How to handle null exception when exporting Grid with foreign key columns in .NET MVC application?
Problem
When we export the grid with foreign key columns, the dataSource type of the foreign key columns is passed as generic object to the export function. As we don’t have support to export generic type list, a null exception is thrown like mentioned below.
<Exception>
System.NullReferenceException was unhandled by user code
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=Syncfusion.EJ.Export
StackTrace:
at Syncfusion.EJ.Export.GridExcelExport.ProcessRecordCell(Object row, Column column)
at Syncfusion.EJ.Export.GridExcelExport.<>c__DisplayClasse.<ProcessRecordRow>b__d(Column column)
at System.Collections.Generic.List`1.ForEach(Action`1 action)
at Syncfusion.EJ.Export.GridExcelExport.ProcessRecordRow(Object row)
at Syncfusion.EJ.Export.GridExcelExport.RenderRecord()
at Syncfusion.EJ.Export.GridExcelExport.ProcessGridContents()
at Syncfusion.EJ.Export.GridExcelExport.IterateElements()
at Syncfusion.EJ.Export.GridExcelExport.ExportHandler()
at Syncfusion.EJ.Export.GridExcelExport.ExecuteResult(GridProperties GridModel, IEnumerable dataSource)
at Syncfusion.EJ.Export.GridExcelExport.Export(GridProperties gridModel, IEnumerable dataSource, Boolean multipleExport)
at Syncfusion.EJ.Export.ExcelExport.Export(GridProperties gridmaodel, IEnumerable datasource, String excelname, ExcelVersion excelversion, Boolean isHideColumnIncude, Boolean isTemplateColumnIclude, String theme)
at EMIMReports._Default.dgReport_OnServerExcelExporting(Object sender, GridEventArgs e) in C:\Visual Studio Projects\2014\ESJS\EMIMReports\EMIMReports\Default.aspx.vb:line 99
at Syncfusion.JavaScript.Web.Grid.PostBackEventHandler(String EventName, Dictionary`2 args)
at Syncfusion.JavaScript.Web.CommonDataBoundControl.RaisePostBackEvent(String EventArgument)
InnerException:
</Exception>
Reason
Since we have deserialized the grid model obtained from the client side (where the column dataSource is a generic JSON object), it is deserialized to generic list
Solution
In order to overcome this issue, we need to dynamically set the dataSource for the foreign key columns before calling the Export method as explained in the below example.
Grid Rendering Code.
@(Html.EJ().Grid<object>("FlatGrid") .Datasource((IEnumerable<object>)ViewBag.dataSource) .AllowPaging() .ToolbarSettings(toolbar => { toolbar.ShowToolbar(true) .ToolbarItems( items => { items.AddTool(ToolBarItems.ExcelExport); items.AddTool(ToolBarItems.WordExport); items.AddTool(ToolBarItems.PdfExport); }); }) .Mappers(map => map.ExportToExcelAction("/Home/ExportToExcel").ExportToPdfAction("/Home/ExportToPdf").ExportToWordAction("/Home/ExportToWord")) .Columns(col => { col.Field("OrderID").HeaderText("Order ID").IsPrimaryKey(true).Width(90).Add(); col.Field("CustomerID").HeaderText("Customer ID").Width(90).Add(); col.Field("EmployeeID").HeaderText("Employee Name").ForeignKeyField("EmployeeID").ForeignKeyValue("FirstName").DataSource((IEnumerable<object>)ViewBag.data).Width(75).Add(); col.Field("Freight").HeaderText("Freight").Width(75).Format("{0:C}").Add(); col.Field("ShipCity").HeaderText("Ship City").Width(80).Add(); }) )
Code Behind
public class HomeController : Controller { public ActionResult Index() { ViewBag.dataSource = OrderRepository.GetAllRecords().ToList(); ViewBag.data = EmployeeRepository.GetAllRecords().ToList(); return View(); } public void ExportToExcel(string GridModel) { ExcelExport exp = new ExcelExport(); var dataSource = OrderRepository.GetAllRecords().ToList(); GridProperties obj = ConvertGridObject(GridModel); obj.Columns[2].DataSource = EmployeeRepository.GetAllRecords().ToList();//set the dataSource for the foreign key column after deserializing the grid model properties. exp.Export(obj, dataSource, "Pedidos.xlsx", Syncfusion.XlsIO.ExcelVersion.Excel2010, false, false, "flat-saffron"); } public void ExportToWord(string GridModel) { WordExport exp = new WordExport(); var dataSource = OrderRepository.GetAllRecords().ToList(); GridProperties obj = ConvertGridObject(GridModel); obj.Columns[2].DataSource = EmployeeRepository.GetAllRecords().ToList();//set the dataSource for the foreign key column after deserializing the grid model properties. exp.Export(obj, dataSource, "Pedidos.docx", false, false, "flat-saffron"); } public void ExportToPdf(string GridModel) { PdfExport exp = new PdfExport(); var dataSource = OrderRepository.GetAllRecords().ToList(); GridProperties obj = ConvertGridObject(GridModel); obj.Columns[2].DataSource = EmployeeRepository.GetAllRecords().ToList();//set the dataSource for the foreign key column after deserializing the grid model properties. exp.Export(obj, dataSource, "Pedidos.pdf", false, false, true, "flat-saffron"); } private GridProperties ConvertGridObject(string gridProperty) { JavaScriptSerializer serializer = new JavaScriptSerializer(); IEnumerable div = (IEnumerable)serializer.Deserialize(gridProperty, typeof(IEnumerable)); GridProperties gridProp = new GridProperties(); foreach (KeyValuePair<string, object> ds in div) { var property = gridProp.GetType().GetProperty(ds.Key, BindingFlags.Instance | BindingFlags.Public | BindingFlags.IgnoreCase); if (property != null) { Type type = property.PropertyType; string serialize = serializer.Serialize(ds.Value); object value = serializer.Deserialize(serialize, type); property.SetValue(gridProp, value, null); } } return gridProp; }
Conclusion
I hope you enjoyed learning about how to handle null exception when exporting Grid with foreign key columns in .NET MVC application.
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