Model Binding and Strongly Typed Data Controls
Strongly Typed Data Controls Support
When template fields are used into the Telerik’s data bound controls for customizing templates and bound the field value the late-bound expressions are typically used. For example, below we are using the Eval() helper method to data-bind the "CategoryName" property from an objects which is bound to theRadGrid:
<telerik:GridTemplateColumn HeaderText="Category" UniqueName="CategoryID"
DataField="CategoryID" SortExpression="CategoryID">
<ItemTemplate>
<%# Eval("Category.CategoryName") %>
<ItemTemplate>
</telerik:GridTemplateColumn
When we perform two-way data-binding the Bind() method is used:
<telerik:GridTemplateColumn HeaderText="Category" UniqueName="CategoryID"
DataField="CategoryID" SortExpression="CategoryID">
<EditItemTemplate>
<telerik:RadComboBox RenderMode="Lightweight" Skin="Metro" ID="ComboBox1" runat="server" SelectMethod="GetCategories"
DataValueField="CategoryID" DataTextField="CategoryName"
SelectedValue='<%# Bind("CategoryID") %>'></telerik:RadComboBox>
</EditItemTemplate>
</telerik:GridTemplateColumn>
On the other side the .NET 4.5 provides ability to enable strongly-typed data templates.To enable them the ItemType property needs to be set on the data bound control. After setting it two new types will be generated in the scope of the control’s template: Item and BindItem. For example the code snippet above could be rewritten as:
<telerik:GridTemplateColumn HeaderText="Category" UniqueName="CategoryID"
DataField="CategoryID" SortExpression="CategoryID">
<ItemTemplate>
<%# Item.Category.CategoryName %>
</ItemTemplate>
<EditItemTemplate>
<telerik:RadComboBox RenderMode="Lightweight" Skin="Metro" ID="ComboBox1" runat="server" SelectMethod="GetCategories"
DataValueField="CategoryID" DataTextField="CategoryName" SelectedValue="<%# BindItem.CategoryID %>"></telerik:RadComboBox>
</EditItemTemplate>
</telerik:GridTemplateColumn>
The developers could use these variables in data-binding expressions and to get full intellisense support.
Model Binding Selecting Data, Paging and Sorting
To bind databound controls via ModelBinding you need to set only the SelectMethod property to the name of the public method placed into the page's code-behind file:
<telerik:RadGrid RenderMode="Lightweight" ID="RadGrid1" GridLines="None" runat="server" AllowSorting="true" PageSize="10" AllowPaging="True" SelectMethod="GetProducts"
AutoGenerateColumns="False">
The GetProducts method has following declaration:
DataClassesDataContext context = new DataClassesDataContext();
public IQueryable<Employee> GetProducts()
{
return from e in context.Employees
select e;
}
Or it can be with parameters:
public IQueryable<Employee> GetProducts(string sortByExpression, int startRowIndex, int maximumRows, out int totalRowCount)
{
....
}
In the second signature the developer have to build query which sort and page the datasource items.
When we run the page, the data bound controls will call the above method and automatically retrieve the data and render it. The method has to return IEnumerable or IQueryable. Thus users could easily page and sort through the data within our bound controls. The benefits are that our controls will automatically add the appropriate sort and page operators onto an IQueryable query before executing it.
For example if SelectMethod returns data from Linq DataContext and if the paging of the bound control is turned on, the executed database query will return only items for the current page. If the bound control is sorted by a column the sorting also will be executed on the database and the sorted result will be returned. That is because the Linq will optimize the query to perform the sort and page operation as part of the database query.
When paging and sorting are applied the entire data source is returned from the database, because the RadTreeList control is a hierarchical control and the data source’s items are not shown in the order that they are ordered into the data source. When the Select method are parameterized the startRowIndex and maximumRows have to be Nullables,because the RadTreeList always get entire data source and does not pass startRowIndex and maximumRows:
public IQueryable<Employee> GetProducts(string sortByExpression, int? startRowIndex, int? maximumRows, out int totalRowCount)
{
....
}
Model Binding Filtering
In order to filter the data source of the data bound control and pass the filtered data to the control you could pass filter parameters to the SelectMethod. You could get these parameters from query string, cookies, form values, controls, viewstate, session and profile. For example:
public IQueryable<Product> GetProducts([Control("RadComboBoxCategories")] int? categoryID, [QueryString]string name)
{
// Filter the data source based on categoryID and ProductName
}
The code snippet above will get the name parameter from the QueryString and integer value of the selected item of the RadComboBox with ID equals to “RadComboBoxCategories”.
When the control is used to pass the filter parameter the control needs to perform post back and the Rebind() method of our data bound control need to be called in order to call the SelectMethod. Otherwise the SelectMethod will not be called and the new data source will not be passed to the data bound control. Need to add System.Web.ModelBinding namespace on the page
Model Binding CRUD operations
Editing
In order to have editing enabled into the data bound controls you need to set the UpdateMethod of the corresponding control to the web form page’s method. The UpdateMethod can have following signature:
public void UpdateProduct(int ProductID)
{
Product updatedProduct = context.Products.Where(p => p.ProductID == ProductID).First();
TryUpdateModel(updatedProduct);
if (ModelState.IsValid)
{
context.SubmitChanges();
}
}
Where the “ProductID” is one of the fields set as DataKeyNames of the corresponding bound control.
Or you could use following signature:
public void UpdateProduct(Product product)
{
Product updatedProduct = context.Products.Where(p => p.ProductID == product.ProductID).First();
TryUpdateModel(updatedProduct);
if (ModelState.IsValid)
{
context.SubmitChanges();
}
}
Inserting
In order to have inserting enabled into the data bound controls you need to set the InsertMethod property of the corresponding control to the name of the web form page’s insert method. The InsertMethod can have following signatures:
Deleting
In order to have deleting enabled into the data bound controls you need to set the DeleteMethod property of the corresponding control to the name of the web form page’s delete method. The DeleteMethod can have following signature:
public void DeleteProduct(int ProductID)
{
Product deletedProduct = context.Products.Where(p => p.ProductID == ProductID).First();
context.Products.DeleteOnSubmit(deletedProduct);
context.SubmitChanges();
}
ModelBinding Validation
Due to the fact that Model Binding system in Web Forms supports model validation using the same validation attributes from the System.ComponentModel.DataAnnotations you could use validation into our databound controls. You could decorate properties from your model classes with the attributes provided in System.ComponentModel.DataAnnotations namespace. For example if you have DataContext mapped to a Northwind database “Product” table and you want to ensure that when inserting new product or update existing one the ProductName field is populated, you could set [Required] attribute to it into the DataClasses.designer.cs file:
[Required]
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ProductName", DbType="NVarChar(40) NOT NULL", CanBeNull=false)]
public string ProductName
{
get
{
return this._ProductName;
}
set
{
if ((this._ProductName != value))
{
this.OnProductNameChanging(value);
this.SendPropertyChanging();
this._ProductName = value;
this.SendPropertyChanged("ProductName");
this.OnProductNameChanged();
}
}
}
Then when values from databound control editors are submitted to the server the the Web Forms Model Binding system will track whether any of these validation rules are violated in the page's ModelState property.
public void InsertProduct(Product p)
{
if (ModelState.IsValid)
{
context.Products.InsertOnSubmit(p);
context.SubmitChanges();
}
}
To show any validation errors you could use asp:ValidationSummary control or asp:ModelErrorMessage:
<asp:ValidationSummary runat="server" ID="ValidationSummary1" />
You need to call TryUpdateModel(object) before checking the ModelState.IsValid when inserting items. Otherwise the validation will not track any errors. The other approach is to pass the entire object as a parameter to the function:
public void InsertProduct(int productID)
{
Product pr = new Product();
TryUpdateModel(pr);
if (ModelState.IsValid)
{
context.Products.InsertOnSubmit(p);
context.SubmitChanges();
}
}
public void InsertProduct(Product p)
{
if (ModelState.IsValid)
{
context.Products.InsertOnSubmit(p);
context.SubmitChanges();
}
}
ModelBinding Limitations
We do not support model binding when the ViewState of the page isdisabled. In order to use the model binding you need to set Page.EnableViewState = “true”