linq to objects - Page 410

Is there equivalences between Microsoft and Oracle/Sun technologies?

- by Junior Mayhé

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Please help, now I have a matrix, I want use Combination algorithm to generate a array for length 6

- by user313429

The first thanks a lot for your help , the following is my matrix, I want to implement combination algorithm between multiple arrays in LINQ for this matrix. int[,] cj = { { 10, 23, 16, 20 }, { 22, 13, 1, 33 }, { 7, 19, 31, 12 }, { 30, 14, 21, 4 }, { 2, 29, 32, 6 }, { 18, 26, 17, 8 }, { 25, 11, 5, 28 }, { 24, 3, 15, 27 } }; other: public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<T> elements, int k) { return k == 0 ? new[] { new T[0] } : elements.SelectMany((e, i) => elements.Skip(i + 1).**Combinations**(k - 1).Select(c => (new[] { e }).Concat(c))); } The above method has a error in my project, System.Collections.Generic.IEnumerable' does not contain a definition for 'Combinations' and no extension method 'Combinations' accepting a first argument of type 'System.Collections.Generic.IEnumerable' could be found (are you missing a using directive or an assembly reference? I use .Net Framework3.5, what is the reason it?

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Enumerating all combinations of lists of different types

- by jball

Given two IEnumberables of different types, what is the best practice (considering readability and maintainability) for iterating over both lists to perform an action on all possible combinations? My initial solution was to use nested foreach loops, iterating over the first IEnumerable, and then within that loop, iterating over the second IEnumerable and passing the value from the outer and the current loop into the target method. Eg.: enum ParamOne { First, Second, Etc } List<int> paramTwo = new List<int>() { 1, 2, 3 }; void LoopExample() { foreach (ParamOne alpha in Enum.GetValues(typeof(ParamOne))) { foreach (int beta in paramTwo) { DoSomething(alpha, beta); } } } I tried to restructure it with LINQ, but ended up with something that had no obvious advantages and seemed less intuitive. A search here shows lots of questions about nesting foreachs to iterate over child properties, but I couldn't find anything about iterating over two distinct lists.

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Is it dangerous to store user-enterable text into a hidden form via javascript?

- by KallDrexx

In my asp.net MVC application I am using in place editors to allow users to edit fields without having a standard form view. Unfortunately, since I am using Linq to Sql combined with my data mapping layer I cannot just update one field at a time and instead need to send all fields over at once. So the solution I came up with was to store all my model fields into hidden fields, and provide span tags that contain the visible data (these span tags become editable due to my jquery plugin). When a user triggers a save of their edits of a field, jquery then takes their value and places it in the hidden form, and sends the whole form to the server to commit via ajax. When the data goes into the hidden field originally (page load) and into the span tags the data is properly encoded, but upon the user changing the data in the contenteditable span field, I just run $("#hiddenfield").val($("#spanfield").html(); Am I opening any holes this method? Obviously the server also properly encodes stuff prior to database entry.

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Entity Framework query builder methods: why "it" and not lambdas?

- by nlawalker

I'm just getting started with EF and a query like the following strikes me as odd: var departmentQuery = schoolContext.Departments.Include("Courses"). OrderBy("it.Name"); Specifically, what sticks out to me is "it.Name." When I was tooling around with LINQ to SQL, pretty much every filter in a query-builder query could be specified with a lambda, like, in this case, d = d.Name. I see that there are overrides of OrderBy that take lambdas that return an IOrderedQueryable or an IOrderedEnumable, but those obviously don't have the Execute method needed to get the ObjectResult that can then be databound. It seems strange to me after all I've read about how lambdas make so much sense for this kind of stuff, and how they are translated into expression trees and then to a target language - why do I need to use "it.Name"?

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why does an event handler never gets called if its added within a loop on an ienumerable

- by André Carvalho

For instance: IEnumerable<MyType> list = someCollection.Select(i => new MyType(i)); foreach (var item in list) item.PropertyChanged += item_PropertyChanged; <-- this never gets called Bu if list is assigned like list = someCollection.Select(i => new MyType(i)).ToArray(); the event handler does get called.. Why? (i imagine it has something to do with the fact that a linq query is lazy, but the fact of looping through the result isn't enough??)

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Does MVC replace traditional manually created UI, BLL, DAL ?

- by used2could

I'm use to creating the UI, BLL, DAL by hand (some times i've used LINQ-SQL or SubSonic for the DAL). I've done several small projects using MVC since it's release. On these projects i've still continued to write a BLL and DAL by hand and then incorporate those into the MVC's models/controllers. Looking to optimize my time on projects this seems like over kill and a potential waste of time. My question is: Would it be acceptable to roll a DAL such as SubSonic and directly use it in the Models/Controllers of my MVC web app? Now the models & controllers would act as the BLL. I just see this as a major time savor to not have to worry about another tier. (Agree ? "Please state way" : "Make argument")

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what is wrong with this insert method in asp.net mvc?

- by Pandiya Chendur

My controller calls a repository class method on insert, [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create([Bind(Exclude = "Id")]FormCollection collection) { try { MaterialsObj materialsObj = new MaterialsObj(); materialsObj.Mat_Name = collection["Mat_Name"]; materialsObj.Mes_Id = Convert.ToInt64(collection["MeasurementType"]); materialsObj.Mes_Name = collection["Mat_Type"]; materialsObj.CreatedDate = System.DateTime.Now; materialsObj.CreatedBy = Convert.ToInt64(1); materialsObj.IsDeleted = Convert.ToInt64(1); consRepository.createMaterials(materialsObj); return RedirectToAction("Index"); } catch { return View(); } } and my repository class has this, public MaterialsObj createMaterials(MaterialsObj materialsObj) { db.Materials.InsertOnSubmit(materialsObj); return materialsObj; } But when i compile this i get The best overloaded method match for 'System.Data.Linq.Table<CrMVC.Models.Material>.InsertOnSubmit(CrMVC.Models.Material)' has some invalid arguments... cannot convert from 'CrMVC.BusinessObjects.MaterialsObj' to 'CrMVC.Models.Material'.. am i missing something?

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Lamda expression will not compile

- by John Soer

I am very confused I have this lamba expression tvPatientPrecriptionsEntities.Sort((p1, p2) => p1.MedicationStartDate.Value.CompareTo(p2.MedicationStartDate.Value)); Visual studio will not compile it and complains about syntax. I converted the lamba expression to an anonymous delegate as so tvPatientPrecriptionsEntities.Sort( delegate(PatientPrecriptionsEntity p1, PatientPrecriptionsEntity p2) { return p1.MedicationStartDate.Value.CompareTo(p2.MedicationStartDate.Value); } ); and it works fine. The project is uses the .net 3.5 framework and I have a reference to system.linq.

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Methods of pulling data from a database

- by kingrichard2005

I'm getting ready to start a C# web application project and just wanted some opinions regarding pulling data from a database. As far as I can tell, I can either use C# code to access the database from the code behind (i.e. LINQ) of my web app or I can call a stored procedure that will collect all the data and then read it with a few lines of code in my code behind. I'm curious to know which of these two approaches, or any other approach, would be the most efficient, elegant, future proof and easiest to test.

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What production software have you written in F# in the past year or so that you would previously hav

- by Peter McGrattan

Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#.

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Call function in query in Entity framework 3.5

- by Ashwani K

Hello All: I am trying to run following query in entity framework 3.5 var test = from e in customers where IsValid(e) select e; Here IsValid function takes current customer and validate against some conditions and returns false or true. But when I am trying to run the query it is giving error "LINQ Method cannot be translated into a store expression." Can any body tell me any other approach? One approach I can think of is to write all validation conditions here, but that will make the code difficult to read. Thanks Ashwani

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NHibernate - get List<long> representing primary keys?

- by Nathan

I have a situation where I definitely don't want to get the whole domain object. Basically, the entity has a primary key of long (.NET)/bigint(sql server 2005). I simply need to pass the primary key to an external system which will access the database directly - and since the list of ids could be large, I don't want to rehydrate the entire domain object just to get the Id. In linq2sql, I could accomplish this with a projection, but I am restricted to NHibernate 1.2.1.4000, which doesn't support Linq. Is there a way to accomplish this using NHibernate 1.2.1.4000? (I am open to using a named-query if that will work)

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Succinct code over verbose?

- by WeNeedAnswers

With C# becoming more and more declarative and becoming the new Swiss army knife of Programming. Is it better to be succinct thus reducing the actual code base, or long winded but verbose. Is there a performance issue with succinct or does being succinct improve performance because your putting more of your code in the hands of the compiler. (LINQ being an example when used correctly). I know that verbosity should override succinct where code would become less readable, but is this a good idea when your style could affect the performance.

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Need some suggestions on my softwares architecture. [Code review]

- by Sergio Tapia

I'm making an open source C# library for other developers to use. My key concern is ease of use. This means using intuitive names, intuitive method usage and such. This is the first time I've done something with other people in mind, so I'm really concerned about the quality of the architecture. Plus, I wouldn't mind learning a thing or two. :) I have three classes: Downloader, Parser and Movie I was thinking that it would be best to only expose the Movie class of my library and have Downloader and Parser remain hidden from invocation. Ultimately, I see my library being used like this. using FreeIMDB; public void Test() { var MyMovie = Movie.FindMovie("The Matrix"); //Now MyMovie would have all it's fields set and ready for the big show. } Can you review how I'm planning this, and point out any wrong judgement calls I've made and where I could improve. Remember, my main concern is ease of use. Movie.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Drawing; namespace FreeIMDB { public class Movie { public Image Poster { get; set; } public string Title { get; set; } public DateTime ReleaseDate { get; set; } public string Rating { get; set; } public string Director { get; set; } public List<string> Writers { get; set; } public List<string> Genres { get; set; } public string Tagline { get; set; } public string Plot { get; set; } public List<string> Cast { get; set; } public string Runtime { get; set; } public string Country { get; set; } public string Language { get; set; } public Movie FindMovie(string Title) { Movie film = new Movie(); Parser parser = Parser.FromMovieTitle(Title); film.Poster = parser.Poster(); film.Title = parser.Title(); film.ReleaseDate = parser.ReleaseDate(); //And so an so forth. } public Movie FindKnownMovie(string ID) { Movie film = new Movie(); Parser parser = Parser.FromMovieID(ID); film.Poster = parser.Poster(); film.Title = parser.Title(); film.ReleaseDate = parser.ReleaseDate(); //And so an so forth. } } } Parser.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; using HtmlAgilityPack; namespace FreeIMDB { /// <summary> /// Provides a simple, and intuitive way for searching for movies and actors on IMDB. /// </summary> class Parser { private Downloader downloader = new Downloader(); private HtmlDocument Page; #region "Page Loader Events" private Parser() { } public static Parser FromMovieTitle(string MovieTitle) { var newParser = new Parser(); newParser.Page = newParser.downloader.FindMovie(MovieTitle); return newParser; } public static Parser FromActorName(string ActorName) { var newParser = new Parser(); newParser.Page = newParser.downloader.FindActor(ActorName); return newParser; } public static Parser FromMovieID(string MovieID) { var newParser = new Parser(); newParser.Page = newParser.downloader.FindKnownMovie(MovieID); return newParser; } public static Parser FromActorID(string ActorID) { var newParser = new Parser(); newParser.Page = newParser.downloader.FindKnownActor(ActorID); return newParser; } #endregion #region "Page Parsing Methods" public string Poster() { //Logic to scrape the Poster URL from the Page element of this. return null; } public string Title() { return null; } public DateTime ReleaseDate() { return null; } #endregion } } ----------------------------------------------- Do you guys think I'm heading towards a good path, or am I setting myself up for a world of hurt later on? My original thought was to separate the downloading, the parsing and the actual populating to easily have an extensible library. Imagine if one day the website changed its HTML, I would then only have to modifiy the parsing class without touching the Downloader.cs or Movie.cs class. Thanks for reading and for helping!

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Are these libraries okay to distribute with my C# application?

- by HoNgOuRu

I included these libraries or namespaces in my C# application and published the solution as freeware. I used Visual C# Express 2008. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Media; using System.Management; using System.Diagnostics; using System.Runtime.InteropServices; using System.Drawing.Text; Is it okay to give the application as freeware or am I violating any license here???

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In what specific areas has F# proven more applicable than C#?

- by Peter McGrattan

Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#. EDIT: Altered title with the intent of reducing perceived ambiguity.

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Passing an empty IEnumerable argument to a method

- by avance70

I have this method (simplified): void DoSomething(IEnumerable<int> numbers); And I invoke it like this: DoSomething(condition==true?results:new List<int>()); The variable results is formed with a LINQ select condition (IEnumerable). I was wondering is this List<int>() the best way (the fastest?) to pass an empty collection, or is new int[0] better? Or, something else would be faster, a Collection, etc.? In my example null wouldn't be ok.

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EF4: common interface for EF entities

- by Feryt

Hi. I have public interface: public interface IEntity { int ID { get; set; } string Name { get; set; } bool IsEnabled { get; set; } } ehich some EF entities implements(thanks to partial class) and extesion method: public static IEnumerable<SelectListItem> ToSelectListItems<T>(this IQueryable<T> entities, int? selectedID = null) where T : IEntity { return entities.Select(c => new { c.Name, c.ID }).ToList().Select(c => new SelectListItem { Text = c.Name, Value = c.ID.ToString(), Selected = (c.ID == selectedID) }); } Calling ToSelectListItems return exception: Unable to cast the type '<EF entity name>' to type 'IEntity'. LINQ to Entities only supports casting Entity Data Model primitive types. Why, any ideas? Thank you.

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Which external DSLs do you like to use?

- by Max Toro

The reason I'm asking is because right now there seems to be tendency to make DSLs internal. One example is LINQ in C# and VB. You can use it against in-memory objects, or you can use it as a replacement of SQL or other external DSL. Another example is HTML5 vs XHTML2. XHTML2 supported decentralized extensibility through namespaces, in other words you embed external DSL code (XForms, SVG, MathML, etc.) in your XHTML code. Sadly HTML5 doesn't seem to have such mechanism, instead new features are internal (e.g. <canvas> instead of SVG). I'd like to know what other developers think about this. Do you like using external DSLs ? Which ones ? If not, why ?

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Too Many Left Outer Joins in Entity Framework 4?

- by Adam

I have a product entity, which has 0 or 1 "BestSeller" entities. For some reason when I say: db.Products.OrderBy(p = p.BestSeller.rating).ToList(); the SQL I get has an "extra" outer join (below). And if I add on a second 0 or 1 relation ship, and order by both, then I get 4 outer joins. It seems like each such entity is producing 2 outer joins rather than one. LINQ to SQL behaves exactly as you'd expect, with no extra join. Has anyone else experienced this, or know how to fix it? SELECT [Extent1].[id] AS [id], [Extent1].[ProductName] AS [ProductName] FROM [dbo].[Products] AS [Extent1] LEFT OUTER JOIN [dbo].[BestSeller] AS [Extent2] ON [Extent1].[id] = [Extent2].[id] LEFT OUTER JOIN [dbo].[BestSeller] AS [Extent3] ON [Extent2].[id] = [Extent3].[id] ORDER BY [Extent3].[rating] ASC

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Create DataGridView columns from Table values

- by fireBand

Hi, I am using data grid view to display items as excel spread sheet in VB.NET. I got a table named CostTypes with column names [CostTypeID, CostType] and values [1,External] and [2,Internal] (These are constant but more values can be added to table). I want to create columns with names of the values[External , Internal] in DataGridView. If I use databiding directly I get columns [CostTypeID,CostType] which is not what I am looking for. If some one could explain how to create columns at runtime in datagridview or how to retrieve data from data base using LINQ so that [External , Internal] turn out to be columns that would be great. Thanks in advance.

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ASP.NET MVC Using Multiple user controls on a single .aspx(view)

- by Pinu

I am getting this following error , when i am tring to having two user controls in one page. The model item passed into the dictionary is of type 'System.Linq.EnumerableQuery1[Data.EventLog]' but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable1[Data.Notes]'. <%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server"> Test </asp:Content> <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server"> <h2>Test</h2> <% Html.RenderPartial("~/Views/Shared/UserControl/Tracking.ascx"); %> <% Html.RenderPartial("~/Views/Shared/UserControl/Notes.ascx"); %> </asp:Content>

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How to sort a list by the 2nd tuple element in python and C#

- by user350468

I had a list of tuples where every tuple consists of two integers and I wanted to sort by the 2nd integer. After looking in the python help I got this: sorted(myList, key=lambda x: x[1]) which is great. My question is, is there an equally succinct way of doing this in C# (the language I have to work in)? I know the obvious answer involving creating classes and specifying an anonymous delegate for the whole compare step but perhaps there is a linq oriented way as well. Thanks in advance for any suggestions.

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How to add .Net3.5 dll into .Net2.0 project?

- by macias

I have a dll which is based on .net 3.5 -- it uses internally for example Linq, but the exposed API is straightforward, no fancy stuff. Since C# generics are resolved at compile time I assume that for calling party all it counts is API (all public parts). However when I try to use this dll from net2.0 project I get info, that the dll cannot be referenced because the dll or one of its dependencies requires a later version of .net framework. I can install any .net version I want on target computer (when entire app is installed), but I cannot change .net version for the project itself. So: how to solve this? When adding a C dll to this project I had no such problems, so are C# dlls self-contained or not?

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- by Junior Mayhé

- by user313429

- by jball

- by KallDrexx

- by nlawalker

- by André Carvalho

- by used2could

- by Pandiya Chendur

- by John Soer

- by kingrichard2005

- by Peter McGrattan

- by Ashwani K

- by Nathan

- by WeNeedAnswers

- by Sergio Tapia

- by HoNgOuRu

- by Peter McGrattan

- by avance70

- by Feryt

- by Max Toro

- by Adam

- by fireBand

- by Pinu

- by user350468

- by macias

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