linq

问题 Take this: int? item1 = null; int? item2 = null; someObjectList.Where(x => x.SomeItem1 == (item1 ?? x.SomeItem1) && x.SomeItem2 == (item2 ?? x.SomeItem2) ); Where someObjectList is not empty and SomeItem1 and SomeItem2 is null in all the objects in the list. Why is it returning nothing? EDIT: My Code: public void GetPlacementsByMaterial(long clientMaterialID) { ClientMaterial clientMaterial = ((ApplicationEntityModel)NavigationItem.ObjectContext).ClientMaterial.FirstOrDefault(x => x

问题 I would like my Web API to be able to sort its output by a string parameter such as this one: http://myapi.com/api/people?skip=0&take=50&orderBy=lastName&descending=true . Because I also have pagination support (with skip and take ) in my API, I would like the orderBy and descending parameter to be applied to the SQL query directly, so that the correct result comes from the database. When doing this however, the code can become very hard to manage when trying to match the parameters for

问题 Just getting my head around Linq and having lots of fun! Can any one aid me with a query for this: I have a list of data: Key Value Aaa 12 AaA 10 AAa 5 BBB 2 Bbb 1 1. I want to group by Key.ToUpper() 2. For every group I need the Max(Value) & Sum(Value) 3. For every group I want to select the entries There the Value != Max(value) the final result should be like this: Key Max Total AaA 12 27 AAa 12 27 Bbb 2 3 Thanks! Update, actually I also need the Key from the Maximum entry: Key Max Total

问题 Just getting my head around Linq and having lots of fun! Can any one aid me with a query for this: I have a list of data: Key Value Aaa 12 AaA 10 AAa 5 BBB 2 Bbb 1 1. I want to group by Key.ToUpper() 2. For every group I need the Max(Value) & Sum(Value) 3. For every group I want to select the entries There the Value != Max(value) the final result should be like this: Key Max Total AaA 12 27 AAa 12 27 Bbb 2 3 Thanks! Update, actually I also need the Key from the Maximum entry: Key Max Total

问题 I wonder why is the reason why this code never finishes its execution. It makes use of MoreLinq void Main() { var values = MoreEnumerable.Random(1, 200); var filtered = MyMethod(values) .Take(2) .Dump(); } public IEnumerable<int> MyMethod(IEnumerable<int> source) { return source .Select(x => new[] { x }) .Aggregate((a, b) => new[] { a.Last() + b.First()}); } 回答1: Because MoreEnumerable.Random(1, 200) returns an infinite sequence and the .Aggregate statement in MyMethod is trying to enumerate

问题 I want to filter a list using LINQ with Where extension method. But apart from filtering I also want to update a global variable inside Where . However I cannot do it. Consider this example: var list = new List<string> { "1", "2", "3", "4", "5" }; bool flag = false; var newList = list.Where(item => { flag = true; return item == "2"; }); // Here I expect flag = true, but in fact it's false Console.Write(flag); As you can see I set flag = true , still the value flag == false after execution. It

问题 I did my best search to convert PARTION BY command from TSQL to LINQ command. But apparently there is no way to convert it. This is my code to which I am going to convert: WITH MyRowSet AS ( SELECT OrderDate ,SalesOrderNumber ,AccountNumber ,CustomerID ,ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY CustomerID, OrderDate DESC) AS RowNum FROM [Sales].[SalesOrderHeader] ) SELECT * FROM MyRowSet WHERE RowNum = 1 If exist any solution I would be greatful to know. 回答1: linq2db has this

问题 in my .NET Core 3.1 application, I am getting a null reference exception when I include .ToList() on the following emailAddress =... line: var customersTask = eshop.TieredCustomer .Where(customer => customer != null) .Where(customer => customer.SendPriceListAutomatically.HasValue && customer.SendPriceListAutomatically.Value && customer.DistributionList.HasValue && !string.IsNullOrWhiteSpace(customer.Emails)) .Select(customer => new Customer { distributionList = customer.DistributionList.Value

问题 Please be kind to a LINQ dummy... Say I have 8 rows data like this: +-------------------+ | ID WORKTYPEDESC| +-------------------+ | 1 plumber | | 1 carpenter | | 1 electrician | | 2 juggler | | 2 mime | | 3 writer | | 3 actor | +-------------------+ As an 8-item IList<Worktype> collection where Worktype looks like public class Worktype { public int Id { get; set; } public string WorktypeDesc { get; set; } } And what I want is to aggregate by Id to get a list with 3 Worktypes, each with a

问题 Please be kind to a LINQ dummy... Say I have 8 rows data like this: +-------------------+ | ID WORKTYPEDESC| +-------------------+ | 1 plumber | | 1 carpenter | | 1 electrician | | 2 juggler | | 2 mime | | 3 writer | | 3 actor | +-------------------+ As an 8-item IList<Worktype> collection where Worktype looks like public class Worktype { public int Id { get; set; } public string WorktypeDesc { get; set; } } And what I want is to aggregate by Id to get a list with 3 Worktypes, each with a