ADO.NET :: Uses LINQ To Validate Datacontext Of A Textbox To See If Record Exists Already
Aug 20, 2010
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 would like to check if a particular value already exist in the database Gidview row. If the value already exist, tell the user that he has already entered the record and don't save. otherwise save the record. In my case I want to check the "Random number".
I have a aspxtextbox and its validated from database.If text exists in database then it shows message Username exist.Now this is all happens on click of a aspxbutton after typing some text into aspxtextbox.I just want that when user defocus the textbox then it will automatically check from database and shows the message if exists.
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 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 tried to illustrate the problem by providing the following instructions, unfortunately the data was deleted and the example failed. It is now working. I have been working through one of Scott Mitchells ASP.NET Application Tutorials Title "Using TemplateFields in the GridView Control"
The URL is ...
The example demonstrates a temporary field being used in different ways, one of which involves dates in a Calender. If the HireDate in the example is deleted or not available the program fails. Providing the date is a valid date it works fine....
I am very new to this and have watched a lot of the videos. While trying out VWD2010 and SQL2008 Express, I come across many things, I just don't know how to do. Here is the latest:
I have a Table UserId - Int - AutoIncrement FirstName - Var(10) LastName - Var(10)
I also have an ASP web page that allow the user to enter a first name and last name. It also has a button to submit. What I would like to do is have a Select statement check to see if the name already exists, then send a comment back to the user via a label. If it doesn't exist, then I would like to Insert the info and then again inform the user via label.
On the code behind, I get lost. (Obviously this doesn't work, but I don't know how to go about getting a results back. Protected Sub bSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles bSubmit.Click
SqlDataSource1.Select(DataSourceSelectArguments.Empty) (get a return) (check return value, if <>0 then lblResults.Text = "exists!" else SqlDataSource1.Insert() lblResults.Text="added!" end if) End Sub
I want to check if the record is already exists before insert using Ajax ActionLink in Create View. I am getting error 'Object reference not set to an instance of an object.' Here is a code in View :
<div class="editor-label"> <%= Html.LabelFor(model => model.PolicyId) %> </div> <div class="editor-field"> <%= Html.TextBoxFor(model => model.PolicyId) %> <%= Html.ValidationMessageFor(model => model.PolicyId) %> <em>can not be changed later.</em> //error occurs here <%= Ajax.ActionLink("Check", "CheckIfExists", "Life", new { PolicyId = Model.PolicyId }, null)%> </div>
And Controller action :
public JavaScriptResult CheckIfExists(string PolicyId) { if (lifeRepository.IsExists(PolicyId)) return JavaScript("alert(' Already Exists');"); else return JavaScript("alert(' Not Exists');"); }
I have a SQL database that creates a record for every document uploaded by the user to the server. I want to check this table before a user uploads a document to ensure they don't upload a file with name that already exists.
I know how to make the connection and make the SqlCommand to query the table for an existing record. But I don't know how to check the record count from the sqlCommand I made.
Does that make sense?
Using myConnectionCheck As New SqlConnection(myConnectionStringCheck) Dim myCommandCheck As New SqlCommand() myCommandCheck.Connection = myConnectionCheck myCommandCheck.CommandText = "SELECT * FROM Req_Docs WHERE Doc_Name =" & DocName myConnectionCheck.Open() myCommandCheck.ExecuteNonQuery() End Using
Just have a problem, I want people to join a mailing list, I just have a textbox and button. When a user enter's their email address, the address and time are inserted into a database. However, if the same email is added again I would like for a message to appear saying the record already exists.
Can someone show me how to do this, here is my current code:
I am using Microsoft SQL database, C# and stored procedures. How would I check if record exists on the form or in SQL. I will design a from that has employee name, id and 3 other fields.
If record exists (I could for example test if EmployeeId exists, and then display a message saying that "record already exists". Should I do it in Stored procedure or in code?
