safe_ports port 1025-65535 # unregistered ports acl Safe_ports port 280 # http-mgmt acl Safe_ports port 488 # gss-http acl Safe_ports port 591 # filemaker acl Safe_ports port 777 # multiling http acl SSL_ports port 7272 # multiling http acl CONNECT method CONNECT # # Recommended minimum Access Permission configuration: # # Only allow cachemgr access from localhost http_access allow manager localhost http_access deny manager http_access deny !allowdomain http_access allow urlwhitelist http_access allow CONNECT SSL_ports http_access deny CONNECT !SSL_ports # Deny requests to certain unsafe ports http_access deny !Safe_ports # Deny CONNECT to other than secure SSL ports http_access deny CONNECT !SSL_ports # We strongly recommend the following be uncommented to protect innocent # web applications running on the proxy server who think the only # one who can access services on "localhost" is a local user #http_access deny to_localhost # # INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS # # Example rule allowing access from your local networks. # Adapt localnet in the ACL section to list your (internal) IP networks # from where browsing should be allowed http_access allow localhost # And finally deny all other access to this proxy http_access deny all # Squid normally listens to port 3128 http_port 3128 # We recommend you to use at least the following line. hierarchy_stoplist cgi-bin ? # Uncomment and adjust the following to add a disk cache directory. #cache_dir ufs /var/spool/squid 100 16 256 # Leave coredumps in the first cache dir coredump_dir /var/spool/squid append_domain .zmedia.com # Add any of your own refresh_pattern entries above these. refresh_pattern ^ftp: 1440 20% 10080 refresh_pattern ^gopher: 1440 0% 1440 refresh_pattern -i (/cgi-bin/|\?) 0 0% 0 refresh_pattern . 0 20% 4320 Please correct me , If i did anything wrong?

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• Best Design Pattern for Coupling User Interface Components and Data Structures

  - by szahn

  I have a windows desktop application with a tree view. Due to lack of a sound data-binding solution for a tree view, I've implemented my own layer of abstraction on it to bind nodes to my own data structure. The requirements are as follows: Populate a tree view with nodes that resemble fields in a data structure. When a node is clicked, display the appropriate control to modify the value of that property in the instance of the data structure. The tree view is populated with instances of custom TreeNode classes that inherit from TreeNode. The responsibility of each custom TreeNode class is to (1) format the node text to represent the name and value of the associated field in my data structure, (2) return the control used to modify the property value, (3) get the value of the field in the control (3) set the field's value from the control. My custom TreeNode implementation has a property called "Control" which retrieves the proper custom control in the form of the base control. The control instance is stored in the custom node and instantiated upon first retrieval. So each, custom node has an associated custom control which extends a base abstract control class. Example TreeNode implementation: //The Tree Node Base Class public abstract class TreeViewNodeBase : TreeNode { public abstract CustomControlBase Control { get; } public TreeViewNodeBase(ExtractionField field) { UpdateControl(field); } public virtual void UpdateControl(ExtractionField field) { Control.UpdateControl(field); UpdateCaption(FormatValueForCaption()); } public virtual void SaveChanges(ExtractionField field) { Control.SaveChanges(field); UpdateCaption(FormatValueForCaption()); } public virtual string FormatValueForCaption() { return Control.FormatValueForCaption(); } public virtual void UpdateCaption(string newValue) { this.Text = Caption; this.LongText = newValue; } } //The tree node implementation class public class ExtractionTypeNode : TreeViewNodeBase { private CustomDropDownControl control; public override CustomControlBase Control { get { if (control == null) { control = new CustomDropDownControl(); control.label1.Text = Caption; control.comboBox1.Items.Clear(); control.comboBox1.Items.AddRange( Enum.GetNames( typeof(ExtractionField.ExtractionType))); } return control; } } public ExtractionTypeNode(ExtractionField field) : base(field) { } } //The custom control base class public abstract class CustomControlBase : UserControl { public abstract void UpdateControl(ExtractionField field); public abstract void SaveChanges(ExtractionField field); public abstract string FormatValueForCaption(); } //The custom control generic implementation (view) public partial class CustomDropDownControl : CustomControlBase { public CustomDropDownControl() { InitializeComponent(); } public override void UpdateControl(ExtractionField field) { //Nothing to do here } public override void SaveChanges(ExtractionField field) { //Nothing to do here } public override string FormatValueForCaption() { //Nothing to do here return string.Empty; } } //The custom control specific implementation public class FieldExtractionTypeControl : CustomDropDownControl { public override void UpdateControl(ExtractionField field) { comboBox1.SelectedIndex = comboBox1.FindStringExact(field.Extraction.ToString()); } public override void SaveChanges(ExtractionField field) { field.Extraction = (ExtractionField.ExtractionType) Enum.Parse(typeof(ExtractionField.ExtractionType), comboBox1.SelectedItem.ToString()); } public override string FormatValueForCaption() { return string.Empty; } The problem is that I have "generic" controls which inherit from CustomControlBase. These are just "views" with no logic. Then I have specific controls that inherit from the generic controls. I don't have any functions or business logic in the generic controls because the specific controls should govern how data is associated with the data structure. What is the best design pattern for this?

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• Design pattern for logging changes in parent/child objects saved to database

  - by andrew

  I’ve got a 2 database tables in parent/child relationship as one-many. I’ve got three classes representing the data in these two tables: Parent Class { Public int ID {get; set;} .. other properties } Child Class { Public int ID {get;set;} Public int ParentID {get; set;} .. other properties } TogetherClass { Public Parent Parent; Public List<Child> ChildList; } Lastly I’ve got a client and server application – I’m in control of both ends so can make changes to both programs as I need to. Client makes a request for ParentID and receives a Together Class for the matching parent, and all of the child records. The client app may make changes to the children – add new children, remove or modify existing ones. Client app then sends the Together Class back to the server app. Server app needs to update the parent and child records in the database. In addition I would like to be able to log the changes – I’m doing this by having 2 separate tables one for Parent, one for child; each containing the same columns as the original plus date time modified, by whom and a list of the changes. I’m unsure as to the best approach to detect the changes in records – new records, records to be deleted, records with no fields changed, records with some fields changed. I figure I need to read the parent & children records and compare those to the ones in the Together Class. Strategy A: If Together class’s child record has an ID of say 0, that indicates a new record; insert. Any deleted child records are no longer in the Together Class; see if any of the comparison child records are not found in the Together class and delete if not found (Compare using ID). Check each child record for changes and if changed log. Strategy B: Make a new Updated TogetherClass UpdatedClass { Public Parent Parent {get; set} Public List<Child> ListNewChild {get;set;} Public List<Child> DeletedChild {get;set;} Public List<Child> ExistingChild {get;set;} // used for no changes and modified rows } And then process as per the list. The reason why I’m asking for ideas is that both of these solutions don’t seem optimal to me and I suspect this problem has been solved already – some kind of design pattern ? I am aware of one potential problem in this general approach – that where Client App A requests a record; App B requests same record; A then saves changes; B then saves changes which may overwrite changes A made. This is a separate locking issue which I’ll raise a separate question for if I’ve got trouble implementing. The actual implementation is c#, SQL Server and WCF between client and server - sharing a library containing the class implementations. Apologies if this is a duplicate post – I tried searching various terms without finding a match though.

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• Design Pattern for Complex Data Modeling

  - by Aaron Hayman

  I'm developing a program that has a SQL database as a backing store. As a very broad description, the program itself allows a user to generate records in any number of user-defined tables and make connections between them. As for specs: Any record generated must be able to be connected to any other record in any other user table (excluding itself...the record, not the table). These "connections" are directional, and the list of connections a record has is user ordered. Moreover, a record must "know" of connections made from it to others as well as connections made to it from others. The connections are kind of the point of this program, so there is a strong possibility that the number of connections made is very high, especially if the user is using the software as intended. A record's field can also include aggregate information from it's connections (like obtaining average, sum, etc) that must be updated on change from another record it's connected to. To conserve memory, only relevant information must be loaded at any one time (can't load the entire database in memory at load and go from there). I cannot assume the backing store is local. Right now it is, but eventually this program will include syncing to a remote db. Neither the user tables, connections or records are known at design time as they are user generated. I've spent a lot of time trying to figure out how to design the backing store and the object model to best fit these specs. In my first design attempt on this, I had one object managing all a table's records and connections. I attempted this first because it kept the memory footprint smaller (records and connections were simple dicts), but maintaining aggregate and link information between tables became....onerous (ie...a huge spaghettified mess). Tracing dependencies using this method almost became impossible. Instead, I've settled on a distributed graph model where each record and connection is 'aware' of what's around it by managing it own data and connections to other records. Doing this increases my memory footprint but also let me create a faulting system so connections/records aren't loaded into memory until they're needed. It's also much easier to code: trace dependencies, eliminate cycling recursive updates, etc. My biggest problem is storing/loading the connections. I'm not happy with any of my current solutions/ideas so I wanted to ask and see if anybody else has any ideas of how this should be structured. Connections are fairly simple. They contain: fromRecordID, fromTableID, fromRecordOrder, toRecordID, toTableID, toRecordOrder. Here's what I've come up with so far: Store all the connections in one big table. If I do this, either I load all connections at once (one big db call) or make a call every time a user table is loaded. The big issue here: the size of the connections table has the potential to be huge, and I'm afraid it would slow things down. Store in separate tables all the outgoing connections for each user table. This is probably the worst idea I've had. Now my connections are 'spread out' over multiple tables (one for each user table), which means I have to make a separate DB called to each table (or make a huge join) just to find all the incoming connections for a particular user table. I've avoided making "one big ass table", but I'm not sure the cost is worth it. Store in separate tables all outgoing AND incoming connections for each user table (using a flag to distinguish between incoming vs outgoing). This is the idea I'm leaning towards, but it will essentially double the total DB storage for all the connections (as each connection will be stored in two tables). It also means I have to make sure connection information is kept in sync in both places. This is obviously not ideal but it does mean that when I load a user table, I only need to load one 'connection' table and have all the information I need. This also presents a separate problem, that of connection object creation. Since each user table has a list of all connections, there are two opportunities for a connection object to be made. However, connections objects (designed to facilitate communication between records) should only be created once. This means I'll have to devise a common caching/factory object to make sure only one connection object is made per connection. Does anybody have any ideas of a better way to do this? Once I've committed to a particular design pattern I'm pretty much stuck with it, so I want to make sure I've come up with the best one possible.

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• Apache Reverse Proxy not working inside a VirtualHost running a Mono Web Application

  - by Arwen

  I have a mono web application running with this virtual host below. It is running on Apache 2.2.20 / Ubuntu 11.10. I tried to add a reverse proxy inside this virtualhost so I can make asynchronous or AJAX type calls back to this same domain. My asynchronous requests would have problems in many browsers calling services that are on another domain (cross domain requests problem). I am wanting to do reverse proxy calls to this other service using http://www.whatever.com/monkey/. So, I added the directive and top directive to try to make this work. It is weird though...nothing I do seems to have any effect. I can put the exact same markup in my default website virtualhost file and it works great. What is the deal? Are some of these Mono directives causing problems? <VirtualHost *:80> ServerName www.whatever.com ServerAlias whatever.com *.whatever.com ServerAdmin [email protected] DocumentRoot /home/myuser/web/whatever ProxyRequests off <Proxy *> Order allow,deny Allow from all </Proxy> <Location /monkey/> ProxyPass http://www.google.com/ ProxyPassReverse http://www.google.com/ </Location> MonoServerPath www.whatever.com "/usr/bin/mod-mono-server2" MonoSetEnv www.whatever.com MONO_IOMAP=all MonoApplications www.whatever.com "/:/home/myuser/web/whatever" <Location "/"> Allow from all Order allow,deny MonoSetServerAlias www.whatever.com SetHandler mono SetOutputFilter DEFLATE SetEnvIfNoCase Request_URI "\.(?:gif|jpe?g|png)$" no-gzip dont-vary </Location> <IfModule mod_deflate.c> AddOutputFilterByType DEFLATE text/html text/plain text/xml text/javascript </IfModule> </VirtualHost>

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• Apache Proxy Pass and Web Sockets

  - by James

  I'm using Apache with the mod_proxy module to reverse proxy my Node.js application through to port 80, so that we can access it as an internal application. I have a file in sites-enabled which contains this: VirtualHost *:80> DocumentRoot /var/www/internal/ ServerName internal ServerAlias internal <Directory /var/www/internal/public/> Options All AllowOverride All Order allow,deny Allow from all </Directory> ProxyRequests off <Proxy *> Order deny,allow Allow from all </Proxy> ProxyPass / http://localhost:8080/ retry=0 ProxyPassReverse / http://localhost:8080/ ProxyPreserveHost on ProxyTimeout 1200 LogLevel debug AllowEncodedSlashes on </VirtualHost> As I said, our application is written in Node.js and we're using socket.io to make use of web-sockets, as our application also contains realtime elements to it. The problem is, mod_proxy doesn't seem to handle web sockets and we get errors when trying to use them: WebSocket connection to 'ws://bloot/socket.io/1/websocket/nHtTh6ZwQjSXlmI7UMua' failed: Unexpected response code: 502 How can we fix this issue and keep sockets working, as the only way we can get it working currently is to access the site via ip:port which we don't want to do. Also, as a side question, how can I get ErrorDocument to work properly? Our error files are stored in /var/www/internal/public/error/ but they seem to get put through the proxy too?

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• reverse proxy not rewriting to https

  - by polishpt

  I need your help. I'm having problems with reverse proxy rewriting to https: I have an alfresco app running on top of tomcat and as a front and an Apache server - it's site-enabled looks like that: <VirtualHost *:80> ServerName alfresco JkMount /* ajp13_worker <Directory /var/www/> Options Indexes FollowSymLinks MultiViews AllowOverride None Order allow,deny allow from all </Directory> ErrorLog /var/log/apache2/error.log # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. LogLevel warn CustomLog /var/log/apache2/access.log combined ServerSignature Off </VirtualHost> I also have a reverse proxy server running on second machine and i want it to rewrite queries to https. It's site-enabled looks like that: <VirtualHost 192.168.251.50:80> ServerName alfresco DocumentRoot /var/www/ RewriteEngine on RewriteRule (.*) https://alfresco/ [R] LogLevel warn ErrorLog /var/log/apache2/alfresco-80-error.log CustomLog /var/log/apache2/alfresco-80-access.log combined ServerSignature Off </VirtualHost> <VirtualHost 192.168.251.50:443> ServerName alfresco DocumentRoot /var/www/ SSLEngine On SSLProxyEngine On SSLCertificateFile /etc/ssl/certs/alfresco.pem SSLCertificateKeyFile /etc/ssl/private/alfresco.key SetEnvIf User-Agent ".*MSIE.*" nokeepalive ssl-unclean-shutdown \ downgrade-1.0 force-response-1.0 ProxyRequests Off ProxyPreserveHost On <Proxy *> Order deny,allow Allow from all </Proxy> ProxyPass /alfresco http://192.168.251.50:8080/alfresco ProxyPassReverse /alfresco http://192.168.251.50:8080/alfresco LogLevel warn ErrorLog /var/log/apache2/alfresco-443-error.log CustomLog /var/log/apache2/alfresco-443-access.log combined ServerSignature Off </VirtualHost> Now, ProxyPass works, when I go to alfresco/alfrsco in a browser application opens, but rewriting to https doesn't work. Plese help. Regards when I go to 192.168.251.50 Tomcat configuration page shows up. When I go to 192.268.251.50:8080 - the same as above when I go to 192.168.251.50:8080/alfresco - alfresco app page shows app when I go to alfresco/alfresco - same as above when i go to https://alfresco or https://alfresco i get an error connecting to a server

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• Can nginx be used as a reverse proxy for a backend websocket server?

  - by John Reilly

  We're working on a Ruby on Rails app that needs to take advantage of html5 websockets. At the moment, we have two separate "servers" so to speak: our main app running on nginx+passenger, and a separate server using Pratik Naik's Cramp framework (which is running on Thin) to handle the websocket connections. Ideally, when it comes time for deployment, we'd have the rails app running on nginx+passenger, and the websocket server would be proxied behind nginx, so we wouldn't need to have the websocket server running on a different port. Problem is, in this setup it seems that nginx is closing the connections to Thin too early. The connection is successfully established to the Thin server, then immediately closed with a 200 response code. Our guess is that nginx doesn't realize that the client is trying to establish a long-running connection for websocket traffic. Admittedly, I'm not all that savvy with nginx config, so, is it even possible to configure nginx to act as a reverse proxy for a websocket server? Or do I have to wait for nginx to offer support for the new websocket handshake stuff? Assuming that having both the app server and the websocket server listening on port 80 is a requirement, might that mean I have to have Thin running on a separate server without nginx in front for now? Thanks in advance for any advice or suggestions. :) -John

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• Squid: caching *.swf with variables

  - by stfn

  I'd recently upgraded my Ubuntu 11.10 x64 server to 12.04. In this process Squid was updated from 2.7 to 3.1. Squid 3.1 has many different options witch broke my setup. So I completely removed squid 2.7 and 3.1 and started from scratch. Everything is now working as before except for 1 thing: caching of .swf files with ?/variables. Squid 3 sees a ? as dynamic content and does not cache it. For example, Squid 2.7 was caching the .swf file at http://ninjakiwi.com/Games/Tower-Defense/Play/Bloons-Tower-Defense-5.html and 3.1 is not. <object id="mov" name="movn" classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" width="800" height="620"> <param name="movie" value="http://www.ninjakiwifiles.com/Games/gameswfs/btd5.swf?v=160512-2"> <param name="allowscriptaccess" value="always"> <param name="bgcolor" value="#000000"> <param name="flashvars" value="file=http://www.ninjakiwifiles.com/Games/gameswfs/btd5-dat.swf?v=280512"> <p>Get Flash play Ninja Kiwi games.</p> </object> It is because of the "?v=160512-2" and "?v=280512" part. This line should be responsible for that: refresh_pattern -i (/cgi-bin/|\?) 0 0% 0 But disabling it still doesn't cache the .swf files. How do I configure Squid 3.1 to cache those files? My current config is: acl manager proto cache_object acl localhost src 127.0.0.1/32 ::1 acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1 acl SSL_ports port 443 acl Safe_ports port 80 # http acl Safe_ports port 21 # ftp acl Safe_ports port 443 # https acl Safe_ports port 70 # gopher acl Safe_ports port 210 # wais acl Safe_ports port 1025-65535 # unregistered ports acl Safe_ports port 280 # http-mgmt acl Safe_ports port 488 # gss-http acl Safe_ports port 591 # filemaker acl Safe_ports port 777 # multiling http acl CONNECT method CONNECT acl localnet src 192.168.2.0-192.168.2.255 acl localnet src 192.168.3.0-192.168.3.255 http_access allow manager localhost http_access deny manager http_access deny !Safe_ports http_access deny CONNECT !SSL_ports http_access allow localhost http_access allow localnet http_access deny all http_port 3128 cache_dir ufs /var/spool/squid 10240 16 256 maximum_object_size 100 MB coredump_dir /var/spool/squid3 refresh_pattern ^ftp: 1440 20% 10080 refresh_pattern ^gopher: 1440 0% 1440 refresh_pattern -i \.(gif|png|jpg|jpeg|ico)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private refresh_pattern -i \.(iso|avi|wav|mp3|mp4|mpeg|swf|flv|x-flv)$ 43200 90% 432000 override-expire ignore-no-cache ignore-no-store ignore-private refresh_pattern -i \.(deb|rpm|exe|zip|tar|tgz|ram|rar|bin|ppt|doc|tiff)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private refresh_pattern -i \.index.(html|htm)$ 0 40% 10080 refresh_pattern -i \.(html|htm|css|js)$ 1440 40% 40320 refresh_pattern Packages\.bz2$ 0 20% 4320 refresh-ims refresh_pattern Sources\.bz2$ 0 20% 4320 refresh-ims refresh_pattern Release\.gpg$ 0 20% 4320 refresh-ims refresh_pattern Release$ 0 20% 4320 refresh-ims refresh_pattern . 0 40% 40320 cache_effective_user proxy cache_effective_group proxy

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• Design Patterns for Coordinating Change Event Listeners

  - by mkraken

  I've been working with the Observer pattern in JavaScript using various popular libraries for a number of years (YUI & jQuery). It's often that I need to observe a set of property value changes (e.g. respond only when 2 or more specific values change). Is there a elegant way to 'subscribe' the handler so that it is only called one time? Is there something I'm missing or doing wrong in my design?

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