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  • LINQ query for tag system: Matching any of several tags?

    - by David Veeneman
    I am just getting started with LINQ. I am creating an Entity Framework app that uses the canonical Post and Tag model. A Post contains an ID, Text, and Tags, and a Tag contains an ID, a Name, and Posts. A previous thread on StackOverflow showed me how to query for a Post that matches all Tag objects (A and B and C) in a search list. But how would I query for a Post that matches any Tag (A or B or C) in the list? Thanks for your help.

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  • Why did the following linq to sql query generate a subquery?

    - by Xaisoft
    I did the following query: var list = from book in books where book.price > 50 select book; list = list.Take(50); I would expect the above to generate something like: SELECT top 50 id, title, price, author FROM Books WHERE price > 50 but it generates: SELECT [Limit1].[C1] as [C1] [Limit1].[id] as [Id], [Limit1].[title] as [title], [Limit1].[price] as [price], [Limit1].[author] FROM (SELECT TOP (50) [Extent1].[id] as as [Id], [Extent1].[title] as [title], [Extent1].[price] as [price], [Extent1].[author] as [author] FROM Books as [Extent1] WHERE [Extent1].[price] > 50 ) AS [Limit1] Why does the above linq query generate a subquery and where does the C1 come from?

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  • How to format complex chained Linq statements for readibility?

    - by Joan Venge
    I have some code like this: var effects = xElement.Elements ( "Effects" ).Elements ( "Effect" ).Select ( e => new Effect ( ( EffectType ) Enum.Parse ( typeof ( EffectType ), ( string ) e.Elements ( "Type" ).FirstOrDefault ( ) ), e.Elements ( "Options" ).Any ( ) ? e.Elements ( "Options" ).Select ( o => ( object ) o.Elements ( "Option" ).Select ( n => n.Value ).First ( ) ) : null ) ) .ToList ( ); But currently this doesn't look as readable and I am not sure where I should add a new line and/or indent for readability. Any suggestions I could use to make consistent, readable linq blocks?

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  • Linq GroupBy - how to specify the grouping key at runtime?

    - by toasteroven
    is there a good way to do a Linq GroupBy where the grouping key is determined at runtime? e.g. I want the grouping key to be built from a user-selected list of fields - can you do this? I know I can do it easily if I convert everything to a table of strings, but I was wondering if there was an elegant or clever way to accomplish this otherwise. class Item { public int A, B; public DateTime D; public double X, Y, Z; } I have a List<Item> called data. I want to do things like retrieve the sum of X grouped by A, or the sums of X, Y, and Z, grouped by A and B. but what fields go into the grouping should be able to be specified at runtime in some way.

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  • Please help me convert this C# 2.0 snippet to Linq.

    - by Hamish Grubijan
    This is not a homework ;) I need to both A) optimize the following code (between a TODO and a ~TODO) and B) convert it to [P]Linq. Better readability is desired. It might make sense to provide answers to A) and B) separately. Thanks! lock (Status.LockObj) { // TODO: find a better way to merge these dictionaries foreach (KeyValuePair<Guid, Message> sInstance in newSInstanceDictionary) { this.sInstanceDictionary.Add(sInstance.Key, sInstance.Value); } foreach (KeyValuePair<Guid, Message> sOperation in newSOperationDictionary) { this.sOperationDictionary.Add(sOperation.Key, sOperation.Value); } // ~TODO }

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  • Linq to SQL - How to compare against a collection in the where clause?

    - by Sgraffite
    I'd like to compare against an IEnumerable collection in my where clause. Do I need to manually loop through the collection to pull out the column I want to compare against, or is there a generic way to handle this? I want something like this: public IEnumerable<Cookie> GetCookiesForUsers(IEnumerable<User> Users) { var cookies = from c in db.Cookies join uc in db.UserCookies on c.CookieID equals uc.CookieID join u in db.Users on uc.UserID equals u.UserID where u.UserID.Equals(Users.UserID) select c; return cookies.ToList(); } I'm used to using the lambda Linq to SQL syntax, but I decided to try the SQLesque syntax since I was using joins this time. What is a good way to do this?

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  • Is there a way to make this C# method shorter and more readable with the help of Linq?

    - by Hamish Grubijan
    The following works, but I figured - since it is all based on IEnumerable, Linq can come handy here is well. By the way, is there an equivalent to Directory.GetFiles() which would return an IEnumerable instead of the array? If it exists, then would it make the code run any faster? The last part of the question is inspired by Python language which favors lightweight generators over concrete lists. private IEnumerable<string> getFiles(string strDirectory, bool bCompressedOnly) { foreach (var strFile in Directory.GetFiles(strDirectory)) { // Don't add any existing Zip files since we don't want to delete previously compressed files. if (!bCompressedOnly || Path.GetExtension(strFile).ToLower().Equals(".zip")) { yield return strFile; } } foreach (var strDir in Directory.GetDirectories(strDirectory)) { foreach (var strFile in getFiles(strDir, bCompressedOnly)) { yield return strFile; } } }

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  • Help Please, I want use LINQ to Query Count in a matrix according to a array!

    - by Bob Feng
    I have a matrix, IEnumerable<IEnumerable<int>> matrix, for example: { {10,23,16,20,2,4}, {22,13,1,33,21,11 }, {7,19,31,12,6,22}, ... } and another array: int[] arr={ 10, 23, 16, 20} I want to filter the matrix on the condition that I group all rows of the matrix which contain the same number of elements from arr. That is to say the first row in the matrix {10,23,16,20,2,4} has 4 numbers from arr, this array should be grouped with the rest of the rows with 4 numbers from arr. better to use linq, thank you very much!

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  • How to build a LINQ query from text at runtime?

    - by Danvil
    I have a class A { public int X; public double Y; public string Z; // and more fields/properties ... }; and a List<A> data and can build a linq query like e.g. var q = from a in data where a.X > 20 select new {a.Y, a.Z}; Then dataGridView1.DataSource = q.ToList(); displays the selection in my DataGridView. Now the question, is it possible to build the query from a text the user has entered at runtime? Like var q = QueryFromText("from a in data where a.X > 20 select new {a.Y, a.Z}"); The point being, that the user (having programming skills) can dynamically and freely select the displayed data.

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  • How is a set partitioned into valid and invalid items using LINQ?

    - by Aaron Anodide
    Is there a way to write a single LINQ expression to get the same result of the following code? var validations = new Func<conversion, bool>[] { c => c.affiliate.affiliate_id > 0, c => c.campaign_id > 0 }; var invalidConversions = from c in extractedConversions where validations.Any(valid => !valid(c)) select c; var validConversions = from c in extractedConversions where validations.All(valid => valid(c)) select c;

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  • Any way for linq query to check against existing select?

    - by danrhul
    I have an an offer, that can be in any number of categories. I don't however want that offer to then appear twice or however more. I was wondering if its possible to have a where clause that ascertains whether that offer already exists in that select statement and if so obviously to ignore it. Here is the linq query: Offers = from o in offerCategories orderby o.RewardCategory.Ordering, o.Order where o.RewardOffer.IsDeleted == false select new OfferOverviewViewModel { Partner = o.RewardOffer.Partner, Description = String.Format("{0} {1}", o.RewardOffer.MainTitle, o.RewardOffer.SecondaryTitle), OfferId = o.OfferId, FeaturedOffer = o.RewardOffer.FeaturedOfferOrder.HasValue, Categories = from c in offerCategories.Where(oc => oc.OfferId == o.OfferId) orderby c.RewardCategory.Ordering select new CategoryDetailViewModel { Description = c.RewardCategory.DisplayName } },

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  • LINQ to SQL, how to write a method which checks if a row exists when we have multiple tables

    - by Beles
    Hi, I'm trying to write a method in C# which can take as parameter a tabletype, column and a columnvalue and check if the got a row with a with value the method looks like: public object GetRecordFromDatabase(Type tabletype, string columnname, string columnvalue) I'm using LINQ to SQL and need to to this in a generic way so I don't need to write each table I got in the DB. I have been doing this so far for each table, but with more than 70 of these it becomes cumbersome and boring to do. Is there a way to generate the following code dynamically, And swap out the hardcoded tablenames with the values from the parameterlist? In this example I have a table in the DB named tbl_nation, which the DataContext pluralizes to tbl_nations, and I'm checking the column for the value if (DB.tbl_nations.Count(c => c.code.Equals(columnvalue)) == 1) { return DB.tbl_nations.Single(c => c.code.Equals(columnvalue)); }

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  • Precompiling LINQ Queries

    Did you know that by precompiling LINQ queries you might actually be degrading your app’s performance if you’re not careful? Julie Lerman explains how to ensure you’re not re-precompiling queries each time and losing the expected performance benefits across post-backs, short-lived service operations and other code where critical instances are going out of scope.

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  • Specify Linq To SQL ConnectionString explicitly

    - by Michael Freidgeim
    When modifying Linq to  Sql data model in Visual Studio 2010,  it re-assigns ConnectionString that is available on developer’s machine. Because the name can be different on different machines, Designer often replace it with something like ConnectionString1, which causes errors during deployment.It requires developers to ensure that ConnectionString stays unchanged.  More reliable way is to use context constructor with explicit ConnectionString name instead of parameterless default constructor GOOD:   var ctx = new MyModelDataContext(Settings.Default.ConnectionString);Not good:          var ctx = new MyModelDataContext();

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  • Top 10 posts of 2010

    - by nmarun
    I quote one of my professors when I say: “We Share – We Improve”. It is through blogging that I’ve learned quite a bit. The ‘R&D’ done to learn and perfect a technology and the comments by other experts adds towards skill-set building. Below are some of the articles that I’m glad I blogged about. ASP.NET MVC 2 Model Binding for a Collection MVC 3 - first look To ref or not to ref Xap Reflector – Silverlight 4 Beware of const members LINQ to JS COM Automation with OpenOffice – Silverlight 4 VS 2010 Productivity Power Tools Using Unity Application Block – from basics to generics ASP.NET MVC Model Binding Wishing you all a happy 2011 and keep/start blogging!

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  • Algorithm to optimize grouping

    - by Jeroen
    I would like to know if there's a known algorithm or best practice way to do the following: I have a collection with a subcollection, for example: R1 R2 R3 -- -- -- M M M N N L L A What i need is an algorithm to get the following result: R1, R2: M N L R2: A R3: M This is -not- what i want, it has more repeating values for R than the above: R1, R2, R3: M R1, R2: N L R2: A I need to group in way that i get the most optimized groups of R. The least amount of groups of R the better so i get the largest sub collections. Another example (with the most obvious result): R1 R2 R3 -- -- -- M M A V V B L L C Should result in: R1, R2: M V L R3: A B C I need to do this in LINQ/C#. Any solutions? Tips? Links?

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  • Why LINQ to Entities won't let me initialize just some properties of an Entity?

    - by emzero
    So I've started to add Entity Framework 4 into a legacy web application (ASP.NET WebForms). As a start I have auto-generated some entities from the database. Also I want to apply Repository Pattern. There is an entity called Visitor and its repository VisitorRepository In VisitorRepository I have the following method: public IEnumerable<Visitor> GetActiveVisitors() { var visitors = from v in _context.Visitors where v.IsActive select new Visitor { VisitorID = v.VisitorID, EmailAddress = v.EmailAddress, RegisterDate = v.RegisterDate, Company = v.Company, Position = v.Position, FirstName = v.FirstName, LastName = v.LastName }; return visitors.ToList(); } That List is then bound to a repeater and when trying to do <%# Eval('EmailAddress') #%> it throws the following exception. The entity or complex type 'Model.Visitor' cannot be constructed in a LINQ to Entities query. A) Why is this happening? How I can workaround this? Do I need to select an anonymous type and then use that to initialize my entities??? B) Why every example I've seen makes use of 'select new' (anonymous object) instead of initializing a known type? Anonymous types are useless unless you are retrieving the data and showing it in the same layer. As far as I know anonymous types cannot be returned from methods? So what's the real point of them??? Thank you all

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  • Linq The specified type 'string' is not a valid provider type.

    - by Joe Pitz
    Using Linq to call a stored procedure that passes a single string, The stored procedure returns a data set row that contains a string and an int. Code: PESQLDataContext pe = new PESQLDataContext(strConnStr); pe.ObjectTrackingEnabled = false; gvUnitsPassed.DataSource = pe.PassedInspection(Line); gvUnitsPassed.DataBind(); pe.dispose(); When the code runs an exception gets called below: The exception is thrown at the IExecuteResult result = statement: Enclosed is my result class in the designer.cs file. [Function(Name = "dbo.PassedInspection")] public ISingleResult<PassedInspectionResult> PassedInspection([Parameter(Name = "Model", DbType = "VarChar(4)")] string model) { IExecuteResult result = this.ExecuteMethodCall(this, ((MethodInfo)(MethodInfo.GetCurrentMethod())), model); return ((ISingleResult<PassedInspectionResult>)(result.ReturnValue)); } public partial class PassedInspectionResult { private string _Date; private int _Passed; public PassedInspectionResult() { } [Column(Storage = "_Date", DbType = "string NULL")] public string Date { get { return this._Date; } set { if ((this._Date != value)) { this._Date = value; } } } [Column(Storage = "_Passed", DbType = "Int NULL")] public int Passed { get { return this._Passed; } set { if ((this._Passed != value)) { this._Passed = value; } } } } } I have other stored procedures with similar arguments that run just fine. Thanks

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  • Validate MVC 2 form using Data annotations and Linq-to-SQL, before the model binder kicks in (with D

    - by Stefanvds
    I'm using linq to SQL and MVC2 with data annotations and I'm having some problems on validation of some types. For example: [DisplayName("Geplande sessies")] [PositiefGeheelGetal(ErrorMessage = "Ongeldige ingave. Positief geheel getal verwacht")] public string Proj_GeplandeSessies { get; set; } This is an integer, and I'm validating to get a positive number from the form. public class PositiefGeheelGetalAttribute : RegularExpressionAttribute { public PositiefGeheelGetalAttribute() : base(@"\d{1,7}") { } } Now the problem is that when I write text in the input, I don't get to see THIS error, but I get the errormessage from the modelbinder saying "The value 'Tomorrow' is not valid for Geplande sessies." The code in the controller: [HttpPost] public ActionResult Create(Projecten p) { if (ModelState.IsValid) { _db.Projectens.InsertOnSubmit(p); _db.SubmitChanges(); return RedirectToAction("Index"); } else { SelectList s = new SelectList(_db.Verbonds, "Verb_ID", "Verb_Naam"); ViewData["Verbonden"] = s; } return View(); } What I want is being able to run the Data Annotations before the Model binder, but that sounds pretty much impossible. What I really want is that my self-written error messages show up on the screen. I have the same problem with a DateTime, which i want the users to write in the specific form 'dd/MM/yyyy' and i have a regex for that. but again, by the time the data-annotations do their job, all i get is a DateTime Object, and not the original string. So if the input is not a date, the regex does not even run, cos the data annotations just get a null, cos the model binder couldn't make it to a DateTime. Does anyone have an idea how to make this work?

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