Develop Reference

Why is this sporadically throwing a null reference error?

Okay, this code sporadically throws a null reference error because the return ((AVMain)this.Page).Model isn't returning anything. I have not been able to make this error recur, even with the same ID value that fails for other people. Any help would be greatly appreciated!
protected AVModel Model
{
get
{
return ((AVMain)this.Page).Model;
}
}
protected void Page_Load(object sender, EventArgs e)
{
if (SessionData.IsAudit.HasValue && SessionData.IsAudit.Value == true)
{
cbFlagAudit.Visible = false;
}
if (!IsPostBack)
{
cbFlagAudit.Checked = this.Model.FlagForAudit.HasValue ? this.Model.FlagForAudit.Value : false;
}
}

I'd start by adding some null-reference checks throughout the logic. That should prevent a NullReferenceException from being thrown.
How's this?
protected AVModel Model
{
get
{
if(this.Page is AVMain)
{
var page = this.Page as AVMain;
return page.Model;
}
return null;
}
}
protected void Page_Load(object sender, EventArgs e)
{
if (SessionData.IsAudit.HasValue && SessionData.IsAudit.Value == true)
{
cbFlagAudit.Visible = false;
}
if (!IsPostBack)
{
var model = this.Model;
Boolean? value = null;
if(model != null)
{
value = model.FlagForAudit;
}
cbFlagAudit.Checked = (value.HasValue && value.Value)
}
}

Thank you all for your advice, but the error was actually being generated due to a permissions error in the database. It was causing a stored procedure to fail and not return the data needed to populate the object, hence it was null. The initial developers did not put error trapping in this project, so something that should taken no time to find, took a few days. ALWAYS trap your errors!

Entity framework different contexts exception within Asp.net application

I'm new in the use of Entity Framework and i have this problem :
List<Metier> listofjobs = new List<Metier>();
Guid userId;
WorkEntities notrecontexte;
Candidat CurrentCandidat;
protected void Page_Load(object sender, EventArgs e)
{
userId = new Guid(Membership.GetUser().ProviderUserKey.ToString());
notrecontexte = new WorkEntities ();
CurrentCandidat = notrecontexte.Candidat
.Include("Metier1")
.Include("Mobilite1")
.Include("NiveauDuDiplome1")
.Include("NiveauDuPoste1")
.Include("Disponibilite_Candidat")
.Include("Contrats1")
.First(x => x.UserId.Equals(userId) == true);
}
protected void btn_Click(object sender, EventArgs e)
{
listofjobs = (List<Metier>)Session["listofjobs"];
if (listofjobs != null)
{
CurrentCandidat.Metier1.Clear();
try
{
notrecontexte.SaveChanges();
}
catch { }
for (int i = 0; i < listofjobs.Count; i++)
{
CurrentCandidat.Metier1.Add(listofjobs[i]);
try
{
notrecontexte.SaveChanges();
}
catch { }
}
}
}
protected void Button1_Click(object sender, EventArgs e)
{
if ((List<Metier>)Session["listofjobs"] != null)
{
listofjobs = (List<Metier>)Session["listofjobs"];
}
string newjob = tbAddMetier.Text;
Metier m = new Metier { Lebelle = newjob };
tbAddMetier.Text = "";
listofjobs.Add(m);
rptrMetier.DataSource = listofjobs;
rptrMetier.DataBind();
C_Compte.Update();
Session["listofjobs"] = listofjobs;
}
protected void ImageButton1_Click(object sender, CommandEventArgs e)
{
if ((List<Metier>)Session["listofjobs"] != null)
{
listofjobs = (List<Metier>)Session["listofjobs"];
}
string newjob = e.CommandArgument.ToString().Split(',')[0];
listofjobs.Remove(listofjobs.Find(x => x.Lebelle == newjob));
rptrMetier.DataSource = listofjobs;
rptrMetier.DataBind();
C_Compte.Update();
Session["listofjobs"] = listofjobs;
}
I have problem in these lines :
CurrentCandidat.Metier1.Add(listofjobs[i]);
try
{
notrecontexte.SaveChanges();
}
catch { }
when i try to save the changes i got this exception The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects. .
What are the reasons of this exception?
How can i fix it?

Entity Framework has a context dependent behaviour. If an entity belongs to an instance of a context, you cannot use it in another instance of context unless you detach the entity from the first context and attach to the second.
For your case, at the point where you save your list of entities to the session, you need to detach the list first, and at the button click event, you need to attach listofJobs to the your current context.
I am not clear about your program flow but, if you can attach the list right after every listofjobs = (List<Metier>)Session["listofjobs"]; and detach right before every Session["listofjobs"] = listofjobs; that might work.
You can see how to detach and attach objects in Entity framework you can use links below:
http://msdn.microsoft.com/en-us/library/vstudio/bb896271(v=vs.100).aspx
http://msdn.microsoft.com/en-us/library/vstudio/bb896245(v=vs.100).aspx
http://msdn.microsoft.com/en-us/library/vstudio/bb738697(v=vs.100).aspx

How to override a session

I have a question can I overwrite a session that I allredy have set (I set the the user specific department)
Session:
int depId = user.HtDepartments.FirstOrDefault().DepartmentId;
Session["DepId"] = depId;
I want to override this id that I saved in the session with a new "id" that the user selectes out of the RadComboBox.
So when the user is coming back to this page not his "pre selected" department is selected , selected is the new department that he slected before
My code so far:
protected void Page_Load(object sender, EventArgs e)
{
if (!this.Page.IsPostBack)
{
this.parameterDepId = this.Request["depId"];
if (string.IsNullOrEmpty(parameterDepId))
{
parameterDepId = Session["depId"].ToString();
}
this.LoadDE(parameterDepId);
this.UserGrid.DataBind();
}
}
Loading the session
Here how I load my department
protected void LoadDE(string depId)
{
IEnumerable<HtDepartment> departments = null;
if (this.selectedBu != null)
{
departments = this.selectedBu.HtDepartments;
}
this.rcbDepartments.DataTextField = "Name";
this.rcbDepartments.DataValueField = "DepartmentId";
this.rcbDepartments.DataSource = departments;
this.rcbDepartments.DataBind();
this.rcbDepartments.Items.Insert(0, new RadComboBoxItem("-All-"));
if (depId != null)
{
int index = this.rcbDepartments.Items.IndexOf(this.rcbDepartments.Items.Where(i => i.Value == depId).SingleOrDefault());
if (index > -1)
{
this.rcbDepartments.Items[index].Selected = true;
this.selectedDepartment = departments.Where(i => i.DepartmentId == int.Parse(depId)).SingleOrDefault();
}
}
}
protected void rcbDepatments_SelectedIndexChanged(object sender, RadComboBoxSelectedIndexChangedEventArgs e)
{
if (this.rcbDepartments.Items.Count > 1 && this.rcbDepartments.SelectedIndex > 0)
{
this.selectedDepartment = HtDepartment.GetById(int.Parse(e.Value));
parameterDepId = this.selectedDepartment.ToString();
}
else
{
this.selectedDepartment = null;
}
this.dataSourceFilterChanged();
}
A resume of my question:
How and where should I override my session in the load method or in SelectedIndexChanged ?

It makes sense to check for the saved variable when loading a page, as the user won't be able to interact with the controls until this method has completed.
private void OnLoad(object sender, EventArgs e)
{
this.parameterDepId = this.Request["depId"];
}
But to override it with a new value you simply set a new value. Then the next time you loaded the page this newly set value would be returned in the OnLoad method.
private void MyControl_SelectedIndexChanged(object sender, EventArgs e)
{
Session["DepId"] = MyControl.SelectedValue;
}
I'm finding your question a bit unclear but hopefully this answers the main point of it and helps with your code logic.

Reloading and Updating using Entity Framework and DBContext

Ok so I have tried a few things and keep getting stuck. I had the update button working at one point and now it will not update. The delete button will work and delete records but I can not get the gridview to refresh after the record is deleted. I also want the gridview to reload after the update button is pressed and the record is updated. Here is what I have:
protected void btnDelete_Click(object sender, EventArgs e)
{
switch (btnDelete.Text)
{
case DeleteButton:
try
{
if (txtLocationName.Text != null && txtSubAccountName.Text != null)
{
Location locationCheck = _context.Locations.ToList()
.First(x => x.Name == txtLocationName.Text && x.SubAccount == txtSubAccountName.Text);
if (locationCheck != null)
{
Location n = new Location
{
Id = grdvwLocationList.SelectedIndex,
Name = txtLocationName.Text,
SubAccount = txtSubAccountName.Text
};
_context.Locations.Remove(n);
_context.SaveChanges();
}
}
}
catch (Exception)
{
lblLocationNameNotification.Text = "Please type in a location/sub-account or select a location/sub-account that doesn't have a asset to delete.";
txtLocationName.Text = "";
txtSubAccountName.Text = "";
}
break;
case CancelButton:
Reload();
break;
}
}
public void PopulateLocationGridView()
{
var locations = _context.Locations.Where(l => l.CompanyId == CompanyId)
.OrderBy(l => l.Name)
.ToList();
grdvwLocationList.DataSource = locations;
grdvwLocationList.DataBind();
if (locations.Count > 0)
{
grdvwLocationList.SelectedIndex = 0;
RowSelected();
}
else
{
txtLocationName.Text = "";
txtSubAccountName.Text = "";
}
}
The add button works just fine it just seems to be refreshing the grid view

I have the following exampe working in a winforms application
The trick is the dset.local
private void Form1_Load(object sender, EventArgs e)
{
var dset = Db.Tasks; // Db is my context.
DbSet<Task> qry = dset;
qry.Load();
bindingSource1.DataSource =dset.Local.ToBindingList();
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
Debug.Print(Db.Tasks.Count().ToString());
bindingSource1.EndEdit();
Db.SaveChanges();
}

After working on it last night I knew there was something that I was missing. I ended up going about it like this:
protected void btnDelete_Click(object sender, EventArgs e)
{
try
{
_context = new IMSDBContext();
switch (btnDelete.Text)
{
case DeleteButton:
if (txtLocationName.Text != null && txtSubAccountName.Text != null)
{
Location location = _context.Locations.ToList()
.First(x => x.Name == txtLocationName.Text && x.SubAccount == txtSubAccountName.Text);
_context.Locations.Remove(location);
_context.SaveChanges();
PopulateLocationGridView();
grdvwLocationList.SelectedIndex = 0;
RowSelected();
}
break;
case CancelButton:
Reload();
break;
}
}
catch (Exception ex)
{
lblLocationNameNotification.Text = ex.Message;
}
finally
{
if (_context != null)
{
_context.Dispose();
}
}
}
I had tried to use the PopulateLocationGridView() and RowSelect() methods by themselves and it was still having trouble. I ended up putting in the grdvwLocationList.SelectedIndex = 0; in to set the selected index on the first index in the list instead of the index of the record that I just deleted. That is where I was having trouble. I thought that the SelectRow() would reselect the index again but I had to reset it back to another index. If there are any questions or comments please feel free. I am still learning and would like all of the advise that I can get.

ASP.NET LINQ (C#) UPDATE SYNTAX

I am using LINQ to Entities in an ASP.NET C# app. The below code is my attempt to update (or reset, really) a value 'AvgRideTime' in my sql db to null. However it seems to do nothing, no errors, just nothing. Any thoughts?
protected void ResetAvgRT_Click(object sender, EventArgs e)
{
using (RamRideOpsEntities myEntities = new RamRideOpsEntities())
{
var avgTime = (from a in myEntities.AdminOptions
select a.AvgRideTime).First();
if (avgTime != null)
{
avgTime = null;
myEntities.SaveChanges();
}
}
}

var avgTime = myEntities.AdminOptions.First();
if (avgTime != null)
{
avgTime.AvgRideTime = null;
myEntities.SaveChanges();
}
Try the above code.

avgTime this is link to object and when you set avgTime = null, avgTime no referenced to object, but myEntities.AdminOptions contains this object.

Maybe the avgTime gets a null value.

Try the following code
protected void ResetAvgRT_Click(object sender, EventArgs e)
{
using (RamRideOpsEntities myEntities = new RamRideOpsEntities())
{
var avgTime = (from a in myEntities.AdminOptions
select a).First();
if (a.avgTime != null)
{
a.avgTime = null;
myEntities.Entry(a).State = EntityState.Modified;
myEntities.SaveChanges();
}
}
}