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  • LINQ nested joins

    - by ace
    Im trying to convert a SQL join to LINQ. I need some help in getting the nested join working in LINQ. This is my SQL query, Ive cut it short just to show the nested join in SQL: LEFT OUTER JOIN dbo.TaskCommentRecipient RIGHT OUTER JOIN dbo.TaskComment ON dbo.TaskCommentRecipient.TaskCommentID = dbo.TaskComment.TaskCommentID ON dbo.Task.Taskid = dbo.TaskComment.TaskCommentTaskId

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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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  • .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 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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  • 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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  • Intersection() and Except() is too slow with large collections of custom objects

    - by Theo
    I am importing data from another database. My process is importing data from a remote DB into a List<DataModel> named remoteData and also importing data from the local DB into a List<DataModel> named localData. I am then using LINQ to create a list of records that are different so that I can update the local DB to match the data pulled from remote DB. Like this: var outdatedData = this.localData.Intersect(this.remoteData, new OutdatedDataComparer()).ToList(); I am then using LINQ to create a list of records that no longer exist in remoteData, but do exist in localData, so that I delete them from local database. Like this: var oldData = this.localData.Except(this.remoteData, new MatchingDataComparer()).ToList(); I am then using LINQ to do the opposite of the above to add the new data to the local database. Like this: var newData = this.remoteData.Except(this.localData, new MatchingDataComparer()).ToList(); Each collection imports about 70k records, and each of the 3 LINQ operation take between 5 - 10 minutes to complete. How can I make this faster? Here is the object the collections are using: internal class DataModel { public string Key1{ get; set; } public string Key2{ get; set; } public string Value1{ get; set; } public string Value2{ get; set; } public byte? Value3{ get; set; } } The comparer used to check for outdated records: class OutdatedDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { var e = string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2) && ( !string.Equals(x.Value1, y.Value1) || !string.Equals(x.Value2, y.Value2) || x.Value3 != y.Value3 ); return e; } public int GetHashCode(DataModel obj) { return 0; } } The comparer used to find old and new records: internal class MatchingDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { return string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2); } public int GetHashCode(DataModel obj) { return 0; } }

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  • Linq to SQL, Repository, IList and Persist All

    - by Dr. Zim
    This discusses a repository which returns IList that also uses Linq to SQL as a DAL. Once you do a .ToList(), IQueryable object is gone once you exit the Repository. This means that I need to send the objects back in to the Repo methods .Create(Model model), .Update(Model model), and .Delete(int ID). Assuming that is correct, how do you do the PersistAll()? For example, if you did the following, how would you code that in the repository? Changed a single string property in the object Called .Update(object); Changed a different string property in the object Called .Update(object); Called .PersistAll(), which would update the database with both changed strings. How would you associate the objects in the Repository parameters with the objects in the Linq to Sql data context, especially over multiple calls? I am sure this is a standard thing. Links to examples on the web would be great!

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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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  • 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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  • Retaining Managed objects - more general retaining objects

    - by Luuk D. Jansen
    A quick question regarding Managed Objects. I created an Array with Managed Objects (in Object 1: TableViewConbtroller), and pass one of those objects to another class/object (object 2: TableCell). The original array should still be retained in the original caller class. Then Object 2 is released, does that mean that that particular item in the array is released as well, as the reference to it in Object 2 was released? I am trying to better understand how to work with ManagedObjects as I get 'Object was released' errors. [EDIT] After some experimenting I came across the following scenario: I have the main AppDelegate. In a different class I create an AppDelegate to obtain the ManagedObjectContext. appDelegate = (iDomsAppDelegate *)[[UIApplication sharedApplication] delegate]; [self setContext:[appDelegate managedObjectContext]]; When the class is finished, and I release it, the variable in the class 'appDelegate' is also released. But then the ManagedObjectContext is closed, and obvious any future attempt to use it will cause a crash. So should I leave the appDelegate unreleased? This comes to the same question as the above about when and how to release in those situations where an objects is used from another class. I think a way of putting it is, how to know when you own an object and when not.

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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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  • 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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  • 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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