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• Database design for credit based purchases

  - by FreshCode

  I need an elegant way to implement credit-based purchases for an online store with a small variety of products which can be purchased using virtual credit or real currency. Alternatively, products could only be priced in credits. Previous work I have implemented credit-based purchasing before using different product types (eg. Credit, Voucher or Music) with post-order processing to assign purchased credit to users in the form of real currency, which could subsequently be used to discount future orders' charge totals. This worked fairly well as a makeshift solution, but did not succeed in disconnecting the virtual currency from the real currency, which is what I'd like to do, since spending credits is psychologically easier for customers than spending real currency. Design I need guidance on designing the database correctly with support for the simultaneous bulk purchase of credits at a discount along with real currency products. Alternatively, should all products be priced in credits and only credit have a real currency value? Existing Database Design Partial Products table: ProductId Title Type UnitPrice SalePrice Partial Orders table: OrderId UserId (related to Users table, not shown) Status Value Total Partial OrderItems table (similar to CartItems table): OrderItemId OrderId (related to Orders table) ProductId (related to Products table) Quantity UnitPrice SalePrice Prospective UserCredits table: CreditId UserId (related to Users table, not shown) Value (+/- value. Summed over time to determine saldo.) Date I'm using ASP.NET MVC and LINQ-to-SQL on a SQL Server database.

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• Should the entity framework + self tracking entities be saving me time

  - by sipwiz

  I've been using the entity framework in combination with the self tracking entity code generation templates for my latest silverlight to WCF application. It's the first time I've used the entity framework in a real project and my hope was that I would save myself a lot of time and effort by being able to automatically update the whole data access layer of my project when my database schema changed. Happily I've found that to be the case, updating my database schema by adding a new table, changing column names, adding new columns etc. etc. can be propagated to my business object classes by using the update from database option on the entity framework model. Where I'm hurting is the CRUD operations within my WCF service in response to actions on my Silverlight client. I use the same self tracking entity framework business objects in my Silverlight app but I find I'm continually having to fight against problems such as foreign key associations not being handled correctly when updating an object or the change tracker getting confused about the state of an object at the Silverlight end and the data access operation within the WCF layer throwing a wobbly. It's got to a point where I have now spent more time dealing with this quirks than I have on my previous project where I used Linq-to-SQL as the starting point for rolling my own business objects. Is it just me being hopeless or is the self tracking entities approach something that should be avoided until it's more mature?

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• Model relationships in ASP.NET MVC

  - by Fabiano

  Hi I recently started evaluating ASP.NET MVC. While it is really easy and quick to create Controllers and Views for Models with only primitive properties (like shown in the starter videos from the official page) I didn't find any good way to work with references to complex types. Let's say, I have these Models: public class Customer { public int Id { get; set; } public string Name { get; set; } public Address Address { get; set; } public IList<Order> Orders { get; set; } } public class Address { public int Id { get; set; } public string ..... ..... } public class Order { public int Id { get; set; } public Customer Customer { get; set; } public string OrderName { get; set; } ..... } Note that I don't have foreign keys in the models (like it's typical for LINQ to SQL, which is also used in the sample video) but an object reference. How can I handle such references in asp.net mvc? Does someone has some good tips or links to tutorials about this problem? maybe including autobinding with complex types.

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• How to display two grids in same page using jquery?

  - by kumar

  hello friends, I have this code to display jquery grid <div> <%= Html.Trirand().JQGrid(Model.OrdersGrid, "JQGrid1") %> </div> Server side I have this code.. using System; using System.Collections.Generic; using System.Linq; using System.Web; using Trirand.Web.Mvc; using System.Web.UI.WebControls; namespace JQGridMVCExamples.Models { public class OrdersJqGridModel { public OrdersJqGridModel() { OrdersGrid = new JQGrid { Columns = new List<JQGridColumn>() { new JQGridColumn { DataField = "OrderID", Width = 50 }, new JQGridColumn { DataField = "OrderDate", Width = 100, DataFormatString = "{0:d}" }, new JQGridColumn { DataField = "CustomerID", Width = 100 }, new JQGridColumn { DataField = "Freight", Width = 75 }, new JQGridColumn { DataField = "ShipName" } }, Width = Unit.Pixel(640) }; OrdersGrid.ToolBarSettings.ShowRefreshButton = true; } public JQGrid OrdersGrid { get; set; } } } This is displaying only one grid... I I want to display two grids that Is how to display other grid in Same page? that is can I do like this? <div> <%= Html.Trirand().JQGrid(Model.OrdersGrid, "JQGrid1") %> </div> <div> <%= Html.Trirand().JQGrid(Model.OrdersGrid, "JQGrid2") %> </div> in the same page.. if yes how to handle the Sever side grid? bec Server side grid columns are differnt from jqGrid1 and Jqgrid2,,,, On Row Click on JQGrid1 I need to display JqGrid2. Please can anyone help me out about this.. Thanks

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• Sorting, Filtering and Paging in ASP.NET MVC

  - by ali62b

  What is the best approach to implement these features and which part of project would involved? I see some example of JavaScript grids, but I'm talking about a general approach which best fits the MVC architecture. I've considered configuring routes and models to implement these features but I don't have a clear idea that if this is the right approach to implementing such features. On the one hand, I think if we put logic in routes (item/page/sort/), we would have benefits like bookmarking and avoiding JavaScript. On the other hand if we use JavaScript grids, we can have behavior like the old school grid views in ASP.NET web forms. I find that using HTML helpers may be useful for paging, but have no idea if they are good for sorting or not. I've looked at jQuery, tableSorter and quick search plug-ins, but they work just on the currently-fetched data and won't help in real sorting and filtering that may need to touch the database. I have some thoughts on using these tools side by side with AJAX to get something which works, but I have no idea if there are similar efforts done yet anywhere. Another approach I looked at was using Dynamic Data on web forms, but I didn't find any suggestions out there as to whether or not it is a good idea to integrate MVC and DD. I know implementing filtering and sorting for an individual case is simple (although it has some issues like using Dynamic LINQ, which is not yet a standard approach), but creating a sorting or filtering tool which works in all cases is the idea I'm looking for. (Maybe this is because I want have something in hand when web form developers are wondering why I'm writing same code each time I want to implement a sort scenario for different Entities).

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• Using a custom IList obtained through NHibernate

  - by Abu Dhabi

  Hi.I'm trying to write a web page in .NET, using C# and NHibernate 2.1. The pertinent code looks like this: var whatevervar = session.CreateSQLQuery("select thread_topic, post_time, user_display_name, user_signature, user_avatar, post_topic, post_body from THREAD, [USER], POST, THREADPOST where THREADPOST.thread_id=" + id + " and THREADPOST.thread_id=THREAD.thread_id and [USER].user_id=POST.user_id and POST.post_id=THREADPOST.post_id ORDER BY post_time;").List(); (I have tried to use joins in HQL, but then fell back on this query, due to HQL's unreadability.) The problem is that I'm getting a result that is incompatible with a repeater. When I try this: posts.DataSource = whatevervar.; posts.DataBind(); ...I get this: DataBinding: 'System.Object[]' does not contain a property with the name 'user_avatar'. In an earlier project, I used LINQ to SQL for this same purpose, and it looked like so: var whatevervar = from threads in context.THREADs join threadposts in context.THREADPOSTs on threads.thread_id equals threadposts.thread_id join posts1 in context.POSTs on threadposts.post_id equals posts1.post_id join users in context.USERs on posts1.user_id equals users.user_id orderby posts1.post_time where threads.thread_id == int.Parse(id) select new { threads.thread_topic, posts1.post_time, users.user_display_name, users.user_signature, users.user_avatar, posts1.post_body, posts1.post_topic }; That worked, and now I want to do the same with NHibernate. Unfortunately, I don't know how to make the repeater recognize the fields of the result of the query. Thanks in advance!

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• Extension methods in class library project

  - by Mostafa

  I've implemented some extension methods and put those in separate Class Library project. Imagine I have a simple extension method like this in class library called MD.Utility: namespace MD.Utility { public static class ExtenMethods { public static bool IsValidEmailAddress(this string s) { Regex regex = new Regex(@"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$"); return regex.IsMatch(s); } } } But nowhere in WebApp like App_code folder or WebFroms code-behind page I can't use this Extension method. If I do like this: using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using MD.Utility; public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { string email = "[email protected]"; if (email.IsValidEmailAddress()) { //To do } } } The compiler doesn't recognize IsValidEmailAddress() and even no intellisense support. While if I put my extension method in App_Code folder it's ok for using in another cs file in App_code Folder or Web Form code-behind pages.

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• What Language Feature Can You Just Not Live Without?

  - by akdom

  I always miss python's built-in doc strings when working in other languages. I know this may seem odd, but it allows me to cut down significantly on excess comments while still providing a clean description of my code and any interfaces therein. What Language Feature Can You Just Not Live Without? If someone were building a new language and they asked you what one feature they absolutely must include, what would it be? This is getting kind of long, so I figured I'd do my best to summarize: Paraphrased to be language agnostic. If you know of a language which uses something mentioned, please at it in the parenthesis to the right of the feature. And if you have a better format for this list, by all means try it out (if it doesn't seem to work, I'll just roll back). Regular Expressions ~ torial (Perl) Garbage Collection ~ SaaS Developer (Python, Perl, Ruby, Java, .NET) Anonymous Functions ~ Vinko Vrsalovic (Lisp, Python) Arithmetic Operators ~ Jeremy Ross (Python, Perl, Ruby, Java, C#, Visual Basic, C, C++, Pascal, Smalltalk, etc.) Exception Handling ~ torial (Python, Java, .NET) Pass By Reference ~ Chris (Python) Unified String Format WalloWizard (C#) Generics ~ torial (Python, Java, C#) Integrated Query Equivalent to LINQ ~ Vyrotek (C#) Namespacing ~ Garry Shutler () Short Circuit Logic ~ Adam Bellaire ()

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• C# Why can't I find Sum() of this HashSet. says "Arithmetic operation resulted in an overflow."

  - by user2332665

  I was trying to solve this problem projecteuler,problem125 this is my solution in python(just for understanding the logic) import math lim=10**8 found=set() for start in xrange(1,int(math.sqrt(lim))): sos = start*start for i in xrange(start+1,int(math.sqrt(lim))): sos += (i*i) if sos >= lim: break s=str(int(sos)) if s==s[::-1]: found.add(sos) print sum(found) the same code I wrote in C# is as follows using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace ConsoleApplication1 { class Program { public static bool isPalindrome(string s) { string temp = ""; for (int i=s.Length-1;i>=0;i-=1){temp+=s[i];} return (temp == s); } static void Main(string[] args) { int lim = Convert.ToInt32(Math.Pow(10,8)); var found = new HashSet<int>(); for (int start = 1; start < Math.Sqrt(lim); start += 1) { int s = start *start; for (int i = start + 1; start < Math.Sqrt(lim); i += 1) { s += i * i; if (s > lim) { break; } if (isPalindrome(s.ToString())) { found.Add(s); } } } Console.WriteLine(found.Sum()); } } } the code debugs fine until it gives an exception at Console.WriteLine(found.Sum()); (line31). Why can't I find Sum() of the set found

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• How to invalidate cache when benchmarking?

  - by Michael Buen

  I have this code, that when swapping the order of UsingAs and UsingCast, their performance also swaps. using System; using System.Diagnostics; using System.Linq; using System.IO; class Test { const int Size = 30000000; static void Main() { object[] values = new MemoryStream[Size]; UsingAs(values); UsingCast(values); Console.ReadLine(); } static void UsingCast(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = 0; foreach (object o in values) { if (o is MemoryStream) { var m = (MemoryStream)o; sum += (int)m.Length; } } sw.Stop(); Console.WriteLine("Cast: {0} : {1}", sum, (long)sw.ElapsedMilliseconds); } static void UsingAs(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = 0; foreach (object o in values) { if (o is MemoryStream) { var m = o as MemoryStream; sum += (int)m.Length; } } sw.Stop(); Console.WriteLine("As: {0} : {1}", sum, (long)sw.ElapsedMilliseconds); } } Outputs: As: 0 : 322 Cast: 0 : 281 When doing this... UsingCast(values); UsingAs(values); ...Results to this: Cast: 0 : 322 As: 0 : 281 When doing just this... UsingAs(values); ...Results to this: As: 0 : 322 When doing just this: UsingCast(values); ...Results to this: Cast: 0 : 322 Aside from running them independently, how to invalidate the cache so the second code being benchmarked won't receive the cached memory of first code? Benchmarking aside, just loved the fact that modern processors do this caching magic :-)

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• How do I implement repository pattern and unit of work when dealing with multiple data stores?

  - by Jason

  I have a unique situation where I am building a DDD based system that needs to access both Active Directory and a SQL database as persistence. Initially this wasnt a problem because our design was setup where we had a unit of work that looked like this: public interface IUnitOfWork { void BeginTransaction() void Commit() } and our repositories looked like this: public interface IRepository<T> { T GetByID() void Save(T entity) void Delete(T entity) } In this setup our load and save would handle the mapping between both data stores because we wrote it ourselves. The unit of work would handle transactions and would contain the Linq To SQL data context that the repositories would use for persistence. The active directory part was handled by a domain service implemented in infrastructure and consumed by the repositories in each Save() method. Save() was responsible with interacting with the data context to do all the database operations. Now we are trying to adapt it to entity framework and take advantage of POCO. Ideally we would not need the Save() method because the domain objects are being tracked by the object context and we would just need to add a Save() method on the unit of work to have the object context save the changes, and a way to register new objects with the context. The new proposed design looks more like this: public interface IUnitOfWork { void BeginTransaction() void Save() void Commit() } public interface IRepository<T> { T GetByID() void Add(T entity) void Delete(T entity) } This solves the data access problem with entity framework, but does not solve the problem with our active directory integration. Before, it was in the Save() method on the repository, but now it has no home. The unit of work knows nothing other than the entity framework data context. Where should this logic go? I argue this design only works if you only have one data store using entity framework. Any ideas how to best approach this issue? Where should I put this logic?

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• Are lambda expressions/delegates in C# "pure", or can they be?

  - by Bob

  I recently asked about functional programs having no side effects, and learned what this means for making parallelized tasks trivial. Specifically, that "pure" functions make this trivial as they have no side effects. I've also recently been looking into LINQ and lambda expressions as I've run across examples many times here on StackOverflow involving enumeration. That got me to wondering if parallelizing an enumeration or loop can be "easier" in C# now. Are lambda expressions "pure" enough to pull off trivial parallelizing? Maybe it depends on what you're doing with the expression, but can they be pure enough? Would something like this be theoretically possible/trivial in C#?: Break the loop into chunks Run a thread to loop through each chunk Run a function that does something with the value from the current loop position of each thread For instance, say I had a bunch of objects in a game loop (as I am developing a game and was thinking about the possibility of multiple threads) and had to do something with each of them every frame, would the above be trivial to pull off? Looking at IEnumerable it seems it only keeps track of the current position, so I'm not sure I could use the normal generic collections to break the enumeration into "chunks". Sorry about this question. I used bullets above instead of pseudo-code because I don't even know enough to write pseudo-code off the top of my head. My .NET knowledge has been purely simple business stuff and I'm new to delegates and threads, etc. I mainly want to know if the above approach is good for pursuing, and if delegates/lambdas don't have to be worried about when it comes to their parallelization.

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• How to form submit and show a different page in ASP.Net MVC?

  - by melaos

  hi guys i'm new to asp.net mvc.. so basically i just build up a two page app which takes the registration information of the user and post it to the database. i use a lot of jquery and ajax calls to retrieve data from the database using linq to sql stored proc object. and currently i'm stuck at one page where after the user submits the form it should redirect him to /Home/AddProduct. What i found was the error: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. what used on my form are basically a combination of html controls, asp.net controls and some asp.net mvc type controls. i submit the form using action="/Home/ProductAdded" and after doing some googling i found i was supposed to add in the machine key but after doing so, the index page becomes unviewable. because it couldn't find the index file now. removing the action helps, but now it just doesn't go anywhere. so what am i missing here? i feel i'm missing a lot of fundamentals understanding about asp.net mvc and i don't even know how to submit a form and go to a different page here!!

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• Why can't I create a database in an empty ASP MVC 2 project using Project->Add->New Item->SQL Server

  - by Dr Dork

  I'm diving head first into ASP MVC and am playing around with creating and manipulating a database. I did a search and found this tutorial for creating a database, however when I follow it, I get this error when trying to add a new database to my fresh, empty ASP MVC 2 project... A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) The only requirement the tutorial mentioned was SQL Server Express, but when I went to download it, it said it was already installed. I'm assuming it was part of the VS 2010 RC I installed and am running. So I don't know what else I need if I am missing something. This is all new to me, so I'm sure I'm missing something obvious here and after I'm done posting this question, I plan to do some more research into the topic of databases and how they work with ASP MVC. In the meantime, I was you could help me answer a couple high level questions... What am I missing/forgetting to do that is causing this error? Any suggestions for good resources/tutorials that focus on using databases with ASP MVC? I've done a lot of database programming in the past, so I'm familiar with the concepts of relational databases and the SQL language. I wish I could find a good resource for learning how to work with them in an ASP dev environment, as well as a good breakdown of all the related technologies used for working with them (i.e. LINQ to SQL). Thanks so much in advance for all your help! I'm going to start researching these questions right now.

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• What's the best way to develop a debugging window for an ajax ASP.Net MVC application

  - by KallDrexx

  While developing my ASP.NET MVC, I have started to see the need for a debugging console window to assist in figuring out what is going right and wrong in my code. I read the last few chapters of the Pro Asp.net MVC book, and the author details how to use http modules to show page load/creation times and linq to sql query logs, both of which I definitely want to be able to see. However, since I am loading a lot of small sections of my page individually with ajax I don't want the debug information right there in the middle of my screen. So the idea I came up with was to have a separate browser window (open-able by a link or some javascript) with a console log, that can contain logged entries both from javascript and from the asp.net mvc run. The former should be relatively easy, but I'm having trouble coming up with a way to log the asp.net information in ajax requests. The direction I have been thinking of going is to create an httpmodule (like the Pro MVC book does), and have that module contain some that append the javascript's log to console calls with the messages. The issue I see with this is finding a way to get the log messages from the controller's action methods to the httpmodule's methods. The only way I see to do this is with a singleton, but I'm not sure if singletons are bad practice for a stateless web application. Furthermore, it seems like if I return json with my ajax calls (instead of pure html) then that won't work at all anyways and unless there is a way to add data to an existing json structure inside the httpmodule. How does everyone else handle this type of debugging in heavily ajax applications? For reference, the javascript library I am using is jquery.

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• Change in behaviour & generation of nullreference exception

  - by peril brain

  I made this program 2hr ago and it ran quit well when i confronted this to presaved .xls file. But when i closed that and started new instance,it started generating null refrence exception why??plz explain. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.IO; using System.Threading; using Microsoft.Office.Interop; using Excel = Microsoft.Office.Interop.Excel; namespace svchost { class MainClass { Excel.Application oExcelApp; static void Main(string[] args) { MainClass mc = new MainClass(); while (true) { if (mc.chec()) { Console.WriteLine("RUNNING"); Thread.Sleep(4000); } else { Console.WriteLine("NOT RUNNING"); Thread.Sleep(8000); } } } public bool chec() { try { oExcelApp = (Excel.Application)System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application"); Excel.Workbook xlwkbook = (Excel.Workbook)oExcelApp.ActiveWorkbook; //****PROBLEM FROM HERE********* Console.WriteLine(xlwkbook.Name + "\n"); ke kw = new ke(ref oExcelApp,ref xlwkbook); Console.WriteLine(xlwkbook.Author); xlwkbook = null; } catch (Exception ec) { oExcelApp = null; System.GC.Collect(); Console.WriteLine(ec); return false; } oExcelApp = null; System.GC.Collect(); return true; } } class ke { public ke(ref Excel.Application a1, ref Excel.Workbook b1) { Excel.Worksheet ws = (Excel.Worksheet)a1.ActiveSheet; Console.WriteLine(a1.ActiveWorkbook.Name + "\n" + ws.Name); Excel.Range rn; rn = ws.Cells.Find("657/07", Type.Missing, Excel.XlFindLookIn.xlValues, Excel.XlLookAt.xlPart, Excel.XlSearchOrder.xlByRows, Excel.XlSearchDirection.xlNext, false, Type.Missing, Type.Missing); Console.WriteLine(rn.Text); } } }

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• C#, finding the largest prime factor of a number

  - by Juan

  Hello! I am new at programming and I am practicing my C# programming skills. My application is meant to find the largest prime factor of a number entered by the user. But my application is not returning the right answer and I dont really know where the problem is. Can you please help me? using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace ConsoleApplication1 { class Program { static void Main(string[] args) { Console.WriteLine("Calcular máximo factor primo de n. De 60 es 5."); Console.Write("Escriba un numero: "); long num = Convert.ToInt64(Console.ReadLine()); long mfp = maxfactor(num); Console.WriteLine("El maximo factor primo es: " + num); Console.Read(); } static private long maxfactor (long n) { long m=1 ; bool en= false; for (long k = n / 2; !en && k > 1; k--) { if (n % k == 0 && primo(k)) { m = k; en = true; } } return m; } static private bool primo(long x) { bool sp = true; for (long i = 2; i <= x / 2; i++) { if (x % i == 0) sp = false; } return sp; } } }

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• Use the repository pattern when using PLINQO generated data?

  - by Chad

  I'm "upgrading" an MVC app. Previously, the DAL was a part of the Model, as a series of repositories (based on the entity name) using standard LINQ to SQL queries. Now, it's a separate project and is generated using PLINQO. Since PLINQO generates query extensions based on the properties of the entity, I started using them directly in my controller... and eliminated the repositories all together. It's working fine, this is more a question to draw upon your experience, should I continue down this path or should I rebuild the repositories (using PLINQO as the DAL within the repository files)? One benefit of just using the PLINQO generated data context is that when I need DB access, I just make one reference to the the data context. Under the repository pattern, I had to reference each repository when I needed data access, sometimes needing to reference multiple repositories on a single controller. The big benefit I saw on the repositories, were aptly named query methods (i.e. FindAllProductsByCategoryId(int id), etc...). With the PLINQO code, it's _db.Product.ByCatId(int id) - which isn't too bad either. I like both, but where it gets "harrier" is when the query uses predicates. I can roll that up into the repository query method. But on the PLINQO code, it would be something like _db.Product.Where(x = x.CatId == 1 && x.OrderId == 1); I'm not so sure I like having code like that in my controllers. Whats your take on this?

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• Using NHibernate to select entities based on activity of children entities

  - by mannish

  I'm having a case of the Mondays... I need to select blog posts based on recent activity in the post's comments collection (a Post has a List<Comment> property and likewise, a Comment has a Post property, establishing the relationship. I don't want to show the same post twice, and I only need a subset of the entities, not all of the posts. First thought was to grab all posts that have comments, then order those based on the most recent comment. For this to work, I'm pretty sure I'd have to limit the comments for each Post to the first/newest Comment. Last I'd simply take the top 5 (or whatever max results number I want to pass into the method). Second thought would be to grab all of the comments, ordered by CreatedOn, and filter so there's only one Comment per Post. Then return those top (whatever) posts. This seems like the same as the first option, just going through the back door. I've got an ugly, two query option I've got working with some LINQ on the side for filtering, but I know there's a more elegant way to do it in using the NHibernate API. Hoping to see some good ideas here.

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• Does WPF break an Entity Framework ObjectContext?

  - by David Veeneman

  I am getting started with Entity Framework 4, and I am getting ready to write a WPF demo app to learn EF4 better. My LINQ queries return IQueryable<T>, and I know I can drop those into an ObservableCollection<T> with the following code: IQueryable<Foo> fooList = from f in Foo orderby f.Title select f; var observableFooList = new ObservableCollection<Foo>(fooList); At that point, I can set the appropriate property on my view model to the observable collection, and I will get WPF data binding between the view and the view model property. Here is my question: Do I break the ObjectContext when I move my foo list to the observable collection? Or put another way, assuming I am otherwise handling my ObjectContext properly, will EF4 properly update the model (and the database)? The reason why I ask is this: NHibernate tracks objects at the collection level. If I move an NHibernate IList<T> to an observable collection, it breaks NHibernate's change tracking mechanism. That means I have to do some very complicated object wrapping to get NHibernate to work with WPF. I am looking at EF4 as a way to dispense with all that. So, to get EF4 working with WPF, is it as simple as dropping my IQueryable<T> results into an ObservableCollection<T>. Does that preserve change-tracking on my EDM entity objects? Thanks for your help.

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• Pair-wise iteration in C# or sliding window enumerator

  - by f3lix

  If I have an IEnumerable like: string[] items = new string[] { "a", "b", "c", "d" }; I would like to loop thru all the pairs of consecutive items (sliding window of size 2). Which would be ("a","b"), ("b", "c"), ("c", "d") My solution was is this public static IEnumerable<Pair<T, T>> Pairs(IEnumerable<T> enumerable) { IEnumerator<T> e = enumerable.GetEnumerator(); e.MoveNext(); T current = e.Current; while ( e.MoveNext() ) { T next = e.Current; yield return new Pair<T, T>(current, next); current = next; } } // used like this : foreach (Pair<String,String> pair in IterTools<String>.Pairs(items)) { System.Out.PrintLine("{0}, {1}", pair.First, pair.Second) } When I wrote this code, I wondered if there are already functions in the .NET framework that do the same thing and do it not just for pairs but for any size tuples. IMHO there should be a nice way to do this kind of sliding window operations. I use C# 2.0 and I can imagine that with C# 3.0 (w/ LINQ) there are more (and nicer) ways to do this, but I'm primarily interested in C# 2.0 solutions. Though, I will also appreciate C# 3.0 solutions.

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• Retrive data from two tables in asp.net mvc using ADO.Net Entity Framework

  - by user192972

  Please read my question carefully and reply me. I have two tables as table1 and table2. In table1 i have columns as AddressID(Primary Key),Address1,Address2,City In table2 i have columns as ContactID(Primary Key),AddressID(Foriegn Key),Last Name,First Name. By using join operation i can retrive data from both the tables. I created a Model in my MVC Application.I can see both the tables in enitity editor. In the ViewData folder of my solution explorer i created two class as ContactViewData.cs and SLXRepository.cs In the ContactViewData.cs i have following code public IEnumerable<CONTACT> contacts { get; set; } In the SLXRepository.cs i have following code public IEnumerable<CONTACT> GetContacts() { var contact = ( from c in context.CONTACT join a in context.ADDRESS on c.ADDRESSID equals a.ADDRESSID select new { a.ADDRESS1, a.ADDRESS2, a.CITY, c.FIRSTNAME, c.LASTNAME } ); return contact; } I am getting the error in return type Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)

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• SQL Express under IIS 7.5

  - by fampinheiro

  I´m developing a web service that access a SQL Express database, it works very well in the Visual Studio host but when i deploy it to IIS 7.5 i get this exception. Please help me. Stack Trace: System.Data.EntityException: The underlying provider failed on Open. ---> System.Data.SqlClient.SqlException: Failed to generate a user instance of SQL Server due to failure in retrieving the user's local application data path. Please make sure the user has a local user profile on the computer. The connection will be closed. at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) at System.Data.SqlClient.SqlInternalConnectionTds.CompleteLogin(Boolean enlistOK) at System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, Int64 timerExpire, SqlConnection owningObject) at System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(String host, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject, SqlConnectionString connectionOptions, Int64 timerStart) at System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance) at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance) at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection, DbConnectionPool pool, DbConnectionOptions options) at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject) at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject) at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject) at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open() at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition, DbConnection storeConnectionToOpen, DbConnection originalConnection, String exceptionCode, String attemptedOperation, Boolean& closeStoreConnectionOnFailure) --- End of inner exception stack trace --- at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition, DbConnection storeConnectionToOpen, DbConnection originalConnection, String exceptionCode, String attemptedOperation, Boolean& closeStoreConnectionOnFailure) at System.Data.EntityClient.EntityConnection.Open() at System.Data.Objects.ObjectContext.EnsureConnection() at System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) at System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator() at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source) at WSCinema.CinemaService.Movie() in D:\Documents\My Dropbox\Projects\sd.v0910\trab3\code\WSCinema\CinemaService.asmx.cs:line 46

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• Extending EF4 SQL Generation

  - by Basiclife

  Hi, We're using EF4 in a fairly large system and occasionally run into problems due to EF4 being unable to convert certain expressions into SQL. At present, we either need to do some fancy footwork (DB/Code) or just accept the performance hit and allow the query to be executed in-memory. Needless to say neither of these is ideal and the hacks we've sometimes had to use reduce readability / maintainability. What we would ideally like is a way to extend the SQL generation capabilities of the EF4 SQL provider. Obviously there are some things like .Net method calls which will always have to be client-side but some functionality like date comparisons (eg Group by weeks in Linq to Entities ) should be do-able. I've Googled but perhaps I'm using the wrong terminology as all I get is information about the new features of EF4 SQL Generation. For such a flexible and extensible framework, I'd be surprised if this isn't possible. In my head, I'm imagining inheriting from the [SQL 2008] provider and extending it to handle additional expressions / similar in the expression tree it's given to convert to SQL. Any help/pointers appreciated. We're using VS2010 Ultimate, .Net 4 (non-client profile) and EF4. The app is in ASP.Net and is running in a 64-Bit environment in case it makes a difference.

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• Instead of trigger in SQL Server - looses SCOPE_IDENTITY?

  - by kastermester

  Hey StackOverflow, I am (once again) having some issues with some SQL. I have a table, on which I have created an INSTEAD OF trigger to enforce some buissness rules (rules not really important). This works as intended. My issue is, that now when inserting data into this table, SCOPE_IDENTITY() now returns a NULL value, rather than the actual inserted identity, my guess is that this is because it is now out of scope - but then how do I get this in scope? I am using SQL Server 2008. Per request, here's the SQL: Insert + Scope code INSERT INTO [dbo].[Payment]([DateFrom], [DateTo], [CustomerId], [AdminId]) VALUES ('2009-01-20', '2009-01-31', 6, 1) SELECT SCOPE_IDENTITY() Trigger: CREATE TRIGGER [dbo].[TR_Payments_Insert] ON [dbo].[Payment] INSTEAD OF INSERT AS BEGIN -- SET NOCOUNT ON added to prevent extra result sets from -- interfering with SELECT statements. SET NOCOUNT ON; IF NOT EXISTS(SELECT 1 FROM dbo.Payment p INNER JOIN Inserted i ON p.CustomerId = i.CustomerId WHERE (i.DateFrom >= p.DateFrom AND i.DateFrom <= p.DateTo) OR (i.DateTo >= p.DateFrom AND i.DateTo <= p.DateTo) ) AND NOT EXISTS (SELECT 1 FROM Inserted p INNER JOIN Inserted i ON p.CustomerId = i.CustomerId WHERE (i.DateFrom <> p.DateFrom AND i.DateTo <> p.DateTo) AND ((i.DateFrom >= p.DateFrom AND i.DateFrom <= p.DateTo) OR (i.DateTo >= p.DateFrom AND i.DateTo <= p.DateTo)) ) BEGIN INSERT INTO dbo.Payment (DateFrom, DateTo, CustomerId, AdminId) SELECT DateFrom, DateTo, CustomerId, AdminId FROM Inserted END ELSE BEGIN ROLLBACK TRANSACTION END END The code did work before the creation of this trigger, also I am using LINQ to SQL in C# and as far as I can see, I have no way of changing SCOPE_IDENTITY to @@IDENITY - is there really no way out of this one?

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