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• How to understand existing projects

  - by John

  Hi. I am a trainee developer and have been writing .NET applications for about a year now. Most of the work I have done has involved building new applications (mainly web apps) from scratch and I have been given more or less full control over the software design. This has been a great experience however, as a trainee developer my confidence about whether the approaches I have taken are the best is minimal. Ideally I would love to collaborate with more experienced developers (I find this the best was I learn) however in the company I work for developers tend to work in isolation (a great shame for me). Recently I decided that a good way to learn more about how experienced developers approach their design might be to explore some open source projects. I found myself a little overwhelmed by the projects I looked at. With my level of experience it was hard to understand the body of code I faced. My question is slight fuzzy one. How do developers approach the task of understanding a new medium to large scale project. I found myself pouring over lots of code and struggling to see the wood for the trees. At any one time I felt that I could understand a small portion of the system but not see how its all fits together. Do others get this same feeling? If so what approaches do you take to understanding the project? Do you have any other advice about how to learn design best practices? Any advice will be very much appreciated. Thank you.

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• Implementing search functionality with multiple optional parameters against database table.

  - by quarkX

  Hello, I would like to check if there is a preferred design pattern for implementing search functionality with multiple optional parameters against database table where the access to the database should be only via stored procedures. The targeted platform is .Net with SQL 2005, 2008 backend, but I think this is pretty generic problem. For example, we have customer table and we want to provide search functionality to the UI for different parameters, like customer Type, customer State, customer Zip, etc., and all of them are optional and can be selected in any combinations. In other words, the user can search by customerType only or by customerType, customerZIp or any other possible combinations. There are several available design approaches, but all of them have some disadvantages and I would like to ask if there is a preferred design among them or if there is another approach. Generate sql where clause sql statement dynamically in the business tier, based on the search request from the UI, and pass it to a stored procedure as parameter. Something like @Where = ‘where CustomerZip = 111111’ Inside the stored procedure generate dynamic sql statement and execute it with sp_executesql. Disadvantage: dynamic sql, sql injection Implement a stored procedure with multiple input parameters, representing the search fields from the UI, and use the following construction for selecting the records only for the requested fields in the where statement. WHERE (CustomerType = @CustomerType OR @CustomerType is null ) AND (CustomerZip = @CustomerZip OR @CustomerZip is null ) AND ………………………………………… Disadvantage: possible performance issue for the sql. 3.Implement separate stored procedure for each search parameter combinations. Disadvantage: The number of stored procedures will increase rapidly with the increase of the search parameters, repeated code.

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• Eclipc java,writting a program [closed]

  - by ghassar

  I have an important exercise for that i found in the internet please i need help in using eclipc java thanks i have to design, implement, test and document a Java program (a set of classes) for one of the following problem specifications: Problem 1 – Jubilee Estate Agency Property Management System A local Estate Agent would like a prototype system to keep track of properties that are offered for sale. The Estate Agent sells domestic and commercial properties. You will need to define classes that represent the Estate Agency System. You should design your system and the classes that you will need before starting coding. Your system must have a graphical user interface and be designed and developed using the object-oriented principles of the MVC architecture design pattern i.e. the user interface class must be separate from the other classes. The initial basic requirements for the system are as follows: • Include a list of domestic properties for sale that include details of: address, description, selling price, and number of rooms • Include a list of commercial properties for sale that include details of: address, description, selling price, and area in square metres • Enable the properties that are for sale to be viewed on the screen • Allow the customer to select one or more properties to be placed on a ‘viewing list’ so that the properties can be visited in person • Display on the screen the viewing list that shows the details of the properties chosen • Provide a basic search facility to find properties that are for sale in a particular price band and display the results • Enable a property to be marked as sold

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• design of orm tool

  - by ifree

  Hello , I want to design a orm tool for my daily work, but I'm always worry about the mapping of foreign key. Here's part of my code: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Data; namespace OrmTool { [AttributeUsage(AttributeTargets.Property)] public class ColumnAttribute:Attribute { public string Name { get; set; } public SqlDbType DataType { get; set; } public bool IsPk { get; set; } } [AttributeUsage(AttributeTargets.Class,AllowMultiple=false,Inherited=false)] public class TableAttribute:Attribute { public string TableName { get; set; } public string Description { get; set; } } [AttributeUsage(AttributeTargets.Property)] public class ReferencesAttribute : ColumnAttribut { public Type Host { get; set; } public string HostPkName{get;set;} } } I want to use Attribute to get the metadata of Entity ,then mapping them,but i think it's really hard to get it done; public class DbUtility { private static readonly string CONNSTR = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString; private static readonly Type TableType = typeof(TableAttribute); private static readonly Type ColumnType = typeof(ColumnAttribute); private static readonly Type ReferenceType = typeof(ReferencesAttribute); private static IList<TEntity> EntityListGenerator<TEntity>(string tableName,PropertyInfo[] props,params SqlParameter[] paras) { return null; } private static IList<TEntity> ResultList() { return null; } private static SqlCommand PrepareCommand(string sql,SqlConnection conn,params SqlParameter[] paras) { SqlCommand cmd = new SqlCommand(); cmd.CommandText = sql; cmd.Connection = conn; if (paras != null) cmd.Parameters.AddRange(paras); conn.Open(); return cmd; } } I don't know how to do the next step, if every Entity has it's own foreign key,how do I get the return result ? If the Entity like this: [Table(Name="ArtBook")] public class ArtBook{ [column(Name="id",IsPk=true,DataType=SqlDbType.Int)] public int Id{get;set;} [References(Name="ISBNId",DataType=SqlDataType.Int,Host=typeof(ISBN),HostPkName="Id")] public ISBN BookISBN{get;set;} public .....more properties. } public class ISBN{ public int Id{get;set;} public bool IsNative{get;set;} } If I read all ArtBooks from database and when I get a ReferencesAttribute how do I set the value of BookISBN?

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• Sockets server design advice

  - by Rob

  We are writing a socket server in c# and need some advice on the design. Background: Clients (from mobile devices) connect to our server app and we leave their socket open so we can send data back down to them whenever we need to. The amount of data varies but we generally send/receive data from each client every few seconds, so it's quite intensive. The amount of simultaneous connections can range from 50-500 (and more in the future). We have already written a server app using async sockets and it works, however we've come across some stumbling blocks and we need to make sure that what we're doing is correct. We have a collection which holds our client states (we have no socket/connection pool at the moment, should we?). Each time a client connects we create a socket and then wait for them to send us some data and in receiveCallBack we add their clientstate object to our connections dictionary (once we have verified who they are). When a client object then signs off we shutdown their socket and then close it as well as remove them from our collection of clients dictionary. Presumably everything happens in the right order, everything works as expected. However, almost everyday it stops accepting connections, or so we think, either that or it connects but doesn't actually do anything past that and we can't work out why it's just stopping. There are few things that we'r'e unsure about 1) Should we be creating some kind of connection pool as opposed to just a dictionary of client sockets 2) What happens to the sockets that connect but then don't get added to our dictionary, they just linger around in memory doing nothing, should we create ANOTHER dictionary that holds the sockets as soon as they are created? 3) What's the best way of finding if clients are no longer connected? We've read some many methods but we're not sure of the best one to use, send data or read data, if so how? 4) If we loop through the connections dictonary to check for disposed clients, should we be locking the dictionary, if so how does this affect other clients objects trying to use it at the same time, will it throw an error or just wait? 5) We often get disposedSocketException within ReceiveCallBack method at random times, does this mean we are safe to remove that socket from the collection? We can't seem to find any production type examples which show any of this working. Any advice would be greatly received

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• Design-time failure: WPF, Usercontrols and Namespaces

  - by Simon Woods

  Hi I have a very simple WPF project comprising a Window and Usercontrol. I'm very much in a learning phase. It works fine when I run it. However, I am unable to see the form in design time. The problem, I believe is something to do with namespaces, but I don't understand where. It may well be a simple error Main Window XML <Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:views="clr-namespace:UserLogin" x:Class="UserLogin.MainView" x:Name="MainViewWindow" mc:Ignorable="d" Title="Login" Height="141" Width="347" > <Grid> <views:LoginView /> </Grid> </Window> Main Window CodeBehind Imports Microsoft.VisualBasic Imports System Imports System.Windows Imports UserLogin Namespace UserLogin Partial Public Class MainView Inherits System.Windows.Window Public Sub New() InitializeComponent() End Sub End Class End Namespace Usercontrol XAML <UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" x:Class="UserLogin.LoginView" x:Name="LoginViewControl" mc:Ignorable="d" d:DesignHeight="96" d:DesignWidth="298"> <Grid Height="96" Width="298"> <Button Command="{Binding OKCommand}" Height="21" Margin="0,0,90,16" Name="btnOK" VerticalAlignment="Bottom" HorizontalAlignment="Right" Width="76">OK</Button> <Button Command="{Binding CancelCommand}" Height="21" HorizontalAlignment="Right" Margin="0,0,9,16" Name="btnCancel" VerticalAlignment="Bottom" Width="75">Cancel</Button> <Label Height="23" HorizontalAlignment="Left" Margin="10,5,0,0" Name="Label1" VerticalAlignment="Top" Width="85">Name:</Label> <Label HorizontalAlignment="Left" Margin="10,32,0,0" Name="Label2" Width="85" Height="29" VerticalAlignment="Top">Password:</Label> <TextBox Margin="0,31,6,0" Name="txtPassword" Height="22" VerticalAlignment="Top" HorizontalAlignment="Right" Width="182" /> <ComboBox Height="22" Margin="110,6,6,0" Name="cboNames" VerticalAlignment="Top" /> </Grid> </UserControl> Usercontrol CodeBehind Imports Microsoft.VisualBasic Imports System Imports UserLogin Namespace UserLogin Partial Public Class LoginView Inherits System.Windows.Controls.UserControl Public Sub New() InitializeComponent() End Sub End Class End Namespace I think I'm missing something this namespace xmlns:views="clr-namespace:UserLogin" since intellisense doesn't give me the usercontrol declared within it in the XAML designer but rather reports the error "Unable to load the metadata for the assembly ... etc etc" Thx for any suggestions Simon

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• How to design this ?

  - by Akku

  how can i make this entire process as 1 single event??? http://code.google.com/apis/visualization/documentation/dev/dsl_get_started.html and draw the chart on single click? I am new to servlets please guide me When a user clicks the "go " button with some input. The data goes to the servlet say "Test3". The servlet processes the data by the user and generates/feeds the data table dynamically Then I call the html page to draw the chart as shown in the tutorial link above. The problem is when I call the servlet it gives me a long json string in the browser as given in the tutorials "google.visualization.Query.setResponse({version:'0.6',status:'ok',sig:'1333639331',table:{cols:[{............................" Then when i manually call the html page to draw the chart i am see the chart. But when I call html page directly using the request dispatcher via the servlet I dont get the result. This is my code and o/p...... I need sugession as to how should be my approach to call the chart public class Test3 extends HttpServlet implements DataTableGenerator { protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { DataSourceHelper.executeDataSourceServletFlow(request, response, this , isRestrictedAccessMode() ); RequestDispatcher rd; rd = request.getRequestDispatcher("new.html");// it call's the html page which draws the chart as per the data added by the servlet..... rd.include(request, response);//forward(request, response); @Override public Capabilities getCapabilities() { return Capabilities.NONE; } protected boolean isRestrictedAccessMode() { return false; } @Override public DataTable generateDataTable(Query query, HttpServletRequest request) { // Create a data table. DataTable data = new DataTable(); ArrayList<ColumnDescription> cd = new ArrayList<ColumnDescription>(); cd.add(new ColumnDescription("name", ValueType.TEXT, "Animal name")); cd.add......... I get the following result along with unprocessed html page google.visualization.Query.setResponse({version:'0.6',statu..... <html> <head> <title>Getting Started Example</title> .... Entire html page as it is on the Browser. What I need is when a user clicks the go button the servlet should process the data and call the html page to draw the chart....Without the json string appearing on the browser.(all in one user click) What should be my approach or how should i design this.... there are no error in the code. since when i run the servlet i get the json string on the browser and then when i run the html page manually i get the chart drawn. So how can I do (servlet processing + html page drawing chart as final result) at one go without the long json string appearing on the browser. There is no problem with the html code....

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• Advice for Architecture Design Logic for software application

  - by Prasad

  Hi, I have a framework of basic to complex set of objects/classes (C++) running into around 500. With some rules and regulations - all these objects can communicate with each other and hence can cover most of the common queries in the domain. My Dream: I want to provide these objects as icons/glyphs (as I learnt recently) on a workspace. All these objects can be dragged/dropped into the workspace. They have to communicate only through their methods(interface) and in addition to few iterative and conditional statements. All these objects are arranged finally to execute a protocol/workflow/dataflow/process. After drawing the flow, the user clicks the Execute/run button. All the user interaction should be multi-touch enabled. The best way to show my dream is : Jeff Han's Multitouch Video. consider Jeff is playing with my objects instead of the google maps. :-) it should be like playing a jigsaw puzzle. Objective: how can I achieve the following while working on this final product: a) the development should be flexible to enable provision for web services b) the development should enable easy web application development c) The development should enable client-server architecture - d) further it should also enable mouse based drag/drop desktop application like Adobe programs etc. I mean to say: I want to economize on investments. Now I list my efforts till now in design : a) Created an Editor (VB) where the user writes (manually) the object / class code b) On Run/Execute, the code is copied into a main() function and passed to interpreter. c) Catch the output and show it in the console. The interpreter can be separated to become a server and the Editor can become the client. This needs lot of standard client-server architecture work. But some how I am not comfortable in the tightness of this system. Without interpreter is there much faster and better embeddable solution to this? - other than writing a special compiler for these objects. Recently learned about AXIS-C++ can help me - looks like - a friend suggested. Is that the way to go ? Here are my questions: (pl. consider me a self taught programmer and NOT my domain) a) From the stage of C++ objects to multi-touch product, how can I make sure I will develop the parallel product/service models as well.? What should be architecture aspects I should consider ? b) What technologies are best suited for this? c) If I am thinking of moving to Cloud Computing, how difficult/ how redundant / how unnecessary my efforts will be ? d) How much time in months would it take to get the first beta ? I take the liberty to ask if any of the experts here are interested in this project, please email me: [email protected] Thank you for any help. Looking forward.

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• Design time error - multiple controls with the same Id

  - by ilivewithian

  I'm using VS 2008, I have a very simple page that has a bunch of uniquely named controls. When I try to view it in design mode I get the following error: Error Rendering Control - Label12 An unhanded exception has occurred. Multiple controls with the same ID 'Label1' were found. FindControl requires that controls have unique IDs I've checked the HTML and the designer file and I can only see one control called Label1. What might be causing this? Also, here is the aspx markup I'm having trouble with? <%@ Page Language="vb" AutoEventWireup="false" CodeBehind="CoachingAppearanceReport.aspx.vb" Inherits="AcademyPro.CoachingAppearanceReport" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> </head> <body> <form id="form1" runat="server"> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <div id="appearanceDetail" class="Left CriteriaContainer"> <asp:Label ID="Label1" runat="server" Text="Appearance Type" AssociatedControlID="ddlAppearanceType" /> <asp:DropDownList ID="ddlAppearanceType" runat="server" CssClass="AppType" OnDataBound="ddlAppearanceType_DataBound" DataSourceID="odsAppearanceType" DataTextField="AppearanceType" DataValueField="AppearanceTypeCode"> </asp:DropDownList> <asp:RequiredFieldValidator ID="rfvAppearanceType" runat="server" ControlToValidate="ddlAppearanceType" InitialValue="" Text="*" ErrorMessage="The appearance type must be selected" /> <asp:Label ID="lblAppearanceType" runat="server" /> <br /> <div class="SubSettings"> <asp:Label ID="Label12" runat="server" Text="Subbed for" AssociatedControlID="ddlSubbedFor" /> <asp:DropDownList ID="ddlSubbedFor" runat="server" OnDataBound="ddlSubbedFor_DataBound" DataSourceID="odsPlayersInAgeGroup" DataTextField="PlayerName" DataValueField="PlayerID"> </asp:DropDownList> <asp:Label ID="lblSubbedFor" runat="server" /> <br /> <asp:Label ID="Label13" runat="server" Text="Mins" AssociatedControlID="txtSubMins" /> <asp:TextBox ID="txtSubMins" runat="server" MaxLength="3" CssClass="TinyWidth" /> <asp:Label ID="lblSubMins" runat="server" /> </div> </div> </ContentTemplate> </asp:UpdatePanel> </form> </body> </html>

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• Parallel Task Library WaitAny Design

  - by colithium

  I've just begun to explore the PTL and have a design question. My Scenario: I have a list of URLs that each refer to an image. I want each image to be downloaded in parallel. As soon as at least one image is downloaded, I want to execute a method that does something with the downloaded image. That method should NOT be parallelized -- it should be serial. I think the following will work but I'm not sure if this is the right way to do it. Because I have separate classes for collecting the images and for doing "something" with the collected images, I end up passing around an array of Tasks which seems wrong since it exposes the inner workings of how images are retrieved. But I don't know a way around it. In reality there is more to both of these methods but that's not important for this. Just know that they really shouldn't be lumped into one large method that both retrieves and does something with the image. Task<Image>[] downloadTasks = collector.RetrieveImages(listOfURLs); for (int i = 0; i < listOfURLs.Count; i++) { //Wait for any of the remaining downloads to complete int completedIndex = Task<Image>.WaitAny(downloadTasks); Image completedImage = downloadTasks[completedIndex].Result; //Now do something with the image (this "something" must happen serially) } /////////////////////////////////////////////////// public Task<Image>[] RetrieveImages(List<string> urls) { Task<Image>[] tasks = new Task<Image>[urls.Count]; int index = 0; foreach (string url in urls) { string lambdaVar = url; //Required... Bleh tasks[index] = Task<Image>.Factory.StartNew(() => { using (WebClient client = new WebClient()) { //TODO: Replace with live image locations string fileName = String.Format("{0}.png", i); client.DownloadFile(lambdaVar, Path.Combine(Application.StartupPath, fileName)); } return Image.FromFile(Path.Combine(Application.StartupPath, fileName)); }, TaskCreationOptions.LongRunning | TaskCreationOptions.AttachedToParent); index++; } return tasks; }

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• Database design advice needed.

  - by user346271

  Hi all, I'm a lone developer for a telecoms company, and am after some database design advice from anyone with a bit of time to answer. I am inserting into one table ~2 million rows each day, these tables then get archived and compressed on a monthly basis. Each monthly table contains ~15,000,000 rows. Although this is increasing month on month. For every insert I do above I am combining the data from rows which belong together and creating another "correlated" table. This table is currently not being archived, as I need to make sure I never miss an update to the correlated table. (Hope that makes sense) Although in general this information should remain fairly static after a couple of days of processing. All of the above is working perfectly. However my company now wishes to perform some stats against this data, and these tables are getting too large to provide the results in what would be deemed a reasonable time. Even with the appropriate indexes set. So I guess after all the above my question is quite simple. Should I write a script which groups the data from my correlated table into smaller tables. Or should I store the queries result sets in something like memcache? I'm already using mysqls cache, but due to having limited control over how long the data is stored for, it's not working ideally. The main advantages I can see of using something like memcache: No blocking on my correlated table after the query has been cashed. Greater flexibility of sharing the collected data between the backend collector and front end processor. (i.e custom reports could be written in the backend and the results of these stored in the cache under a key which then gets shared with anyone who would want to see the data of this report) Redundancy and scalability if we start sharing this data with a large amount of customers. The main disadvantages I can see of using something like memcache: Data is not persistent if machine is rebooted / cache is flushed. The main advantages of using MySql Persistent data. Less code changes (although adding something like memcache is trivial anyway) The main disadvantages of using MySql Have to define table templates every time I want to store provide a new set of grouped data. Have to write a program which loops through the correlated data and fills these new tables. Potentially will still grow slower as the data continues to be filled. Apologies for quite a long question. It's helped me to write down these thoughts here anyway, and any advice/help/experience with dealing with this sort of problem would be greatly appreciated. Many thanks. Alan

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• FluentNHibernate Unit Of Work / Repository Design Pattern Questions

  - by Echiban

  Hi all, I think I am at a impasse here. I have an application I built from scratch using FluentNHibernate (ORM) / SQLite (file db). I have decided to implement the Unit of Work and Repository Design pattern. I am at a point where I need to think about the end game, which will start as a WPF windows app (using MVVM) and eventually implement web services / ASP.Net as UI. Now I already created domain objects (entities) for ORM. And now I don't know how should I use it outside of ORM. Questions about it include: Should I use ORM entity objects directly as models in MVVM? If yes, do I put business logic (such as certain values must be positive and be greater than another Property) in those entity objects? It is certainly the simpler approach, and one I am leaning right now. However, will there be gotchas that would trash this plan? If the answer above is no, do I then create a new set of classes to implement business logic and use those as Models in MVVM? How would I deal with the transition between model objects and entity objects? I guess a type converter implementation would work well here. Now I followed this well written article to implement the Unit Of Work pattern. However, due to the fact that I am using FluentNHibernate instead of NHibernate, I had to bastardize the implementation of UnitOfWorkFactory. Here's my implementation: using System; using FluentNHibernate.Cfg; using FluentNHibernate.Cfg.Db; using NHibernate; using NHibernate.Cfg; using NHibernate.Tool.hbm2ddl; namespace ELau.BlindsManagement.Business { public class UnitOfWorkFactory : IUnitOfWorkFactory { private static readonly string DbFilename; private static Configuration _configuration; private static ISession _currentSession; private ISessionFactory _sessionFactory; static UnitOfWorkFactory() { // arbitrary default filename DbFilename = "defaultBlindsDb.db3"; } internal UnitOfWorkFactory() { } #region IUnitOfWorkFactory Members public ISession CurrentSession { get { if (_currentSession == null) { throw new InvalidOperationException(ExceptionStringTable.Generic_NotInUnitOfWork); } return _currentSession; } set { _currentSession = value; } } public ISessionFactory SessionFactory { get { if (_sessionFactory == null) { _sessionFactory = BuildSessionFactory(); } return _sessionFactory; } } public Configuration Configuration { get { if (_configuration == null) { Fluently.Configure().ExposeConfiguration(c => _configuration = c); } return _configuration; } } public IUnitOfWork Create() { ISession session = CreateSession(); session.FlushMode = FlushMode.Commit; _currentSession = session; return new UnitOfWorkImplementor(this, session); } public void DisposeUnitOfWork(UnitOfWorkImplementor adapter) { CurrentSession = null; UnitOfWork.DisposeUnitOfWork(adapter); } #endregion public ISession CreateSession() { return SessionFactory.OpenSession(); } public IStatelessSession CreateStatelessSession() { return SessionFactory.OpenStatelessSession(); } private static ISessionFactory BuildSessionFactory() { ISessionFactory result = Fluently.Configure() .Database( SQLiteConfiguration.Standard .UsingFile(DbFilename) ) .Mappings(m => m.FluentMappings.AddFromAssemblyOf<UnitOfWorkFactory>()) .ExposeConfiguration(BuildSchema) .BuildSessionFactory(); return result; } private static void BuildSchema(Configuration config) { // this NHibernate tool takes a configuration (with mapping info in) // and exports a database schema from it _configuration = config; new SchemaExport(_configuration).Create(false, true); } } } I know that this implementation is flawed because a few tests pass when run individually, but when all tests are run, it would fail for some unknown reason. Whoever wants to help me out with this one, given its complexity, please contact me by private message. I am willing to send some $$$ by Paypal to someone who can address the issue and provide solid explanation. I am new to ORM, so any assistance is appreciated.

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• Core Data Model Design Question - Changing "Live" Objects also Changes Saved Objects

  - by mwt

  I'm working on my first Core Data project (on iPhone) and am really liking it. Core Data is cool stuff. I am, however, running into a design difficulty that I'm not sure how to solve, although I imagine it's a fairly common situation. It concerns the data model. For the sake of clarity, I'll use an imaginary football game app as an example to illustrate my question. Say that there are NSMO's called Downs and Plays. Plays function like templates to be used by Downs. The user creates Plays (for example, Bootleg, Button Hook, Slant Route, Sweep, etc.) and fills in the various properties. Plays have a to-many relationship with Downs. For each Down, the user decides which Play to use. When the Down is executed, it uses the Play as its template. After each down is run, it is stored in history. The program remembers all the Downs ever played. So far, so good. This is all working fine. The question I have concerns what happens when the user wants to change the details of a Play. Let's say it originally involved a pass to the left, but the user now wants it to be a pass to the right. Making that change, however, not only affects all the future executions of that Play, but also changes the details of the Plays stored in history. The record of Downs gets "polluted," in effect, because the Play template has been changed. I have been rolling around several possible fixes to this situation, but I imagine the geniuses of SO know much more about how to handle this than I do. Still, the potential fixes I've come up with are: 1) "Versioning" of Plays. Each change to a Play template actually creates a new, separate Play object with the same name (as far as the user can tell). Underneath the hood, however, it is actually a different Play. This would work, AFAICT, but seems like it could potentially lead to a wild proliferation of Play objects, esp. if the user keeps switching back and forth between several versions of the same Play (creating object after object each time the user switches). Yes, the app could check for pre-existing, identical Plays, but... it just seems like a mess. 2) Have Downs, upon saving, record the details of the Play they used, but not as a Play object. This just seems ridiculous, given that the Play object is there to hold those just those details. 3) Recognize that Play objects are actually fulfilling 2 functions: one to be a template for a Down, and the other to record what template was used. These 2 functions have a different relationship with a Down. The first (template) has a to-many relationship. But the second (record) has a one-to-one relationship. This would mean creating a second object, something like "Play-Template" which would retain the to-many relationship with Downs. Play objects would get reconfigured to have a one-to-one relationship with Downs. A Down would use a Play-Template object for execution, but use the new kind of Play object to store what template was used. It is this change from a to-many relationship to a one-to-one relationship that represents the crux of the problem. Even writing this question out has helped me get clearer. I think something like solution 3 is the answer. However if anyone has a better idea or even just a confirmation that I'm on the right track, that would be helpful. (Remember, I'm not really making a football game, it's just faster/easier to use a metaphor everyone understands.) Thanks.

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• Object validator - is this good design?

  - by neo2862

  I'm working on a project where the API methods I write have to return different "views" of domain objects, like this: namespace View.Product { public class SearchResult : View { public string Name { get; set; } public decimal Price { get; set; } } public class Profile : View { public string Name { get; set; } public decimal Price { get; set; } [UseValidationRuleset("FreeText")] public string Description { get; set; } [SuppressValidation] public string Comment { get; set; } } } These are also the arguments of setter methods in the API which have to be validated before storing them in the DB. I wrote an object validator that lets the user define validation rulesets in an XML file and checks if an object conforms to those rules: [Validatable] public class View { [SuppressValidation] public ValidationError[] ValidationErrors { get { return Validator.Validate(this); } } } public static class Validator { private static Dictionary<string, Ruleset> Rulesets; static Validator() { // read rulesets from xml } public static ValidationError[] Validate(object obj) { // check if obj is decorated with ValidatableAttribute // if not, return an empty array (successful validation) // iterate over the properties of obj // - if the property is decorated with SuppressValidationAttribute, // continue // - if it is decorated with UseValidationRulesetAttribute, // use the ruleset specified to call // Validate(object value, string rulesetName, string FieldName) // - otherwise, get the name of the property using reflection and // use that as the ruleset name } private static List<ValidationError> Validate(object obj, string fieldName, string rulesetName) { // check if the ruleset exists, if not, throw exception // call the ruleset's Validate method and return the results } } public class Ruleset { public Type Type { get; set; } public Rule[] Rules { get; set; } public List<ValidationError> Validate(object property, string propertyName) { // check if property is of type Type // if not, throw exception // iterate over the Rules and call their Validate methods // return a list of their return values } } public abstract class Rule { public Type Type { get; protected set; } public abstract ValidationError Validate(object value, string propertyName); } public class StringRegexRule : Rule { public string Regex { get; set; } public StringRegexRule() { Type = typeof(string); } public override ValidationError Validate(object value, string propertyName) { // see if Regex matches value and return // null or a ValidationError } } Phew... Thanks for reading all of this. I've already implemented it and it works nicely, and I'm planning to extend it to validate the contents of IEnumerable fields and other fields that are Validatable. What I'm particularly concerned about is that if no ruleset is specified, the validator tries to use the name of the property as the ruleset name. (If you don't want that behavior, you can use [SuppressValidation].) This makes the code much less cluttered (no need to use [UseValidationRuleset("something")] on every single property) but it somehow doesn't feel right. I can't decide if it's awful or awesome. What do you think? Any suggestions on the other parts of this design are welcome too. I'm not very experienced and I'm grateful for any help. Also, is "Validatable" a good name? To me, it sounds pretty weird but I'm not a native English speaker.

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• Tips and Suggestions IP Address Re-Addressing?

  - by RSXAdmin

  Hello serverfault Universe, My ever evolving and expanding local area network is currently using a class-C address. My network consists of multiple subnets depending on site/location. 192.168.1.x is site HQ 192.168.5.x is secondary site 192.168.10.x is so on and so forth. Long story short - I have inherited this network design from the previous admin who has left the company which started off with a dozen people and now has just over 300 full time/part time employees. We do not yet have client VPN access; but we do have site to site VPN setup. My question is, in preparation for outside client access to my network via Cisco ASA, I would like to re-address the HQ site because I understand a 192.168.1.x or 192.168.0.x are not very good choices for a company subnet - it may conflict with a home user's LAN when connecting to my LAN, I believe? Through your experience, does anyone out there have any suggestions and tips on how I can proceed with re-addressing my subnets. If I designed this network I would have gone with a 10.0.0.0 (mask 255.255.255.0) so I am leaning towards changing it to fit. Thank you.

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• Designing a software based load balancer

  - by Kishore pandey

  Hello to all Server fault users, I am new to this website but have constantly been using the mother website, stackover flow. Well to begin with, i would like to design a load balancer for the organization i am working for. As i am very new to this whole, idea about load balancing and networks. I am finding it very difficult to start my project. I did a lot of research on already existing load balancer and found some(HAPROXY,NGINX) that could solve my problems, but the point is, I am still in a dilemma if they could answer the following requirements of mine: The client and server in my architecture are distributed. The load balancer should take care of the firewall. LB server should balance the load among all servers present in WWW cloud. The LB server should have some sort of configuration file, with the help of which it is possible to configure the servers. Heart beat: With the help of which it would be possible to check if any server is down, if any server is down the request should be passed to some other server. Various load balancing algorithms of the incoming requests. Easy error handling. It should be fairly possible to prioritize the incoming requests. Is there any already available load balncer solution on the market that could satisfy these requirements? If not is there any base code available with the help of which i could develop my own load balncer. If not where should i start from scratch? I am practically new to everything. Any help from a load balancer expert is very much appreciated. Thanx a ton in advance. Cheers and regards. Kishore

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• .NET interview, code structure and the design

  - by j_lewis

  I have been given the below .NET question in an interview. I don’t know why I got low marks. Unfortunately I did not get a feedback. Question: The file hockey.csv contains the results from the Hockey Premier League. The columns ‘For’ and ‘Against’ contain the total number of goals scored for and against each team in that season (so Alabama scored 79 goals against opponents, and had 36 goals scored against them). Write a program to print the name of the team with the smallest difference in ‘for’ and ‘against’ goals. the structure of the hockey.csv looks like this (it is a valid csv file, but I just copied the values here to get an idea) Team - For - Against Alabama 79 36 Washinton 67 30 Indiana 87 45 Newcastle 74 52 Florida 53 37 New York 46 47 Sunderland 29 51 Lova 41 64 Nevada 33 63 Boston 30 64 Nevada 33 63 Boston 30 64 Solution: class Program { static void Main(string[] args) { string path = @"C:\Users\<valid csv path>"; var resultEvaluator = new ResultEvaluator(string.Format(@"{0}\{1}",path, "hockey.csv")); var team = resultEvaluator.GetTeamSmallestDifferenceForAgainst(); Console.WriteLine( string.Format("Smallest difference in ‘For’ and ‘Against’ goals > TEAM: {0}, GOALS DIF: {1}", team.Name, team.Difference )); Console.ReadLine(); } } public interface IResultEvaluator { Team GetTeamSmallestDifferenceForAgainst(); } public class ResultEvaluator : IResultEvaluator { private static DataTable leagueDataTable; private readonly string filePath; private readonly ICsvExtractor csvExtractor; public ResultEvaluator(string filePath){ this.filePath = filePath; csvExtractor = new CsvExtractor(); } private DataTable LeagueDataTable{ get { if (leagueDataTable == null) { leagueDataTable = csvExtractor.GetDataTable(filePath); } return leagueDataTable; } } public Team GetTeamSmallestDifferenceForAgainst() { var teams = GetTeams(); var lowestTeam = teams.OrderBy(p => p.Difference).First(); return lowestTeam; } private IEnumerable<Team> GetTeams() { IList<Team> list = new List<Team>(); foreach (DataRow row in LeagueDataTable.Rows) { var name = row["Team"].ToString(); var @for = int.Parse(row["For"].ToString()); var against = int.Parse(row["Against"].ToString()); var team = new Team(name, against, @for); list.Add(team); } return list; } } public interface ICsvExtractor { DataTable GetDataTable(string csvFilePath); } public class CsvExtractor : ICsvExtractor { public DataTable GetDataTable(string csvFilePath) { var lines = File.ReadAllLines(csvFilePath); string[] fields; fields = lines[0].Split(new[] { ',' }); int columns = fields.GetLength(0); var dt = new DataTable(); //always assume 1st row is the column name. for (int i = 0; i < columns; i++) { dt.Columns.Add(fields[i].ToLower(), typeof(string)); } DataRow row; for (int i = 1; i < lines.GetLength(0); i++) { fields = lines[i].Split(new char[] { ',' }); row = dt.NewRow(); for (int f = 0; f < columns; f++) row[f] = fields[f]; dt.Rows.Add(row); } return dt; } } public class Team { public Team(string name, int against, int @for) { Name = name; Against = against; For = @for; } public string Name { get; private set; } public int Against { get; private set; } public int For { get; private set; } public int Difference { get { return (For - Against); } } } Output: Smallest difference in for' andagainst' goals TEAM: Boston, GOALS DIF: -34 Can someone please review my code and see anything obviously wrong here? They were only interested in the structure/design of the code and whether the program produces the correct result (i.e lowest difference). Much appreciated. "P.S - Please correct me if the ".net-interview" tag is not the right tag to use"

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• I can write code...but can't design well. Any suggestions?

  - by user396089

  I feel that I am good at writing code in bits and pieces, but my designs really suck. The question is how do I improve my designs (in order to become a better designer). I think schools and colleges do a good job of teaching people as to how to become good at mathematical problem solving, but lets admit the fact that most programs taught at school are generally around 1000 - 2000 lines long, which means that it is mostly an academic exercise and no way reflects the complexity of real world software (a few hundred thousand to millions of lines of code). This is where I believe that even projects like topcoder/project euler also won't be of much help, they might sharpen your mathematical problem solving ability - but you might become a theoretician programmer; someone who is more interested in the nice, clean stuff, and someone who is utterly un-interested in the day to day mundane and hairy stuff that most application programmers deal with. So my question is how do I improve my design skills? That is the ability to design small/medium scale applications that will go into a few thousand of lines of code? How can I learn design skills that would help me build a better html editor kit, or some graphics program like gimp?

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• how to create multiple pages in Xcode iphone apps

  - by al7r

  Hi there, i am starting my experience with iphone sdk. and i have a question, which is i am trying to create two pages to the app but i don't know how to link them or design them. like when i start the Xcode i find one page named View to design in it, i want to make that page a welcoming page then the user choose one of the three choices he see in that page. Once he clicked on one of them the program take him to the next page or the page he chose. thank you

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• problem with seam and mdb on jboss5.1

  - by simoncigoj

  I have a problem when using a mdb as a seam component. In the bean I inject some other seam somponents. The problem is that when the server restart after a crash and the mdb is deployed it starts reading the messages but seam is not initialized yet and I got an exception(listed above). If i start the server whith the queues empty and submit a message to queue after the server start it is working ok. Is there a posibility to stop or delay the sending off messages on server startup and start sending them only when seam is fully funcional? I tried the @Depends antotatin on the bean but withowt success my environment : jboss5.1 GA seam 2.2.0 GA jboss messaging 1.4 Any help would be appreceated the error on startup : 11:24:20,477 ERROR [TxPolicy] javax.ejb.EJBTransactionRolledbackException: java.lang.IllegalStateException: Attempted to invoke a Seam component outside an initialized application 11:24:30,483 ERROR [TxPolicy] javax.ejb.EJBException: Failed to acquire the pool semaphore, strictTimeout=10000

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• Proper Way to Create Standards-Compliant Webpage Structure

  - by Sakamoto Kazuma

  I have been working through projects involving packages that do all the web design stuff for me for the past few years. I will admit that I have not been able to focus any on actual web design. I was wondering what the standard is these days for website layouts. Are layout-tables looked down upon now? Or are all layouts done with div tags and controlled through CSS? Are frames even used anymore? Note I am not talking about chart-table tables when I say layout tables.

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• Product table, many kinds of product, each product has many parameters

  - by StoneHeart

  Hi, i'm have not much experience in table design. My goal is a product table(s), it must design to fix some requirement below: Support many kind of products (TV, Phone, PC, ...). Each kind of product has different set of parameters like: Phone will have Color, Size, Weight, OS... PC will have CPU, HDD, RAM... Set of parameters must be dynamic. You can add or edit any parameter you like. I don't want make a table for each kind of product. So I need help to find a correct solution. Thanks.

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• Synchronizing an ERWin model with a Visual Studio 2008 GDR 2/2010 db project

  - by Grant Back

  I am looking for options to get our vast collection of DB objects across many DBs into source control (TFS 2010). Once we succeed here, we will work toward generating our alter scripts for a particular DB change via TFS build. The problem is, our data architecture group is responsible for maintaining the DB objects (excluding SPs), and they work within a model centric process, via ERWin. What this means, is that they maintain the DBs via ERWin models, and generate alters from them that are used to release changes. In order to achieve our goal of getting the DB objects (not just the ERWin models) into TFS, I believe the best option is to do this via Visual Studio DB projects. From what I can tell, there is very little urgency for CA to continue supporting an integration between ERWin and Visual Studio, that no longer works as of Visual Studio 2008 DB Ed. GDR. If I have been mislead in this regard, please feel free to set me straight. One potential solution is to: Perform changes in the ERWin model. Take the alter script generated from ERWin, and import the script into the appropriate Visual Studio DB project, updating the objects in the in the DB project Check the changed objects in the DB project into TFS. TFS Build executes to generate the alter scripts that will be used to push the changes through our release process. My question is, is this solution viable, or are there any other options?

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• Saving State Dynamic UserControls...Help!

  - by Cognitronic

  I have page with a LinkButton on it that when clicked, I'd like to add a Usercontrol to the page. I need to be able to add/remove as many controls as the user would like. The Usercontrol consists of three dropdownlists. The first dropdownlist has it's auotpostback property set to true and hooks up the OnSelectedIndexChanged event that when fired will load the remaining two dropdownlists with the appropriate values. My problem is that no matter where I put the code in the host page, the usercontrol is not being loaded properly. I know I have to recreate the usercontrols on every postback and I've created a method that is being executed in the hosting pages OnPreInit method. I'm still getting the following error: The control collection cannot be modified during DataBind, Init, Load, PreRender or Unload phases. Here is my code: Thank you!!!! bool createAgain = false; IList<FilterOptionsCollectionView> OptionControls { get { if (SessionManager.Current["controls"] != null) return (IList<FilterOptionsCollectionView>)SessionManager.Current["controls"]; else SessionManager.Current["controls"] = new List<FilterOptionsCollectionView>(); return (IList<FilterOptionsCollectionView>)SessionManager.Current["controls"]; } set { SessionManager.Current["controls"] = value; } } protected void Page_Load(object sender, EventArgs e) { Master.Page.Title = Title; LoadViewControls(Master.MainContent, Master.SideBar, Master.ToolBarContainer); } protected override void OnPreInit(EventArgs e) { base.OnPreInit(e); System.Web.UI.MasterPage m = Master; Control control = GetPostBackControl(this); if ((control != null && control.ClientID == (lbAddAndCondtion.ClientID) || createAgain)) { createAgain = true; CreateUserControl(control.ID); } } protected void AddAndConditionClicked(object o, EventArgs e) { var control = LoadControl("~/Views/FilterOptionsCollectionView.ascx"); OptionControls.Add((FilterOptionsCollectionView)control); control.ID = "options" + OptionControls.Count.ToString(); phConditions.Controls.Add(control); } public event EventHandler<Insight.Presenters.PageViewArg> OnLoadData; private Control FindControlRecursive(Control root, string id) { if (root.ID == id) { return root; } foreach (Control c in root.Controls) { Control t = FindControlRecursive(c, id); if (t != null) { return t; } } return null; } protected Control GetPostBackControl(System.Web.UI.Page page) { Control control = null; string ctrlname = Page.Request.Params["__EVENTTARGET"]; if (ctrlname != null && ctrlname != String.Empty) { control = FindControlRecursive(page, ctrlname.Split('$')[2]); } else { string ctrlStr = String.Empty; Control c = null; foreach (string ctl in Page.Request.Form) { if (ctl.EndsWith(".x") || ctl.EndsWith(".y")) { ctrlStr = ctl.Substring(0, ctl.Length - 2); c = page.FindControl(ctrlStr); } else { c = page.FindControl(ctl); } if (c is System.Web.UI.WebControls.CheckBox || c is System.Web.UI.WebControls.CheckBoxList) { control = c; break; } } } return control; } protected void CreateUserControl(string controlID) { try { if (createAgain && phConditions != null) { if (OptionControls.Count > 0) { phConditions.Controls.Clear(); foreach (var c in OptionControls) { phConditions.Controls.Add(c); } } } } catch (Exception ex) { throw ex; } } Here is the usercontrol's code: <%@ Control Language="C#" AutoEventWireup="true" CodeBehind="FilterOptionsCollectionView.ascx.cs" Inherits="Insight.Website.Views.FilterOptionsCollectionView" %> namespace Insight.Website.Views { [ViewStateModeById] public partial class FilterOptionsCollectionView : System.Web.UI.UserControl { protected void Page_Load(object sender, EventArgs e) { } protected override void OnInit(EventArgs e) { LoadColumns(); ddlColumns.SelectedIndexChanged += new RadComboBoxSelectedIndexChangedEventHandler(ColumnsSelectedIndexChanged); base.OnInit(e); } protected void ColumnsSelectedIndexChanged(object o, EventArgs e) { LoadCriteria(); } public void LoadColumns() { ddlColumns.DataSource = User.GetItemSearchProperties(); ddlColumns.DataTextField = "SearchColumn"; ddlColumns.DataValueField = "CriteriaSearchControlType"; ddlColumns.DataBind(); LoadCriteria(); } private void LoadCriteria() { var controlType = User.GetItemSearchProperties()[ddlColumns.SelectedIndex].CriteriaSearchControlType; var ops = User.GetItemSearchProperties()[ddlColumns.SelectedIndex].ValidOperators; ddlOperators.DataSource = ops; ddlOperators.DataTextField = "key"; ddlOperators.DataValueField = "value"; ddlOperators.DataBind(); switch (controlType) { case ResourceStrings.ViewFilter_ControlTypes_DDL: criteriaDDL.Visible = true; criteriaText.Visible = false; var crit = User.GetItemSearchProperties()[ddlColumns.SelectedIndex].SearchCriteria; ddlCriteria.DataSource = crit; ddlCriteria.DataBind(); break; case ResourceStrings.ViewFilter_ControlTypes_Text: criteriaDDL.Visible = false; criteriaText.Visible = true; break; } } public event EventHandler OnColumnChanged; public ISearchCriterion FilterOptionsValues { get; set; } } }

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• Singleton: How should it be used

  - by Loki Astari

  Edit: From another question I provided an answer that has links to a lot of questions/answers about singeltons: More info about singletons here: So I have read the thread Singletons: good design or a crutch? And the argument still rages. I see Singletons as a Design Pattern (good and bad). The problem with Singleton is not the Pattern but rather the users (sorry everybody). Everybody and their father thinks they can implement one correctly (and from the many interviews I have done, most people can't). Also because everybody thinks they can implement a correct Singleton they abuse the Pattern and use it in situations that are not appropriate (replacing global variables with Singletons!). So the main questions that need to be answered are: When should you use a Singleton How do you implement a Singleton correctly My hope for this article is that we can collect together in a single place (rather than having to google and search multiple sites) an authoritative source of when (and then how) to use a Singleton correctly. Also appropriate would be a list of Anti-Usages and common bad implementations explaining why they fail to work and for good implementations their weaknesses. So get the ball rolling: I will hold my hand up and say this is what I use but probably has problems. I like "Scott Myers" handling of the subject in his books "Effective C++" Good Situations to use Singletons (not many): Logging frameworks Thread recycling pools /* * C++ Singleton * Limitation: Single Threaded Design * See: http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf * For problems associated with locking in multi threaded applications * * Limitation: * If you use this Singleton (A) within a destructor of another Singleton (B) * This Singleton (A) must be fully constructed before the constructor of (B) * is called. */ class MySingleton { private: // Private Constructor MySingleton(); // Stop the compiler generating methods of copy the object MySingleton(MySingleton const& copy); // Not Implemented MySingleton& operator=(MySingleton const& copy); // Not Implemented public: static MySingleton& getInstance() { // The only instance // Guaranteed to be lazy initialized // Guaranteed that it will be destroyed correctly static MySingleton instance; return instance; } }; OK. Lets get some criticism and other implementations together. :-)

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