Edit Model in Blazor TreeList
- 9 minutes to read
Once a user starts editing a row, the TreeList creates a clone of the edited data item – an edit model. The edit model has the same data type and property values as the edited data item. This topic describes how to access, initialize, customize, and save the edit model. The approaches listed below apply to all edit modes.
Initialize New Rows
Follow the steps below to initialize an edit model for new data rows:
- Handle the CustomizeEditModel event.
- Check the event argument’s IsNew property to identify new rows.
- Use EditModel and ParentDataItem properties to link a new node to its parent.
- (Optional) Use the EditModel property to initialize model fields with predefined values.
The following snippet initializes an edit model for new tasks:
<DxTreeList Data="TreeListData"
KeyFieldName="Id"
ParentKeyFieldName="ParentId"
@* ... *@
CustomizeEditModel="TreeList_CustomizeEditModel">
<Columns>
<DxTreeListCommandColumn />
<DxTreeListDataColumn FieldName="Name" Caption="Task" />
<DxTreeListDataColumn FieldName="EmployeeName" />
<DxTreeListDataColumn FieldName="StartDate" />
<DxTreeListDataColumn FieldName="DueDate" />
</Columns>
</DxTreeList>
@code {
List<EmployeeTask> TreeListData { get; set; }
void TreeList_CustomizeEditModel(TreeListCustomizeEditModelEventArgs e) {
if(e.IsNew) {
var newTask = (EmployeeTask)e.EditModel;
newTask.Id = TreeListData.Max(x => x.Id) + 1;
newTask.Name = "New task";
newTask.StartDate = DateTime.Today;
newTask.DueDate = DateTime.Today.AddDays(7);
if(e.ParentDataItem != null)
newTask.ParentId = ((EmployeeTask)e.ParentDataItem).Id;
}
}
// ...
}
Save Changes
During edit operations, the TreeList applies user changes only to the edit model and keeps the data item unchanged. Handle the events listed below to process changes:
- EditModelSaving
This event fires if validation succeeds after a user saves changes or you call the SaveChangesAsync() method. Handle this event to check access permissions, assign changes from the edit model to the corresponding data item, and post changes to the underlying data source. The IsNew event argument identifies whether the edit model corresponds to a new or existing row.
Call the CopyChangesToDataItem() method to copy all changed fields including nested properties from the edit model to the data item. This method copies changes regardless of how you make changes: in the event handler, razor code, or business logic.
- DataItemDeleting
- This event fires when a user confirms the row delete operation in the confirmation dialog. Handle this event to check user access permissions and delete the corresponding data item from the data source. The DataItem and ParentDataItem event arguments allow you to access the processed data item and its parent.
TreeList data should be reloaded after you post updates to the data source. The TreeList component automatically reloads its data in response to the following actions:
- After the EditModelSaving or DataItemDeleting event handler is executed.
- After you change an instance of a field/property bound to the Data parameter.
In other cases, call the Reload() method to reload TreeList data.
In the following example, the TreeList component reloads data after an event handler saves changes:
@inject EmployeeTaskService EmployeeTaskService
<DxTreeList Data="TreeListData"
KeyFieldName="Id"
ParentKeyFieldName="ParentId"
EditModelSaving="TreeList_EditModelSaving"
DataItemDeleting="TreeList_DataItemDeleting"
CustomizeEditModel="TreeList_CustomizeEditModel">
<Columns>
<DxTreeListCommandColumn />
<DxTreeListDataColumn FieldName="Name" Caption="Task" />
<DxTreeListDataColumn FieldName="EmployeeName" />
<DxTreeListDataColumn FieldName="StartDate" />
<DxTreeListDataColumn FieldName="DueDate" />
</Columns>
</DxTreeList>
@code {
List<EmployeeTask> TreeListData { get; set; }
protected override void OnInitialized() {
TreeListData = EmployeeTaskService.GenerateData();
}
void TreeList_CustomizeEditModel(TreeListCustomizeEditModelEventArgs e) {
if(e.IsNew) {
var newTask = (EmployeeTask)e.EditModel;
newTask.Id = TreeListData.Max(x => x.Id) + 1;
newTask.Name = "New task";
newTask.StartDate = DateTime.Today;
newTask.DueDate = DateTime.Today.AddDays(7);
if(e.ParentDataItem != null)
newTask.ParentId = ((EmployeeTask)e.ParentDataItem).Id;
}
}
async Task TreeList_EditModelSaving(TreeListEditModelSavingEventArgs e) {
if(e.IsNew)
TreeListData.Add((EmployeeTask)e.EditModel);
else
e.CopyChangesToDataItem();
}
async Task TreeList_DataItemDeleting(TreeListDataItemDeletingEventArgs e) {
TreeListData.Remove((EmployeeTask)e.DataItem);
}
}
Create a Custom Edit Model
The TreeList component cannot generate an edit model in the following cases:
- A data item class does not have a parameterless constructor.
- Data item fields bound to TreeList columns are read-only.
- In a hierarchical data source, a data type of children nodes differs from the parent node’s data type. In this case, the TreeList cannot determine which data type to use for new rows and generates edit models only for existing rows.
You can create a custom edit model or customize an automatically generated edit model as follows:
- Handle the CustomizeEditModel event.
- Use the DataItem event argument to access the proccessed data item. Note that the data item is
nullfor new rows. - Assign your custom edit model to the EditModel event argument.
When you obtain an EditModel object in event handlers or edit templates, cast this object to your custom edit model class as shown below:
<DxTreeList Data="TreeListData"
KeyFieldName="Id"
ParentKeyFieldName="ParentId"
EditMode="TreeListEditMode.EditForm"
EditModelSaving="TreeList_EditModelSaving"
DataItemDeleting="TreeList_DataItemDeleting"
CustomizeEditModel="TreeList_CustomizeEditModel">
<Columns>
<DxTreeListCommandColumn />
<DxTreeListDataColumn FieldName="Name" Caption="Task" />
<DxTreeListDataColumn FieldName="EmployeeName" />
<DxTreeListDataColumn FieldName="StartDate" />
<DxTreeListDataColumn FieldName="DueDate" />
</Columns>
<EditFormTemplate Context="editFormContext">
@{
var editModel = (EmployeeTaskEditModel)editFormContext.EditModel;
}
@* ... *@
</EditFormTemplate>
</DxTreeList>
@code {
List<EmployeeTask> TreeListData { get; set; }
class EmployeeTaskEditModel {
public int Id { get; set; }
public int ParentId { get; set; }
[Required]
public string Name { get; set; }
public string EmployeeName { get; set; }
public DateTime StartDate { get; set; }
[Required]
[Range(typeof(DateTime), "1/12/2016", "1/12/2025", ErrorMessage = "DueDate must be between {1:d} and {2:d}")]
public DateTime DueDate { get; set; }
}
async Task TreeList_EditModelSaving(TreeListEditModelSavingEventArgs e) {
var editModel = (EmployeeTaskEditModel)e.EditModel;
}
void TreeList_CustomizeEditModel(TreeListCustomizeEditModelEventArgs e) {
if(e.IsNew) {
var newTask = new EmployeeTaskEditModel { };
newTask.Id = TreeListData.Max(x => x.Id) + 1;
newTask.Name = "New task";
newTask.StartDate = DateTime.Today;
newTask.DueDate = DateTime.Today.AddDays(7);
e.EditModel = newTask;
}
else {
var dataItem = (EmployeeTask)e.DataItem;
e.EditModel = new EmployeeTaskEditModel {
Id = dataItem.Id,
ParentId = dataItem.ParentId,
Name = dataItem.Name,
EmployeeName = dataItem.EmployeeName,
StartDate = dataItem.StartDate,
DueDate = dataItem.DueDate
};
}
}
// ...
}
Edit Data with Nested Properties
When you edit data, the TreeList clones a bound data item – namely creates an object of the same type and copies all property values into it. If a property is of a reference type, the reference is copied but the referred object is not copied. As the result, the original object and its clone refer to the same object.
To edit nested objects, create a copy of these objects manually (make a deep copy of the original data item object). You can use the following approaches to implement a deep copy operation:
Handle the CustomizeEditModel event, clone the nested object, and assign it to field whose value is the reference type.
void OnCustomizeEditModel(TreeListCustomizeEditModelEventArgs obj) { var customer = (Customer)obj.EditModel; customer.Address = customer.Address?.Clone() ?? new Address(); } public class Person { public int ID { get; set; } public string FirstName {get; set;} public string LastName { get; set; } public Address Address { get; set; } } public class Address { public string StreetLine1 { get; set; } public string City { get; set; } public string State { get; set; } public int ZipCode { get; set; } public Address Clone() { return (Address) MemberwiseClone(); } }Create constructors for the data item type and the nested object’s type. In the data item type constructor, the nested object type constructor clones the nested object with its property values. Handle the CustomizeEditModel event and call a data item’s class constructor to initialize the edit model.
void OnCustomizeEditModel(TreeListCustomizeEditModelEventArgs e) { e.EditModel = new Person((Person)e.DataItem); } public Person(Person person) { this.ID = person.ID; this.FirstName = person.FirstName; this.LastName = person.LastName; this.Address = new Address(person.Address); } public Address(Address address) { this.StreetLine1 = address.StreetLine1; this.City = address.City; this.State = address.State; this.ZipCode = address.ZipCode; }