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  • LINQ to SQL: Reusable expression for property?

    - by coenvdwel
    Pardon me for being unable to phrase the title more exact. Basically, I have three LINQ objects linked to tables. One is Product, the other is Company and the last is a mapping table Mapping to store what Company sells which products and by which ID this Company refers to this Product. I am now retrieving a list of products as follows: var options = new DataLoadOptions(); options.LoadWith<Product>(p => p.Mappings); context.LoadOptions = options; var products = ( from p in context.Products select new { ProductID = p.ProductID, //BackendProductID = p.BackendProductID, BackendProductID = (p.Mappings.Count == 0) ? "None" : (p.Mappings.Count > 1) ? "Multiple" : p.Mappings.First().BackendProductID, Description = p.Description } ).ToList(); This does a single query retrieving the information I want. But I want to be able to move the logic behind the BackendProductID into the LINQ object so I can use the commented line instead of the annoyingly nested ternary operator statements for neatness and re-usability. So I added the following property to the Product object: public string BackendProductID { get { if (Mappings.Count == 0) return "None"; if (Mappings.Count > 1) return "Multiple"; return Mappings.First().BackendProductID; } } The list is still the same, but it now does a query for every single Product to get it's BackendProductID. The code is neater and re-usable, but the performance now is terrible. What I need is some kind of Expression or Delegate but I couldn't get my head around writing one. It always ended up querying for every single product, still. Any help would be appreciated!

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  • In a combobox, how do I determine the highlighted item (not selected item)?

    - by Harold Bamford
    First, fair warning: I am a complete newbie with C# and WPF. I have a combobox (editable, searchable) and I would like to be able to intercept the Delete key and remove the currently highlighted item from the list. The behavior I'm looking for is like that of MS Outlook when entering in email addresses. When you give a few characters, a dropdown list of potential matches is displayed. If you move to one of these (with the arrow keys) and hit Delete, that entry is permanently removed. I want to do that with an entry in the combobox. Here is the XAML (simplified): <ComboBox x:Name="Directory" KeyUp="Directory_KeyUp" IsTextSearchEnabled="True" IsEditable="True" Text="{Binding Path=CurrentDirectory, Mode=TwoWay}" ItemsSource="{Binding Source={x:Static self:Properties.Settings.Default}, Path=DirectoryList, Mode=TwoWay}" / The handler is: private void Directory_KeyUp(object sender, KeyEventArgs e) { ComboBox box = sender as ComboBox; if (box.IsDropDownOpen && (e.Key == Key.Delete)) { TrimCombobox("DirectoryList", box.HighlightedItem); // won't compile! } } When using the debugger, I can see box.HighlightedItem has the value I want but when I try and put in that code, it fails to compile with: System.Windows.Controls.ComboBox' does not contain a definition for 'HighlightedItem'... So: how do I access that value? Keep in mind that the item has not been selected. It is merely highlighted as the mouse hovers over it. Thanks for your help.

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  • Just need someone familiar with HTTPClient to check over a piece of code

    - by jax
    here are two little helper methods I have made for downloading files. I have had to mix and match different tutorials of the web to get what I have here. Now is there anything that I have done blatantly wrong here? public static InputStream simplePostRequest(URL url, List<NameValuePair> postData) throws ClientProtocolException, IOException { DefaultHttpClient httpclient = new DefaultHttpClient(); HttpPost postMethod=new HttpPost(url.toExternalForm()); postMethod.setEntity(new UrlEncodedFormEntity(postData, HTTP.UTF_8)); HttpResponse response = httpclient.execute(postMethod); HttpEntity entity = response.getEntity(); return entity.getContent(); } public static InputStream simpleGetRequest(URL url, List<NameValuePair> queryString) throws ClientProtocolException, IOException { Uri.Builder uri = new Uri.Builder(); uri.path(url.getPath()); for(NameValuePair nvp: queryString) { uri.appendQueryParameter(nvp.getName(), nvp.getValue()); } DefaultHttpClient httpClient = new DefaultHttpClient(); HttpHost host = new HttpHost(url.getHost()); HttpResponse response = httpClient.execute(host, new HttpGet(uri.build().toString())); HttpEntity entity = response.getEntity(); return entity.getContent(); }

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  • Python: Serial Transmission

    - by Silent Elektron
    I have an image stack of 500 images (jpeg) of 640x480. I intend to make 500 pixels (1st pixels of all images) as a list and then send that via COM1 to FPGA where I do my further processing. I have a couple of questions here: How do I import all the 500 images at a time into python and how do i store it? How do I send the 500 pixel list via COM1 to FPGA? I tried the following: Converted the jpeg image to intensity values (each pixel is denoted by a number between 0 and 255) in MATLAB, saved the intensity values in a text file, read that file using readlines(). But it became too cumbersome to make the intensity value files for all the 500 images! Used NumPy to put the read files in a matrix and then pick the first pixel of all images. But when I send it, its coming like: [56, 61, 78, ... ,71, 91]. Is there a way to eliminate the [ ] and , while sending the data serially? Thanks in Advance! :)

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  • Don't serealize a especific data member , but DESEREALIZE, any chance???

    - by CrazyJoe
    Im using DataContractJsonSerializer to serealize this class: public class User { public string id { get; set; } public string name { get; set; } public string password { get; set; } public string email { get; set; } public bool is_broker { get; set; } public string branch_id { get; set; } public string created_at { get; set; } public string updated_at { get; set; } public UserGroup UserGroup {get;set;} public UserAddress UserAddress { get; set; } public List<UserContact> UserContact {get; set;} public User() { UserGroup = new UserGroup(); UserAddress = new UserAddress(); UserContact = new List<UserContact>(); } } The question is when i serealize to json , the property UserGroup is serealized, but i dont need this, i like to serealize to json whitout UserGroup property. Obs: When Deserealize it´s all fine to have UserGroup, i need that!! Any Trick ?????? Thanks!!!

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  • Creating a complex tree model in Qt

    - by Zeke
    I'm writing an IRC Client (yes another one). Long story short. I'm writing a Server dialogue that keeps a list of this: Identity Networks Channels Addresses I have 3 different list views that will be for the Networks, Channels and Addresses. When the user changes the Identity (combo box). The network listview will lookup all the networks for that specific Identity. After it loads up the Networks it will automatically select the first network and then load all the channels and addresses for that specific network. The problem is I want to have 3 views for 1 model, to minimise all the memory and the loading of data. So that it makes it much easier to manage and not do a bunch of work. If you'd look at QColumnView it's the same exact thing. But I don't need it to be on one exact page since the views are on entirely different tabs to make it easier to go through the Server dialogue. I'm wondering what will be the best way to go about handling this complexity. The information is stored in a SQLite database. I already have the classes written to extract and store it. Just the modelling is the painful part of this solution.

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  • How to add a service to the type descriptor context of a property grid in .Net?

    - by Jules
    I have an app that allows the user to choose an image, at design time, either as a straight image, or from an image list. All cool so far, except that this is not happening from the visual studio property browser, its happening from a property grid that is a part of a type editor. My problem is, both the image picker (actually resource picker), and the imagelist type converter rely on some design-time services to get the job done. In the case of imagelist, its the IReferenceService and in the case of the resource picker its a service called _DTE. In the first instance of an edit from the visual studio property browser, I could get a reference to these services but (1) how can I add them to the type descriptor context of my property grid? It would be better, for future proofing, if I could just copy a reference to all of the services in the type descriptor context. (2) Where does the property browser get these services from in the first place? ETA: I still don't know how to do it, but I now know it is possible. (1) Sub-class control and add a property whose type is an array of buttons. (2) Add it to a form. (3) Select the new control on the design service and edit the new property in the property browser. (4) The collection editor dialog pops-up (5) Add a button (6) Edit image and image list - the type editor and type converter, respectively, behave as they should.

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  • Sharing a COM port over TCP

    - by guinness
    What would be a simple design pattern for sharing a COM port over TCP to multiple clients? For example, a local GPS device that could transmit co-ordinates to remote hosts in realtime. So I need a program that would open the serial port and accept multiple TCP connections like: class Program { public static void Main(string[] args) { SerialPort sp = new SerialPort("COM4", 19200, Parity.None, 8, StopBits.One); Socket srv = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); srv.Bind(new IPEndPoint(IPAddress.Any, 8000)); srv.Listen(20); while (true) { Socket soc = srv.Accept(); new Connection(soc); } } } I would then need a class to handle the communication between connected clients, allowing them all to see the data and keeping it synchronized so client commands are received in sequence: class Connection { static object lck = new object(); static List<Connection> cons = new List<Connection>(); public Socket socket; public StreamReader reader; public StreamWriter writer; public Connection(Socket soc) { this.socket = soc; this.reader = new StreamReader(new NetworkStream(soc, false)); this.writer = new StreamWriter(new NetworkStream(soc, true)); new Thread(ClientLoop).Start(); } void ClientLoop() { lock (lck) { connections.Add(this); } while (true) { lock (lck) { string line = reader.ReadLine(); if (String.IsNullOrEmpty(line)) break; foreach (Connection con in cons) con.writer.WriteLine(line); } } lock (lck) { cons.Remove(this); socket.Close(); } } } The problem I'm struggling to resolve is how to facilitate communication between the SerialPort instance and the threads. I'm not certain that the above code is the best way forward, so does anybody have another solution (the simpler the better)?

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  • What should go in each MVVM triad?

    - by Harry
    OK, let's say I am creating a program that will list users contacts in a ListBox on the left side of the screen. When a user clicks on the contact, a bunch of messages or whatever appears in the main part of the window. Now my question is: how should the MVVM triads look? I have two models: Contact, and Message. The Contact model contains a list of Message models. Each ViewModel object will contain a single corresponding Model, right? And what about the Views? I have a "MainView" that is the main window, that will have things like the menu, toolbar etc. Do I put the ListBox in the MainView? My confusion is with what to put where; for example, what should the ContactView contain? Just a single instance of a contact? So the DataTemplate, ControlTemplate, context menus, styles etc for that single contact, and then just have a ListBox of them in the MainView...? Thanks.

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  • Vim: Making Auto-Completion Smarter

    - by Rafid K. Abdullah
    I use ctags, taglist, etc., to have auto completion in Vim. However, it is very limited compared to Visual Studio intellisense or Eclipse auto-completion. I am wondering whether it is possible to tune Vim to: Show auto-completion whenever . or - are typed. But only after some text that might be a variable (e.g. avoid showing auto completion after a number). Show function parameters when ( is typed. Stop removing the auto completion list when some delete all characters after . or -: When I enter a variable name, then press . or - to search for a certain member, I frequently have to delete all the characters I type after the . or -, but this makes Vim hide the auto completion list. I would like to keep it visible unless I press Esc. Showing related auto completion: When I type a variable and press ^X ^O, it usually shows me all the tags in the ctags file. I would like to have it showing only the tags related to the variable. Thanks for the help. EDIT: Some people are voting for this question, but no body seems to know the answer. So just wanted to mention that you don't have to provide a complete answer; partial answers to any of the mentioned points would be good also.

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  • Project euler problem 3 in haskell

    - by shk
    I'm new in Haskell and try to solve 3 problem from http://projecteuler.net/. The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ? My solution: import Data.List getD :: Int -> Int getD x = -- find deviders let deriveList = filter (\y -> (x `mod` y) == 0) [1 .. x] filteredList = filter isSimpleNumber deriveList in maximum filteredList -- Check is nmber simple isSimpleNumber :: Int -> Bool isSimpleNumber x = let deriveList = map (\y -> (x `mod` y)) [1 .. x] filterLength = length ( filter (\z -> z == 0) deriveList) in case filterLength of 2 -> True _ -> False I try to run for example: getD 13195 > 29 But when i try: getD 600851475143 I get error Exception: Prelude.maximum: empty list Why? Thank you @Barry Brown, I think i must use: getD :: Integer -> Integer But i get error: Couldn't match expected type `Int' with actual type `Integer' Expected type: [Int] Actual type: [Integer] In the second argument of `filter', namely `deriveList' In the expression: filter isSimpleNumber deriveList Thank you.

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  • Regular expression, excluding .. in suffix of email addy

    - by user1754700
    This is homework, I've been working on it for a while, I've done lots of reading and feel I have gotten pretty familiar with regex for a beginner. I am trying to find a regular expression for validating/invalidating a list of emails. There are two addresses which are giving me problems, I can't get them both to validate the correct way at the same time. I've gone through a dozen different expressions that work for all the other emails on the list but I can't get those two at the same time. First, the addresses. [email protected] - invalid [email protected] - valid The part of my expression which validates the suffix I originally started with @.+\\.[[a-z]0-9]+ And had a second pattern for checking some more invalid addresses and checked the email against both patterns, one checked for validity the other invalidity but my professor said he wanted it all in on expression. @[[\\w]+\\.[\\w]+]+ or @[\\w]+\\.[\\w]+ I've tried it written many, many different ways but I'm pretty sure I was just using different syntax to express these two expressions. I know what I want it to do, I want it to match a character class of "character+"."character+"+ The plus sign being at least one. It works for the invalid class when I only allow the character class to repeat one time(and obviously the ip doesn't get matched), but when I allow the character class to repeat itself it matches the second period even thought it isn't preceded by a character. I don't understand why.

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  • changing the serialization procedure for a graph of objects (.net framework)

    - by pierusch
    Hello I'm developing a scientific application using .net framework. The application depends heavily upon a large data structure (a tree like structure) that has been serialized using a standard binaryformatter object. The graph structure looks like this: <serializable()>Public class BigObjet inherits list(of smallObject) end class <serializable()>public class smallObject inherits list(of otherSmallerObjects) end class ... The binaryFormatter object does a nice job but it's not optimized at all and the entire data structure reaches around 100Mb on my filesystem. Deserialization works too but it's pretty slow (around 30seconds on my quad core). I've found a nice .dll on codeproject (see "optimizing serialization...") so I wrote a modified version of the classes above overriding the default serialization/deserialization procedure reaching very good results. The problem is this: I can't lose the data previosly serialized with the old version and I'd like to be able to use the new serialization/deserialization method. I have some ideas but I'm pretty sure someone will be able to give me a proper and better advice ! use an "helper" graph of objects who takes care of the entire serialization/deserialization procedure reading data from the old format and converting them into the classes I nedd. This could work but the binaryformatter "needs" to know the types being serialized so........ :( modify the "old" graph to include a modified version of serialization procedure...so I'll be able to deserialize old file and save them with the new format......this doesn't sound too good imho. well any help will be higly highly appreciated :)

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  • upgrading to spring 3.0 problem with interceptorNames

    - by mkoryak
    I am trying to upgrade to Spring 3.0 and i have the following issues: Finding the dependencies. People recommend using maven, but id rather not try to learn how to use maven/install it if the jars are available somewhere for download. The following bean declaration is now longer valid but i dont know how to fix it: <bean id="service" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces" value="com.service.SomeService" /> <property name="target"> <bean class="com.service.SomeServiceImpl"> </bean> </property> <property name="interceptorNames"> <list> <value>hibernateInterceptor</value> </list> </property> </bean> The complaint is that <property name="interceptorNames"> is no longer supported and should be done some other way

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  • Open source real life license examples: yours or others

    - by donpal
    I'm aware of the usual list of open source licenses, so I'm not even going to list it here. What I'd like to ask is about your open source projects (whether out or planned for the future), and why you're planning to choose a certain license over the other. Basically say I went for X license because I wanted Y and that other license didn't provide it for me. I understand that the language itself can make a difference in the choice of license: interpreted languages like PHP vs. compiled languages like Java. I'm mostly interested in hearing about PHP projects, but of course additional insights are welcome. You may even have chosen that particular language for a licensing reason. Ideally I want to hear answers from people who were involved in the actual project (i.e. your own project), because that usually means you've put some thought into the license yourself and understand the implications of that license. But examples of existing projects that aren't your own are OK. Please just say why you think that license was good/bad for them. But first-hand experience is preferred. Looking forward to hearing some informative input.

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  • Appengine JDO dataclasses to python model

    - by M.A. Cape
    Does anyone have tried to implement an app in GAE having both java and python? I have an existing app and my front end is in java. Now I want to use the existing datastore to be interfaced by python. My problem is i don't know how to define the relationships and model that would be equivalent to the one in java. I have tried the one-to-many relationship in python but when stored in the datastore, the fields are different than the one-to-many of java. My data classes are as follows. //one-to-many owned Parent Class public class Parent{ @PrimaryKey @Persistent private String unitID; //some other fields... @Persistent @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="dateCreated desc")) private List <Child> child; //methods & constructors were omitted } Child public class Child{ @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key uId; @Persistent private String name; /* etc... */ }

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  • Android: How to put ListView in XML?

    - by FloIancu
    I want to make a simple app that shows a list of contacts (name, surname). My code: package lista.android; import java.util.*; import android.app.ListActivity; import android.os.Bundle; import android.widget.*; class Contact{ String nume; String prenume; Contact(String nume, String prenume){ this.nume=nume; this.prenume=prenume; } public String toString(){ return prenume +" "+ nume; } } public class Lista1Activity extends ListActivity { /** Called when the activity is first created. */ ArrayList <Contact> lista; ArrayAdapter <Contact> adaptor; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); setListAdapter(adaptor); lista=new ArrayList<Contact>(); adaptor=new ArrayAdapter<Contact>(this, R.id.element, lista); adaugaContact("Florian", "Iancu"); adaugaContact("Ioana", "Constantina"); } public void adaugaContact(String nume, String prenume){ lista.add(new Contact(nume, prenume)); adaptor.notifyDataSetChanged(); } } In the XML I have the LinearLayout and a TextView that is the list element. When I run it, the simulator says "Sorry, the application [...] has stopped unexpectedly. Please try again." The LogCat tells me I have to have a ListView whose id is android.R.id.lista. If I create a random ListView field in the XML file and give it the "lista" id, it still doesn't work. How to I call that ListView from XML to match something in my Java code? In other words, I know I'm wrong, but where and how do I fix it?

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  • How do I make a serialization class for this?

    - by chobo2
    I have something like this (sorry for the bad names) <root xmlns="http://www.domain.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.Domain.com Schema.xsd> <product></product> <SomeHighLevelElement> <anotherElment> <lowestElement> </lowestElement> </anotherElment> </SomeHighLevelElement> </root> I have something like this for my class public class MyClass { public MyClass() { ListWrapper= new List<UserInfo>(); } public string product{ get; set; } public List<SomeHighLevelElement> ListWrapper{ get; set; } } public class SomeHighLevelElement { public string lowestElement{ get; set; } } But I don't know how to write the code for the "anotherElement" not sure if I have to make another wrapper around it. Edit I know get a error in my actual xml file. I have this in my tag xmlns="http://www.domain.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.Domain.com Schema.xsd Throws an exception on the root line saying there was a error with this stuff. So I don't know if it is mad at the schemaLocation since I am using local host right now or what.

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  • SELECT * FROM <table> BETWEEN <value typed in a JTextField> AND <idem>

    - by Rodrigo Sieja Bertin
    In this part of the program, the JInternalFrame file FrmMovimento, I made a button called Visualizar ("View"). Based on what we type on the text fields, it must show the interval the user defined. There are these JTextFields: Code from: _ To: _ Asset: _ And these JFormattedTextFields: Date from: _ To: _ There are registers appearing already in the JDesktopPane from JInternalFrame FrmListarMov, if I use another SELECT statement selecting all registers, for example. But not if I type as I did in the title: public List<MovimentoVO> Lista() throws ErroException, InformacaoException{ List<MovimentoVO> listaMovimento = new ArrayList<> (); try { MySQLDAO.getInstancia().setAutoCommit(false); try (PreparedStatement stmt = MySQLDAO.getInstancia().prepareStatement( "SELECT * FROM Cadastro2 WHERE Codigo BETWEEN "+ txtCodDeMov +" AND "+ txtCodAteMov +";") { ResultSet registro = stmt.executeQuery(); while(registro.next()){ MovimentoVO Movimento = new MovimentoVO(); Movimento.setCodDeMov(registro.getInt(1)); Movimento.setCodAteMov(registro.getInt(2)); Movimento.setAtivoMov(registro.getString(3)); Movimento.setDataDeMov(registro.getString(4)); Movimento.setDataAteMov(registro.getString(5)); listaMovimento.add(Movimento); } } } catch (SQLException ex) { throw new ErroException(ex.getMessage()); } catch (InformacaoException ex) { throw ex; } return listaMovimento; } In the SELECT line, txtCodDeMov is how I named the JTextField of "Code from" and txtCodAtemov is how I named the JTextField of the first "To". Oh, I'm using NetBeans 7.1.2 (Build 201204101705) and MySQL Ver 14.14 Distrib 5.1.63 in a Linux Mint 12 64-bits.

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  • Java: design for using many executors services and only few threads

    - by Guillaume
    I need to run in parallel multiple threads to perform some tests. My 'test engine' will have n tests to perform, each one doing k sub-tests. Each test result is stored for a later usage. So I have n*k processes that can be ran concurrently. I'm trying to figure how to use the java concurrent tools efficiently. Right now I have an executor service at test level and n executor service at sub test level. I create my list of Callables for the test level. Each test callable will then create another list of callables for the subtest level. When invoked a test callable will subsequently invoke all subtest callables test 1 subtest a1 subtest ...1 subtest k1 test n subtest a2 subtest ...2 subtest k2 call sequence: test manager create test 1 callable test1 callable create subtest a1 to k1 testn callable create subtest an to kn test manager invoke all test callables test1 callable invoke all subtest a1 to k1 testn callable invoke all subtest an to kn This is working fine, but I have a lot of new treads that are created. I can not share executor service since I need to call 'shutdown' on the executors. My idea to fix this problem is to provide the same fixed size thread pool to each executor service. Do you think it is a good design ? Do I miss something more appropriate/simple for doing this ?

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  • Is Assert.Fail() considered bad practice?

    - by Mendelt
    I use Assert.Fail a lot when doing TDD. I'm usually working on one test at a time but when I get ideas for things I want to implement later I quickly write an empty test where the name of the test method indicates what I want to implement as sort of a todo-list. To make sure I don't forget I put an Assert.Fail() in the body. When trying out xUnit.Net I found they hadn't implemented Assert.Fail. Of course you can always Assert.IsTrue(false) but this doesn't communicate my intention as well. I got the impression Assert.Fail wasn't implemented on purpose. Is this considered bad practice? If so why? @Martin Meredith That's not exactly what I do. I do write a test first and then implement code to make it work. Usually I think of several tests at once. Or I think about a test to write when I'm working on something else. That's when I write an empty failing test to remember. By the time I get to writing the test I neatly work test-first. @Jimmeh That looks like a good idea. Ignored tests don't fail but they still show up in a separate list. Have to try that out. @Matt Howells Great Idea. NotImplementedException communicates intention better than assert.Fail() in this case @Mitch Wheat That's what I was looking for. It seems it was left out to prevent it being abused in another way I abuse it.

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  • How to add files to a document library in a site definition in SharePoint 2007?

    - by jaloplo
    Hi all, I'm doing a site definition for SharePoint 2007. When the site is created, a document library called "Folder2" is created also. Now, I need to add some documents to this document library and appear as items in the document library standard views. My code is: <Lists> <List FeatureId="00bfea71-e717-4e80-aa17-d0c71b360101" Type="101" Title="Folder2" Url="Folder2"> <Data> <Rows> <Row> <Field Name="Name">MyFile.txt</Field> <Field Name="Title">MyFile.txt</Field> <Field Name="FileLeafRef">MyFile.txt</Field> </Row> </Rows> </Data> </List> </Lists> When I see the items of the Document Library there is one element with title "1_". Does anybody know how to add files in a site definition? The onet.xml I used is the same as blank site. Thanks!!!

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  • Will my LinqToSql execution be deffered if i filter with IEnumerable<T> instead of IQueryable<T>?

    - by cottsak
    I have been using these common EntityObjectFilters as a "pipes and filters" way to query from a collection a particular item with an ID: public static class EntityObjectFilters { public static T WithID<T>(this IQueryable<T> qry, int ID) where T : IEntityObject { return qry.SingleOrDefault<T>(item => item.ID == ID); } public static T WithID<T>(this IList<T> list, int ID) where T : IEntityObject { return list.SingleOrDefault<T>(item => item.ID == ID); } } ..but i wondered to myself: "can i make this simpler by just creating an extension for all IEnumerable<T> types"? So i came up with this: public static class EntityObjectFilters { public static T WithID<T>(this IEnumerable<T> qry, int ID) where T : IEntityObject { return qry.SingleOrDefault<T>(item => item.ID == ID); } } Now while this appears to yield the same result, i want to know that when applied to IQueryable<T>s will the expression tree be passed to LinqToSql for evaluating as SQL code or will my qry be evaluated in it's entirety first, then iterated with Funcs? I'm suspecting that (as per Richard's answer) the latter will be true which is obviously what i don't want. I want the same result, but the added benefit of the delayed SQL execution for IQueryable<T>s. Can someone confirm for me what will actually happen and provide simple explanation as to how it would work?

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  • Delivering activity feed items in a moderately scalable way

    - by sotangochips
    The application I'm working on has an activity feed where each user can see their friends' activity (much like Facebook). I'm looking for a moderately scalable way to show a given users' activity stream on the fly. I say 'moderately' because I'm looking to do this with just a database (Postgresql) and maybe memcached. For instance, I want this solution to scale to 200k users each with 100 friends. Currently, there is a master activity table that stores the rendered html for the given activity (Jim added a friend, George installed an application, etc.). This master activity table keeps the source user, the html, and a timestamp. Then, there's a separate ('join') table that simply keeps a pointer to the person who should see this activity in their friend feed, and a pointer to the object in the main activity table. So, if I have 100 friends, and I do 3 activities, then the join table will then grow to 300 items. Clearly this table will grow very quickly. It has the nice property, though, that fetching activity to show to a user takes a single (relatively) inexpensive query. The other option is to just keep the main activity table and query it by saying something like: select * from activity where source_user in (1, 2, 44, 2423, ... my friend list) This has the disadvantage that you're querying for users who may never be active, and as your friend list grows, this query can get slower and slower. I see the pros and the cons of both sides, but I'm wondering if some SO folks might help me weigh the options and suggest one way or they other. I'm also open to other solutions, though I'd like to keep it simple and not install something like CouchDB, etc. Many thanks!

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  • Macro and array crossing

    - by Thomas
    I am having a problem with a lisp macro. I would like to create a macro which generate a switch case according to an array. Here is the code to generate the switch-case: (defun split-elem(val) `(,(car val) ',(cdr val))) (defmacro generate-switch-case (var opts) `(case ,var ,(mapcar #'split-elem opts))) I can use it with a code like this: (generate-switch-case onevar ((a . A) (b . B))) But when I try to do something like this: (defparameter *operators* '((+ . OPERATOR-PLUS) (- . OPERATOR-MINUS) (/ . OPERATOR-DIVIDE) (= . OPERATOR-EQUAL) (* . OPERATOR-MULT))) (defmacro tokenize (data ops) (let ((sym (string->list data))) (mapcan (lambda (x) (generate-switch-case x ops)) sym))) (tokenize data *operators*) I got this error: *** - MAPCAR: A proper list must not end with OPS. But I don't understand why. When I print the type of ops I get SYMBOL I was expecting CONS, is it related? Also, for my function tokenize how many times the lambda is evaluated (or the macro expanded)?

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