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• LINQ parent child relation

  - by Shane Km

  I'm working on the BLOG functionality in MVC. I need to be able to create 'blog comments'. So each comment may have a parent comment etc. Given table "Comments": CommentId - int - identity autoincrement PostId - int ParentId - int Comment - string Is there a way to get a list of comments for a given article ordered by CreateDate and ParentId? Or maybe there is a better table design you may suggest. What is the best design when inserting Post comments like this? I'm using Entity framework. thanks

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• Linq To Sql Entity Updated from Trigger

  - by James Helms

  I have a Table called Address. I have a Trigger for insert on that table that does some spacial calculations on the address that determines what neighborhood boundaries it is in. address = new Address { Street = this.Street, City = this.City, State = this.State, ZipCode = this.ZipCode, latitude = this.Latitude, longitude = this.Longitude, YearBuilt = this.YearBuilt, LotSize = this.LotSize, FinishedSize = this.FinishedSize, Bedrooms = this.Bedrooms, Bathrooms = this.Bathrooms, UseCode = this.UseCode, HOA = this.HOA, UpdateDate = DateTime.Now }; db.AddToAddresses(address); db.SaveChanges(); In the database i can clearly see that the Trigger ran and updated the neighborhoodID in the address table for the row. I tried to just reload that record to get the assigned id like this: address = (from a in db.Addresses where a.AddressID == address.AddressID select a).First(); In the debugger i can clearly see that the address.AddressID is correct, entity doesn't update in memory. Is there any work around for this?

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• LINQ to SQL left outer joins

  - by César

  Is this query equivalent to a LEFT OUTER join? var rows = from a in query join s in context.ViewSiteinAdvise on a.Id equals s.SiteInAdviseId where a.Order == s.Order select new {....}; I tried this but it did not result from s in ViewSiteinAdvise join q in query on s.SiteInAdviseId equals q.Id into sa from a in sa.DefaultIfEmpty() where s.Order == a.Order select new {s,a} I need all columns from View

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• Linq to xml : can't load all elements

  - by aleo

  hello i'm trying to load some elements from a xml file. but it XDocument.Load seems not treating xml file properly in this case, the method returns the content of the xml file as one node. here is my xml content: <processes> <process>winamp</process> <process>Acrobat</process> <process>WinRAR</process> </processes> and the code that reads the file: XDocument loaded = XDocument.Load("/process_list.xml"); var x = from a in loaded.Descendants("processes") select a.Element("process"); foreach (var t in x) { Console.WritleLine(t.Value.ToString()); } thank you

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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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• Keeping Linq to SQL alive when using ViewModels (ASP.NET MVC)

  - by Kohan

  I have recently started using custom ViewModels (For example, CustomerViewModel) public class CustomerViewModel { public IList<Customer> Customers{ get; set; } public int ProductId{ get; set; } public CustomerViewModel(IList<Customer> customers, int productId) { this.Customers= customers; this.ProductId= productId; } public CustomerViewModel() { } } ... and am now passing them to my view instead of the Entities themselves (for example, var Custs = repository.getAllCusts(id) ) as it seems good practice to do so. The problem i have encountered is that when using ViewModels; by the time it has got to the the view i have lost the ability to lazy load on customers. I do not believe this was the case before using them. Is it possible to retain the ability of Lazy Loading while still using ViewModels? Or do i have to eager load using this method? Thanks, Kohan.

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• LINQ, creating unique collection of a collection

  - by Wish

  I have class Vertex and a class Edge (Edge holds 2 properties - Vertex Source and Vertex Target); Edges and Vertexes are collected into lists Some example: A-->B // edge from vertex A to B B-->C // edge from vertex B to C C-->A // edge from vertex C to A A-->C // edge from vertex A to C -- this is two way edge So I would like to make IDictionary<Edge, bool> which would hold edges (A--B and B--A would be like 1), and bool - if it is two way or no. I need it because when I draw them now, it draws 2 arrows under one another. I would better make 1 arrow. So I'm pretty stuck right here... May anybody help me a bit ?

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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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• LINQ to SQL: NOTing a prebuilt expression

  - by ck

  I'm building a library of functions for one of my core L2S classes, all of which return a bool to allow checking for certain situations. Example: Expression<Func<Account, bool>> IsSomethingX = a => a.AccountSupplementary != null && a.AccountSupplementary.SomethingXFlag != null && a.AccountSupplementary.SomethingXFlag.Value; Now to query where this is not true, I CAN'T do this: var myAccounts= context.Accounts .Where(!IsSomethingX); // does not compile However, using the syntax from the PredicateBuilder class, I've come up with this: public static IQueryable<T> WhereNot<T>(this IQueryable<T> items, Expression<Func<T, bool>> expr1) { var invokedExpr = Expression.Invoke(expr1, expr1.Parameters.Cast<Expression>()); return items.Where(Expression.Lambda<Func<T, bool>> (Expression.Not(invokedExpr), expr1.Parameters)); } var myAccounts= context.Accounts .WhereNot(IsSomethingX); // does compile which actually produces the correct SQL. Does this look like a good solution, and is there anything I need to be aware of that might cause me problems in future?

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• LINQ - more than or equal to

  - by trnTash

  Part of the code: ...where se.DateFrom >= pDateFrom && se.DateTo <= pDateTo select se... Does not work. There is no any error but the To and From days do not get returned. How do I query "more than or equal to" and "less than or equal to"? Thanks :)

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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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• 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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• 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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• 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 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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• 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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• 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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• 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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• 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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• 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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• 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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