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• Cocoa Core Data - Efficient Related Entities Counts

  - by Gary

  I am working on my first iPhone application and I've hit a wall. I'm trying to develop a 'statistics' page for a three entity relationship. My entities are the following: Department - Name, Address, Building, etc. People - Name, Gender (BOOL), Phone, etc If I have fetched a specific department how do I filter those results and only return people that are Male (Gender == 0)? If I do NSLog(@"%d", [department.people count]); I get the correct number of people in that department so I know I'm in the neighborhood. I know I could re-fetch and modify the predicate each time but with 20+ stats in my app that seems inefficient. Thanks for any advice!

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• Generate non-identity primary key

  - by MikeWyatt

  My workplace doesn't use identity columns or GUIDs for primary keys. Instead, we retrieve "next IDs" from a table as needed, and increment the value for each insert. Unfortunatly for me, LINQ-TO-SQL appears to be optimized around using identity columns. So I need to query and update the "NextId" table whenever I perform an insert. For simplicity, I do this immediately creating the new object. Since all operations between creation of the data context and the call to SubmitChanges are part of one transaction, do I need to create a separate data context for retrieving next IDs? Each time I need an ID, I need to query and update a table inside a transaction to prevent multiple apps from grabbing the same value. Is a separate data context the only way, or is there something better I could try?

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• Is an IQueryable a query or just an object which can be queried?

  - by Albic

  I'm kinda confused what the IQueryable interface actually represents. The MSDN documentation for IQueryable says: "Provides functionality to evaluate queries against a specific data source." The documentation for IQueryProvider says: "Defines methods to create and execute queries that are described by an IQueryable object." The name and the documentation summary suggest that it is an object/data store which can be queried. The second quote and the fact the ObjectQuery class from the Entity Framework implements IQueryable suggest it is a query which can be executed. Did I misunderstood something or is it really kinda fuzzy?

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• Closing an EDM ObjectContext?

  - by David Veeneman

  I am getting started with the ADO.NET Entity Framework 4.0. I have created an EDM and data store for the app, and it successfully retrieves entities. The application holds the EDM's ObjectContext as a member-level variable, which it uses to call ObjectContext.SaveChanges(). So far, so good. I am going to refactor to repositories later. Right now, my question is a bit more basic: When I am finished with the EDM, what do I need to do to release it? Is it as simple as calling Dispose() on the ObjectContext? Thanks for your help.

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• Sorting the data returned by a database

  - by Rishabh Ohri

  hi all, In our project we have a requirement that when a set of records are returned by the database the records should be sorted with respect to the TITLE field in the record. The records will have to be sorted alphabetically but if the title of a record has a number in it then it should come after the records whose title only consists of alphabets. Details: we are using SQL Server , and c#. The data from the database comes to an Entity class whic forwards the data to other layers. So, What will be the possible and effective solution for this requirement.

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• How to flush DNS cache in Windows Mobile programmatically?

  - by Bounded

  Hello, My windows mobile application (written in C# with the compact framework) needs to know if a particular machine is active or not. To achieve this goal, I thought to use a ping mechanism. I tried to use the Ping class implemented in the opennetcf framework (the System.Net.NetworkInformation.Ping class for the .NET Framework is not part of the compact framework). Because I give to the Ping.Send function a host name, it first tries to resolve this host name and to retrieve an IP address. But i observe the following problem : If the first dns resolution fails (because the network is down at this moment), and if the application tries immediately again to send the ping, it fails too, even if the network is note down anymore. I check with a famous network protocol analyzer and i saw that only the requests concerning the first dns resolution are sent. The requests concerning the dns resolution of the second ping are not sent. Why is the second dns request not sent ? Is there any dns cache mechanism on such Windows Mobile devices ? If yes, can this mechanism beeing flushed programmatically ? EDIT : I gave up finding a solution to this DNS flush. I chose to ping an IP adress instead of a name machine. The problem of pinging an hard coded adress IP is that we have to be 100% sure that this IP will not change. The gateway IP can be used because it's always reachable (if it does not, it means the network is down).

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• Core Data Relationships in pre-populated SQLite database

  - by Cardinal

  Hi All, I'm new to Core Data. Currently I have following tables on hand: tbl_teahcer tbl_student tbl_course tbl_student_course_map ----------- ----------- ---------- ---------------------- teacher_id student_id course_id student_id name name name course_id teahcer_id And I'm going to make the xcdatamodel as below: Course Teacher ------ ------- name name teacher <<----------> courses students <<---| | Student | ------- | name |----->> courses My questions are as follows: As I'd like to create TableView for Cource Entity, is it a must to create the Inverse Relationship from Teacher to Course, and Student to Course? What is the beneit for having the Inverse Relationship? I got some pre-defined data on hand, and I'd like to create a SQLite storage for pre-populated source. How can I set up the relationships (both directions) in SQLite? Thank you for your help! Regards, Cardinal

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• Deleting objects through foreign key relationship with T-SQL query

  - by LaserBeak

  Looking for a way to write the following LinQ to entities query as a T-SQL statement. repository.ProductShells.Where(x => x.ShellMembers.Any(sm => sm.ProductID == pid)).ToList().ForEach(x => repository.ProductShells.Remove(x)); The below is obviously not correct but I need it to delete respective ProductShell object where any ShellMember contains a ProductID equal to the passed in variable pid. I would presume this would involve a join statement to get the relevant ShellMembers. repository.Database.ExecuteSqlCommand("FROM Shellmembers WHERE ProductID={0} DELETE FK_ProductShell", pid); I have cascade delete enabled for the FK_ShellMembers_ProductShells foreign key, so when I delete the ProductShell it will delete all the ShellMembers that are associated with it. I am going to pass this statement to System.Data.Entity Database.ExecuteSqlCommand method.

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• Fluent Nhibernate expression to select on flagged enum

  - by mbalkema

  I have a domain entity that has a flagged enum as a property. The flagged enum is the target audience for the these entities. The user then has a flagged enum value of the entities they should see. I am trying to figure out the correct expression to select entities that meet the target audience for the user. public class File { public virtual TargetAudience TargetAudience { get; set; } } [Flags] public enum TargetAudience { Audience1 = 1, Audience2 = 2, Audience3 = 4, Audience4 = 8 } Expression: (This works when performed on a IList<File>, but doesn't work on a query to the database.) public Expression<Func<File, bool>> Expression { get { return ((x.TargetAudience & UserTargetedAudience) > 0); } } Any suggestions would be helpful.

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• Enumerable Contains Enumerable

  - by Tim

  For a method I have the following parameter IEnumerable<string> tags and with to query a list of objects, let's call them Post, that contains a property IEnumerable<string> Tags { get; set; }. My question is: How do I use linq to query for objects that contains all the tags from the tags parameter? private List<Post> posts = new List<Post>(); public IEnumerable<Post> GetPostsWithTags(IEnumerable<string> tags) { return ???; }

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• C# - Convert Implict Type to ObservableCollection

  - by user70192

  Hello, I have a LINQ statement that returns an implicit type. I need to get this type to be an ObservableCollection in my Silverlight 3 application. The ObservableCollection constructor in Silverlight 3 only provides an empty constructor. Because of this, I cannot directly convert my results to an ObservableCollection. Here is my code: ObservableCollection<MyTasks> visibleTasks = e.Result; var filteredResults = from visibleTask in visibleTasks select visibleTask; filteredResults = filteredResults.Where(p => p.DueDate == DateTime.Today); visibleTasks = filteredResults.ToList(); // This throws a compile time error How can I go from an implicitly typed variable to an observable collection? Thank you

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• Cannot implicitly convert type System.Collection.Generic.IEnumberable

  - by Cen

  I'm receiving this error in my Linq statement --- Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'hcgames.ObjectClasses.ShoppingCart.ShoppingCartCartAddon'. An explicit conversion exists (are you missing a cast?) From this query ShoppingCartItems items = Cart.GetAllItems(); ShoppingCartCartAddons addons = Cart.GetAllAddons(); var stuff = from x in items select new ShoppingCartItem() { ProductID = x.ProductID, Quantity = x.Quantity, Name = x.Name, Price = x.Price, Weight = x.Weight, Addons = (from y in addons where y.ShoppingCartItemID == x.ID select y) }; I can not figure out how to cast this properly. Any suggestions? Thanks for your help!

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• Treat multiple IEnumerable objects as a single IEnumerable

  - by MainMa

  Hi, My question seems to be something easy, but I can't figure it out. Let's say I have a "root" IEnumerable of objects. Each object has IEnumerable of strings. How can I obtain a single IEnumerable of those strings? A possible solution is to do: public IEnumerable<string> DoExample() { foreach (var c in rootSetOfObjects) { foreach (var n in c.childSetOfStrings) { yield return n; } } } But maybe there is a magic solution with Linq?

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• How to serve a View as CSV in ASP.NET Web Forms

  - by ChessWhiz

  Hi, I have a MS SQL view that I want to make available as a CSV download in my ASPNET Web Forms app. I am using Entity Framework for other views and tables in the project. What's the best way to enable this download? I could add a HyperLink whose click handler iterates over the view, writes its CSV form to the disk, and then serves that file. However, I'd prefer not to write to the disk if it can be avoided, and that involves iteration code that may be avoided with some other solution. Any ideas?

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• How can I access IEnumerable<T> extension methods on my custom subclass of BindingList<T>?

  - by Dan

  I have a custom subclass of BindingList<T> that I want to execute a LINQ query over using the handy extension methods. For example: public int GetSum(MyList<T> list) { return list.Sum(x => x.Value); } But the compiler complains that it can't resolve Sum because it doesn't recognize list as an IEnumerable<T>, which it obviously is, because this works: public int GetSum(MyList<T> list) { return ((IEnumerable<T>)list).Sum(x => x.Value); } Anyone have a clever way I can avoid the ugly and unecessary cast?

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• Do you use enums in your data applications and how?

  - by Ivan

  My practice shows that a general enterprise application has a lot of entities which's nature corresponds to an elementary enumeration. For example We may have an Order entity which may have such fields as "OrderType", "OrderStatus", "Currency", etc. referencing corresponding Entities which are nothing more than just a textual name bound to a key to be referenced. Using enums would look very natural here. But entities have to be defined in application code at design-time, am I right? While in we need to be able to CRUD enum value variants at runtime and use enums in server-side SQL queries (like stored procedures and views). What are you practices and thoughts on this subject? I am particularly interested in C#4, linq and T-SQL.

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• dynamically create sitemap xml using php

  - by rekhasathvika

  Hi, I have created sitemap for my site using some reference code in the below link http://stackoverflow.com/questions/2747801/creating-an-xml-sitemap-with-php But I am getting error as XML Parsing Error: undefined entity Location: as my content is as follows << alt attribute and it says something like < loc http://www.example.com/700- & laquo;alt & raquo;-attributes-in-images.php< /loc Can anyone tell me how to get rid of this error.

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• LINQtoSQL: Query to return List<String>

  - by ctrlShiftBryan

  I have a LINQ query that returns some object like this... var query = from c in db.Customers where ... select c; Then I do this List<String> list = new List<String>(); foreach (ProgramLanguage c in query) { //GetUL returns a String list.Add(GetUL(c.Property,c.Property2)); } Is there a way to combine into something list this? var query = from c in db.Customers where ... select new { GetUL(c.Property,c.Property2) }).ToList<String>();

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• Extraction Event

  - by Anicho

  So I have the following code: public override void Extract(object sender, ExtractionEventArgs e) { if (e.Response.HtmlDocument != null) { var myParam = e.Request.QueryStringParameters.Where(parameter => parameter.Name == QueryName).Select(parameter => parameter.Value).Distinct(); myParam. // add the extracted value to the web performance test context e.WebTest.Context.Add(this.ContextParameterName, myParam.ToString()); e.Success = true; return; } // If the extraction fails, set the error text that the user sees e.Success = false; e.Message = String.Format(CultureInfo.CurrentCulture, "Not Found: {0}", QueryName); } It's returning: System.Linq.Enumerable+<DistinctItem>d_81`1[system.string] I am expecting something along the lines of: 0152-1231-1231-123d My question is how do I extract the querystring's actual value from extractioneventargs. They say it's possible, but I have no idea.

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• Why does SQL Server keep throwing exceptions?

  - by Augusto Càzares

  I have my project in .NET that uses a database in SQL Server. I'm using Linq-to-SQL, sometimes when the project throws me an exception (Constraint) in a part of the project this same error keeps showing in other part of the project when I do another thing with the database. Like when I do an insertion and I had before an exception on delete the insertion throws me the delete exception, and it remains this way until I close and open again the project. My major problem is when this happen in my online project, this error in my project causes me problems in the project I'm testing online (I use the same database). I don't know if this exception is on the memory or something but its have been causing me a lot of headaches.

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• Microsoft SQL Server 2008 - 99% fragmentation on non-clustered, non-unique index

  - by user550441

  I have a table with several indexes (defined below). One of the indexes (IX_external_guid_3) has 99% fragmentation regardless of rebuilding/reorganizing the index. Anyone have any idea as to what might cause this, or the best way to fix it? We are using Entity Framework 4.0 to query this, the EF queries on the other indexed fields about 10x faster on average then the external_guid_3 field, however an ADO.Net query is roughly the same speed on both (though 2x slower than the EF Query to indexed fields). Table id(PK, int, not null) guid(uniqueidentifier, null, rowguid) external_guid_1(uniqueidentifier, not null) external_guid_2(uniqueidentifier, null) state(varchar(32), null) value(varchar(max), null) infoset(XML(.), null) -- usually 2-4K created_time(datetime, null) updated_time(datetime, null) external_guid_3(uniqueidentifier, not null) FK_id(FK, int, null) locking_guid(uniqueidentifer, null) locked_time(datetime, null) external_guid_4(uniqueidentifier, null) corrected_time(datetime, null) is_add(bit, not null) score(int, null) row_version(timestamp, null) Indexes PK_table(Clustered) IX_created_time(Non-Unique, Non-Clustered) IX_external_guid_1(Non-Unique, Non-Clustered) IX_guid(Non-Unique, Non-Clustered) IX_external_guid_3(Non-Unique, Non-Clustered) IX_state(Non-Unique, Non-Clustered)

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• Property in class is IEnumerable<TDto> get TDto.A == a

  - by Miau

  So I have a class is something like this public class Order { //some other stuff ... //setting the internal _orderItems collection ... IEnumerable<OrderItems> OrderItems { get { return _orderItems; } } public class OrderItem { //other stuff public string ProductName {get; set;} } If I have a collection of orders of some sort and have access via linq to the order, something like myOrderRespository.Where(x=>x.OrderItems) Then I only have access to getEnumerator there, waht I would like it to be able to do something like myOrderRespository.Where(x=>x.OrderItems.ProductName == "Blah") Is this possible? this is a made up scenario and its pseudo code I m trying to simplify the problem so its easy to explain ( so please forgive me if there are a few errors) Cheers

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• First try StructureMap and MVC3 via NuGet

  - by Angel Escobedo

  Hello Guys, I'm trying to figure how to config StructureMap for ASP.NET MVC3 I've already using NuGet and I notice that it creates App_Start Folder with a cs file named as StructuremapMVC, so I check it and notice that is the same code but simplified that will be written manually on App_Start section placed on Global.asax... My Question is when I inject some IoC on my Controllers as the follow (I use this pattern : Entity Framework 4 CTP 4 / CTP 5 Generic Repository Pattern and Unit Testable) : private readonly IAsambleaRepository _aRep; private readonly IUnitOfWork _uOw; public AsambleaController(IAsambleaRepository aRep, IUnitOfWork uOw) { _aRep = aRep; this._uOw = uOw; } public ActionResult List(string period) { var rs = _aRep.ByPeriodo(period).ToList<Asamblea>(); return View(); } I got an Exception Exception Details: System.MissingMethodException: No parameterless constructor defined for this object.

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• Why am I getting "Collection was modified; enumeration operation may not execute" when not modifying

  - by ccornet

  I have two collections of strings: CollectionA is a StringCollection property of an object stored in the system, while CollectionB is a List generated at runtime. CollectionA needs to be updated to match CollectionB if there are any differences. So I devised what I expected to be a simple LINQ method to perform the removal. var strDifferences = CollectionA.Where(foo => !CollectionB.Contains(foo)); foreach (var strVar in strDifferences) { CollectionA.Remove(strVar); } But I am getting a "Collection was modified; enumeration operation may not execute" error on strDifferences... even though it is a separate enumerable from the collection being modified! I originally devised this explicitly to evade this error, as my first implementation would produce it (as I was enumerating across CollectionA and just removing when !CollectionB.Contains(str)). Can anyone shed some insight into why this enumeration is failing?

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• How to replace for-loops with a functional statement in C#?

  - by Lernkurve

  A colleague once said that God is killing a kitten every time I write a for-loop. When asked how to avoid for-loops, his answer was to use a functional language. However, if you are stuck with a non-functional language, say C#, what techniques are there to avoid for-loops or to get rid of them by refactoring? With lambda expressions and LINQ perhaps? If so, how? Questions So the question boils down to: Why are for-loops bad? Or, in what context are for-loops to avoid and why? Can you provide C# code examples of how it looks before, i.e. with a loop, and afterwards without a loop?

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