C# - Context Is Closed When EF Tries To Access Null Property?
Jan 26, 2011
I have an object defined by my entity framework model that has navigation properties, but whenever the navigation property is null, entity framework seems to try to pull it down again from the database. This is fine for now and I can work on this problem later, but when it tries to get the navigation property from the database, I get the error from the model:The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
Well this isn't too good that it's blowing chunks like this. Is there anything I can do to ensure that this is only attempted when the context is still open?
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Edit 2: Not really relevant to the specific problem, but I resolved the problem I was having with the pager rendering so i've updated the code posted. I found the trick here: [URL]
#region Fields
private int totalRows = -1;
#endregion
#region Constructors
/// <summary>
/// Initializes a new instance of the <see cref="GridHelper"/> class.
/// Adds EventHandlers to the GridView to display results from the ObjectDataSource in the footer.
/// Marked as obsolete because AddResultsToFooter method provides a static access to the same functionality
/// An instance of GridHelper is required by the passed in GridView to store the totalRows value between the two event handlers
/// </summary>
/// <param name="grid">The grid.</param>
/// <param name="source">The ObjectDataSource linked to the GridView.</param>
[Obsolete("Use AddResultsToFooter instead.")]
[EditorBrowsable(EditorBrowsableState.Never)]
public GridHelper(GridView grid, ObjectDataSource source)
{
source.Selected += source_Selected;
grid.PreRender += grid_PreRender;
}
#endregion
#region Event Handlers
private void grid_PreRender(object sender, EventArgs e)
{
GridView grid = (GridView)sender;
if (grid.HeaderRow != null)
grid.HeaderRow.TableSection = TableRowSection.TableHeader;
//Add a cell to the bottom pager row to display the total results
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//http://michaelmerrell.com/2010/01/dynamically-modifying-the-asp-net-gridview-paging-control/
Table tblPager = grid.BottomPagerRow.Cells[0].Controls[0] as Table;
if (tblPager == null)
return;
if (totalRows < 0)
{
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addResultsToPagerTable(tblPager, grid.Attributes["results"]);
return;
}
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int lastRow = firstRow + grid.Rows.Count - 1;
string results;
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grid.Attributes.Add("results", results);
}
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/// </summary>
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private void source_Selected(object sender, ObjectDataSourceStatusEventArgs e)
{
if (e.ReturnValue is DataView)
totalRows = ((DataView)e.ReturnValue).Count;
else if (e.ReturnValue is EntitySet)
totalRows = ((EntitySet)e.ReturnValue).Count;
}
#endregion
#region Private Methods
private static void addResultsToPagerTable(Table tblPager, string results)
{
//http://michaelmerrell.com/2010/01/dynamically-modifying-the-asp-net-gridview-paging-control/
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TableRow pagesTableRow = tblPager.Rows[0];
//Add enough cells to make the pager row bigger than the label we're adding
while (pagesTableRow.Cells.Count < 10)
pagesTableRow.Cells.Add(new TableCell { BorderStyle = BorderStyle.None });
//Add a new cell in a new row to the table
TableRow newTableRow = new TableRow();
newTableRow.Cells.AddAt(0, new TableCell
{
Text = results,
BorderStyle = BorderStyle.None,
ColumnSpan = pagesTableRow.Cells.Count
});
tblPager.Rows.AddAt(0, newTableRow);
}
#endregion
#region Public Methods
/// <summary>
/// Adds EventHandlers to the GridView to display results from the ObjectDataSource in the footer.
/// </summary>
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/// <param name="source">The ObjectDataSource linked to the GridView.</param>
public static void AddResultsToFooter(GridView grid, ObjectDataSource source)
{
if (grid == null)
throw new ArgumentNullException("grid", "grid is null.");
if (source == null)
throw new ArgumentNullException("source", "source is null.");
new GridHelper(grid, source);
}
#endregion
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Jan 12, 2011
A common problem in repeater controls where you want to display data for update (like a list of user phone numbers that can be updated and submitted back to the database) is where to store the database unique row identifier. So, I created a custom Textbox control that I've added a Data property to. I populate this data property with the unique row id. The problem is that when I post back the list and go through the repeater items the control's data property is null. The custom control looks like this:
[Code]....
The tag in the repeater looks like this:
[Code]....
I have a custom checkbox with the same data property and it works fine. I actually put in the same repeater with the textbox control and the checkbox control have the row id on postback but the textbox did not. Is there some limitation on the textbox control that might be causing this.
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