.net - Linq To Sql Datacontext For A Web Application
Mar 20, 2010
I'm trying to use linq to sql for my project (very short deadline), and I'm kind of in a bind. I don't know the best way to have a data context handy per request thread. I want something like a singleton class from which all my repository classes can access the current data context. However, singleton class is static and is not thread-safe and therefore not suitable for web apps. I want something that would create a data context at the beginning of the request and dispose of it along with the request
For no apparent reason (of course there must be one), my web project will no longer generate LINQ to SQL classes/data contexts!!!I am going about the usual routine of right clicking the project, adding new item, selected LINQ to SQL classes, then dragging over a table from Server Explorer, saving and build but no...the bloody thing won't appear!!!Does anyone know why this might be happening/what have I done wrong?
i am working on Linq,as we know to use any table in linq we have to drag and drop it on our datacontext's Designer File,and at run time we got its value,till here no any problem,main point is if any changes in respective data source's schema has made ,then on datacontext we will not get that changes,for it we have to change this datacontext manually by by again drag and drop,it will not happen implicitly when this changes has been made on the data source. how i solve this problem so that datacontext change implicitly without any over head using .net 3.5.
System.Data.Linq.ChangeConflictException: 2 of X updates failed. at System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode failureMode) at System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode) at PROJECT.Controllers.HomeController.ClickProc(Int32 id, String code, String n)
This is what I get very often. This action is done thousands of times a day, and I get this exception about once every 5 seconds. From what I understand it happens when something changes in the database in the period between creating DataContext and updating it. Am I right?How can I fix it?I just debugged the error and found the following:
[Code]....
The Stats table is updated constantly. So how can I still make LINQsave the changes. With "classical" MS SQL access through SqlDataCommand I never had problems like that.
I have a linq DataSource and a Grid in my htnl and I want to access the DataContext from code behind. Now in the past when I do evrything in code behind I just use...
DataContextName db = new DataContextName();
and I have my reference.
Now I can still do that and it works fine it just seems odd to be making a second class object when there is one that is made from the linq DataSource in the html. But I can't figure out how to get a reference to the DataContext that is created from my html code.
I am trying to return all records from a table using a Linq strongly typed datacontext. I want this in its own dll and accessible via a public method. I am basing this on the following MSDN example:
[URL]
I get no intellisense for appt in the Linq code and I also get a compile error for Table<Appointments>: The type or namespace name 'Appointments' could not be found (are you missing a using directive or an assembly reference?)
I am writing an application in C# that uses LINQ to validate a datacontext off a textbox to see if the record exists already. If the record does exist I inserted an if statement to advise the user that the record exists, if the record does not exist I would like to allow the record to be added to the database. If I take out my else statement everything works fine as far as inserting goes, but I do not want to allow inserts in this scenario. I have tried moving the if and else statement to different parts of the code but can't quite figure this one out.
I need my linq to sql datacontext to be available across my business/data layer for all my repository objects to access. However since this is a web app, I want to create and destroy it per request. I'm wondering if having a singleton class that can lazily create and attach the datacontext to current HttpContext would work. My question is: would the datacontext get disposed automatically when the request ends? Below is the code for what I'm thinking. Would this accomplish my purpose: have a thread-safe datacontext instance that is lazily available and is automatically disposed when the request ends?
public class SingletonDC { public static NorthwindDataContext Default { get { NorthwindDataContext defaultInstance = (NorthwindDataContext)System.Web.HttpContext.Current.Items["datacontext"]; if (defaultInstance == null) { defaultInstance = new NorthwindDataContext(); System.Web.HttpContext.Current.Items.Add("datacontext", defaultInstance); } return defaultInstance; } } }
I'm new to LINQ and have a problem with my query not showing me the Table Collection. I manually created my Cart class and specified the table attributes on each property (works fine for inserting records via LINQ see below). DataContext dc = new DataContext(Conn);
var q = (from c in dc.NOTABLES?? where ((c.UserID == userID)) orderby c.CreateDateTime Based on examples I would expect to see dc.Cart But I don't, so I tried to access it via dc.GetTable<Cart>() which at least gets me data but doesn't seem to convert the rows to my Cart object since this: foreach (var cart in q) Log.Info("UserID: " + cart.UserID + " CartID: " + cart.ID.ToString()); blows up with a "Specified Cast is Not Valid" exception.
No Problem Inserting Also, I had no problem inserting data into the database:
DataContext dc = new DataContext(Conn); Table<Cart> Carts = dc.GetTable<Cart>(); Cart aCart = new Cart(); aCart.UserID = userId; aCart.Description = description; aCart.CreateDateTime = System.DateTime.Now; aCart.UpdateDateTime = System.DateTime.Now; Carts.InsertOnSubmit(aCart); Carts.Context.SubmitChanges();
I am trying to run a linq query but I need the result as a datatable as I am using that to store records from different queries in the same viewstate object.The 2 versions below compile, but return an empty set. The exact error is "Value cannot be null.Parameter name: source". (and yes I have checked there is data):
MyDatabaseDataContext db = new MyDatabaseDataContext(conn); IEnumerable<DataRow> queryProjects = (from DataRow p in db.STREAM_PROJECTs.AsEnumerable()
I have a System.Data.Linq.DataContext object and need to know the proper way of closing it out before it goes out of scope in order to prevent the following error when making a bunch of database changes:
Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
Can I just call obj.Dispose() or do I need to call obj.Connection.Dispose() or obj.Connection.Close()?
I guess what I want to know is will calling obj.Dispose() end up executing the functionality in obj.Connection.Dispose() and obj.Connection.Close(). The MSDN documentation that I found on these functions does not have this information (at least I didn't see it - I could have mistakenly overlooked it).
I have a strange problem. I am adding a LinqDatasource object, and set the context:
[Code]....
Then I get this error:The type 'System.Data.Linq.DataContext' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
I'm running Visual Web Developer 2010 Express on Windows XP and I'm having some trouble linking my DataContext to a control.If I create a new "Web Site", add a new LINQ to SQL Class and add the database tables I want, then add a Control such as FormView and choose a new LINQ Data Source Type; my DataContext I created is visible in the list and all work OK.If I do the same after creating a new "Web Application", my DataContext doesn't show up in the list, but if I go into my Code Behind I can access my DataContext through:
DataContext db = new DataContext(conString); var dvd = db.GetTable<DvdList>(); var category = db.GetTable<CategoryList>(); var query= from b in dvd join category on dvd.CategoryId equals category.CategoryId where b.Title.Contains(txtSearch.Text) select b; GridView1.DataSource =query;
I am using LINQ to SQL in a project. I create a new DataContext class (a "DBML").
This is a DotNetNuke portal, module project. DNN has a standard connection string named "SiteSQLServer." Of course, I want my DataContext class to use this same connection string.
In Server Explorer in Visual Studio, I have a connection to the development database. Of course, that connection knows nothing of the "SiteSQLServer" connection string in web.config.
When I drag a table into the DBML design screen, I get a popup message that the table I'm dragging in is from a different connection, and is it OK if it changes the connection string? If I say "No," then the table never comes in to the designer. If I say "OK," then Visual Studio adds a new connection string to my web.config file. Then I must click in the open area of the designer, then go to the Properties window and reset the connection string. If I miss this, then in testing everything works. But when I deploy to a production server, the connection fails. But even if I do not miss this, that extra connection string remains in my web.config file.
Is there a way to get Visual Studio to drop the table into the designer, and leave web.config alone?
In my experience building web applications, I've always used a n-tier approach. A DAL that gets data from the db and populates the objects, and BLL that gets objects from the DAL and performs any business logic required on them, and the website that gets it's display data from the BLL.I've recently started learning LINQ, and most of the examples show the queries occurring right from the Web Application code-behinds(it's possible that I've only seen overly simplified examples). In the n-tier architectures, this was always seen as a big no-no.I'm a bit unsure of how to architect a new Web Application.
I am developing sample web application which use C#, and LINQ to SQL. The application is very very slow and it takes about 2 secs to navigate between pages. I have already used SQL Profiler and monitor the calls to the SQL server. All SQLs looks normal to me and their execution time is always about 1 or 2 millisecs.I tried the same application in another PC and it is the same. So, it is not because of my computer performance.
I have 2 databases one called DB1, and the other DB2. Both of them has exactly the same design (tables, procedures and etc..)
Now, I am using SQLMETAL to create the DataContext. problem is that there are two lines that direct to a certain database and so I cannot use the same code for both databases.
here is the code:
[Code]....
Now, What I am lookin for is a programmatically way to change this two lines (DataBaseAttribute and the connrection string) .
The easiest solution for me of course is to create the class twice, with the same code and just change manually what I need which is not what I am looking for.
There is a full discussion with microsoft stuff right here: [URL]
I have a page on which I've thrown a LinqDataSource and a GridView. I've created a DataContext LINQ-to-SQL class called dcResidents.dbml. When I attempt to configure the LinqDataSource to utilize the dcResidents data context - it doesn't appear in the list of options...though under class view (tab in VS) it does appear. I do have several other working datacontexts - why is this one not being recognized by VS?
