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  • Macro to Add using System.Linq

    - by Aligned
    I have Visual Studio 2010 setup to remove and sort settings on save with the Power Commands extensions. This is great, but sometimes it removes the using System.Linq at the top. I also find myself scrolling to the top to add the using when I first add System.Linq. So I wrote a quick macro to do it for me. Sub AddUsingLinq()        DTE.ActiveDocument.Selection.StartOfDocument()        DTE.ActiveDocument.Selection.StartOfLine(vsStartOfLineOptions.vsStartOfLineOptionsFirstText)        DTE.ActiveDocument.Selection.Text = "using System.Linq;"        DTE.ActiveDocument.Selection.NewLine()        DTE.ExecuteCommand("Edit.FormatDocument")        DTE.ExecuteCommand("Edit.RemoveAndSort")        DTE.ActiveDocument.Save() DTE.ExecuteCommand("View.NavigateBackward")    End SubHook this up to a shortcut (tools -> options -> keyboard, I chose ctrl + x, c) and you'll be moving faster than ever.

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  • Lambda expressions in C#?

    - by user30457
    Hey I'm rather new to these could someone explain the significance 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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  • How do you unit test a LINQ query using Moq and Machine.Specifications?

    - by Phil.Wheeler
    I'm struggling to get my head around how to accommodate a mocked repository's method that only accepts a Linq expression as its argument. Specifically, the repository has a First() method that looks like this: public T First(Expression<Func<T, bool>> expression) { return All().Where(expression).FirstOrDefault(); } The difficulty I'm encountering is with my MSpec tests, where I'm (probably incorrectly) trying to mock that call: public abstract class with_userprofile_repository { protected static Mock<IRepository<UserProfile>> repository; Establish context = () => { repository = new Mock<IRepository<UserProfile>>(); repository.Setup<UserProfile>(x => x.First(up => up.OpenID == @"http://testuser.myopenid.com")).Returns(GetDummyUser()); }; protected static UserProfile GetDummyUser() { UserProfile p = new UserProfile(); p.OpenID = @"http://testuser.myopenid.com"; p.FirstName = "Joe"; p.LastLogin = DateTime.Now.Date.AddDays(-7); p.LastName = "Bloggs"; p.Email = "[email protected]"; return p; } } I run into trouble because it's not enjoying the Linq expression: System.NotSupportedException: Expression up = (up.OpenID = "http://testuser.myopenid.com") is not supported. So how does one test these sorts of scenarios?

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  • How do you unit test a LINQ expression using Moq and Machine.Specifications?

    - by Phil.Wheeler
    I'm struggling to get my head around how to accommodate a mocked repository's method that only accepts a Linq expression as its argument. Specifically, the repository has a First() method that looks like this: public T First(Expression<Func<T, bool>> expression) { return All().Where(expression).FirstOrDefault(); } The difficulty I'm encountering is with my MSpec tests, where I'm (probably incorrectly) trying to mock that call: public abstract class with_userprofile_repository { protected static Mock<IRepository<UserProfile>> repository; Establish context = () => { repository = new Mock<IRepository<UserProfile>>(); repository.Setup<UserProfile>(x => x.First(up => up.OpenID == @"http://testuser.myopenid.com")).Returns(GetDummyUser()); }; protected static UserProfile GetDummyUser() { UserProfile p = new UserProfile(); p.OpenID = @"http://testuser.myopenid.com"; p.FirstName = "Joe"; p.LastLogin = DateTime.Now.Date.AddDays(-7); p.LastName = "Bloggs"; p.Email = "[email protected]"; return p; } } I run into trouble because it's not enjoying the Linq expression: System.NotSupportedException: Expression up = (up.OpenID = "http://testuser.myopenid.com") is not supported. So how does one test these sorts of scenarios?

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  • How do you unit test a method containing a LINQ expression?

    - by Phil.Wheeler
    I'm struggling to get my head around how to accommodate a mocked method that only accepts a Linq expression as its argument. Specifically, the repository I'm using has a First() method that looks like this: public T First(Expression<Func<T, bool>> expression) { return All().Where(expression).FirstOrDefault(); } The difficulty I'm encountering is with my MSpec tests, where I'm (probably incorrectly) trying to mock that call: public abstract class with_userprofile_repository { protected static Mock<IRepository<UserProfile>> repository; Establish context = () => { repository = new Mock<IRepository<UserProfile>>(); repository.Setup<UserProfile>(x => x.First(up => up.OpenID == @"http://testuser.myopenid.com")).Returns(GetDummyUser()); }; protected static UserProfile GetDummyUser() { UserProfile p = new UserProfile(); p.OpenID = @"http://testuser.myopenid.com"; p.FirstName = "Joe"; p.LastLogin = DateTime.Now.Date.AddDays(-7); p.LastName = "Bloggs"; p.Email = "[email protected]"; return p; } } I run into trouble because it's not enjoying the Linq expression: System.NotSupportedException: Expression up = (up.OpenID = "http://testuser.myopenid.com") is not supported. So how does one test these sorts of scenarios?

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  • Entity Framework 4.0: Optimal and horrible SQL

    - by DigiMortal
    Lately I had Entity Framework 4.0 session where I introduced new features of Entity Framework. During session I found out with audience how Entity Framework 4.0 can generate optimized SQL. After session I also showed guys one horrible example about how awful SQL can be generated by Entity Framework. In this posting I will cover both examples. Optimal SQL Before going to code take a look at following model. There is class called Event and I will use this class in my query. Here is the LINQ To Entities query that uses small anonymous type. var query = from e in _context.Events             select new { Id = e.Id, Title = e.Title }; Debug.WriteLine(((ObjectQuery)query).ToTraceString()); Running this code gives us the following SQL. SELECT      [Extent1].[event_id] AS [event_id],      [Extent1].[title] AS [title]  FROM [dbo].[events] AS [Extent1] This is really small – no additional fields in SELECT clause. Nice, isn’t it? Horrible SQL Ayende Rahien blog shows us darker side of Entiry Framework 4.0 queries. You can find comparison betwenn NHibernate, LINQ To SQL and LINQ To Entities from posting What happens behind the scenes: NHibernate, Linq to SQL, Entity Framework scenario analysis. In this posting I will show you the resulting query and let you think how much better it can be done. Well, it is not something we want to see running in our servers. I hope that EF team improves generated SQL to acceptable level before Visual Studio 2010 is released. There is also morale of this example: you should always check out the queries that O/R-mapper generates. Behind the curtains it may silently generate queries that perform badly and in this case you need to optimize you data querying strategy. Conclusion Entity Framework 4.0 is new product with a lot of new features and it is clear that not everything is 100% super in its first release. But it still great step forward and I hope that on 12.04.2010 we have new promising O/R-mapper available to use in our projects. If you want to read more about Entity Framework 4.0 and Visual Studio 2010 then please feel free to follow this link to list of my Visual Studio 2010 and .NET Framework 4.0 postings.

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  • Getting the first result from a LINQ query - why does ElementAt<T>(0) fails when First<T>() succeeds

    - by Mr Roys
    I have a method AddStudent() which looks for a student with the same name and returns an existing student from the database if there is a student with the same name, otherwise it creates a new student and adds it to the database. I'm curious why se = students.First<StudentEntity>(); succeeds when se = students.ElementAt<StudentEntity>(0); fails when I try to get the first result from the LINQ query. Aren't the two methods the same? The full code for the method is shown below. public Student AddStudent(string name) { using (SchoolEntities db = new SchoolEntities()) { // find student with same name via LINQ var students = from s in db.StudentEntitySet where s.name == name select s; StudentEntity se = default(StudentEntity); // if student with the same name is already present, return // that student if (students.Count<StudentEntity>() > 0) { // if i use ElementAt, if fails with a "LINQ to Entities does not // recognize the method 'StudentEntity ElementAt[StudentEntity] // (System.Linq.IQueryable`1[StudentEntity], Int32)' method, // and this method cannot be translated into a store expression.", // but not when I use First. Why? // se = students.ElementAt<StudentEntity>(0); se = students.First<StudentEntity>(); } else { // passing 0 for first parameter (id) since it's represented by // a BigInt IDENTITY field in the database so any value // doesn't matter. se = StudentEntity.CreateStudentEntity(0, name); db.AddToStudentEntitySet(se); db.SaveChanges(); } // create a Student object from the Entity object return new Student(se); } } Thanks!

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  • 'LINQ query plan' horribly inefficient but 'Query Analyser query plan' is perfect for same SQL!

    - by Simon_Weaver
    I have a LINQ to SQL query that generates the following SQL : exec sp_executesql N'SELECT COUNT(*) AS [value] FROM [dbo].[SessionVisit] AS [t0] WHERE ([t0].[VisitedStore] = @p0) AND (NOT ([t0].[Bot] = 1)) AND ([t0].[SessionDate] > @p1)',N'@p0 int,@p1 datetime', @p0=1,@p1='2010-02-15 01:24:00' (This is the actual SQL taken from SQL Profiler on SQL Server 2008.) The query plan generated when I run this SQL from within Query Analyser is perfect. It uses an index containing VisitedStore, Bot, SessionDate. The query returns instantly. However when I run this from C# (with LINQ) a different query plan is used that is so inefficient it doesn't even return in 60 seconds. This query plan is trying to do a key lookup on the clustered primary key which contains a couple million rows. It has no chance of returning. What I just can't understand though is that the EXACT same SQL is being run - either from within LINQ or from within Query Analyser yet the query plan is different. I've ran the two queries many many times and they're now running in isolation from any other queries. The date is DateTime.Now.AddDays(-7), but I've even hardcoded that date to eliminate caching problems. Is there anything i can change in LINQ to SQL to affect the query plan or try to debug this further? I'm very very confused!

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  • How to use different providers for Linq to entities?

    - by Anders Svensson
    I'm trying to familiarize myself a bit more with database programming, and I'm looking at different ways of creating a data access layer for applications. I've tried out a few ways but there is such a jungle of different database technologies that I don't know what to learn. For instance I've tried using datasets with tableadapters. Using that I am able to switch data provider rather easily (by programming against the interfaces such as IDbConnection). This is one thing I would want to achieve. But I also know everyone's talking about LINQ, and I'm trying to get to know that a bit better too. So I have tried using Linq to Sql classes as the data access layer as well, but apparently this is not provider independent (works only for SQL Server). So then I read about the Entity Framework (which just as Linq to SQL apparently has gotten its share of bashing already...). It's supposed to be provider independent everybody says, but how? I tried out a tutorial to create an entity data model, but the only providers to choose from were SQL Server/Express. Just for learning purposes, I would like to know how to use the entity framework with MS Access/OleDb. Also, I would appreciate some input on what is the preferred database technology for data access. Is it LINQ still after all the bashing, or should you just use datasets because they are provider independent? Any pointers for what to learn would be great, because it's just too much to learn it all if I'm not going to use it in the end...!

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  • How to handle encrypted column in SQL Server Database in LINQ to SQL?

    - by Raja
    Hi Guys, We are in the process of encrypting all the SSN columns (had to do it now due to security audit). We already built the DBML and now we have to change it. Can you guys let me know if there is a good way of handling this in LINQ to SQL? We use stored procedures for Insert, Update and Delete but use LINQ to SQL for all our selects (ease of use). Do I have to change the format for those tables with SSN or Is there any other manner we can handle it in LINQ to SQL? Thanks, Raja

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  • How to specify dynamic field names in a Linq where clause?

    - by Dr. Zim
    If you create a Filter object that contains criteria for Linq that normally goes in a where clause like this: var myFilterObject = FilterFactory.GetBlank(); myFilterObject.AddCondition("Salary", "lessThan", "40000"); var myResult = myRepository.GetEmployees(myFilterObject); How would you match the Linq field to the Field Name without using a big case statement? return from e in db.Employee where e.Salary < 40000 select new IList<EmployeeViewModel> { Name= e.name, Salary= e.Salary }; I assume you need to send an object to the Repository that specifies filtering so that you only pull what records you need. I assume Linq doesn't pre-compile (unless you create a customized delegate and function), so you should be able to dynamically specify which fields you want to filter. It would be nice if you could do something like e["Salary"] like some type of Expando Object.

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  • How to convert linq entitySet AND CHILDREN to lists?

    - by Abe Miessler
    I ran into an error when trying to serialize a linq entitySet. To get around this i converted the entitySet to a list. The problem I have run into now is that it's child entity sets are not converting to a list and when I try to serialize the parent those are now throwing an error. Does anyone know of a way to convert a linq entitySet AND it's children to lists? p.s. I'm new to linq so if any of this dosn't make sense let me know

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  • Linq to SQL Azure genrating Error "Specified cast is not valid."

    - by Rabbi
    B"H I have an application that has been working for months using Linq to SQL connecting to a SQLExpress. I tried migrating it to SQL Azure. I copied the structure and data using the Sync Framework. I viewed the data in SQL Azure using SSMS 2008 R2 and it seams to be exactly what I have in my Sql Server. However when I try to use Linq to SQL against it I get an error "Specified cast is not valid." I seams to be happening any time I get child records. i.e. whenever I fill (the first time I access) an entity set. It seams to be happening after the data returns and when Linq tries to put it into the objects. remember, the application is working perfectly against sqlexpress, even when accessed across the internet or vpn.

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  • Entity framework (3.5): How to translate a certain LINQ query to eSQL?

    - by Sebastian P.R. Gingter
    Hi there, I have the following LINQ query that I need to translate to Entity SQL /eSQL): return (ObjectQuery<User>) from user in Users where !user.Roles.Any(r => r.AnIntegerProperty < 0) select user; User.Roles is an navigation property to the n:m relation to Roles and there also is a Role.Users navigation property the other way round. There aren't User_Roles or Roles_User Entities available in the model, and I can't add these. I also can't use the LINQ statement here, because I need to add .OrderBy("it." + propertyname) (comes from another source, can't change that too) later on which is not possible if the ObjectQuery is build with linq. So how do I translate this to eSQL? And where can I find good eSQL samples? I searched for a whole day until now and must admit that eSQL reference is lousy and there aren't any usable examples around the web.

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  • Is ORM (Linq, Hibernate...) really that useful?

    - by Peter
    I have been playing with some LINQ ORM (LINQ directly to SQL) and I have to admit I like its expressive powers . For small utility-like apps, It also works quite fast: dropping a SQL server on some surface and you're set to linq away. For larger apps however, the DAL never was that big of an issue to me to setup, nor maintain, and more often than not, once it was set, all the programming was not happening there anyway... My, honest - I am an ORM newbie - question : what is the big advantage of ORM over writing a decent DAL by hand? (seems like a double, couldn't find it though) UPDATE : OK its a double :-) I found it myself eventually : ORM vs Handcoded Data Access Layer

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  • How do I pass a parameter from the select list into a function for joining a linq query?

    - by Ryan ONeill
    I have a query that can be summarised in SQL as follows; Select S.StockCode From StockToCheck As S Inner Join GetPOSStock(S.StockCode) As C On S.StockCode = C.StockCode; I'm trying to do the same in Linq but it seems I cannot pass a parameter to the function I am joining on as it has not been parsed by Linq. I imagine it would look like this (vb); Dim x = From S In StockToCheck Join C In GetPOSStock(S) On S Equals C.ProductCode Where the S var is a list of strings. This gives the error 'S' is not declared and points to the S in the function call / join (GetPOSStock). So it does not seem possible to do this in Linq, can anyone confirm? Thanks in advance Ryan

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  • How do I combine these similar linq queries into one?

    - by MikeD
    This is probably a basic LINQ question. I have need to select one object and if it is null select another. I'm using linq to objects in the following way, that I know can be done quicker, better, cleaner... public Attrib DetermineAttribution(Data data) { var one = from c in data.actions where c.actionType == Action.ActionTypeOne select new Attrib { id = c.id, name = c.name }; if( one.Count() > 0) return one.First(); var two = from c in data.actions where c.actionType == Action.ActionTypeTwo select new Attrib { id = c.id, name = c.name }; if (two.Count() > 0 ) return two.First(); } The two linq operations differ only on the where clause and I know there is a way to combine them. Any thoughts would be appreciated.

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  • Linq to SQL Azure generating Error "Specified cast is not valid."

    - by Rabbi
    B"H I have an application that has been working for months using Linq to SQL connecting to a SQLExpress. I tried migrating it to SQL Azure. I copied the structure and data using the Sync Framework. I viewed the data in SQL Azure using SSMS 2008 R2 and it seams to be exactly what I have in my Sql Server. However when I try to use Linq to SQL against it I get an error "Specified cast is not valid." I seams to be happening any time I get child records. i.e. whenever I fill (the first time I access) an entity set. It seams to be happening after the data returns and when Linq tries to put it into the objects. Remember, the application is working perfectly against sqlexpress, even when accessed across the internet or vpn.

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  • How do I perform a dynamic select in Linq?

    - by Matt Mangold
    I am trying to figure out how to dynamically specify the properties for my select clause in a linq query. Lets say I have a collection of employee objects. At run time, the end user will be specifying which properties they would like to see for those employees, so I need to be able to dynamically construct my Linq select clause. I have used the dynamic Linq library, but I prefer not to use that, because it requires me to build a string to pass to the select method. I'd like to understand how to do this via Expressions.

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  • How to make UPDATE queries in LINQ to SQL?

    - by Alex
    I like using LINQ to SQL. The only problem is that I don't like the default way of updating tables. Let's say I have the following table with the following columns: ID (primary key), value1, value2, value3, value4, value5 When I need to update something I call UPDATE ... WHERE ID=@id LINQ to SQL call UPDATE ... WHERE ID=@id and value1=@value1 and value2=@value2 and value3=@value3 and value4=@value4 and value5=@value5 I can override this behavior by adding UpdateCheck=UpdateCheck.Never to every column, but with every update of the DataContext class with the GUI, this will be erased. Is there any way to tell LINQ to use this way of updating data?

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  • Dynamic connection for LINQ to SQL DataContext

    - by Steve Clements
    If for some reason you need to specify a specific connection string for a DataContext, you can of course pass the connection string when you initialise you DataContext object.  A common scenario could be a dev/test/stage/live connection string, but in my case its for either a live or archive database.   I however want the connection string to be handled by the DataContext, there are probably lots of different reasons someone would want to do this…but here are mine. I want the same connection string for all instances of DataContext, but I don’t know what it is yet! I prefer the clean code and ease of not using a constructor parameter. The refactoring of using a constructor parameter could be a nightmare.   So my approach is to create a new partial class for the DataContext and handle empty constructor in there. First from within the LINQ to SQL designer I changed the connection property to None.  This will remove the empty constructor code from the auto generated designer.cs file. Right click on the .dbml file, click View Code and a file and class is created for you! You’ll see the new class created in solutions explorer and the file will open. We are going to be playing with constructors so you need to add the inheritance from System.Data.Linq.DataContext public partial class DataClasses1DataContext : System.Data.Linq.DataContext    {    }   Add the empty constructor and I have added a property that will get my connection string, you will have whatever logic you need to decide and get the connection string you require.  In my case I will be hitting a database, but I have omitted that code. public partial class DataClasses1DataContext : System.Data.Linq.DataContext {    // Connection String Keys - stored in web.config    static string LiveConnectionStringKey = "LiveConnectionString";    static string ArchiveConnectionStringKey = "ArchiveConnectionString";      protected static string ConnectionString    {       get       {          if (DoIWantToUseTheLiveConnection) {             return global::System.Configuration.ConfigurationManager.ConnectionStrings[LiveConnectionStringKey].ConnectionString;          }          else {             return global::System.Configuration.ConfigurationManager.ConnectionStrings[ArchiveConnectionStringKey].ConnectionString;          }       }    }      public DataClasses1DataContext() :       base(ConnectionString, mappingSource)    {       OnCreated();    } }   Now when I new up my DataContext, I can just leave the constructor empty and my partial class will decide which one i need to use. Nice, clean code that can be easily refractored and tested.   Share this post :

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  • How to join two collections with LINQ

    - by JustinGreenwood
    Here is a simple and complete example of how to perform joins on two collections with LINQ. I wrote it for a friend to show him, in one simple file, the power of LINQ queries and anonymous objects. In the file below, there are two simple data classes defined: Person and Item. In the beginning of the main method, two collections are created. Note that the Item's OwnerId field reference the PersonId of a Person object. The effect of the LINQ query below is equivalent to a SQL statement looking like this: select Person.PersonName as OwnerName, Item.ItemName as OwnedItem from Person inner join Item on Item.OwnerId = Person.PersonId order by Item.ItemName desc; using System; using System.Collections.Generic; using System.Linq; namespace LinqJoinAnonymousObjects { class Program { class Person { public int PersonId { get; set; } public string PersonName { get; set; } } class Item { public string ItemName { get; set; } public int OwnerId { get; set; } } static void Main(string[] args) { // Create two collections: one of people, and another with their possessions. var people = new List<Person> { new Person { PersonId=1, PersonName="Justin" }, new Person { PersonId=2, PersonName="Arthur" }, new Person { PersonId=3, PersonName="Bob" } }; var items = new List<Item> { new Item { OwnerId=1, ItemName="Armor" }, new Item { OwnerId=1, ItemName="Book" }, new Item { OwnerId=2, ItemName="Chain Mail" }, new Item { OwnerId=2, ItemName="Excalibur" }, new Item { OwnerId=3, ItemName="Bubbles" }, new Item { OwnerId=3, ItemName="Gold" } }; // Create a new, anonymous composite result for person id=2. var compositeResult = from p in people join i in items on p.PersonId equals i.OwnerId where p.PersonId == 2 orderby i.ItemName descending select new { OwnerName = p.PersonName, OwnedItem = i.ItemName }; // The query doesn't evaluate until you iterate through the query or convert it to a list Console.WriteLine("[" + compositeResult.GetType().Name + "]"); // Convert to a list and loop through it. var compositeList = compositeResult.ToList(); Console.WriteLine("[" + compositeList.GetType().Name + "]"); foreach (var o in compositeList) { Console.WriteLine("\t[" + o.GetType().Name + "] " + o.OwnerName + " - " + o.OwnedItem); } Console.ReadKey(); } } } The output of the program is below: [WhereSelectEnumerableIterator`2] [List`1] [<>f__AnonymousType1`2] Arthur - Excalibur [<>f__AnonymousType1`2] Arthur - Chain Mail

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  • Reading RSS data with Linq to Xml

    - by hakanbilge
     Linq to Xml is the best method, I think, for querying, constructing and writing Xml data. In this article, I'll show how to read Rss data with this powerful Xml technique, Linq. Now, create a Website in Visual Studio, add a Textbox and a  [read more....]

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