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• .Net Linq - Doing a operation on the subset

  - by Melursus

  I need to have the following : (name1 + "a") + (name2 + "a") + ... Dim separator() As String = {"|"} myString.Split(separator, StringSplitOptions.None).SomeLinq(...) I don't know what to add at the end to add an "a" to each element...

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• Linq TakeWhile depending on sum (or aggregate) of elements

  - by martinweser

  I have a list of elements and want to takeWhile the sum (or any aggregation of the elements) satisfy a certain condition. The following code does the job, but i am pretty sure this is not an unusual problem for which a proper pattern should exist. var list = new List<int> { 1, 2, 3, 4, 5, 6, 7 }; int tmp = 0; var listWithSum = from x in list let sum = tmp+=x select new {x, sum}; int MAX = 10; var result = from x in listWithSum where x.sum < MAX select x.x; Does somebody know how to solve the task in nicer way, probably combining TakeWhile and Aggregate into one query? Thx

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• linq to xml return second element

  - by Phil

  Hi Im trying to return to the second element in the xml from flickr. This always returns the first element: ImageUrl = item.Element(ns + "link").Attribute("href").Value, and this errors? ImageUrl = item.Elements(ns + "link")[1].Attribute("href").Value, Thanks

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• For-Loop and LINQ's deferred execution don't play well together

  - by Tim Schmelter

  The title suggests that i've already an idea what's going on, but i cannot explain it. I've tried to order a List<string[]> dynamically by each "column", beginning with the first and ending with the minimum Length of all arrays. So in this sample it is 2, because the last string[] has only two elements: List<string[]> someValues = new List<string[]>(); someValues.Add(new[] { "c", "3", "b" }); someValues.Add(new[] { "a", "1", "d" }); someValues.Add(new[] { "d", "4", "a" }); someValues.Add(new[] { "b", "2" }); Now i've tried to order all by the first and second column. I could do it statically in this way: someValues = someValues .OrderBy(t => t[0]) .ThenBy(t => t[1]) .ToList(); But if i don't know the number of "columns" i could use this loop(that's what I thought): int minDim = someValues.Min(t => t.GetLength(0)); // 2 IOrderedEnumerable<string[]> orderedValues = someValues.OrderBy(t => t[0]); for (int i = 1; i < minDim; i++) { orderedValues = orderedValues.ThenBy(t => t[i]); } someValues = orderedValues.ToList(); // IndexOutOfRangeException But that doesn't work, it fails with an IndexOutOfRangeException at the last line. The debugger tells me that i is 2 at that time, so the for-loop condition seems to be ignored, i is already == minDim. Why is that so?

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• Manual Linq to SQL entity framework mapping

  - by kprobst

  I've been playing with the O/R designer in VS and I was wondering if someone could shed come light on this. I'm used to OR mappers that are largely manual (homegrown and e.g., NHibernate). I don't mind encoding the entity classes myself, since they don't change all that often to begin with, and I have this irrational fear of designers and auto generated code as it is. I have noticed that the generated entity classes contain a lot of boilerplate extensibility methods, e.g. On[Property]Changed() and so on where [Property] is a mapped member of the class. These are placed in the setters of the property accessors. I assume it's OK if I don't include these when I do my hand coding, correct? They would be nice if I needed some sort of interception pattern but that's certainly not the case. I guess I just need to know if any of those methods are required by the entity framework to keep track of changes to the mapping types in order for things to work when updating the database. Thanks!

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• Linq grouping question

  - by Mike C.

  I have the following objects in a collection: Transaction: Type = "Widget" Date = "3/1/2011" Name = "Foo" Transaction: Type = "Widget" Date = "3/4/2011" Name = "Bar" Transaction: Type = "Gadget" Date = "3/2/2011" Name = "Baz" Transaction: Type = "Gizmo" Date = "3/1/2011" Name = "Who" Transaction: Type = "Gizmo" Date = "3/2/2011" Name = "What" Transaction: Type = "Gizmo" Date = "3/6/2011" Name = "When" I want to end up with the following, grouped by Type. If there are multiple, return only the first one chronologically by date. Transaction: Type = "Widget" Date = "3/1/2011" Name = "Foo" Transaction: Type = "Gadget" Date = "3/2/2011" Name = "Baz" Transaction: Type = "Gizmo" Date = "3/1/2011" Name = "Who"

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• C# LINQ filtering with nested if statements

  - by Tim Sumrall

  I have a learning project where a data grid is filtered by 3 controls (a checkbox and 2 dropdowns) I'm about to wrap up and move on to another project as it works well but I don't like the complexity of nesting IF statements to capture all the possible combinations of the 3 filters and was wondering if there is a better way. For example: Something that would allow for more filters to be added easily rather than walking through all the nests and adding another level of madness. private void BuildQuery() { EntityQuery<MASTER_DOCKS> query = QDocksContext.GetMASTER_DOCKSQuery(); if (Tonnage.IsChecked.HasValue && Tonnage.IsChecked.Value) { if (null != FilterWaterWay.SelectedValue) { string WaterwaytoFilterBy = FilterWaterWay.SelectedValue.ToString(); if (!string.IsNullOrWhiteSpace(WaterwaytoFilterBy) && WaterwaytoFilterBy != "[Select WaterWay]") { if (null != FilterState.SelectedValue) { string StateToFilterBy = FilterState.SelectedValue.ToString(); if (null != FilterState.SelectedValue && !string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { if (!string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { query = query.Where(s => s.WTWY_NAME == WaterwaytoFilterBy && s.STATE == StateToFilterBy && (s.Tons != "0" && s.Tons != "")).OrderBy(s => s.WTWY_NAME); MyQuery.Text = "Tonnage, WW and State"; } } if (StateToFilterBy == "[Select State]") //waterway but no state { query = query.Where(s => s.WTWY_NAME == WaterwaytoFilterBy && (s.Tons != "0" && s.Tons != "")).OrderBy(s => s.WTWY_NAME); MyQuery.Text = "Tonnage, WW No State"; } } } else { if (null != FilterState.SelectedValue) { string StateToFilterBy = FilterState.SelectedValue.ToString(); if (null != FilterState.SelectedValue && !string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { if (!string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { query = query.Where(s => s.STATE == StateToFilterBy && (s.Tons != "0" && s.Tons != "")).OrderBy(s => s.WTWY_NAME); MyQuery.Text = "Tonnage State No WW"; } } else { query = query.Where(s => (s.Tons != "0" && s.Tons != "")); MyQuery.Text = "Tonnage No State No WW"; } } } } } else //no tonnage { if (null != FilterWaterWay.SelectedValue) { string WaterwaytoFilterBy = FilterWaterWay.SelectedValue.ToString(); if (!string.IsNullOrWhiteSpace(WaterwaytoFilterBy) && WaterwaytoFilterBy != "[Select WaterWay]") { if (null != FilterState.SelectedValue) { string StateToFilterBy = FilterState.SelectedValue.ToString(); if (null != FilterState.SelectedValue && !string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { if (!string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { query = query.Where(s => s.WTWY_NAME == WaterwaytoFilterBy && s.STATE == StateToFilterBy).OrderBy(s => s.WTWY_NAME); MyQuery.Text = "No Tonnage, WW and State"; } } if (StateToFilterBy == "[Select State]") //waterway but no state { query = query.Where(s => s.WTWY_NAME == WaterwaytoFilterBy).OrderBy(s => s.WTWY_NAME); MyQuery.Text = "No Tonnage, WW No State"; } } } else { if (null != FilterState.SelectedValue) { string StateToFilterBy = FilterState.SelectedValue.ToString(); if (null != FilterState.SelectedValue && !string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { if (!string.IsNullOrWhiteSpace(StateToFilterBy) && StateToFilterBy != "[Select State]") { query = query.Where(s => s.STATE == StateToFilterBy).OrderBy(s => s.WTWY_NAME); MyQuery.Text = "No Tonnage State No WW"; } } else { LoadAllData(); MyQuery.Text = "No Tonnage No State No WW"; } } } } } LoadOperation<MASTER_DOCKS> loadOp = this.QDocksContext.Load(query); DocksGrid.ItemsSource = loadOp.Entities; }

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• Linq to Sql query reuse

  - by UserControl

  Let's say we have a view V1 and V2 that is declared like: create view V2 as select V1.*, V2.C1, V2.C2, V2.C3 from V1 join V2 on V1.Key = V2.Key where bla-bla So V2 narrows down the result set of V1 and adds some joins. And there is a retrieval routine in C# IEnumerable<V1> GetData(MyFilter filter, MySortOrder order) {} I want to reuse with V2. Is it possible without performing joins in L2S rather than in database? Should i manually create a base class in the database context or something?

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• Equivalent lambda syntax for linq query

  - by ilias

  Hi, I am having a mind-freeze here, but I cant seem to find the equivalent lambda syntax for - string[] a = {"a","b","c"}; string[] b = {"1","2","3"}; var x = from a1 in a from b1 in b select new{a1, b1};

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• Forcing LINQ to SQL to make one single call for all child rows

  - by zaph0d

  Let say I have a method (example taken from another post): public IQueryable<CityBlock> GetCityBlocks(){ var results = from o in db.city_blocks let buildings = GetBuildingsOnBlock(o.block_id) //returns Iqueryable select new CityBlock { BuildingsOnBlock = buildings, BlockOwner = o.block_owner }; return results; } In the calling method I add Skip() and Take() methods plus some filtering and then do a ToList(). The trouble is that I am getting dozens of database calls - one for all the city blocks and then a separate one for each building. Is there a way that I can refactor this code to just make two calls: one for the city blocks and one for all the buildings

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• Linq Having Sum(Quantity) = x?

  - by molgan

  Hello I have a function that returns IQueryable, and I would like to add "HAVING SUM(Quantity) = X" to it, but I get error if I try like this: _rep.GetBookings().ByBookingObjectID(bookingObjectID).Sum(x => x.Quantity == somevariablehere); I cant seem to find functions for it to find by sum /M

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• Storing records in a dropdownlist from DB without using LINQ Data source

  - by user1318369

  I have a website for dance academy where Users can register and add/drop dance classes. In the web page to drop a particular dance, for a particular user, the dropdown displays her registered dances. Now I want to delete one of the dances from the list. So i'll remove the row from the table and also from the dropdownlist. The problem is that everytime the item with the lowest ID (index) is getting deleted, no matter which one the user selects. I think I am storing the DataTextField and DataValueField for the dropdown incorrectly. Can someone please help me out? The code is: private void PopulateDanceDropDown() { var registereddanceList = from dd in context.DANCER_AND_DANCE where dd.UserId == dancerId select new { Text = dd.DanceName, Value = dd.DanceId }; dances.DataSource = registereddanceList; dances.DataTextField = "Text"; dances.DataValueField = "Value"; dances.DataBind(); } protected void dropthedance(object o, EventArgs e) { String strDataValueField = dances.SelectedItem.Value; int danceIDFromDropDown = Convert.ToInt32(strDataValueField); var dancer_dance = from dd in context.DANCER_AND_DANCE where dd.DanceId == danceIDFromDropDown select dd; foreach (var dndd in dancer_dance) { context.DANCER_AND_DANCE.DeleteOnSubmit(dndd); } try { context.SubmitChanges(); } catch (Exception ex) { Console.WriteLine(ex); } PopulateDanceDropDown(); }

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• C# Linq - Cannot implicitly convert IEnumerable<string> to List<string>

  - by JL

  I have a List defined like this : public List<string> AttachmentURLS; I am adding items to the list like this: instruction.AttachmentURLS = curItem.Attributes["ows_Attachments"].Value.Split(';').ToList().Where(Attachment => !String.IsNullOrEmpty(Attachment)); But I am getting this error: Cannot implicitly convert IEnumerable to List What am I doing wrong?

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• Is Linq Faster, Slower or the same?

  - by Vaccano

  Is this: Box boxToFind = AllBoxes.Where(box => box.BoxNumber == boxToMatchTo.BagNumber); Faster or slower than this: Box boxToFind ; foreach (Box box in AllBoxes) { if (box.BoxNumber == boxToMatchTo.BoxNumber) { boxToFind = box; } } Both give me the result I am looking for (boxToFind). This is going to run on a mobile device that I need to be performance conscientious of.

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• Linq-to-Entities Dynamic sorting

  - by verror

  This is my query, how can I use string as orderby parameter? string sortColumn="Title"; var items = (from ltem in ctxModel.Items where ltem.ItemID == vId orderby //something here select ltem).Skip(PageSize * PageIndex).Take(PageSize);

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• VB.NET and linQ: How to delete entries from a dictionary using the value

  - by user350233

  I have a dictionary collection as bleow: mydic.addvalue(key1, val1) mydic.addvalue(key2, val1) mydic.addvalue(key3, val1) mydic.addvalue(key4, val2) mydic.addvalue(key5, val2) From the above dictionary I want to delete all the entries where value == "val1", so that the result would have only following entry: mydic.addvalue(key4, val2) mydic.addvalue(key5, val2) My VB source code is on VS2008 and targeted for 3.5

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• How to use the IN operator in linq

  - by Hallaghan

  I'm querying a view and filtering the results with a column named status. I'd like to query it so I can search for rows with different status, by using the IN operator as I'd do in SQL. As so: SELECT * FROM VIEW WHERE Status in ('....', '.....') How can I achieve this?

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• Grabbing Just The Top Entry From A LINQ Query

  - by Soo

  I basically have a lot of poorly designed code to do something that, I'm sure, can be done far more elegantly. What I'm trying to do is grab the last date from a database table. var Result = from a in DB.Table orderby a.Date descending select new {Date = a}; foreach(var Row in Result) { LastDate = Row.Date.Date; break; } Basically, there's a foreach loop that is designed to run only once. Crappy code! What's a "best practice" way to accomplish the same thing?

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• Exploding a range of dates with LINQ

  - by Robert Gowland

  If I have a pair of dates, and I want to generate a list of all the dates between them (inclusive), I can do something like: System.DateTime s = new System.DateTime(2010, 06, 05); System.DateTime e = new System.DateTime(2010, 06, 09); var list = Enumerable.Range(0, (e - s).Days) .Select(value => s.AddDays(value)); What I'm stuck on is that I've got a list of pairs of dates that I want to explode into a list of all the dates between them. Example: {2010-05-06, 2010-05-09}, {2010-05-12, 2010-05-15} should result in {2010-05-06, 2010-05-07, 2010-05-08, 2010-05-09, 2010-05-12, 2010-05-13, 2010-05-14, 2010-05-15} Note the pairs of dates are guaranteed not to overlap each other.

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• Linq-to-sql join/where?

  - by Curtis White

  I've the following table structures Users id Types id isBool UsersTypes userid types I want to select all the UserTypes based on id and isBool. I tried this query var q = from usertype in usertypes from type in types where type.isBool == false where userstypes.user == id select usertype; But this did not work as expected. My questions are: Why? Is there any difference in using the join on syntax vs where, where vs where cond1 && cond2? My understanding is query optimizer will optimize. Is there any difference in using where cond1 == var1 && cond2 == var2 with and without the parenthesis? This seems peculiar that it is possible to build this without parenthesis What type of query do I need in this case? I can see that I could do a subquery or use a group but not 100% sure if it is required. An example might be helpful. I'm thinking a subquery may be required in this case.

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• Making linq avoid using in memory filtering where possible

  - by linqmonkey

  Consider the these two LINQ2SQL data retrieval methods. The first creates a 'proper' SQL statement that filters the data, but requires passing the data context into the method. The second has a nicer syntax but loads the entire list of that accounts projects, then does in memory filtering. Is there any way to preserve the syntax of the second method but with the performance advantage of the first? public partial class Account { public IQueryable<Project> GetProjectsByYear(LinqDataContext context, int year) { return context.Projects.Where(p => p.AccountID==this.AccountID && p.Year==year).OrderBy(p => p.ProjectNo) } public IQueryable<Project> GetProjectsByYear(int year) { return this.Projects.Where(p => p.Year==year).OrderBy(p => p.ProjectNo).AsQueryable() } }

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• linq to sql update data

  - by pranay

  can i update my employee record as given in below function or i have to make query of employee collection first and than i update data public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); db.App3_EMPLOYEEs.Attach(employee); db.SubmitChanges(); return employee.PKEY; } or i have to do this public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY); db.App3_EMPLOYEEs.Attach(employee,emp); db.SubmitChanges(); return employee.PKEY; } But i dont want to use second option is there any efficient way to update data

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• Query decendants in XML to Linq

  - by Gordon

  I have the following xml data: <portfolio> <item> <title>Site</title> <description>Site.com is a </description> <url>http://www.site.com</url> <photos> <photo url="http://www.site.com/site/thumbnail.png" thumbnail="true" description="Main" /> <photo url="http://www.site.com/site/1.png" thumbnail="false" description="Main" /> </photos> </item> </portfolio> In c# I am using the following link query: List list = new List(); XDocument xmlDoc = XDocument.Load(HttpContext.Current.Server.MapPath("~/app_data/portfolio.xml")); list = (from portfolio in xmlDoc.Descendants("item") select new PortfolioItem() { Title = portfolio.Element("title").Value, Description = portfolio.Element("description").Value, Url = portfolio.Element("url").Value }).ToList(); How do I go about querying the photos node? In the PortfolioItem class I have a property: List Photos {get;set;} Any ideas would be greatly appreciated!

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• C# LINQ join With Just One Row

  - by Soo

  I'm trying to make a query that grabs a single row from an SQL database and updates it. TableA AId AValue TableB BId AId BValue Ok, so TableA and TableB are linked by AId. I want to select a row in TableB based on AValue using a join. The following query is what I have and only grabs a value from TableB based on AId, I just don't know how to grab a row from TableB using AValue. I know you would need to use a join, but I'm not sure how to accomplish that. var row = DbObject.TableB.Single(x => x.AId == 1) row.BValue = 1; DbObject.SubmitChanges();

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• LINQ Expression help with Func TEntity,TType

  - by Chris Conway

  I have a repository method that accepts an order by parameter in the form: public IEnumerable<TEntity> Get<TEntity>(Expression<Func<TEntity,string>> orderBy) Now that works fine when trying to sort by a property of type string, var entities = rep.Get(x => x.Name); but what if i want to sort by double or int or any other type. Doing something like var entities = rep.Get(x => x.Price); obviously throws a compile error saying I can't convert double to string. How can I make this more generic so I can sort by any property in my entity, or at least the properties where the type implements IComparable or something similar?

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