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  • Search by Letters using LINQ

    - by Biswo
    hi i m using Linq & C# and i want to filter my data as this syntax in Sql Syntax in sql is I hav one table name Customer in which name is field 'Select name from customer where name like 'C%'' can u help to solve this code in Linq

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  • how to specify literal value in linq union

    - by lowlyintern
    I have the following SQL query, note I want the literal value '0' in the second field in the second SELECT statement from the ItemSale table. How do I express this in LINQ? I get the error message 'Invalid anonymous type member declarator'. SELECT BranchNumber,QuantitySold FROM Department UNION SELECT BranchNumber,0 FROM ItemSale How to express the '0' in LINQ? var unionQuery = (from dept in Department select new { dept.BranchNumber, dept.QuantitySold, }) .Concat(from item in ItemSale select new { item.BranchNumber, 0 });

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  • .Net Linq - Join together all item of a List

    - by Melursus
    How can I write a Linq expression that select item from a List and join them together ? Example IList<string> data = new List<string>(); data.Add("MyData1"); data.Add("MyData2"); string result = //some linq query... I try data.Select(x => x + ","); //result = "MyData1, MyData2"

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  • How do linq Last() work?

    - by acidzombie24
    I dont understand how current can be null and last can be an object while last being a LINQ function. I thought last uses GetEnumerator and keeps going until current == null and returns the object. However as you can see the first GetEnumerator().Current is null and last somehow returns an object. How do linq Last() work? var.GetEnumerator().Current var.Last()

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  • Data access layer using Linq to SQL

    - by Andrei Tanasescu
    I am building a c# - linq - sql server winforms/asp.net application, accessing a database. I would like my business logic layer to be easily testable, and that means not littering it with Linq database queries everywhere. What design patterns/ best practices are available for the following use cases - inserting/updating a new object - searching for an object - loading a bunch of related data into a sort of "presentation" object that could be displayed by various views ?

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  • LINQ - joining multiple lists

    - by kristian
    I've looked at the 101 Linq Samples here but I can't see anything like this in that list. If I'm just not seeing a relevant example there, please link to it. If I have these 3 classes: class Student { int id; string name } class Course { int id, string name } class Enrolment { int studentId; int courseId; } How would I use LINQ to get a list of courses a student is enrolled on? (assume I have an IList of all three classes)

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  • Linq to XSD processing

    - by goel
    For Typed Xml to Linq processing ,do i need to download Linq to XSD alpha installer or is it available in VS 2008 ? (I am using VS 2008 Professional edition).

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  • Cast problem with LINQ

    - by yigit
    I'm tring to get my product's types to a list with Linq. var types = (from t in NHibernateSession.Linq<Product>() select t.Type).Distinct().ToList<Type>(); return types; But its giving an Unable to cast object of type error '...Domain.Product' to type '...Domain.Type'. Please tell where am I going wrong.

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  • Should I be learning Linq, Direct SQL Commands (in .net), EF or other?

    - by Wil
    Basically, I have a very good knowledge of plain old SQL coming from Classic ASP programming. Over the past couple of months, I have been learning C# and today was my first full day at MVC 3 (Razor) which I am loving! I need to get back in to Databases and I know that writing SqlCommand everywhere is obviously outdated (although it is nice I can still do it!). I used to go to a great usergroup as an IT Pro and the developer stuff went completely over my head, however I do remember a few things which kept coming up such as LINQ... However, that was some time ago and now the same people on Twitter are saying how out dated it is. I have tried to do research on both and I am clueless as to what direction I should go in, or when to use one over another (if learning both is a good thing). I am more so confused as I thought EF was a part of the .Net Framework, however, reading through the quick start guide, I had to download a component using Nuget. ... Basically I am out of my depth here and just need some honest advice of where to go!

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  • Use CompiledQuery.Compile to improve LINQ to SQL performance

    - by Michael Freidgeim
    After reading DLinq (Linq to SQL) Performance and in particular Part 4  I had a few questions. If CompiledQuery.Compile gives so much benefits, why not to do it for all Linq To Sql queries? Is any essential disadvantages of compiling all select queries? What are conditions, when compiling makes whose performance, for how much percentage? World be good to have default on application config level or on DBML level to specify are all select queries to be compiled? And the same questions about Entity Framework CompiledQuery Class. However in comments I’ve found answer  of the author ricom 6 Jul 2007 3:08 AM Compiling the query makes it durable. There is no need for this, nor is there any desire, unless you intend to run that same query many times. SQL provides regular select statements, prepared select statements, and stored procedures for a reason.  Linq now has analogs. Also from 10 Tips to Improve your LINQ to SQL Application Performance   If you are using CompiledQuery make sure that you are using it more than once as it is more costly than normal querying for the first time. The resulting function coming as a CompiledQuery is an object, having the SQL statement and the delegate to apply it.  And your delegate has the ability to replace the variables (or parameters) in the resulting query. However I feel that many developers are not informed enough about benefits of Compile. I think that tools like FxCop and Resharper should check the queries  and suggest if compiling is recommended. Related Articles for LINQ to SQL: MSDN How to: Store and Reuse Queries (LINQ to SQL) 10 Tips to Improve your LINQ to SQL Application Performance Related Articles for Entity Framework: MSDN: CompiledQuery Class Exploring the Performance of the ADO.NET Entity Framework - Part 1 Exploring the Performance of the ADO.NET Entity Framework – Part 2 ADO.NET Entity Framework 4.0: Making it fast through Compiled Query

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  • Deploy multiple emails to email providers, but without showing favouritism

    - by Ardman
    We are currently developing a new email deployment system. We have the system currently configured so that it reads a record from the database and loads the email content and deploys it to the target. Now we want to move this over to multiple threads. That is easily done, except we then hit the email providers returning SMTP codes referring to "Too many connections", or "Deferred connection". The solution to this is to have a thread open up a connection to the email provider and deploy n emails and then disconnect. We have currently configured the application so that it will support these session based email deployments. The problem is this, the database table has multiple email addresses in and they aren't grouped by email provider because that will show favouritism. We need to be able to retrieve a set number of, i.e. Hotmail, emails (@hotmail.com, @hotmail.co.uk, @live.co.uk) so that we are reducing the number of connections to Hotmail and reducing the risks of getting the "Too many connections" error. We are at the point now where we have gone round and round in circles trying to get a solution, so I thought I'd throw it out there and see if anyone has any ideas? EDIT I would like to stress that this application is not used for spamming purposes.

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  • LINQ - Select Statement - The null value cannot be assigned to a member with type System.Int32 which

    - by thiag0
    I am trying to achieve the following... _4S.NJB_Request request = (from r in db.NJB_Requests where r.RequestId == referenceId select r).Take(1).SingleOrDefault(); Getting the following exception... Message: The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type. StackTrace: at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult) at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries) at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression) at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source) at DAL.SqlDataProvider.MarkNJBPCRequestAsComplete(Int32 referenceId, Int32 processState) I have verified that 'referenceId' does have a value. Anyone know why this would happen in a select statement? Thanks!

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  • Linq to SQL and concurrency with Rob Conery repository pattern

    - by David Hall
    I have implemented a DAL using Rob Conery's spin on the repository pattern (from the MVC Storefront project) where I map database objects to domain objects using Linq and use Linq to SQL to actually get the data. This is all working wonderfully giving me the full control over the shape of my domain objects that I want, but I have hit a problem with concurrency that I thought I'd ask about here. I have concurrency working but the solution feels like it might be wrong (just one of those gitchy feelings). The basic pattern is: private MyDataContext _datacontext private Table _tasks; public Repository(MyDataContext datacontext) { _dataContext = datacontext; } public void GetTasks() { _tasks = from t in _dataContext.Tasks; return from t in _tasks select new Domain.Task { Name = t.Name, Id = t.TaskId, Description = t.Description }; } public void SaveTask(Domain.Task task) { Task dbTask = null; // Logic for new tasks omitted... dbTask = (from t in _tasks where t.TaskId == task.Id select t).SingleOrDefault(); dbTask.Description = task.Description, dbTask.Name = task.Name, _dataContext.SubmitChanges(); } So with that implementation I've lost concurrency tracking because of the mapping to the domain task. I get it back by storing the private Table which is my datacontext list of tasks at the time of getting the original task. I then update the tasks from this stored Table and save what I've updated This is working - I get change conflict exceptions raised when there are concurrency violations, just as I want. However, it just screams to me that I've missed a trick. Is there a better way of doing this? I've looked at the .Attach method on the datacontext but that appears to require storing the original version in a similar way to what I'm already doing. I also know that I could avoid all this by doing away with the domain objects and letting the Linq to SQL generated objects all the way up my stack - but I dislike that just as much as I dislike the way I'm handling concurrency.

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  • LINQ into SortedList

    - by Chris Simmons
    I'm a complete LINQ newbie, so I don't know if my LINQ is incorrect for what I need to do or if my expectations of performance are too high. I've got a SortedList of objects, keyed by int; SortedList as opposed to SortedDictionary because I'll be populating the collection with pre-sorted data. My task is to find either the exact key or, if there is no exact key, the one with the next higher value. If the search is too high for the list (e.g. highest key is 100, but search for 105), return null. // The structure of this class is unimportant. Just using // it as an illustration. public class CX { public int KEY; public DateTime DT; } static CX getItem(int i, SortedList<int, CX> list) { var items = (from kv in list where kv.Key >= i select kv.Key); if (items.Any()) { return list[items.Min()]; } return null; } Given a list of 50,000 records, calling getItem 500 times takes about a second and a half. Calling it 50,000 times takes over 2 minutes. This performance seems very poor. Is my LINQ bad? Am I expecting too much? Should I be rolling my own binary search function?

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  • Delphi Prism and LINQ to SQL / Entity Framework

    - by Vegar
    I have found many posts and examples of using LINQ-syntax in Delphi Prism (Oxygene), but I have never found anything on LINQ to SQL or Entity Framework. Is it possible to use LINQ to SQL or Entity Framework together with Prism? Where can I found such an example? Update: Olaf is giving an answer through his blog The question is now if any visual tools and code generation is provided, or if everything must be done by hand... Second update: Olaf has answered the tool/code generation-question in a comment on his site: The class designer is there, but there is no Pascal code gen. According to marc hoffman that is currently not on their list. For now you have to live with manual mapping. I guess, if you had Visual Studio (not just the VS shell), that you could add a C# library project to your solution, reference that from your Prism project. Then create the Table-Class mapping in the C# project using the visual designer. Maybe somewhat ugly, but possibly the key to get the Designer + CodeGen integrated into Prism. Who cares what language is used for the mapping . I will say this is a 1 - 0 to c# vs prism. If I did not care which language is used for the mapping - why should I care about which language is used for the rest?

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  • LINQ-to-SQL: Could not find key member 'x' of key 'x' on type 'y'

    - by Austin Hyde
    I am trying to connect my application to a SQLite database with LINQ-to-SQL, and so far everything has worked fine. The only hitch was that the SQLite provider I am using does not support code generation (unless I was doing something wrong), so I manually coded the 4 tables in the DB. The solution builds properly, but will not run, giving me the error message Could not find key member 'ItemType_Id' of key 'ItemType_Id' on type 'Item'. The key may be wrong or the field or property on 'Item' has changed names. I have checked and double checked spellings and field names on the database and in the attribute mappings, but could not find any problems. The SQL for the table looks like this: CREATE TABLE [Items] ( [Id] integer PRIMARY KEY AUTOINCREMENT NOT NULL, [Name] text NOT NULL, [ItemType_Id] integer NOT NULL ); And my mapping code: [Table(Name="Items")] class Item { // [snip] [Column(Name = "Id", IsPrimaryKey=true, IsDbGenerated=true)] public int Id { get; set; } // [snip] [Column(Name="ItemType_Id")] public int ItemTypeId { get; set; } [Association(Storage = "_itemType", ThisKey = "ItemType_Id")] public ItemType ItemType { get { return _itemType.Entity; } set { _itemType.Entity = value; } } private EntityRef<ItemType> _itemType; // [snip] } This is really my first excursion into LINQ-to-SQL, and am learning as I go, but I cannot seem to get past this seeming simple problem. Why cannot LINQ see my association?

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  • extracting RDL data using LINQ

    - by BobC
    I'm working with some SQL Report definition files (RDLs), using LINQ to extract component query statements for validation. I'm trying to extract the <DataSet> elements from under the <DataSets> element. I seem to be getting hung up with one of the elements under <DataSet><Fields><Field> which has a namespace qualifier <rd:TypeName> I've been using LINQ to XML for other parts of the files where there is no namespace qualifiers with no trouble, by specifying a default namespace. The RDL specifies two namespaces: xmlns="http://schemas.microsoft.com/sqlserver/reporting/2005/01/reportdefinition" xmlns:rd="http://schemas.microsoft.com/SQLServer/reporting/reportdesigner"> When I try to get the <DataSets> element, however, I get the following error: System.Xml.XmlException - The ':' character, hexadecimal value 0x3A, cannot be included in a name. I know it has to do with the namespace qualifier (rd:) in one of the child elements, but I'm having difficulty getting a LINQ expression that works. Any help would be appreciated. Thanks!

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  • C# LINQ to XML missing space character.

    - by Fossaw
    I write an XML file "by hand", (i.e. not with LINQ to XML), which sometimes includes an open/close tag containing a single space character. Upon viewing the resulting file, all appears correct, example below... <Item> <ItemNumber>3</ItemNumber> <English> </English> <Translation>Ignore this one. Do not remove.</Translation> </Item> ... the reasons for doing this are various and irrelevent, it is done. Later, I use a C# program with LINQ to XML to read the file back and extract the record... XElement X_EnglishE = null; // This is CRAZY foreach (XElement i in Records) { X_EnglishE = i.Element("English"); // There is only one damned record! } string X_English = X_EnglishE.ToString(); ... and test to make sure it is unchanged from the database record. I detect a change, when processing Items where the field had the single space character... +E+ Text[3] English source has been altered: Was: >>> <<< Now: >>><<< ... the and <<< parts I added to see what was happening, (hard to see space characters). I have fiddled around with this but can't see why this is so. It is not absolutely critical, as the field is not used, (yet), but I cannot trust C# or LINQ or whatever is doing this, if I do not understand why it is so. So what is doing that and why?

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  • Linq: the linked objects are null, why?

    - by user46503
    Hello, I have several linked tables (entities). I'm trying to get the entities using the following linq: ObjectQuery<Location> locations = context.Location; ObjectQuery<ProductPrice> productPrice = context.ProductPrice; ObjectQuery<Product> products = context.Product; IQueryable<ProductPrice> res1 = from pp in productPrice join loc in locations on pp.Location equals loc join prod in products on pp.Product equals prod where prod.Title.ToLower().IndexOf(Word.ToLower()) > -1 select pp; This query returns 2 records, ProductPrice objects that have linked object Location and Product but they are null and I cannot understand why. If I try to fill them in the linq as below: res = from pp in productPrice join loc in locations on pp.Location equals loc join prod in products on pp.Product equals prod where prod.Title.ToLower().IndexOf(Word.ToLower()) > -1 select new ProductPrice { ProductPriceId = pp.ProductPriceId, Product = prod }; I have the exception "The entity or complex type 'PBExplorerData.ProductPrice' cannot be constructed in a LINQ to Entities query" Could someone please explain me what happens and what I need to do? Thanks

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  • Trouble with LINQ databind to GridView and RowDataBound

    - by Michael
    Greetings all, I am working on redesigning my personal Web site using VS 2008 and have chosen to use LINQ to create by data-access layer. Part of my site will be a little app to help manage my budget better. My first LINQ query does successfully execute and display in a GridView, but when I try to use a RowDataBound event to work with the results and refine them a bit, I get the error: The type or namespace name 'var' could not be found (are you missing a using directive or an assembly reference?) This interesting part is, if I just try to put in a var s = "s"; anywhere else in the same file, I get the same error too. If I go to other files in the web project, var s = "s"; compiles fine. Here is the LINQ Query call: public static IQueryable pubGetRecentTransactions(int param_accountid) { clsDataContext db; db = new clsDataContext(); var query = from d in db.tblMoneyTransactions join p in db.tblMoneyTransactions on d.iParentTransID equals p.iTransID into dp from p in dp.DefaultIfEmpty() where d.iAccountID == param_accountid orderby d.dtTransDate descending, d.iTransID ascending select new { d.iTransID, d.dtTransDate, sTransDesc = p != null ? p.sTransDesc : d.sTransDesc, d.sTransMemo, d.mTransAmt, d.iCheckNum, d.iParentTransID, d.iReconciled, d.bIsTransfer }; return query; } protected void Page_Load(object sender, EventArgs e) { if (!this.IsPostBack) { this.prvLoadData(); } } internal void prvLoadData() { prvCtlGridTransactions.DataSource = clsMoneyTransactions.pubGetRecentTransactions(2); prvCtlGridTransactions.DataBind(); } protected void prvCtlGridTransactions_RowDataBound(object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { var datarow = e.Row.DataItem; var s = "s"; e.Row.Cells[0].Text = datarow.dtTransDate.ToShortDateString(); e.Row.Cells[1].Text = datarow.sTransDesc; e.Row.Cells[2].Text = datarow.mTransAmt.ToString("c"); e.Row.Cells[3].Text = datarow.iReconciled.ToString(); }//end if }//end RowDataBound My googling to date hasn't found a good answer, so I turn it over to this trusted community. I appreciate your time in assisting me.

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  • C# LINQ to XML nissing space character.

    - by Fossaw
    I write an XML file "by hand", (i.e. not with LINQ to XML), which sometimes includes an open/close tag containing a single space character. Upon viewing the resulting file, all appears correct, example below... <Item> <ItemNumber>3</ItemNumber> <English> </English> <Translation>Ignore this one. Do not remove.</Translation> </Item> ... the reasons for doing this are various and irrelevent, it is done. Later, I use a C# program with LINQ to XML to read the file back and extract the record... XElement X_EnglishE = null; // This is CRAZY foreach (XElement i in Records) { X_EnglishE = i.Element("English"); // There is only one damned record! } string X_English = X_EnglishE.ToString(); ... and test to make sure it is unchanged from the database record. I detect a change, when processing Items where the field had the single space character... +E+ Text[3] English source has been altered: Was: >>> <<< Now: >>><<< ... the and <<< parts I added to see what was happening, (hard to see space characters). I have fiddled around with this but can't see why this is so. It is not absolutely critical, as the field is not used, (yet), but I cannot trust C# or LINQ or whatever is doing this, if I do not understand why it is so. So what is doing that and why?

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  • LINQ to XML contents of child records.

    - by Fossaw
    I have this LINQ to XML enquiry... var Records = from Item in XDoc.Root.Elements("Item") where (string)Item.Element("ItemNumber") == item.ID.ToString select Item; ... where ItemNumber is a reference number used in the XML, (originally written by this program but manually edited by "others"), and item.ID is the database version of the same thing. The query executes, and I can test for the number of entries in the result fine... if (Records.Count() < 1) ... you get the idea. I have established that there is only one record. Each Item has several child fields. I want to test the values of the child fields are reasonable before passing them on to the database update sub-system. The XML is produced by the program, but edited by users, so I need to really check what is coming back. So I tried... if (DB_English.ToString() != Records.Elements("English").ToString()) ... DB_English is from the database, but the XML in Records, does not contain the contents of that field, it contains... System.Xml.Linq.Extensions+<GetElements>d__29`1[System.Xml.Linq.XElement] ... so, how do I get the value of this element in the XML file? I need to check the field in the XML has not been altered, (the manual editors of this data file are not potentially 100% reliable).

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