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• Using Multiple Foreign Keys to the same table in LINQ

  - by Graeme

  I have a table Users and a table Items In the Items table, I have fields such as ModifiedBy CreatedBy AssignedTo which all have a userId integer. The database is set up to have these as foreign keys back to the Users table. When using LINQToSQL, the relationships which are automatically built from the dbml end up giving me names like User, User1 and User2 e.g. myItem.User1.Name or myItem.User2.Name Obviously this isn't very readable and I'd like it be along the lines of myItem.CreatedByUser.Name or myItem.ModifiedByUser.Name etc I could change the names of the relationships but that means I have to redo that every time I change the db schema and refresh the dbml. Is there any way round this?

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• Anyone knows any Linq to XQuery implementation ?

  - by Tim Mahy

  Hi all, the question is basically in the title. Also if anyone has started some kind of implementation but never finished it and is willing to share it, I'm interested! :) Or if it is being used internally in an open-source project... greetings, Tim

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• Which LINQ query is more effective?

  - by Danny Chen

  I have a huge IEnumerable(suppose the name is myItems), which way is more effective? Solution 1: Filter it first then ForEach. Array.ForEach(myItems.Where(FILTER-IT-HERE).ToArray(),MY-ACTION); Solution 2: Do RETURN in MY-ACTION if the item is not up to the mustard. Array.ForEach(myItems.ToArray(),MY-ACTION-WITH-FILTER); Is one of them always better than another? Or any other good suggestions? Thanks in advance.

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• using Linq to partition data into arrays

  - by user200295

  I have an array of elements where the element has a Flagged boolean value. 1 flagged 2 not flagged 3 not flagged 4 flagged 5 not flagged 6 not flagged 7 not flagged 8 flagged 9 not flagged I want to break it into arrays based on the flagged indicator output array 1 {1,2,3} array 2 {4,5,6,7} array 3 {8,9}

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• What's FirstOrDefault for DateTime in Linq?

  - by Keltex

  If I have a query that returns a DateTime, what's the value of FirstOrDefault? Is there a generic way to get the default value of a C# scalar? Example: var list = (from item in db.Items where item.ID==1234 select item.StartDate).FirstOrDefault(); Edit: Assume that the column StartDate can't be null.

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• linq null parameter

  - by kusanagi

  how can i do the code static string BuildMenu(List<Menu> menu, int? parentId) { foreach (var item in menu.Where(i => i.ParentMenu == parentId || i.ParentMenu.MenuId == parentId).ToList()) { } } return BuildMenu(menuList,null); so if parentId==null then return only records i = i.ParentMenu == null but when parentId is 0 then return records with i.ParentMenu.MenuId == parentId

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• Can I assume interface oriented programming as a good object oriented programming?

  - by david

  I have been programming for decades but I have not been used to object oriented programming. But for recenet years, I had a great opportunity to learn OOP, its principles, and a lot of patterns that are great. Since I've learned OOP, I tried to apply them to a couple of projects and found those projects successful. Unfortunately I didn't follow extreme programming that suggests writing test first, mainly because their time frame were tight. What I did for those projects were Identify all necessary classes and create them with proper properties and methods whenever there is dependency between classes, write interface between them see if there is any patterns for certain relationships between classes to replace By successful, I meant that it was quick development effort, the classes can be reused better, and flexible enough so that another programmer does not have to change something else to fix another part. But I wonder if this is a good practice. Of course, I know I need to put writing unit tests first in my work process. But other than that, is there any problem with this approach - creating lots of interfaces - in long term?

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• linq selecting into custom object

  - by user276640

  what is wrong with such code public List<SearchItem> Search(string find) { return (from i in _dataContext.News where i.Text.Contains(find) select new SearchItem { ControllerAction = "test", id = i.Id.ToString(), LinkText = "test" }).ToList(); } public struct SearchItem { public string ControllerAction; public string LinkText; public string id; }

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• LINQ to XML Query Help

  - by cw

  Hello, I am trying to get a "diff" of 2 xml documents and end up with a list of Elements that are different. Below is the XML, I was wondering if anyone can assist. In the case below, I want the list to contain the "file2.xml" element and the "file3.xml" element because they are both different or new than the first xml document. Thanks in advance! <?xml version="1.0" encoding="utf-8" ?> <versioninfo> <files> <file version="1.0">file1.xml</file> <file version="1.0">file2.xml</file> </files> </versioninfo> <?xml version="1.0" encoding="utf-8" ?> <versioninfo> <files> <file version="1.0">file1.xml</file> <file version="1.1">file2.xml</file> <file version="1.0">file3.xml</file> </files> </versioninfo>

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• Linq-to-Entities Left JOIN

  - by shivesh

  This is my query: from forum in Forums join post in Posts on forum equals post.Forum into postGroup from p in postGroup where p.ParentPostID==0 select new { forum.Title, forum.ForumID, LastPostTitle = p.Title, LastPostAddedDate = p.AddedDate }).OrderBy(o=>o.ForumID) Currently the Join is not left join, meaning if some forum doesn't have a post that belongs to it, it will not be returned. The forum without posts must be returned with null (or default) values for the post properties.

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• linq merge elements with orderby

  - by Sanja Melnichuk

  Hi all. I need to select all terminals sorted by Attributes[2] // get all query IQueryable<ITerminal> itt = repository.Terminals.GetQuery(); // get all with Attributes[2] IQueryable<ITerminal> itt2 = itt .Select(item => new { attrs = item.Attributes[2], term = item }) .OrderBy(x => x.attrs) .Select(x => x.term); Now how to select from itt all terminals but ordered by itt2 results? How to order them by itt2? Example: itt = c,d,r,a,w,b itt2 = a,b,c // after select and after merge: a,b,c d,r,w Thanks all

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• substring with linq??

  - by phenevo

  I've got collection of words, and i wanna create collection from this collection limited to 5 chars Input: Car Collection Limited stackoverflow Output: car colle limit stack word.Substring(0,5) throws exception (length) word.Take(10) is not good idea, too... Any good ideas ??

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• LINQ method chaining and granular error handling

  - by Clafou

  I have a method which can be written pretty neatly through method chaining: return viewer.ServerReport.GetParameters() .Single(p => p.Name == Convention.Ssrs.RegionParamName) .ValidValues .Select(v => v.Value); However I'd like to be able to do some checks at each point as I wish to provide helpful diagnostics information if any of the chained methods returns unexpected results. To achieve this, I need to break up all my chaining and follow each call with an if block. It makes the code a lot less readable. Ideally I'd like to be able to weave in some chained method calls which would allow me to handle unexpected outcomes at each point (e.g. throw a meaningful exception such as new ConventionException("The report contains no parameter") if the first method returns an empty collection). Can anyone suggest a simple way to achieve such a thing?

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• LINQ Join 2 List<T>s

  - by David Murdoch

  Preface: I don't understand what this does: o => o.ID, i => i.ID, (o, id) => o So go easy on me. :-) I have 2 lists that I need to join together: // contains ALL contacts for a customer. // Each item has a unique ID. // There are no duplicates. ContactCollection list1 = myCustomer.GetContacts(); // contains the customer contacts (in list1) relevant to a REPORT // the items in this list may have properties that differ from those in list1. /*****/// e.g.: /*****/ bool SelectedForNotification; /*****/// may be different. ContactCollection list2 = myReport.GetContacts(); I need to create a third ContactCollection that contains all of the contacts in list1 but with the properties of the items in list2, if they are there (list3.Count == list1.Count). I feel as though I'm not making any sense. So, please ask questions in the comments and I'll try to clarify.

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• Using LINQ to remove dupicates in dictionary and the count of those duplicates

  - by Robert

  I have some code that returns unique elements in my dictionary, but I would also like to return the count of the duplicate elements. Basically change dictionary[key, uniqueelement] to dictionary[uniqueelement, count]. Here is my code that just returns the unique elements. var uniqueItems = deviceInstances.Children.GroupBy(pair => pair.Value.Information.UnderlyingDeviceType) .Select(group => group.First()) .ToDictionary(pair => pair.Key, pair => pair.Value.Information.UnderlyingDeviceType.ToString());

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• Windows Azure Table Storage LINQ Operators

  - by Ryan Elkins

  Currently Table Storage supports From, Where, Take, and First. Are there plans to support any of the other 29 operators? If we have to code for these ourselves, how much of a performance difference are we looking at to something similar via SQL and SQL Server? Do you see it being somewhat comparable or will it be far far slower if I need to do a Count or Sum or Group By over a gigantic dataset? I like the Azure platform and the idea of cloud based storage. I like Windows Azure for the amount of data it can store and the schema-less nature of table storage. SQL Azure just won't work due to the high cost to storage space.

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• How to use linq to find the minimum

  - by Danvil

  I have a class A { public float Score; ... } and a List<A> items and would like to find the A which has minimal score. Using items.Min(x => x.Score) gives the minimal score and not the instance with minimal score. How can I get the instance with only iterating once through my Collection?

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• Dynamic Linq query issue

  - by Alex

  Hey All, Im trying to query the Netflix OData feed. I have the following query that works fine in LinqPad: from g in Genres from t in g.Titles where g.Name == "Horror" && t.AverageRating == 2 && t.ReleaseYear == 2004 select t But, when I move it over to my Silverlight app, the user selects what to search on so I may or may not have all of the params. That being the case, I need to construct the query at runtime. Ive looked the the Dynamic Query stuff and that will do fine...the issue that I have is that I need an initial acceptable query to append to and this doesn't fly: from g in Genres from t in g.Titles select t; Any additional thoughts would be appreciated. Thanks in advance

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• How to bind gridview using linq/Entity Framework?

  - by Kay

  I need to bind GridView, I am using this code: ProductDBEntities db = new ProductPDBEntities(); var pro = from u in db.Products where u.PID == 1 select u; if (pro != null) { GridView1.DataSource = pro; GridView1.DataBind(); } and getting this error. System.InvalidOperationException: Sequence contains more than one element Can somebody please tell me what am I doin wrong?

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• LINQ Query returns nothing.

  - by gtas

  Why is this query returns 0 lines? There is a record matching the arguments. Deafkaw.Where(p => (p.ImerominiaKataxorisis >= aDate && p.ImerominiaKataxorisis <= DateTime.Now) && (p.Year == etos && p.IsYpodeigma == false) ).ToList(); Am i missing something?

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• linq expression in vb.net

  - by Thurein

  Hi, Can any body translate the following c# code to vb. I have tried telarik code converter but I got problem at expression.call and it won't compile at all. private static IOrderedQueryable<T> OrderingHelper<T>(IQueryable<T> source, string propertyName, bool descending, bool anotherLevel) { ParameterExpression param = Expression.Parameter(typeof(T), string.Empty); MemberExpression property = Expression.PropertyOrField(param, propertyName); LambdaExpression sort = Expression.Lambda(property, param); MethodCallExpression call = Expression.Call( typeof(Queryable), (!anotherLevel ? "OrderBy" : "ThenBy") + (descending ? "Descending" : string.Empty), new[] { typeof(T), property.Type }, // error line source.Expression, Expression.Quote(sort)); return (IOrderedQueryable<T>)source.Provider.CreateQuery<T>(call); } thanks Thurein

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• Linq DateTime expressions wont compare if only one is nullable

  - by tigermain

  I have been getting the following exception: The binary operator GreaterThanOrEqual is not defined for the types 'System.Nullable`1[System.DateTime]' and 'System.DateTime'. I am getting the left hand expression from a class property which is a nullable datetime variable and my right hand side is using Expression.Constant(new Nullable<DateTime>(DateTime.Now)) However I still get the above exception despite explicitly setting the right hand expression to a nullable type

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• LINQ query null reference exception

  - by user289082

  Hi! I have the next query: var bPermisos = from b in ruc.Permisos where b.IdUsuario == cu.Id select new Permisos(){ Id=b.Id, IdUsuario=b.Id, IdPerfil=b.Id, Estatus=b.Estatus }; var qSisPer = from perm in bPermisos select new { perm.IdPerfil,perm.Cat_Perfil.Nivel,perm.Cat_Perfil.Nombre,Nombre_Sistem=perm.Cat_Perfil.Cat_Sistema.Nombre}; And is throwing me an exception, plz help!

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• linq to sql loadwith vs associatewith

  - by stackoverflowuser

  what is the difference between loadwith and associatewith. From the articles i read it seems that loadwith is used to load addition data (eg all orders for the customers). While AssociateWith is used to filter data. Is that a correct understanding? Also it will be nice if someone can explain this with an example based explanation.

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• LINQ to SQL: making a "double IN" query crashes

  - by Alex

  I need to do the following thing: var a = from c in DB.Customers where (from t1 in DB.Table1 where t1.Date >= DataTime.Now select t1.ID).Contains(c.ID) && (from t2 in DB.Table2 where t2.Date >= DataTime.Now select t2.ID).Contains(c.ID) select a It doesn't want to run. I get the following error: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. But when I try to run var a = from c in DB.Customers where (from t1 in DB.Table1 where t1.Date >= DataTime.Now select t1.ID).Contains(c.ID) select a OR var a = from c in DB.Customers where (from t2 in DB.Table2 where t2.Date = DataTime.Now select t2.ID).Contains(c.ID) select a It works! I'm sure that there both IN queries contain some customers ids.

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