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  • Using Core Data Concurrently and Reliably

    - by John Topley
    I'm building my first iOS app, which in theory should be pretty straightforward but I'm having difficulty making it sufficiently bulletproof for me to feel confident submitting it to the App Store. Briefly, the main screen has a table view, upon selecting a row it segues to another table view that displays information relevant for the selected row in a master-detail fashion. The underlying data is retrieved as JSON data from a web service once a day and then cached in a Core Data store. The data previous to that day is deleted to stop the SQLite database file from growing indefinitely. All data persistence operations are performed using Core Data, with an NSFetchedResultsController underpinning the detail table view. The problem I am seeing is that if you switch quickly between the master and detail screens several times whilst fresh data is being retrieved, parsed and saved, the app freezes or crashes completely. There seems to be some sort of race condition, maybe due to Core Data importing data in the background whilst the main thread is trying to perform a fetch, but I'm speculating. I've had trouble capturing any meaningful crash information, usually it's a SIGSEGV deep in the Core Data stack. The table below shows the actual order of events that happen when the detail table view controller is loaded: Main Thread Background Thread viewDidLoad Get JSON data (using AFNetworking) Create child NSManagedObjectContext (MOC) Parse JSON data Insert managed objects in child MOC Save child MOC Post import completion notification Receive import completion notification Save parent MOC Perform fetch and reload table view Delete old managed objects in child MOC Save child MOC Post deletion completion notification Receive deletion completion notification Save parent MOC Once the AFNetworking completion block is triggered when the JSON data has arrived, a nested NSManagedObjectContext is created and passed to an "importer" object that parses the JSON data and saves the objects to the Core Data store. The importer executes using the new performBlock method introduced in iOS 5: NSManagedObjectContext *child = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; [child setParentContext:self.managedObjectContext]; [child performBlock:^{ // Create importer instance, passing it the child MOC... }]; The importer object observes its own MOC's NSManagedObjectContextDidSaveNotification and then posts its own notification which is observed by the detail table view controller. When this notification is posted the table view controller performs a save on its own (parent) MOC. I use the same basic pattern with a "deleter" object for deleting the old data after the new data for the day has been imported. This occurs asynchronously after the new data has been fetched by the fetched results controller and the detail table view has been reloaded. One thing I am not doing is observing any merge notifications or locking any of the managed object contexts or the persistent store coordinator. Is this something I should be doing? I'm a bit unsure how to architect this all correctly so would appreciate any advice.

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  • Per instance dynamic fields django model

    - by Roberto Rosario
    I have a model with a JSON field or a link to a CouchDB document. I can currently access the dynamic informaction in a way such as: genericdocument.objects.get(pk=1) == genericdocument.json_field['sample subfield'] instead I would like genericdocument.sample_subfield to maintain compatibility with all the apps the project currently shares.

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  • ASP.Net Architecture Specific to Shared/Static functions

    - by Maxim Gershkovich
    Hello All, Could someone please advise in the context of a ASP.Net application is a shared/static function common to all users? If for example you have a function Public shared function GetStockByID(StockID as Guid) as Stock Is that function common to all current users of your application? Or is the shared function only specific to the current user and shared in the context of ONLY that current user? So more specifically my question is this, besides database concurrency issues such as table locking do I need to concern myself with threading issues in shared functions in an ASP.Net application? In my head; let’s say my application namespace is MyTestApplicationNamespace. Everytime a new user connects to my site a new instance of the MyTestApplicationNamespace is created and therefore all shared functions are common to that instance and user but NOT common across multiple users. Is this correct?

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  • Paging & Sorting grids with ASP.Net MVC

    - by Scott Ivey
    I'm new to MVC, and am not following how you'd do paging and sorting on a grid. I'm used to using the asp.Net GridView control with an ObjectDataSource pointed at objects in our business layer - and in that case the ODS handles all of the paging & sorting using the methods that our ORM generates on the objects. I've looked at using the same ORM with MVC - and things work out fine there - i just loop thru the collections to build the table on the page - but without the ODS to handle the paging & sorting, i'm confused as to how I'd handle that. Would I have a separate controller for the paging and sorting? I'm not sure what the best practices are for this scenario, so if someone can point me in the right direction it would be much appreciated. Edit: Ok, so I understand that I need to roll my own - but where do I start? I've created a CustomerController, and a view that displays a table of customers that looks like below - and I want to sort on FirstName or LastName columns. My Model has a Sort() method on it that'll take a string sort expression in the format that would be used by a GridView/ODS pair. Would I create a new Action on my CustomerController called Sort, and put an ActionLink in my header? <table> <tr> <th> First Name </th> <th> Last Name </th> </tr> <% foreach (var item in Model) { %> <tr> <td> <%= Html.Encode(item.FirstName) %> </td> <td> <%= Html.Encode(item.LastName) %> </td> </tr> <% } %> </table>

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  • .NET Deployment of Interface/Classes for Command Pattern Question

    - by Jonno
    In theory I would like to produce 2 projects: 1) Asp.net (Sever A) 2) DAL running (Server B) I would like to utilise command objects to comunicate with the DAL. ASP.net instantiates a command class e.g. CmdGetAllUsers which impliments IMyCommand interface and sends it to the DAL (using ASMX or WCF). My question is: Would the class definition of CmdGetAllUsers need to exist on the DAL server? Or would having the interface definition be enough? My goal is to reduce the need to redeploy the DAL code, and have it as a fairly simple pass-through layer. Many thanks for your time.

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  • MVC-style model binding in WCF?

    - by Mark
    I want to bind POSTed form values to parameters in my WCF operation in the same way that ASP.Net MVC allows me to do. So, for example if my form has "customer.Name" and "customer.Age" parameters, I want to make a standard HTML POST to a named endpoint/operation that takes a customer parameter and have it instantiated and populated like MVC can do... It looks like I can use WebInvoke and its UriTemplate property to map simple parameters - does anyone know if a more MVC-like model-binding way is possible? Thanks, Mark.

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  • Which is the "best" data access framework/approach for C# and .NET?

    - by Frans
    (EDIT: I made it a community wiki as it is more suited to a collaborative format.) There are a plethora of ways to access SQL Server and other databases from .NET. All have their pros and cons and it will never be a simple question of which is "best" - the answer will always be "it depends". However, I am looking for a comparison at a high level of the different approaches and frameworks in the context of different levels of systems. For example, I would imagine that for a quick-and-dirty Web 2.0 application the answer would be very different from an in-house Enterprise-level CRUD application. I am aware that there are numerous questions on Stack Overflow dealing with subsets of this question, but I think it would be useful to try to build a summary comparison. I will endeavour to update the question with corrections and clarifications as we go. So far, this is my understanding at a high level - but I am sure it is wrong... I am primarily focusing on the Microsoft approaches to keep this focused. ADO.NET Entity Framework Database agnostic Good because it allows swapping backends in and out Bad because it can hit performance and database vendors are not too happy about it Seems to be MS's preferred route for the future Complicated to learn (though, see 267357) It is accessed through LINQ to Entities so provides ORM, thus allowing abstraction in your code LINQ to SQL Uncertain future (see Is LINQ to SQL truly dead?) Easy to learn (?) Only works with MS SQL Server See also Pros and cons of LINQ "Standard" ADO.NET No ORM No abstraction so you are back to "roll your own" and play with dynamically generated SQL Direct access, allows potentially better performance This ties in to the age-old debate of whether to focus on objects or relational data, to which the answer of course is "it depends on where the bulk of the work is" and since that is an unanswerable question hopefully we don't have to go in to that too much. IMHO, if your application is primarily manipulating large amounts of data, it does not make sense to abstract it too much into objects in the front-end code, you are better off using stored procedures and dynamic SQL to do as much of the work as possible on the back-end. Whereas, if you primarily have user interaction which causes database interaction at the level of tens or hundreds of rows then ORM makes complete sense. So, I guess my argument for good old-fashioned ADO.NET would be in the case where you manipulate and modify large datasets, in which case you will benefit from the direct access to the backend. Another case, of course, is where you have to access a legacy database that is already guarded by stored procedures. ASP.NET Data Source Controls Are these something altogether different or just a layer over standard ADO.NET? - Would you really use these if you had a DAL or if you implemented LINQ or Entities? NHibernate Seems to be a very powerful and powerful ORM? Open source Some other relevant links; NHibernate or LINQ to SQL Entity Framework vs LINQ to SQL

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  • .NET make a copy of an embedded file resource to the local drive

    - by Matt H.
    Hi, i'm new to the realm to working with Files in .NET I'm creating a WPF application in VB.NET with the 3.5 Framework. (If you provide an example in C#, that's perfectly fine.) In my project I have a Template for an MS Access database. My desired behavior is that when the users clicks File--New, they can create a new copy of this template, give it a filename, and save it to their local directory. The database already has the tables and some starting data needed to interface with my application (a user-friendly data editor) I'm thinking the approach is to include this "template.accdb" file as a resource in the project, and write it to a file somehow at runtime? Any guidance will be very, very appreciated. Thanks!

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  • MVC - Sanitizing data, where?

    - by dierre
    I'm using CakePHP but it's a question about the MVC pattern. I have in my form the input-text for the tags (separated by commas). To add the tags I've created a Tag model method that basically check if the tag exists and then add the new tag or just a new unit in the tag counter (the Tag model has these fields: id, name, slug, count). In the controller I explode the tags field and pass one tag at a time. The question is: where do I sanitize data? In the controller or in the model method? I think it should be in the controller because that's where I explode but in term of reusability I think I should sanitize data in the model. What do you think?

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  • EntityFramework how to Override properties

    - by plotnick
    I've just started using EF in VS2010. That thing is just amazin'. I frankly can't understand something. For example I have EntityType with property, they generated from database structure. Now, I have to simply override that property in my code. I don't need to save value of the property back into DB, but everytime when it gets read from DB it should be substituted with run-time calculated value. Of course I can create derived class based on my EntityType but I've tried and found kinda difficulties, I'm not sure this is kinda right way to do. Anyway even when I try to change the whole EntityType to Abstract, damn Visual Studio doesn't want to validate that and says something like: "Error 2078: The EntityType 'AssetsModel.Asset' is Abstract and can be mapped only using IsTypeOf." "Error 2063: At least one property must be mapped in the set mapping for 'Assets'" What the hell is this suppose to mean I dunno.. Any ideas gentlemen?

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  • C# SQL Data Adapter Fill on existing typed Dataset

    - by René
    I have an option to choose between local based data storing (xml file) or SQL Server based. I already created a long time ago a typed dataset for my application to save data local in the xml file. Now, I have a bool that changes between Server based version and local version. If true my application get the data from the SQL Server. I'm not sure but It seems that Sql Adapter's Fill Method can't fill the Data in my existing schema SqlCommand cmd = new SqlCommand("Select * FROM dbo.Categories WHERE CatUserId = 1", _connection); cmd.CommandType = CommandType.Text; _sqlAdapter = new SqlDataAdapter(cmd); _sqlAdapter.TableMappings.Add("Categories", "dbo.Categories"); _sqlAdapter.Fill(Program.Dataset); This should fill my data from dbo.Categories to Categories (in my local, typed dataset). but it doesn't. It creates a new table with the name "Table". It looks like it can't handle the existing schema. I can't figure it out. Where is the problem? btw. of course the database request I do isn't very useful that way. It's just a simplified version for testing...

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  • ASP.NET - How to edit 'bit' data type?

    - by Peter
    I am coding in Visual Basic. I am using a checkbox control. Now depending on its checked property I need to set/unset a bit column in a SQL Server database. Here's the code: Try conSQL.Open() Dim cmd As New SqlCommand("update Student set send_mail = " + _ sendemailCheckBox.Checked.ToString + " where student_id = '" _ + sidnolabel.Text + "'", conSQL) cmd.ExecuteNonQuery() Finally conSQL.Close() End Try The send_mail attribute is of bit datatype. This code is not working. How do I go about it?

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  • .NET application with an Oracle Database

    - by Pavitar
    I have to code a desktop application and some dynamic web content. I'm planning to develop it in .NET with an Oracle database, though my dilemma is that my professor says that if I do so, there would be a lot of support issues later on. He says .NET is more compatible with MS SQL and MS Access, and so is the trend, everyone does it.Is it true? I have learnt Oracle so I know of a few features which I wouldn't be able to implement on SQL comfortably because of lack of knowledge of SQL databases.I would love to learn the new syntax but again, I don't have much time to spare.

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  • export gridview data

    - by Eric
    What is the best way to export a gridview into an Excel spreadsheet? This seems easy except that my Gridview doesn't have an export attribute. What is the quickest way to do this?

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  • How can i read back an object stored in a session?

    - by strakastroukas
    First of all, here comes the load part. Structure MainStruct Dim Ans1 As String Dim Ans2 As String End Structure Dim Build As New List(Of MainStruct) ... ... ... Session("MyData") = Build The question is how can i read back the contents of the list, stored in the Session? I mean something like... Build = Session("MyData").Ans1

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