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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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  • Tag filtering Query using T-SQL and Linq-to-SQL?

    - by EdenMachine
    I'm trying to figure out how to allow a user to enter in a string of tags (keywords separated by spaces) in a textbox to filter a grid of results. Here are the tables: PACKETS *PacketID Name PACKETTAGS *PacketTagID PacketID TagID Tags *TagID Name Here is the basic query without the WHERE parameters: SELECT Packets.Name, Tags.Name AS Tag, PacketTags.PacketTagID FROM Packets INNER JOIN PacketTags ON Packets.PacketID = PacketTags.PacketID INNER JOIN Tags ON PacketTags.TagID = Tags.TagID I need to filter out all the Packets that don't have tags that match any of the words BUT ALSO ONLY include the Packets that have the tags entered in the string of text (spaces separate the tags when entered into the textbox) I'm starting with the basics by figuring this out in t-SQL first but ultimately I need to be able to do this in Linq-to-SQL

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  • How to OrderBy on a generic IEnumerable (IEnumerable<T>) using LINQ in C#?

    - by Jeffrey
    In my generic repository I have below method: public virtual IEnumerable<T> GetAll<T>() where T : class { using (var ctx = new DataContext()) { ctx.ObjectTrackingEnabled = false; var table = ctx.GetTable<T>().ToList().AsReadOnly(); return table; } } T is a Linq to Sql class and I want to be able to OrderBy on a particular property. Say if T has property name "SortOrder" then do OrderBy on this property. But I am not sure how I can achieve this. So I need some helps. Thank you!

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Exam 71-515: TS: Web Applications Development with Microsoft .NET Framework 4

    - by Ricardo Peres
    I took the 71-515 exam today. 85 questions, 240 minutes. Here are some notes: Great number of jQuery questions, mostly having to do with AJAX Lots of MVC 2 questions also A number of classic ASP.NET web forms, of which only a few were related with the new 4 features Some Entity Framework Some plain old JavaScript, like, changing an image dynamically I think I did OK. As with my previous exam, I still don't know if I passed or not, will have to wait for the end of the beta period.

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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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  • JPA Entity Manager resource handling

    - by chiragshahkapadia
    Every time I call JPA method its creating entity and binding query. My persistence properties are: <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/> <property name="hibernate.cache.provider_class" value="net.sf.ehcache.hibernate.SingletonEhCacheProvider"/> <property name="hibernate.cache.use_second_level_cache" value="true"/> <property name="hibernate.cache.use_query_cache" value="true"/> And I am creating entity manager the way shown below: emf = Persistence.createEntityManagerFactory("pu"); em = emf.createEntityManager(); em = Persistence.createEntityManagerFactory("pu").createEntityManager(); Is there any nice way to manage entity manager resource instead create new every time or any property can set in persistence. Remember it's JPA. See below binding log every time : 15:35:15,527 INFO [AnnotationBinder] Binding entity from annotated class: * 15:35:15,527 INFO [QueryBinder] Binding Named query: * = * 15:35:15,527 INFO [QueryBinder] Binding Named query: * = * 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [QueryBinder] Binding Named query: 15:35:15,527 INFO [EntityBinder] Bind entity com.* on table * 15:35:15,542 INFO [HibernateSearchEventListenerRegister] Unable to find org.hibernate.search.event.FullTextIndexEventListener on the classpath. Hibernate Search is not enabled. 15:35:15,542 INFO [NamingHelper] JNDI InitialContext properties:{} 15:35:15,542 INFO [DatasourceConnectionProvider] Using datasource: 15:35:15,542 INFO [SettingsFactory] RDBMS: and Real Application Testing options 15:35:15,542 INFO [SettingsFactory] JDBC driver: Oracle JDBC driver, version: 9.2.0.1.0 15:35:15,542 INFO [Dialect] Using dialect: org.hibernate.dialect.Oracle10gDialect 15:35:15,542 INFO [TransactionFactoryFactory] Transaction strategy: org.hibernate.transaction.JDBCTransactionFactory 15:35:15,542 INFO [TransactionManagerLookupFactory] No TransactionManagerLookup configured (in JTA environment, use of read-write or transactional second-level cache is not recomm ended) 15:35:15,542 INFO [SettingsFactory] Automatic flush during beforeCompletion(): disabled 15:35:15,542 INFO [SettingsFactory] Automatic session close at end of transaction: disabled 15:35:15,542 INFO [SettingsFactory] JDBC batch size: 15 15:35:15,542 INFO [SettingsFactory] JDBC batch updates for versioned data: disabled 15:35:15,542 INFO [SettingsFactory] Scrollable result sets: enabled 15:35:15,542 INFO [SettingsFactory] JDBC3 getGeneratedKeys(): disabled 15:35:15,542 INFO [SettingsFactory] Connection release mode: auto 15:35:15,542 INFO [SettingsFactory] Default batch fetch size: 1 15:35:15,542 INFO [SettingsFactory] Generate SQL with comments: disabled 15:35:15,542 INFO [SettingsFactory] Order SQL updates by primary key: disabled 15:35:15,542 INFO [SettingsFactory] Order SQL inserts for batching: disabled 15:35:15,542 INFO [SettingsFactory] Query translator: org.hibernate.hql.ast.ASTQueryTranslatorFactory 15:35:15,542 INFO [ASTQueryTranslatorFactory] Using ASTQueryTranslatorFactory 15:35:15,542 INFO [SettingsFactory] Query language substitutions: {} 15:35:15,542 INFO [SettingsFactory] JPA-QL strict compliance: enabled 15:35:15,542 INFO [SettingsFactory] Second-level cache: enabled 15:35:15,542 INFO [SettingsFactory] Query cache: enabled 15:35:15,542 INFO [SettingsFactory] Cache region factory : org.hibernate.cache.impl.bridge.RegionFactoryCacheProviderBridge 15:35:15,542 INFO [RegionFactoryCacheProviderBridge] Cache provider: net.sf.ehcache.hibernate.SingletonEhCacheProvider 15:35:15,542 INFO [SettingsFactory] Optimize cache for minimal puts: disabled 15:35:15,542 INFO [SettingsFactory] Structured second-level cache entries: disabled 15:35:15,542 INFO [SettingsFactory] Query cache factory: org.hibernate.cache.StandardQueryCacheFactory 15:35:15,542 INFO [SettingsFactory] Statistics: disabled 15:35:15,542 INFO [SettingsFactory] Deleted entity synthetic identifier rollback: disabled 15:35:15,542 INFO [SettingsFactory] Default entity-mode: pojo 15:35:15,542 INFO [SettingsFactory] Named query checking : enabled 15:35:15,542 INFO [SessionFactoryImpl] building session factory 15:35:15,542 INFO [SessionFactoryObjectFactory] Not binding factory to JNDI, no JNDI name configured 15:35:15,542 INFO [UpdateTimestampsCache] starting update timestamps cache at region: org.hibernate.cache.UpdateTimestampsCache 15:35:15,542 INFO [StandardQueryCache] starting query cache at region: org.hibernate.cache.StandardQueryCache

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  • Fix: WCF - The type provided as the Service attribute value in the ServiceHost directive could not

    - by Ken Cox [MVP]
    I wanted to expose some raw data to users in my current ASP.NET 3.5 web site project. I created a subdirectory called ‘datafeeds’ and added a WCF Data Service. I wired the dataservice up to the Entity Framework class and, on running the ItemDataService.svc file, was greeted with: The type  <> provided as the Service attribute value in the ServiceHost directive could not be found So why couldn’t it find the class? It was right there in the… oops! Instead of putting the ItemDataService.vb...(read more)

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  • ASP.NET MVC3 checkbox dropdownlist create [migrated]

    - by user95381
    i'm new in asp.net MVC and I/m use view model to poppulate the dropdown list and group of checkboxes. I use SQL Server 2012, where have many to many relationships between Students - Books; Student - Cities. I need collect StudentName, one city and many books for one student. I have next questions: 1. How can I get the values from database to my StudentBookCityViewModel? 2. How can I save the values to my database in [HttpPost] Create method? Here is the code: MODEL public class Student { public int StudentId { get; set; } public string StudentName { get; set; } public ICollection<Book> Books { get; set; } public ICollection<City> Cities { get; set; } } public class Book { public int BookId { get; set; } public string BookName { get; set; } public bool IsSelected { get; set; } public ICollection<Student> Students { get; set; } } public class City { public int CityId { get; set; } public string CityName { get; set; } public bool IsSelected { get; set; } public ICollection<Student> Students { get; set; } } VIEW MODEL public class StudentBookCityViewModel { public string StudentName { get; set; } public IList<Book> Books { get; set; } public StudentBookCityViewModel() { Books = new[] { new Book {BookName = "Title1", IsSelected = false}, new Book {BookName = "Title2", IsSelected = false}, new Book {BookName = "Title3", IsSelected = false} }.ToList(); } public string City { get; set; } public IEnumerable<SelectListItem> CityValues { get { return new[] { new SelectListItem {Value = "Value1", Text = "Text1"}, new SelectListItem {Value = "Value2", Text = "Text2"}, new SelectListItem {Value = "Value3", Text = "Text3"} }; } } } Context public class EFDbContext : DbContext{ public EFDbContext(string connectionString) { Database.Connection.ConnectionString = connectionString; } public DbSet<Book> Books { get; set; } public DbSet<Student> Students { get; set; } public DbSet<City> Cities { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<Book>() .HasMany(x => x.Students).WithMany(x => x.Books) .Map(x => x.MapLeftKey("BookId").MapRightKey("StudentId").ToTable("StudentBooks")); modelBuilder.Entity<City>() .HasMany(x => x.Students).WithMany(x => x.Cities) .Map(x => x.MapLeftKey("CityId").MapRightKey("StudentId").ToTable("StudentCities")); } } Controller public ActionResult Create() { return View(); } [HttpPost] public ActionResult Create() { //I don't understand how I can save values to db context.SaveChanges(); return RedirectToAction("Index"); } View @model UsingEFNew.ViewModels.StudentBookCityViewModel @using (Html.BeginForm()) { Your Name: @Html.TextBoxFor(model = model.StudentName) <div>Genre:</div> <div> @Html.DropDownListFor(model => model.City, Model.CityValues) </div> <div>Books:</div> <div> @for (int i = 0; i < Model.Books.Count; i++) { <div> @Html.HiddenFor(x => x.Books[i].BookId) @Html.CheckBoxFor(x => x.Books[i].IsSelected) @Html.LabelFor(x => x.Books[i].IsSelected, Model.Books[i].BookName) </div> } </div> <div> <input id="btnSubmit" type="submit" value="Submit" /> </div> </div> }

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  • Python web frameworks comparisons

    - by stupidLearner
    I recently asked a question on SO about Python web frameworks: http://stackoverflow.com/questions/4909306/python-web-frameworks-vs-java-web-frameworks-how-is-web-development-in-python-do I want to learn one just for fun but it also has to be able to help me deliver a proper working application. I am looking for a framework with lots of features, powerful, mature, with large community, good documentation, books etc. I need something that will help me be more productive in developing my app and not waste time figuring out how to do a certain thing in the framework or how to write workaround around the limitations of the framework. I was thinking one of the following: django, zope, turbogears, pylons. Off course the war is raging out there and there are other alternatives but seems Django is at the top... or is it just hype? I am interested in pros and cons of each. What was the best feature you think the framework has? What is the thing it lacks? What could have been done differently. Help me chose one to learn for starters.

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