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• OrderBy Linq.Expression as parameter = (Of Func(Of T,IComparable)) to perform LinqToEntity is not working

  - by NicoJuicy

  I'd like to get this working: Call: (Count & Page are used for pagination, so Count = 20 and Page = 1 for example, for the first 20 values). Sorting should be by name LeverancierService.GetLeveranciers(Function(el) el.Name, Count, Page) Equivalent in c#: LeverancierService.GetLeveranciers(el= el.Name, Count, Page) Method that gives an error (parameters shown above): Public Overridable Function GetAllPaged(orderby As Expression(Of Func(Of T, IComparable)), ByVal Count As Integer, ByVal Page As Integer) As IEnumerable(Of T) Return dbset.OrderBy(orderby).Skip((Page - 1) * Count).Take(Count).ToList() End Function Already tried changing it to this, but it gives the same error: Public Overridable Function GetAllPaged(Of TOrderBy)(orderby As Expression(Of Func(Of T, TOrderBy)), ByVal Count As Integer, ByVal Page As Integer) As IEnumerable(Of T) Return dbset.OrderBy(orderby).Skip((Page - 1) * Count).Take(Count).ToList() End Function Error: Unable to cast the type 'System.String' to type 'System.IComparable'. LINQ to Entities only supports casting Entity Data Model primitive types. Any idea how to do this? Extra info: I'm in a DDD-layered application, so the parameter should stay the same as the called method is an overridden interface (eg. if i change this, i have to do this for 200 times or so, because it's in VB.Net and not in C# (= 1 change) ) I know there is a way to change the expression to a string and then use DLinq (= Dynamic Linq), but that's not how it should be.

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• Using deprecated binders and C++0x lambdas

  - by Sumant

  C++0x has deprecated the use of old binders such as bind1st and bind2nd in favor of generic std::bind. C++0x lambdas bind nicely with std::bind but they don't bind with classic bind1st and bind2nd because by default lambdas don't have nested typedefs such as argument_type, first_argument_type, second_argument_type, and result_type. So I thought std::function can serve as a standard way to bind lambdas to the old binders because it exposes the necessary typedefs. However, using std::function is hard to use in this context because it forces you to spell out the function-type while instantiating it. auto bound = std::bind1st(std::function<int (int, int)>([](int i, int j){ return i < j; }), 10); // hard to use auto bound = std::bind1st(std::make_function([](int i, int j){ return i < j; }), 10); // nice to have but does not compile. I could not find a convenient object generator for std::function. Something like std::make_fuction would be nice to have. Does such a thing exist? If not, is there any other better way of binding lamdas to the classic binders?

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• I need to write Linq to SQL Lamda expression query the result of which is IQueryable and i want to u

  - by bbbbb

  I need to write Linq to SQL Lamda expression query the result of which is IQueryable and i want to use orderby and skip,take extension methods on this result object

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• Strange LINQ to SQL Behavior

  - by mcass20

  What is wrong with the last query? Is it a bug or am I missing something? This query returns 2 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>David</value>%")); This query returns 2 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>%David%</value>%")); This query returns 0 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>av</value>%")); This query returns 2 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>%av%</value>%")); This query returns 0 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>v</value>%")); This query returns 15 records (incorrect, should return 2): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>%v%</value>%"));

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• Linq - reuse expression on child property

  - by user175528

  Not sure if what I am trying is possible or not, but I'd like to reuse a linq expression on an objects parent property. With the given classes: class Parent { int Id { get; set; } IList<Child> Children { get; set; } string Name { get; set; } } class Child{ int Id { get; set; } Parent Dad { get; set; } string Name { get; set; } } If i then have a helper Expression<Func<Parent,bool> ParentQuery() { Expression<Func<Parent,bool> q = p => p.Name=="foo"; } I then want to use this when querying data out for a child, along the lines of: using(var context=new Entities.Context) { var data=context.Child.Where(c => c.Name=="bar" && c.Dad.Where(ParentQuery)); } I know I can do that on child collections: using(var context=new Entities.Context) { var data=context.Parent.Where(p => p.Name=="foo" && p.Childen.Where(childQuery)); } but cant see any way to do this on a property that isnt a collection. This is just a simplified example, actually the ParentQuery will be more complex and I want to avoid having this repeated in multiple places as rather than just having 2 layers I'll have closer to 5 or 6, but all of them will need to reference the parent query to ensure security.

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• How to create a function and pass in variable length argument list?

  - by Jian Lin

  We can create a function p in the following code: var p = function() { }; if (typeof(console) != 'undefined' && console.log) { p = function() { console.log(arguments); }; } but the arguments are passed like an array to console.log, instead of passed one by one as in console.log(arguments[0], arguments[1], arguments[2], ... Is there a way to expand the arguments and pass to console.log like the way above? Note that if the original code were var p = function() { }; if (typeof(console) != 'undefined' && console.log) { p = console.log; } then it works well on Firefox and IE 8 but not on Chrome.

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• Filtering two arrays to avoid Inf/NaN values

  - by Gacek

  I have two arrays of doubles of the same size, containg X and Y values for some plots. I need to create some kind of protection against Inf/NaN values. I need to find all that pairs of values (X, Y) for which both, X and Y are not Inf nor NaN If I have one array, I can do it using lambdas: var filteredValues = someValues.Where(d=> !(double.IsNaN(d) || double.IsInfinity(d))).ToList(); Now, for two arrays I use following loop: List<double> filteredX=new List<double>(); List<double> filteredX=new List<double>(); for(int i=0;i<XValues.Count;i++) { if(!double.IsNan(XValues[i]) && !double.IsInfinity(XValues[i]) && !double.IsNan(YValues[i]) && !double.IsInfinity(YValues[i]) ) { filteredX.Add(XValues[i]); filteredY.Add(YValues[i]); } } Is there any way of filtering two arrays at the same time using LINQ/Lambdas, as it was done for single array?

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• Using a message class static method taking in an action to wrap Try/Catch

  - by Chris Marisic

  I have a Result object that lets me pass around a List of event messages and I can check whether an action was successful or not. I've realized I've written this code in alot of places Result result; try { //Do Something ... //New result is automatically a success for not having any errors in it result = new Result(); } catch (Exception exception) { //Extension method that returns a Result from the exception result = exception.ToResult(); } if(result.Success) .... What I'm considering is replacing this usage with public static Result CatchException(Action action) { try { action(); return new Result(); } catch (Exception exception) { return exception.ToResult(); } } And then use it like var result = Result.CatchException(() => _model.Save(something)); Does anyone feel there's anything wrong with this or that I'm trading reusability for obscurity?

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• How to write this in better way?

  - by dario

  Hi all. Let's look at this code: IList<IHouseAnnouncement> list = new List<IHouseAnnouncement>(); var table = adapter.GetData(); //get data from repository object -> DataTable if (table.Rows.Count >= 1) { for (int i = 0; i < table.Rows.Count-1; i++) { var anno = new HouseAnnouncement(); anno.Area = float.Parse(table.Rows[i][table.powierzchniaColumn].ToString()); anno.City = table.Rows[i][table.miastoColumn].ToString(); list.Add(anno); } } return list; Is it better way to write this in less code and better fashion (must be :-) )? Maybe using labda (but let mi know how)? Thanks in advance!

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• View Lambdas in Visual Studio Debugger

  - by Vaccano

  I have the a simple LinqToSQL statement that is not working. Something Like this: List<MyClass> myList = _ctx.DBList .Where(x => x.AGuidID == paramID) .Where(x => x.BBoolVal == false) .ToList(); I look at _ctx.DBList in the debugger and the second item fits both parameters. Is there a way I can dig into this more to see what is going wrong?

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• What's the formal name for this Syntax?

  - by rlb.usa

  Sometimes in Scheme, I have functions that take arguments like this add 3 4 What do you call this kind of "list" where it's elements are like a1 a2 a3 ? I don't think you can call it a list because lists are contained in parenthesis and elements are comma-seperated.

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• How to select a single object using Linq in vb.net

  - by Hucker

  I have done a lot of searching to what appears to be a simple LINQ problem but I can't figure out how to do grab an object out of a collection that has a specified minimum (or max value) without resorting to a sort like this: > dim customers= GetCustomers() > > dim youngest = (From c in customers > Order By c.age Ascending).ToList.First This (untested code) structure works fine with the exception that the entire customer array must be sorted and placed into a list for the only purpose of extracting the first value. That can't be the best way to get the minimum! Note that I want the whole c record in this case, not the minumum age of a customer that can be done like this (a typical example): > dim customers= GetCustomers() > > dim youngest = (From c in customers > Select c.age).Min Or even > dim customers= GetCustomers() > > dim youngest = (From c in customers > Select c).Min(Function(x) x.age) I can't for the life of me figure out how to get the whole object (or even the index) without resorting to the sort...

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• Reference to an instance method of a particular object

  - by Andrey

  In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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• When using a repository is it possible for a type to return a Func that the repository uses to test for existing entities?

  - by Scott Rickman

  For example given a Factory with a method public static T Save<T>(T item) where T : Base, new() { /* item.Id == Guid.Empty therefore item is new */ if (item.Id == Guid.Empty && repository.GetAll<T>(t => t.Name == item.Name)) { throw new Exception("Name is not unique"); } } how do I create a property of Base (say MustNotAlreadyExist) so that I can change the method above to public static T Save<T>(T item) where T : Base, new() { /* item.Id == Guid.Empty therefore item is new */ if (item.Id == Guid.Empty && repository.GetAll<T>(t.MustNotAlreadyExist)) { throw new Exception("Name is not unique"); } } public class Base { ... public virtual Expression<Func<T, bool>> MustNotAlreadyExist() { return (b => b.Name == name); /* <- this clearly doesn't work */ } } and then how can I override MustNotAlreadyExist in Account : Base public class Account : Base { ... public override Expression<Func<T, bool>> MustNotAlreadyExist() { return (b => b.Name == name && b.AccountCode == accountCode); /* <- this doesn't work */ } ... }

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• Dynamic "WHERE IN" on IQueryable (linq to SQL)

  - by user320235

  I have a LINQ to SQL query returning rows from a table into an IQueryable object. IQueryable<MyClass> items = from table in DBContext.MyTable select new MyClass { ID = table.ID, Col1 = table.Col1, Col2 = table.Col2 } I then want to perform a SQL "WHERE ... IN ...." query on the results. This works fine using the following. (return results with id's ID1 ID2 or ID3) sQuery = "ID1,ID2,ID3"; string[] aSearch = sQuery.Split(','); items = items.Where(i => aSearch.Contains(i.ID)); What I would like to be able to do, is perform the same operation, but not have to specify the i.ID part. So if I have the string of the field name I want to apply the "WHERE IN" clause to, how can I use this in the .Contains() method?

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• Is there such a thing as a MemberExpression that handles a many-to-many relationship?

  - by Jaxidian

  We're trying to make it easy to write strongly-typed code in all areas of our system, so rather than setting var sortColumn = "FirstName" we'd like to say sortOption = (p => p.FirstName). This works great if the sortOption is of type Expression<Func<Person, object>> (we actually use generics in our code but that doesn't matter). However, we run into problems for many-to-many relationships because this notation breaks down. Consider this simple code: internal class Business { public IQueryable<Address> Addresses { get; set; } public string Name { get; set; } } internal class Address { public State MyState { get; set; } } internal class State { public string Abbreviation { get; set; } public int StateID { get; set; } } Is it possible to have this sort of MemberExpression to identify the StateID column off of a business? Again, the purpose of using this is not to return a StateID object, it's to just identify that property off of that entity (for sorting, filtering, and other purposes). It SEEMS to me that there should be some way to do this, even if it's not quite as pretty as foo = business.Addresses.SomeExtension(a => a.State.StateID);. Is this really possible? If more background is needed, take a look at this old question of mine. We've since updated the code significantly, but this should give you the general detailed idea of the context behind this question.

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• Search a List inside another with IQueryable

  - by ovini poornima

  public static IQueryable<Institution> WithFunds(this IQueryable<Institution> query, IEnumerable<Fund> allowedFunds) { return query. } I want to get the query to return all Institutions having any of the Fund given in 'allowedFunds' list in Institution.Funds. Please help. My class hierarchy goes like this. public partial class Institution { public int Id { get; set; } public virtual ICollection<Fund> Funds { get; set; } } public partial class Fund { public int Id { get; set; } public virtual Institution Institution { get; set; } }

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• Looking for good Regex book

  - by Cyberherbalist

  I've been trying to get a good grounding with Regular Expressions, and am looking for a single book to do so. I've been going through Amazon.com's listings on this subject, and I've identified a few possibilities, but am unsure which would be best for a C# developer who can write very simple Regexs, but wants to learn more. On a scale of 0-9 where 0 is knowing how to spell "Regex" but nothing else, and 9 where I could write a book on the subject out of my own head, I would place myself at 2. Which of the following would be your choice: Mastering Regular Expressions by Jeffrey E F Friedl Regular Expressions Cookbook by Jan Goyvaerts and Steven Levithan Sams Teach Yourself Regular Expressions in 10 Minutes by Ben Forta Beginning Regular Expressions (Programmer to Programmer) by Andrew Watt Regular Expression Recipes for Windows Developers: A Problem-Solution Approach by Nathan A. Good Regular Expression Recipes: A Problem-Solution Approach by Nathan A. Good Now, according to Amazon, "Regular Expressions Cookbook" (REC) above is rated the highest according to user ratings, but only based on 20 reviews. The first one, "Mastering Regular Expressions" (MRE) is rated second based on 140 reviews. This alone suggests that MRE might be by far the best one. But is it best for a relative beginner? Would I perhaps be better getting "Beginning Regular Expressions" (BRE) instead, to start with? Please help me resolve my confusion!

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• Le C++ expressif n° 4 : une bibliothèque de fonctions lambda en à peine 30 lignes - partie 1, un article d'Eric Niebler traduit par cob59

  Dans cet article, Eric Niebler entre dans les détails de la création de grammaires, en particulier sur le rôle des transformées, qui permettent d'appliquer une action spécifique lorsque l'entrée correspond à la grammaire donnée. De cette manière, il est possible d'étendre les fonctionnalités des expressions de Boost.Proto. Cet article explique aussi comment créer sa propre bibliothèques de fonctions pour faciliter la création d'expression Le C++ expressif n° 4 : une bibliothèque de fonctions lambda en à peine 30 lignes - partie 1 Avec l'ajout des transformées, commencez-vous à voir des doma...

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• Oracle redonne un élan au Projet Lambda sur Java 7 et les closures : Interface evolution via "public

  Bonjour, Depuis quelques temps, on n'entendait plus trop parler des Closures et de leur ajout à Java 7. En réponse à David Flanagan qui s'inquiétait récemment du silence d'Oracle et de la stagnation du Project Lambda, Brian Goetz (Oracle) a soumis il y a quelques jours un document de réflexion sur la notion de virtual extension methods permettant d'ajouter sur une interface existante de nouvelles méthodes (avec des implémentations par défaut) sans casser le contrat avec le code existant.

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• How do you unit test a LINQ query using Moq and Machine.Specifications?

  - by Phil.Wheeler

  I'm struggling to get my head around how to accommodate a mocked repository's method that only accepts a Linq expression as its argument. Specifically, the repository has a First() method that looks like this: public T First(Expression<Func<T, bool>> expression) { return All().Where(expression).FirstOrDefault(); } The difficulty I'm encountering is with my MSpec tests, where I'm (probably incorrectly) trying to mock that call: public abstract class with_userprofile_repository { protected static Mock<IRepository<UserProfile>> repository; Establish context = () => { repository = new Mock<IRepository<UserProfile>>(); repository.Setup<UserProfile>(x => x.First(up => up.OpenID == @"http://testuser.myopenid.com")).Returns(GetDummyUser()); }; protected static UserProfile GetDummyUser() { UserProfile p = new UserProfile(); p.OpenID = @"http://testuser.myopenid.com"; p.FirstName = "Joe"; p.LastLogin = DateTime.Now.Date.AddDays(-7); p.LastName = "Bloggs"; p.Email = "[email protected]"; return p; } } I run into trouble because it's not enjoying the Linq expression: System.NotSupportedException: Expression up = (up.OpenID = "http://testuser.myopenid.com") is not supported. So how does one test these sorts of scenarios?

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• Dijkstra’s algorithm and functions

  - by baris_a

  Hi guys, the question is: suppose I have an input function like sin(2-cos(3*A/B)^2.5)+0.756*(C*D+3-B) specified with a BNF, I will parse input using recursive descent algorithm, and then how can I use or change Dijkstra’s algorithm to handle this given function? After parsing this input function, I need to execute it with variable inputs, where Dijkstra’s algorithm should do the work. Thanks in advance. EDIT: May be I should ask also: What is the best practice or data structure to represent given function?

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• Regex to represent "NOT" in a group

  - by Joe Ijam

  I have this Regex; <(\d+)(\w+\s\d+\s\d+(?::\d+){2})\s([\w\/.-])(.) What I want to do is to return FALSE(Not matched) if the third group is "MSWinEventLog" and returning "matched" for the rest. <166Apr 28 10:46:34 AMC the remaining phrase <11Apr 28 10:46:34 MSWinEventLog the remaining phrase <170Apr 28 10:46:34 Avantail the remaining phrase <171Apr 28 10:46:34 Avantail the remaining phrase <172Apr 28 10:46:34 AMC the remaining phrase <173Apr 28 10:46:34 AMC the remaining phrase <174Apr 28 10:46:34 Avantail the remaining phrase <175Apr 28 10:46:34 AMC the remaining phrase <176Apr 28 10:46:34 AMC the remaining phrase <177Apr 28 10:46:34 Avantail the remaining phrase <178Apr 28 10:46:34 AMC the remaining phrase <179Apr 28 10:46:34 Avantail the remaining phrase <180Apr 28 10:46:34 Avantail the remaining phrase How to put " NOT 'MSWinEventLog' " in the regex group ([\w\/.-]*) ? Note : The second phrase above should return "not matched"

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• How do you unit test a LINQ expression using Moq and Machine.Specifications?

  - by Phil.Wheeler

  I'm struggling to get my head around how to accommodate a mocked repository's method that only accepts a Linq expression as its argument. Specifically, the repository has a First() method that looks like this: public T First(Expression<Func<T, bool>> expression) { return All().Where(expression).FirstOrDefault(); } The difficulty I'm encountering is with my MSpec tests, where I'm (probably incorrectly) trying to mock that call: public abstract class with_userprofile_repository { protected static Mock<IRepository<UserProfile>> repository; Establish context = () => { repository = new Mock<IRepository<UserProfile>>(); repository.Setup<UserProfile>(x => x.First(up => up.OpenID == @"http://testuser.myopenid.com")).Returns(GetDummyUser()); }; protected static UserProfile GetDummyUser() { UserProfile p = new UserProfile(); p.OpenID = @"http://testuser.myopenid.com"; p.FirstName = "Joe"; p.LastLogin = DateTime.Now.Date.AddDays(-7); p.LastName = "Bloggs"; p.Email = "[email protected]"; return p; } } I run into trouble because it's not enjoying the Linq expression: System.NotSupportedException: Expression up = (up.OpenID = "http://testuser.myopenid.com") is not supported. So how does one test these sorts of scenarios?

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• Having trouble with Regular Expression and Ampersand

  - by ajax81

  Hi All, I'm having a bit of trouble with regex's (C#, ASP.NET), and I'm pretty sure I'm doing something fundamentally wrong. My task is to bind a dynamically created gridview to a datasource, and then iterate through a column in the grid, looking for the string "A&I". An example of what the data in the cell (in template column) looks like is: Name: John Doe Phone: 555-123-1234 Email: [email protected] Dept: DHS-A&I-MRB Here's the code I'm using to find the string value: foreach(GridViewRow gvrow in gv.Rows) { Match m = Regex.Match(gvrow.Cells[6].Text,"A&I"); if(m.Success) { gvrow.ForeColor = System.Drawing.Color.Red; } } I'm not having any luck with any of these variations: "A&I" "[A][&][I]" But when I strictly user "&", the row does turn red. Any suggestions? Thanks, Dan

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