Refresh LINQ db-connection object - linq

Question

My collegue helped me with starting programming in c# although I had no experience but I like it. All went well until I came across some problems we both can't fix. He uses SQL himself but started me up with LINQ.
To do a LINQ-query I use this object : _oDBConnection (in clsApplication.cs)
So when opening the programm this object is built. But it creates some problems:
When saving a new object (putting data into table), I cannot load those values with a query. I need to restart the programm.
When running 2 instances of the programm, one is not getting the latest values when changed in the other (but it is showing the new ones but not the changed ones!)
According to these problems I can only conclude that when I call clsApplication._oDBConnection.tblTAble a second time it is not relinking again to the db but is giving me the old db-states back.
This is the code he built:
public static DBReservationDataContext _oDBConnection;
private static frmMain _fMain;
public clsApplication()
{
Thread.CurrentThread.Name = "main";
clsErrorLog.ErrorLocation = "C:\\Software\\ErrorLog";
clsErrorLog.setPassword("*****");
clsErrorLog.LockApplication += new clsErrorLog.dLockApplication(lockApplication);
_oDBConnection = new DBReservationDataContext();
_fMain = new frmMain();
_fMain.Show();
}
What can I do to fix this problem?
Example:
although present in the database, it crashes on this query because the entity with id == iID is not found. But the iID is correct and it does exist in the database. The query will work after closing and restarting the programm. Then the clsApplication is called again.
public clsReservationDetail(int iID)
:this()
{
_oReservationDetail = (from oReservationDetailQuery in clsApplication._oDBConnection.tblReservationDetails
where oReservationDetailQuery.ID == iID
select oReservationDetailQuery).First();
}
thx in advance

Answer 1

Your data context will have a Refresh method which will clear any cached results, and should allow your query to complete with no problems

Answer 2

The static keyword makes it so that you have one reference per AppDomain. That is the wrong way to use DataContext instances.
Each instance of DataContext tracks the objects it has seen. This is for consistency. If you get a Customer instance with CustomerID = 4 from one query, you should get the same Customer instance from another query that returns the CustomerID = 4 record.
If you want to see the changes in the database, you must
1) Tell the datacontext to stop tracking changes. This must be done before the first query and makes the datacontext instance unable to SubmitChanges (since it can't track them anymore).
OR
2) Tell the datacontext to Refresh each instance you suspect has changed. If you do that, you should specify how resolve the conflict between your local changes and the remote changes - the simplest way of resolving this conflict is to have no local changes.
OR
3) (The right way) Make a new DataContext instance and load the record with that!
Also note: Since DataContext implements IDisposable, you are required to call Dispose when you are done with each instance even when exceptions occur. The using block is a good way to get that to happen.