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Filtering Overview

RadGrid natively supports filtering of table columns for its master and detail tables. To enable or disable filtering, set the AllowFilteringByColumn property of the RadGrid or GridTableView control.

To see filtering functionality in action, check out the Filtering Demo.

When filtering is enabled, a filtering item (GridFilteringItem) appears below the column header. The user can enter a filter criterion in the filter box. A drop-down list allows the user to select a filter expression that is applied to the filter criterion for the column, for example, StartsWith.

Filtering

All filters in a single table are applied using the AND operator so that only items (grid rows) that match all filters are displayed.

RadGrid filters data internally, after data binding. If you need to fully customize the filtering, use the GridTableView control and set the value of its FilterExpression property.

  • The value of the FilterExpression property overrides all other filtering settings.
  • The built-in filtering feature is not supported when you bind the grid by explicitly calling DataBind().

Setting Default Filter

You can use the CurrentFilterFunction and CurrentFilterValue properties of the GridColumn object to specify the default filter function and default filter value that appear in the filter text box. When you set these properties, RadGrid displays this value as an initial filter but does NOT apply the filtering. For information on applying an initial filter, see Applying default filter on initial load.

Additionally, you can disable the filtering option for some of the grid columns by setting their AllowFiltering property to False.

Depending on the data source, the filtering may be case-sensitive or case-insensitive. You can control this behavior using the GroupingSettings-CaseSensitive property. In some .NET 3.5 scenarios, you should also turn off the Linq expressions - EnableLinqExpressions="false".

Filtering Menus

The filtering menu is represented by a drop-down list that is independent for each column in RadGrid. The available filter functions in the filtering menu are organized into three groups. You can specify the displayed filter functions group by setting the column's FilterListOptions property:

  • VaryByDataType (the default value) - The list of filter functions depends on the DataType property of the column. For example, filter functions "StartsWith", "EndsWith... " are not available for columns with DataType integer.

    The DataType property of a column is set during data binding. You can, however, set this property explicitly, which can alter the allowed filtering expressions. For example, if you set the DataType property of an integer column to "string", the list of allowed filter expressions will include "StartsWith" and "EndsWith".

  • VaryByDataTypeAllowCustom - The list of filter functions depends on the DataType property of the column, but an additional "Custom" item appears in the menu as well. If the user selects the "Custom" item, the value entered in the filter box is assumed to be a complete filter expression, including data field, operators, and value. This lets the user specify keywords and fields from the data source in the filter text box.

  • AllowAllFilters - The list of filter functions contains all possible filter expressions. Note that some data types do not apply to some filter functions. For example, the 'like' function cannot be applied to an integer data type. In such cases, you should handle the filtering in a custom manner, using the ItemCommand event handler where the command name is Filter..

Users can set a filter expression based on the rules specified in the corresponding column properties: GridColumn.FilterFormatString.

The filtering menu is presented by a single server-side object. This implementation was chosen to speed up the grid's performance by creating one menu instance server-side and cloning the instance for different columns.

Filter functions

The GridKnownFunction enumeration lists the possible filter functions that can appear in the filtering menu. The following table represents the possible GridKnownFunction values:

Value Description
NoFilter No filter is applied, filter controls are cleared.
Contains Same as: dataField LIKE '%value%'
DoesNotContain Same as: dataField NOT LIKE '%value%'
StartsWith Same as: dataField LIKE 'value%'
EndsWith Same as: dataField LIKE '%value'
EqualTo Same as: dataField = value
NotEqualTo Same as: dataField != value
GreaterThan Same as: dataField > value
LessThan Same as: dataField < value
GreaterThanOrEqualTo Same as: dataField >= value
LessThanOrEqualTo Same as: dataField <= value
Between Same as: value1 <= dataField <= value2.Note that value1 and value2 should be separated by [space] when entered as filter.
NotBetween Same as: dataField <= value1 && dataField >= value2.Note that value1 and value2 should be separated by [space] when entered as filter.
IsEmpty Same as: dataField = ''
NotIsEmpty Same as: dataField != ''
IsNull Only null values.
NotIsNull Only those records that do not contain null values in the column.
Custom A custom filter function. The filter value should contain a valid filter expression, including data field, operators, and value.

In addition to the available filter functions, you can create your own filter using the GridFilterFunction class.

With the .NET 3.5 build of RadGrid for ASP.NET AJAX and LINQ filter expressions enabled (EnableLinqExpressions = true), the filter expressions set for the grid either internally by its filtering mechanism or manually in code should conform to the LINQ expression syntax instead to the old T-SQL syntax. Only this way they will be evaluated properly by the control.

There are also some useful shortcuts (achievable with several lines of javascript code) for applying filters when typing in the column header filter box and pressing the [Enter] key from the keyboard (illustrated in this video). Note that a prerequisite to trigger filter operation on [Enter] key press is to set the AutoPostBackOnFilterproperty of the corresponding column to true:

  • If the user enters [some_value]and hits [Enter] key, the grid will automatically use the Contains filter function

  • If the user enters [some_value] and hits [Enter] key, the grid will automatically use the StartsWith filter function

  • If the user enters [some_value] and hits [Enter] key, the grid will automatically use the EndsWith filter function

  • If the user enters =[some_value] and hits [Enter] key, the grid will automatically use the EqualTo filter function

  • If the user enters <>[some_value] and hits [Enter] key, the grid will automatically use the NotEqualTo filter function

  • If the user enters >[some_value] and hits [Enter] key, the grid will automatically use the GreaterThanfilter function

  • If the user enters <[some_value] and hits [Enter] key, the grid will automatically use the LessThan filter function

  • If the user enters >=[some_value] and hits [Enter] key, the grid will automatically use the GreaterThanOrEqualTofilter function

  • If the user enters =<[some_value] and hits [Enter] key, the grid will automatically use the LessThanOrEqualTo filter function

  • If the user enters [some_value][ ][some_other_value] and hits [Enter] key, the grid will automatically use the Betweenfilter function

To define a default filter function applied when you press the [Enter] key from the keyboard (when no shortcuts are used), use the CurrentFilterFunction property of the respective grid column.

Using the ItemCommand event with filters

When the user clicks the filter button, a server-side ItemCommand event occurs with a command name of "Filter". You can use this command to replace the filter that is applied with your own value. For an example of this approach, see Custom option for filtering (FilterListOptions -> VaryByDataTypeAllowCustom).

AutoPostBackOnFilter

If you set AutoPostBackOnFilter property of a column to True, the user does not need to press the filter button to initiate filtering. Instead, a postback filter operation occurs when the user types a filter in the filter box and presses [Enter] from the keyboard.

When AutoPostBackOnFilter is True, the column assumes a filter operation of Contains for string types or EqualTo for numeric types.You can change this to another filter function by setting the CurrentFilterFunction property. For example:

<telerik:GridBoundColumn DataField="ProductName" HeaderText="ProductName" SortExpression="ProductName"
  UniqueName="ProductName" CurrentFilterFunction="StartsWith" AutoPostBackOnFilter="true" />

Another option is to set FilterDelay property for grid column that can be filtered. Thus filtering operations will be executed after the delay specified through that property elapses. For example:

<telerik:GridNumericColumn DataField="OrderID" HeaderText="OrderID" SortExpression="OrderID"
  UniqueName="OrderID" FilterControlWidth="40px" AutoPostBackOnFilter="false" CurrentFilterFunction="EqualTo"
  FilterDelay="4000" ShowFilterIcon="false" />

When the FilterDelay property is set, the filtering will be triggered after the last keystroke with the filter delay time span being respected or immediately if [ENTER] has been hit. In addition, if AutoPostBackOnFilter has been set to true along with a FilterDelay time span, the filtering should be triggered immediately on [TAB] key press. If only AutoPostBackOnFilter has been set to true, the filtering should be triggered immediately on [TAB] and [ENTER] key press.

TroubleShooting

In some cases when the RadGrid uses absolute positioning, you may find the filtering pop-up hidden behind the grid. You can easily fix the problem by setting the Z-index of the corresponding element in the ASPX to 0:

<telerik:RadGrid RenderMode="Lightweight" ID="RadGrid1" Style="z-index: 0; left: 64; position: absolute..." />
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