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  • Regular expression for Regular expressions?

    - by kavoir.com
    I have an app that enables the user to input a regular expression, my question is how to check against any input of regular expressions and make sure they are valid ones because if they are not there will be preg_match errors. I don't want to use the '@' before preg_match, so if there's a way to check the validity of the user input of regular expressions that'd be great. The regular expression system of PHP seems to be rather too complicated for me to come up with a regular expression for them. Any idea or any alternatives would be possible in achieving this?

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  • Double interpolation of regular expressions in Perl

    - by tomdee
    I have a Perl program that stores regular expressions in configuration files. They are in the form: regex = ^/d+$ Elsewhere, the regex gets parsed from the file and stored in a variable - $regex. I then use the variable when checking the regex, e.g. $lValid = ($valuetocheck =~ /$regex/); I want to be able to include perl variables in the config file, e.g. regex = ^\d+$stored_regex$ But I can't work out how to do it. When regular expressions are parsed by Perl they get interpreted twice. First the variables are expanded, and then the the regular expression itself is parsed. What I need is a three stage process: First interpolate $regex, then interpolate the variables it contains and then parse the resulting regular expression. Both the first two interpolations need to be "regular expression aware". e.g. they should know that the string contain $ as an anchor etc... Any ideas?

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  • Lua pattern matching vs. regular expressions

    - by harald
    hello, i'm currently learning lua. regarding pattern-matching in lua i found the following sentence in the lua documentation on lua.org: Nevertheless, pattern matching in Lua is a powerful tool and includes some features that are difficult to match with standard POSIX implementations. as i'm familiar with posix regular expressions i would like to know if there are any common samples where lua pattern matching is "better" compared to regular expression -- or did i misinterpret the sentence? and if there are any common examples: why is any of pattern-matching vs. regular expressions better suited? thanks very much, harald

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  • lambda expressions in C#?

    - by Matt
    Hey I'm rather new to these could someone explain the significance (of the following code) or prehaps give a link to some useful information on lambda expressions? I encounter the following code in a test and I am wondering why someone would do this: foo.MyEvent += (o, e) => { fCount++; Console.WriteLine(fCount); }; foo.MyEvent -= (o, e) => { fCount++; Console.WriteLine(fCount); }; My instinct tells me it is something simple and not a mistake, but I don't know enough about these expressions to understand why this is being done. Regards,

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  • Regular expressions in findstr

    - by Johannes Rössel
    I'm doing a little string validation with findstr and its /r flag to allow for regular expressions. In particular I'd like to validate integers. The regex ^[0-9][0-9]*$ worked fine for non-negative numbers but since I now support negative numbers as well I tried ^([1-9][0-9]*|0|-[1-9][0-9]*)$ for either positive or negative integers or zero. The regex works fine theoretically. I tested it in PowerShell and it matches what I want. However, with findstr /r /c:"^([1-9][0-9]*|0|-[1-9][0-9]*)$" it doesn't. While I know that findstr doesn't have the most advanced regex support (even below Notepad++ which is probably quite an achievement), I would have expected such simple expressions to work. Any ideas what I'm doing wrong here?

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  • Code Golf: Evaluating Mathematical Expressions

    - by Noldorin
    Challenge Here is the challenge (of my own invention, though I wouldn't be surprised if it has previously appeared elsewhere on the web). Write a function that takes a single argument that is a string representation of a simple mathematical expression and evaluates it as a floating point value. A "simple expression" may include any of the following: positive or negative decimal numbers, +, -, *, /, (, ). Expressions use (normal) infix notation. Operators should be evaluated in the order they appear, i.e. not as in BODMAS, though brackets should be correctly observed, of course. The function should return the correct result for any possible expression of this form. However, the function does not have to handle malformed expressions (i.e. ones with bad syntax). Examples of expressions: 1 + 3 / -8 = -0.5 (No BODMAS) 2*3*4*5+99 = 219 4 * (9 - 4) / (2 * 6 - 2) + 8 = 10 1 + ((123 * 3 - 69) / 100) = 4 2.45/8.5*9.27+(5*0.0023) = 2.68... Rules I anticipate some form of "cheating"/craftiness here, so please let me forewarn against it! By cheating, I refer to the use of the eval or equivalent function in dynamic languages such as JavaScript or PHP, or equally compiling and executing code on the fly. (I think my specification of "no BODMAS" has pretty much guaranteed this however.) Apart from that, there are no restrictions. I anticipate a few Regex solutions here, but it would be nice to see more than just that. Now, I'm mainly interested in a C#/.NET solution here, but any other language would be perfectly acceptable too (in particular, F# and Python for the functional/mixed approaches). I haven't yet decided whether I'm going to accept the shortest or most ingenious solution (at least for the language) as the answer, but I would welcome any form of solution in any language, except what I've just prohibited above! My Solution I've now posted my C# solution here (403 chars). Update: My new solution has beaten the old one significantly at 294 chars, with the help of a bit of lovely regex! I suspected that this will get easily beaten by some of the languages out there with lighter syntax (particularly the funcional/dynamic ones), and have been proved right, but I'd be curious if someone could beat this in C# still. Update I've seen some very crafty solutions already. Thanks to everyone who has posted one. Although I haven't tested any of them yet, I'm going to trust people and assume they at least work with all of the given examples. Just for the note, re-entrancy (i.e. thread-safety) is not a requirement for the function, though it is a bonus. Format Please post all answers in the following format for the purpose of easy comparison: Language Number of characters: ??? Fully obfuscated function: (code here) Clear/semi-obfuscated function: (code here) Any notes on the algorithm/clever shortcuts it takes.

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  • Using numeric_limits::max() in constant expressions

    - by FireAphis
    Hello, I would like to define inside a class a constant which value is the maximum possible int. Something like this: class A { ... static const int ERROR_VALUE = std::numeric_limits<int>::max(); ... } This declaration fails to compile with the following message: numeric.cpp:8: error: 'std::numeric_limits::max()' cannot appear in a constant-expression numeric.cpp:8: error: a function call cannot appear in a constant-expression I understand why this doesn't work, but two things look weird to me: It seems to me a natural decision to use the value in constant expressions. Why did the language designers decide to make max() a function thus not allowing this usage? The spec claims in 18.2.1 that For all members declared static const in the numeric_limits template, specializations shall define these values in such a way that they are usable as integral constant expressions. Doesn't it mean that I should be able to use it in my scenario and doesn't it contradict the error message? Thank you.

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  • How to query with the datetime value using LINQ to XML ?

    - by Shailesh Jaiswal
    I am developing window phone 7 application in silverlight. I am new to the silverlight. I am also new to LINQ to XML. In my application the user select the date & submit some transaction details into the application. The details gets stored in XML File. I am using the custom date control in my application for the date selection as follows private void DatePicker_ValueChanged(object sender, DateTimeValueChangedEventArgs e) { AppObj = Application.Current as App; AppObj.date = (DateTime)EntryDate.Value; } Then the value of AppObj.date gets stored in the XML file. Sometimes I use the DateTime.Now to store the date in the XML File. Now I want to generate the report of submitted transaction details by querying through LINQ to XML. I want to generate the report for today's date, current week & current month. For this purpose I am using the following code public void GetTransactionObjects(String strXMLFile, DateTime VDateTime) { XDocument doc = null; XMLFileManager XMLDocObj = new XMLFileManager(); doc = XMLDocObj.LoadXMLFile(strXMLFile); var vTransaction = from s in doc.Descendants("Transaction") .Where(x => x.Element("Current_Date").Value == VDateTime.ToShortDateString()) select new Transaction(s); this.Clear(); AddRange(vTransaction); } The Transaction class contains the following constructor. public Transaction(XElement xElement) { Transaction_ID = Convert.ToInt32(xElement.Element("Transaction_ID").Value.ToString()); TransactionType_ID = Convert.ToInt32(xElement.Element("TransactionType_ID").Value.ToString()); Alphabet_ID = Convert.ToInt32(xElement.Element("Alphabet_ID").Value.ToString()); ID = Convert.ToInt32(xElement.Element("ID").Value.ToString()); SubCategory_ID = Convert.ToInt32(xElement.Element("SubCategory_ID").Value.ToString()); Item_ID = Convert.ToInt32(xElement.Element("Item_ID").Value.ToString()); Currency_ID = Convert.ToInt32(xElement.Element("Currency_ID").Value.ToString()); InputTypeMethod_ID = Convert.ToInt32(xElement.Element("InputTypeMethod_ID").Value.ToString()); Principle = Convert.ToInt32(xElement.Element("InputTypeMethod_ID").Value.ToString()); Interest = Convert.ToInt32(xElement.Element("Interest").Value.ToString()); ROI = Convert.ToInt32(xElement.Element("InputTypeMethod_ID").Value.ToString()); Amount = Convert.ToInt32(xElement.Element("InputTypeMethod_ID").Value.ToString()); Current_Date = Convert.ToDateTime(xElement.Element("Current_Date").Value.ToString()); } In the XML File the value gets stored for date & time. The value gets stored as follows 0 0 3 0 0 0 3 0 0 0 0 5000 2010-12-31T18:08:23.433+05:30 Look at the node <Current_Date>2010-12-31T18:08:23.433+05:30</Current_Date> The date format is yyyy-mm-dd. Now how should I write the following query to get all the submitted transaction details for today's date ? var vTransaction = from s in doc.Descendants("Transaction") .Where(x => x.Element("Current_Date").Value == VDateTime.ToShortDateString()) select new Transaction(s); Similarly how should I write the query to get all the transaction details for the current week & current month? Can you please provide me any code or link through which I can resolve the above issue ? If I am doing anything wrong then please guide me.

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  • .NET Regular expressions on bytes instead of chars

    - by brickner
    Hi, I'm trying to do some parsing that will be easier using regular expressions. The input is an array (or enumeration) of bytes. I don't want to convert the bytes to chars for the following reasons: Computation efficiency Memory consumption efficiency Some non-printable bytes might be complex to convert to chars. Not all the bytes are printable. So I can't use Regex. The only solution I know, is using Boost.Regex (which works on bytes - C chars), but this is a C++ library that wrapping using C++/CLI will take considerable work. How can I use regular expressions on bytes in .NET directly, without working with .NET strings and chars? Thank you.

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  • Add values to standard expressions list in Regular Expression Editor dialog in VS 2008

    - by Alex
    Hi. In the "Regular Expression Editor" dialog in VS 2008 ( or 2005 for this matter ) , there is a list of "standard expressions" like : "French phone number" , "French postal code" etc.. And of course there is an option to select a "Custom" and then enter your own regular expression. Well.. I want to add a predefined expressions to that list . Like : "Israeli phone number" . I don't want to enter it every time by selecting a custom value . I want my developers in the team available items for them to choose. Anyone knows how to alter that list ? I've found some question about it on the web - and the answer given is that it's not possible . But that was at 2004. Anyone ?!?! Thanks.

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  • Insert string from database into an aspx and have databinding expressions within that text evaluated

    - by Christopher Edwards
    Well, as you can see I want something quick-and-dirty! How can I get a string from a db that has aspx databinding syntax in it and have the databinding expressions evaluated? So I have text such as this stored in the DB:- Hello <%=User.Name %> I haven't seen you since <%=User.LastVisit %> And I want it to be inserted here say:- ... <body> <form id="form1" runat="server"> <div> <asp:FormView ID="FormView1" DataSourceID="DataSource1" runat="server"> <ItemTemplate> <-- insert stuff here! --> ... But with the databinding expressions evaluated. I'd rather not build a full parsing, templating and evaluation engine...

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  • php array regular expressions

    - by bell
    I am using regular expressions in php to match postcodes found in a string. The results are being returned as an array, I was wondering if there is any way to assign variables to each of the results, something like $postcode1 = first match found $postcode2 = second match found here is my code $html = "some text here bt123ab and another postcode bt112cd"; preg_match_all("/([a-zA-Z]{2})([0-9]{2,3})([a-zA-Z]{2})/", $html, $matches, PREG_SET_ORDER); foreach ($matches as $val) { echo $val[0]; } I am very new to regular expressions and php, forgive me if this is a stupid question. Thanks in advance

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  • template expressions and visual studio 2005 c++

    - by chris
    I'd like to build the olb3d library with my visual studio 2005 compiler but this failes due to template errors. To be more specific, the following expression seem to be a problem: void function(T u[Lattice::d]) On the website of the project is stated that prpably my compiler is not capable of such complicated template expressions - one should use the gcc 3.4.1. My question is now if there is a way to upgrade my vs c++ compiler so it can handle template expressions on the level as the gcc 3.4.1? Maybe it helps if I get a newer version of visual studio? Cheers C.

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  • LINQ-like or SQL-like DSL for end-users to run queries to select (not modify) data?

    - by Mark Rushakoff
    For a utility I'm working on, the client would like to be able to generate graphic reports on the data that has been collected. I can already generate a couple canned graphs (using ZedGraph, which is a very nice library); however, the utility would be much more flexible if the graphs were more programmable or configurable by the end-user. TLDR version I want users to be able to use something like SQL to safely extract and select data from a List of objects that I provide and can describe. What free tools or libraries will help me accomplish this? Full version I've given thought to using IronPython, IronRuby, and LuaInterface, but frankly they're all a bit overpowered for what I want to do. My classes are fairly simple, along the lines of: class Person: string Name; int HeightInCm; DateTime BirthDate; Weight[] WeighIns; class Weight: int WeightInKg; DateTime Date; Person Owner; (exact classes have been changed to protect the innocent). To come up with the data for the graph, the user will choose whether it's a bar graph, scatter plot, etc., and then to actually obtain the data, I would like to obtain some kind of List from the user simply entering something SQL-ish along the lines of SELECT Name, AVG(WeighIns) FROM People SELECT WeightInKg, Owner.HeightInCm FROM Weights And as a bonus, it would be nice if you could actually do operations as well: SELECT WeightInKg, (Date - Owner.BirthDate) AS Age FROM Weights The DSL doesn't have to be compliant SQL in any way; it doesn't even have to resemble SQL, but I can't think of a more efficient descriptive language for the task. I'm fine filling in blanks; I don't expect a library to do everything for me. What I would expect to exist (but haven't been able to find in any way, shape, or form) is something like Fluent NHibernate (which I am already using in the project) where I can declare a mapping, something like var personRequest = Request<Person>(); personRequest.Item("Name", (p => p.Name)); personRequest.Item("HeightInCm", (p => p.HeightInCm)); personRequest.Item("HeightInInches", (p => p.HeightInCm * CM_TO_INCHES)); // ... var weightRequest = Request<Weight>(); weightRequest.Item("Owner", (w => w.Owner), personRequest); // Indicate a chain to personRequest // ... var people = Table<Person>("People", GetPeopleFromDatabase()); var weights = Table<Weight>("Weights", GetWeightsFromDatabase()); // ... TryRunQuery(userInputQuery); LINQ is so close to what I want to do, but AFAIK there's no way to sandbox it. I don't want to expose any unnecessary functionality to the end user; meaning I don't want the user to be able to send in and process: from p in people select (p => { System.IO.File.Delete("C:\\something\\important"); return p.Name }) So does anyone know of any free .NET libraries that allow something like what I've described above? Or is there some way to sandbox LINQ? cs-script is close too, but it doesn't seem to offer sandboxing yet either. I'd be hesitant to expose the NHibernate interface either, as the user should have a read-only view of the data at this point in the usage. I'm using C# 3.5, and pure .NET solutions would be preferred. The bottom line is that I'm really trying to avoid writing my own parser for a subset of SQL that would only apply to this single project.

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  • Read XML Files using LINQ to XML and Extension Methods

    - by psheriff
    In previous blog posts I have discussed how to use XML files to store data in your applications. I showed you how to read those XML files from your project and get XML from a WCF service. One of the problems with reading XML files is when elements or attributes are missing. If you try to read that missing data, then a null value is returned. This can cause a problem if you are trying to load that data into an object and a null is read. This blog post will show you how to create extension methods to detect null values and return valid values to load into your object. The XML Data An XML data file called Product.xml is located in the \Xml folder of the Silverlight sample project for this blog post. This XML file contains several rows of product data that will be used in each of the samples for this post. Each row has 4 attributes; namely ProductId, ProductName, IntroductionDate and Price. <Products>  <Product ProductId="1"           ProductName="Haystack Code Generator for .NET"           IntroductionDate="07/01/2010"  Price="799" />  <Product ProductId="2"           ProductName="ASP.Net Jumpstart Samples"           IntroductionDate="05/24/2005"  Price="0" />  ...  ...</Products> The Product Class Just as you create an Entity class to map each column in a table to a property in a class, you should do the same for an XML file too. In this case you will create a Product class with properties for each of the attributes in each element of product data. The following code listing shows the Product class. public class Product : CommonBase{  public const string XmlFile = @"Xml/Product.xml";   private string _ProductName;  private int _ProductId;  private DateTime _IntroductionDate;  private decimal _Price;   public string ProductName  {    get { return _ProductName; }    set {      if (_ProductName != value) {        _ProductName = value;        RaisePropertyChanged("ProductName");      }    }  }   public int ProductId  {    get { return _ProductId; }    set {      if (_ProductId != value) {        _ProductId = value;        RaisePropertyChanged("ProductId");      }    }  }   public DateTime IntroductionDate  {    get { return _IntroductionDate; }    set {      if (_IntroductionDate != value) {        _IntroductionDate = value;        RaisePropertyChanged("IntroductionDate");      }    }  }   public decimal Price  {    get { return _Price; }    set {      if (_Price != value) {        _Price = value;        RaisePropertyChanged("Price");      }    }  }} NOTE: The CommonBase class that the Product class inherits from simply implements the INotifyPropertyChanged event in order to inform your XAML UI of any property changes. You can see this class in the sample you download for this blog post. Reading Data When using LINQ to XML you call the Load method of the XElement class to load the XML file. Once the XML file has been loaded, you write a LINQ query to iterate over the “Product” Descendants in the XML file. The “select” portion of the LINQ query creates a new Product object for each row in the XML file. You retrieve each attribute by passing each attribute name to the Attribute() method and retrieving the data from the “Value” property. The Value property will return a null if there is no data, or will return the string value of the attribute. The Convert class is used to convert the value retrieved into the appropriate data type required by the Product class. private void LoadProducts(){  XElement xElem = null;   try  {    xElem = XElement.Load(Product.XmlFile);     // The following will NOT work if you have missing attributes    var products =         from elem in xElem.Descendants("Product")        orderby elem.Attribute("ProductName").Value        select new Product        {          ProductId = Convert.ToInt32(            elem.Attribute("ProductId").Value),          ProductName = Convert.ToString(            elem.Attribute("ProductName").Value),          IntroductionDate = Convert.ToDateTime(            elem.Attribute("IntroductionDate").Value),          Price = Convert.ToDecimal(elem.Attribute("Price").Value)        };     lstData.DataContext = products;  }  catch (Exception ex)  {    MessageBox.Show(ex.Message);  }} This is where the problem comes in. If you have any missing attributes in any of the rows in the XML file, or if the data in the ProductId or IntroductionDate is not of the appropriate type, then this code will fail! The reason? There is no built-in check to ensure that the correct type of data is contained in the XML file. This is where extension methods can come in real handy. Using Extension Methods Instead of using the Convert class to perform type conversions as you just saw, create a set of extension methods attached to the XAttribute class. These extension methods will perform null-checking and ensure that a valid value is passed back instead of an exception being thrown if there is invalid data in your XML file. private void LoadProducts(){  var xElem = XElement.Load(Product.XmlFile);   var products =       from elem in xElem.Descendants("Product")      orderby elem.Attribute("ProductName").Value      select new Product      {        ProductId = elem.Attribute("ProductId").GetAsInteger(),        ProductName = elem.Attribute("ProductName").GetAsString(),        IntroductionDate =            elem.Attribute("IntroductionDate").GetAsDateTime(),        Price = elem.Attribute("Price").GetAsDecimal()      };   lstData.DataContext = products;} Writing Extension Methods To create an extension method you will create a class with any name you like. In the code listing below is a class named XmlExtensionMethods. This listing just shows a couple of the available methods such as GetAsString and GetAsInteger. These methods are just like any other method you would write except when you pass in the parameter you prefix the type with the keyword “this”. This lets the compiler know that it should add this method to the class specified in the parameter. public static class XmlExtensionMethods{  public static string GetAsString(this XAttribute attr)  {    string ret = string.Empty;     if (attr != null && !string.IsNullOrEmpty(attr.Value))    {      ret = attr.Value;    }     return ret;  }   public static int GetAsInteger(this XAttribute attr)  {    int ret = 0;    int value = 0;     if (attr != null && !string.IsNullOrEmpty(attr.Value))    {      if(int.TryParse(attr.Value, out value))        ret = value;    }     return ret;  }   ...  ...} Each of the methods in the XmlExtensionMethods class should inspect the XAttribute to ensure it is not null and that the value in the attribute is not null. If the value is null, then a default value will be returned such as an empty string or a 0 for a numeric value. Summary Extension methods are a great way to simplify your code and provide protection to ensure problems do not occur when reading data. You will probably want to create more extension methods to handle XElement objects as well for when you use element-based XML. Feel free to extend these extension methods to accept a parameter which would be the default value if a null value is detected, or any other parameters you wish. NOTE: You can download the complete sample code at my website. http://www.pdsa.com/downloads. Choose “Tips & Tricks”, then "Read XML Files using LINQ to XML and Extension Methods" from the drop-down. Good Luck with your Coding,Paul D. Sheriff  

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  • LINQ, "Argument types do not match" error, what does it mean, how do I address it?

    - by Biff MaGriff
    Hello, I'm new to linq and I'm trying to databind to an anonymous type. I'm using SubSonic 3.0 as my DAL. I'm doing a select from 2 tables like so var myDeal = (from u in db.Users select new { UserID = u.UserID, UserRoleID = (from ur in u.UserRoles where u.UserRoleID == ur.UserRoleID select ur).FirstOrDefault().UserRoleID }); foreach (var v in myDeal) //dies first time here { } Then when I databind or try to iterate through the collection I get the "Argument types do not match" error during run time. I'm not sure what is going on here.

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  • Linq to Sql saying that item by 'Customer' already exists. Choose a different name.

    - by Anthony Potts
    I have been going round and round with a linq to sql file while using svn for quite some time. The latest is that my dbml file shows as having an error which states that An item named "Customer" already exists. Please choose a different name. And then it repeats that again. In fact, it says it for almost every object. What is my fix? I have tried renaming the one named Customer, but that didn't fix it. I don't know where to go to fix this. I went to the .dbml file and don't see any duplication, and I went to the .dbml.layout file and didn't see any duplication there either.

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  • Reading XML using XDocument & Linq - check if element is NULL?

    - by adchased
    I'm using LINQ together with XDocument to read a XML File. This is the code: XDocument xml = XDocument.Load(filename); var q = from b in xml.Descendants("product") select new { name = b.Element("name").Value, price = b.Element("price").Value, extra = b.Element("extra1").Value, deeplink = b.Element("deepLink").Value }; Now the problem is, the extra1 field is not always present. There are items in the XML file without that node. If that happens it's crashing with a NullReferenceException. Is there any possibility to include a "check if null" so I can prevent it from crashing?

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  • How do I get Linq-to-SQL to refresh its local copy of a database record?

    - by Gary McGill
    Suppose I have an Orders table in my database and a corresponding model class generated by the VS2008 "Linq to SQL Classes" designer. Suppose I also have a stored procedure (ProcessOrder) in my database that I use to do some processing on an order record. If I do the following: var order = dataContext.Orders.Where(o => o.id == orderId).First(); // More code here dataContext.ProcessOrder(orderId); order.Status = "PROCESSED"; dataContext.SubmitChanges(); ...then I'll get a concurrency violation if the ProcessOrder stored proc has modified the order (which is of course very likely), because L2S will detect that the order record has changed, and will fail to submit the changes to that order. That's all fairly logical, but what if I want to update the order record after calling the stored proc? How do I tell L2S to forget about its cached copy and refresh it from the DB?

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  • Finding if a target number is the sum of two numbers in an array via LINQ and get the and Indices

    - by Dr.H
    Hello I am new to Linq , I found this thread which explain 90% of what I need http://stackoverflow.com/questions/2331882?tab=newest#tab-top , thanks "pdr" but what I need is to get the Indices too , here is my modification I get the index of the first number but I don't know how to get the index of the second number int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; var result = from item in numbers.Select((n1, idx) => new { n1,idx, shortList = numbers.Take(idx) }) from n2 in item.shortList where item.n1 + n2 == 7 select new { nx1 = item.n1,index1=item.idx, nx2=n2 };

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  • Query data using LINQ to SQL and Entity Framework with foreign key? (Help me please)

    - by The Wind
    Hello! There is a problem I need help with your query on the data using LINQ to SQL and Entity Framework (I'm using Visual Studio 2010). My picure here: http://img.tamtay.vn/files/photo2/2010/5/28/10/962/4bff3a3b_1093f58f_untitled-1.gif I have three tables: tbl NewsDetails tblNewsCategories tblNewsInCategories (See screen 1 in my picture) Now, I want to retrieve records in the tblNewsDetails table, with condition: CategoryId=1, as the following results: (See screen 2 in my picture) But NewsID and CategoryId in tblNewsInCategories table is two foreign key, I do not see them and I do not know how to use them in your code. My code has errors: (See screen 3 in my picture) Please help me. Thanks! (I am a new member, should not have the right to insert images)

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  • How can I subsample data from a time series with LINQ to SQL?

    - by Chris Farmer
    I have a database table full of time points and experimental values at those time points. I need to retrieve the values for an experiment and create a thumbnail image showing an XY plot of its data. Because the actual data set for each experiment is potentially 100,000 data points and my image is only 100 pixels wide, I want to sample the data before creating the image. My current query (which retrieves all the data without sampling) is something simple like this: var points = from p in db.DataPoints where p.ExperimentId == myExperimentId orderby p.Time select new { X = p.Time, Y = p.Value } So, how can I best take every nth point from my result set in a LINQ to SQL query?

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  • How do I improve the efficiency of the queries executed by this generic Linq-to-SQL data access clas

    - by Lee D
    Hi all, I have a class which provides generic access to LINQ to SQL entities, for example: class LinqProvider<T> //where T is a L2S entity class { DataContext context; public virtual IEnumerable<T> GetAll() { return context.GetTable<T>(); } public virtual T Single(Func<T, bool> condition) { return context.GetTable<T>().SingleOrDefault(condition); } } From the front end, both of these methods appear to work as you would expect. However, when I run a trace in SQL profiler, the Single method is executing what amounts to a SELECT * FROM [Table], and then returning the single entity that meets the given condition. Obviously this is inefficient, and is being caused by GetTable() returning all rows. My question is, how do I get the query executed by the Single() method to take the form SELECT * FROM [Table] WHERE [condition], rather than selecting all rows then filtering out all but one? Is it possible in this context? Any help appreciated, Lee

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