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• DBnull in Linq query causing problems

  - by nat

  hi there i am doing a query thus: int numberInInterval = (from dsStatistics.J2RespondentRow item in jStats.J2Respondent where item.EndTime > dtIntervalLower && item.EndTime <= dtIntervalUpper select item).count(); there appear to be some dbnulls in the endtime column.. any way i can avoid these? tried adding && where item.endtime != null.. and even != dbnull.value do i have to do a second (first) query to grab all that arent null then run the above one? im sure its super simple fix, but im still missing it.. as per thanks nat

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• Linq To Sql: Compiled Queries and Extension Methods

  - by Beni

  Hi community, I'm interessted, how does Linq2Sql handles a compiled query, that returns IQueryable. If I call an extension method based on a compiled query like "GetEntitiesCompiled().Count()" or "GetEntitiesCompiled().Take(x)". What does Linq2Sql do in the background? This would be very bad, so in this situation I should write a compiled query like "CountEntitiesCompiled". Does he load the result (in this case "GetEntitiesCompiled()") into the memory (mapped to the entity class like "ToList()")? So what situations make sense, when the compiled queries return IQueryable, that query is not able to modify, before request to the Sql-Server. So in my opinion I can just as good return List. Thanks for answers!

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• Why LINQ will work this way?

  - by Benny

  public static ArrayList GetStudentAsArrayList() { ArrayList students = new ArrayList { new Student() { RollNumber = 1,Name ="Alex " , Section = 1 ,HostelNumber=1 }, new Student() { RollNumber = 2,Name ="Jonty " , Section = 2 ,HostelNumber=2 }, }; return students; } this doesn't compile: ArrayList is not IEnumerable ArrayList lstStudents = GetStudentAsArrayList(); var res = from r in lstStudents select r; but this will compile: ArrayList lstStudents = GetStudentAsArrayList(); var res = from Student r in lstStudents select r; Can anybody explain? what's the magic here?

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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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• Linq 2 SQL Store inherited classes - not mapped to tables in the database

  - by user348672

  Hi. I'm trying to introduce the Linq2SQL technique into the project and have encountered the following issue: I've created ORM classes based on the Northwind database. In some other application I create several classes derived from the Linq2SQL classes. I'm able to add such a class to EntitySet but the application fails to submit changes. Is there any way around this? Sample code(MyClass is derived from the Order): DataClasses1DataContext northwind = new DataClasses1DataContext(); Product chai = northwind.Products.Single(p => p.ProductName == "Chai"); Product tofu = northwind.Products.Single(p => p.ProductName == "Tofu"); Order myOrder = new Order(); myOrder.OrderDate = DateTime.Now; myOrder.RequiredDate = DateTime.Now.AddDays(1); myOrder.Freight = 34; Order_Detail myItem1 = new Order_Detail(); myItem1.Product = chai; myItem1.Quantity = 12345; Order_Detail myItem2 = new Order_Detail(); myItem2.Product = tofu; myItem2.Quantity = 3; myOrder.Order_Details.Add(myItem1); myOrder.Order_Details.Add(myItem2); Customer myCustomer = northwind.Customers.Single(c => c.CompanyName == "B's Beverages"); MyClass newOrder = new MyClass(); newOrder.OrderDate = DateTime.Now; newOrder.RequiredDate = DateTime.Now.AddDays(31); newOrder.Freight = 35; Order_Detail myItem3 = new Order_Detail(); myItem3.Product = tofu; myItem3.Quantity = 3; newOrder.Order_Details.Add(myItem3); myCustomer.Orders.Add(myOrder); myCustomer.Orders.Add(newOrder); As I said I'm able to add the newOrder object but unable to submit into the database.

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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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• 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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• 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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• 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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• 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 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 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 SQL repository - caching data

  - by creativeincode

  I have built my first MVC solution and used the repository pattern for retrieving/inserting/updating my database. I am now in the process of refactoring and I've noticed that a lot of (in fact all) the methods within my repository are hitting the database everytime. This seems overkill and what I'd ideally like is to do is 'cache' the main data object e.g. 'GetAllAdverts' from the database and to then query against this cached object for things like 'FindAdvert(id), AddAdvert(), DeleteAdvert() etc..' I'd also need to consider updating/deleting/adding records to this cache object and the database. What is the best apporoach for something like this? My knowledge of this type of things is minimal and really looking for advice/guidance/tutorial to point me in the right direction. Thanks in advance.

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• Return an empty collection when Linq where returns nothing

  - by ahsteele

  I am using the below statement with the intent of getting all of the machine objects from the MachineList collection (type IEnumerable) that have a MachineStatus of i. The MachineList collection will not always contain machines with a status of i. At times when no machines have a MachineStatus of i I'd like to return an empty collection. My call to ActiveMachines (which is used first) works but InactiveMachines does not. public IEnumerable<Machine> ActiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "a"); } } public IEnumerable<Machine> InactiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "i"); } } Edit Upon further examination it appears that any enumeration of MachineList will cause subsequent enumerations of MachineList to throw an exeception: Object reference not set to an instance of an object. Therefore, it doesn't matter if a call is made to ActiveMachines or InactiveMachines as its an issue with the MachineList collection. This is especially troubling because I can break calls to MachineList simply by enumerating it in a Watch before it is called in code. At its lowest level MachineList implements NHibernate.IQuery being returned as an IEnumerable. What's causing MachineList to lose its contents after an initial enumeration?

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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 to sql C# updating reference Tables

  - by Laurence Burke

  ok reclarification I am adding a new address and I know the structure as AddressID = PK and all other entities are non nullable. Now on insert of a new row the addrID Pk is autogened and I am wondering if I would have to get that to create a new row in the referencing table or does that automatically get generated also. also I want to be able to repopulate the dropdownlist that lists the current employee's addresses with the newly created address. static uint _curEmpID; protected void btnAdd_Click(object sender, EventArgs e) { if (txtZip.Text != "" && txtAdd1.Text != "" && txtCity.Text != "") { TestDataClassDataContext dc = new TestDataClassDataContext(); Address addr = new Address() { AddressLine1 = txtAdd1.Text, AddressLine2 = txtAdd2.Text, City = txtCity.Text, PostalCode = txtZip.Text, StateProvinceID = Convert.ToInt32(ddlState.SelectedValue) }; dc.Addresses.InsertOnSubmit(addr); lblSuccess.Visible = true; lblErrMsg.Visible = false; dc.SubmitChanges(); // // TODO: add reference from new address to CurEmp Table // SetAddrList(); } else { lblErrMsg.Text = "Invalid Input"; lblErrMsg.Visible = true; } } protected void ddlAddList_SelectedIndexChanged(object sender, EventArgs e) { lblErrMsg.Visible = false; lblSuccess.Visible = false; TestDataClassDataContext dc = new TestDataClassDataContext(); dc.ObjectTrackingEnabled = false; if (ddlAddList.SelectedValue != "-1") { var addr = (from a in dc.Addresses where a.AddressID == Convert.ToInt32(ddlAddList.SelectedValue) select a).FirstOrDefault(); txtAdd1.Text = addr.AddressLine1; txtAdd2.Text = addr.AddressLine2; txtCity.Text = addr.City; txtZip.Text = addr.PostalCode; ddlState.SelectedValue = addr.StateProvinceID.ToString(); btnSubmit.Visible = true; btnAdd.Visible = false; } else { txtAdd1.Text = ""; txtAdd2.Text = ""; txtCity.Text = ""; txtZip.Text = ""; btnAdd.Visible = true; btnSubmit.Visible = false; } } protected void SetAddrList() { TestDataClassDataContext dc = new TestDataClassDataContext(); dc.ObjectTrackingEnabled = false; var addList = from addr in dc.Addresses from eaddr in dc.EmployeeAddresses where eaddr.EmployeeID == _curEmpID && addr.AddressID == eaddr.AddressID select new { AddValue = addr.AddressID, AddText = addr.AddressID, }; ddlAddList.DataSource = addList; ddlAddList.DataValueField = "AddValue"; ddlAddList.DataTextField = "AddText"; ddlAddList.DataBind(); ddlAddList.Items.Add(new ListItem("<Add Address>", "-1")); } OK I am hoping that I did not include too much code. I would really appreciate any other comments about I could otherwise improve this code in any other ways also.

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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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• 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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• 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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• 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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• Submitting changes to 2 tables with C# linq only one table is changing

  - by Laurence Burke

  SO I am changing the values in 2 different tables and the only table changing is the address table any one know why? protected void btnSubmit_Click(object sender, EventArgs e) { TestDataClassDataContext dc = new TestDataClassDataContext(); var addr = (from a in dc.Addresses where a.AddressID == Convert.ToInt32(ddlAddList.SelectedValue) select a).FirstOrDefault(); var caddr = (from ca in dc.CustomerAddresses where addr.AddressID == ca.AddressID select ca).FirstOrDefault(); if (txtZip.Text != "" && txtAdd1.Text != "" && txtCity.Text != "") { addr.AddressLine1 = txtAdd1.Text; addr.AddressLine2 = txtAdd2.Text; addr.City = txtCity.Text; addr.PostalCode = txtZip.Text; addr.StateProvinceID = Convert.ToInt32(ddlState.SelectedValue); caddr.AddressTypeID = Convert.ToInt32(ddlAddrType.SelectedValue); dc.SubmitChanges(); lblErrMsg.Visible = false; lblSuccess.Visible = true; } else { lblErrMsg.Text = "Invalid Input"; lblErrMsg.Visible = true; } }

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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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• Referencing object's identity before submitting changes in LINQ

  - by Axarydax

  Hi, is there a way of knowing ID of identity column of record inserted via InsertOnSubmit beforehand, e.g. before calling datasource's SubmitChanges? Imagine I'm populating some kind of hierarchy in the database, but I wouldn't want to submit changes on each recursive call of each child node (e.g. if I had Directories table and Files table and am recreating my filesystem structure in the database). I'd like to do it that way, so I create a Directory object, set its name and attributes, then InsertOnSubmit it into DataContext.Directories collection, then reference Directory.ID in its child Files. Currently I need to call InsertOnSubmit to insert the 'directory' into the database and the database mapping fills its ID column. But this creates a lot of transactions and accesses to database and I imagine that if I did this inserting in a batch, the performance would be better. What I'd like to do is to somehow use Directory.ID before commiting changes, create all my File and Directory objects in advance and then do a big submit that puts all stuff into database. I'm also open to solving this problem via a stored procedure, I assume the performance would be even better if all operations would be done directly in the database.

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• Adding rows with linq trouble with reference table

  - by Laurence Burke

  I am adding a new address and I know the structure as AddressID = PK and all other entities are non nullable. Now on insert of a new row the addrID Pk is autogened and I am wondering if I would have to get that to create a new row in the referencing table EmployeeAddress or does that automatically get generated also. also I want to be able to repopulate the dropdownlist that lists the current employee's addresses with the newly created address. static uint _curEmpID; protected void btnAdd_Click(object sender, EventArgs e) { if (txtZip.Text != "" && txtAdd1.Text != "" && txtCity.Text != "") { TestDataClassDataContext dc = new TestDataClassDataContext(); Address addr = new Address() { AddressLine1 = txtAdd1.Text, AddressLine2 = txtAdd2.Text, City = txtCity.Text, PostalCode = txtZip.Text, StateProvinceID = Convert.ToInt32(ddlState.SelectedValue) }; dc.Addresses.InsertOnSubmit(addr); lblSuccess.Visible = true; lblErrMsg.Visible = false; dc.SubmitChanges(); // // TODO: insert new row in EmployeeAddress to reference CurEmp to newly created address // SetAddrList(); } else { lblErrMsg.Text = "Invalid Input"; lblErrMsg.Visible = true; } } protected void ddlAddList_SelectedIndexChanged(object sender, EventArgs e) { lblErrMsg.Visible = false; lblSuccess.Visible = false; TestDataClassDataContext dc = new TestDataClassDataContext(); dc.ObjectTrackingEnabled = false; if (ddlAddList.SelectedValue != "-1") { var addr = (from a in dc.Addresses where a.AddressID == Convert.ToInt32(ddlAddList.SelectedValue) select a).FirstOrDefault(); txtAdd1.Text = addr.AddressLine1; txtAdd2.Text = addr.AddressLine2; txtCity.Text = addr.City; txtZip.Text = addr.PostalCode; ddlState.SelectedValue = addr.StateProvinceID.ToString(); btnSubmit.Visible = true; btnAdd.Visible = false; } else { txtAdd1.Text = ""; txtAdd2.Text = ""; txtCity.Text = ""; txtZip.Text = ""; btnAdd.Visible = true; btnSubmit.Visible = false; } } protected void SetAddrList() { TestDataClassDataContext dc = new TestDataClassDataContext(); dc.ObjectTrackingEnabled = false; var addList = from addr in dc.Addresses from eaddr in dc.EmployeeAddresses where eaddr.EmployeeID == _curEmpID && addr.AddressID == eaddr.AddressID select new { AddValue = addr.AddressID, AddText = addr.AddressID, }; ddlAddList.DataSource = addList; ddlAddList.DataValueField = "AddValue"; ddlAddList.DataTextField = "AddText"; ddlAddList.DataBind(); ddlAddList.Items.Add(new ListItem("<Add Address>", "-1")); } OK I am hoping that I did not include too much code. I would really appreciate any other comments about I could otherwise improve this code in any other ways also.

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