iqueryable

I'm having a similar problem that was asked here: LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression I'm trying to paginate my source, but in my case, I can't put the result of GetPropertyValue in a variable, because I need x to do that: public IEnumerable<TModel> Paginate(IQueryable<TModel> source, ref int totalPages, int pageIndex, int pageSize, string sortfield, SortDirection? sortdir) { totalPages = (int)Math.Ceiling(source.Count() / (double)pageSize); if (sortdir == SortDirection.Descending) {

Is it possible to access the DataContext object behind an IQueryable? If so, how? DataContext is specific to LINQ to SQL, so presumably you're talking about LINQ to SQL queries? If so, there's no safe way to do this - you have to resort to a hack such as using reflection to retrieve the private "context" field of the underlying DataQuery object: static DataContext GetContext (IQueryable q) { if (!q.GetType().FullName.StartsWith ("System.Data.Linq.DataQuery`1")) return null; var field = q.GetType().GetField ("context", BindingFlags.NonPublic | BindingFlags.Instance); if (field == null) return

Update 2013-08-22: After having a look at the 'Building an IQueryable provider series' (thanks for the link!) I got a bit further. I updated the code accordingly. It is still not fully working though. If I understand the tutorial correctly, the GetEnumerator is invoked in case multiple elements are requested (e.g. by a ToList() call on the queryable, or any aggregation function). So all the GetEnumerator implementation of the wrapper has to do is call an Execute on the provider and pass the queryable's expression. In the other case, if only a single element is requested, Execute is called

I am building a repository and I've seen in many places 2 reasons not to expose IQueryable outside the repository. 1) The first is because different LINQ providers could behave differently, and this difference should be contained within the repository. 2) The second is to prevent service level developers from modifying the database query such that it accidentally causes performance issues. I guess issue 2 can only be prevented by keeping all query logic within the repository and not allowing any form of external query building? But that does seem a bit impractical to me. Issue 1 would seem to

I know this could be opinion, but I'm looking for best practices. As I understand, IQueryable<T> implements IEnumerable<T> , so in my DAL, I currently have method signatures like the following: IEnumerable<Product> GetProducts(); IEnumerable<Product> GetProductsByCategory(int cateogoryId); Product GetProduct(int productId); Should I be using IQueryable<T> here? What are the pros and cons of either approach? Note that I am planning on using the Repository pattern so I will have a class like so: public class ProductRepository { DBDataContext db = new DBDataContext(<!-- connection string -->);

I'm simply wondering why there is a IQueryable<T> version without the generic capability ? The generic IQueryable<T> is the one you use most often in method signatures and the like. The non-generic IQueryable exist primarily to give you a weakly typed entry point primarily for dynamic query building scenarios . by Matt Warren from LINQ: Building an IQueryable Provider - Part I You should use generic IQueryable<T> everywhere it's possible. neontapir I imagine it's the same reason as Jon Skeet gives in Difference between IEnumerable and IEnumerable<T>? , to allow use in a foreach loop. IQuerable

If i have the following Repository: public IQueryable<User> Users() { var db = new SqlDataContext(); return db.Users; } I understand that the connection is opened only when the query is fired: public class ServiceLayer { public IRepository repo; public ServiceLayer(IRepository injectedRepo) { this.repo = injectedRepo; } public List<User> GetUsers() { return repo.Users().ToList(); // connection opened, query fired, connection closed. (or is it??) } } If this is the case, do i still need to make my Repository implement IDisposable? The Visual Studio Code Metrics certainly think i should. I'm

I am using my own extension methods of IQueryable<> to create chainable queries such as FindAll().FindInZip(12345).NameStartsWith("XYZ").OrderByHowIWantIt() etc. which then on deferred execution creates a single query based on my extension methods chain. The problem with this though, is that all Where's in the extension chain (FindXYZ, FindInZip etc.) will always combine as AND which means I can't do something like this: FindAll().FirstNameStartsWith("X").OrLastNameStartsWith("Z") because I don't know how I can inject the OR in a separate Where method. Any idea how I can solve this? additional