Using Linq to filter a ComboBox.DataSource ?

Question

Hi board,

in another topic, I've stumbled over this very elegant solution by Darin Dimitrov to filter the DataSource of one ComboBox with the selection of another ComboBox: how to filter combobox in combobox using c#

combo2.DataSource = ((IEnumerable<string>)c.DataSource)
.Where(x => x == (string)combo1.SelectedValue);

I would like to do a similar thing, but intead of filtering by a second combobox, I would like to filter by the text of a TextBox. (Basically, instead of choosing from a second ComboBox, the user simply enters his filter in to a TextBox). However, it turned out to be not as straight forward as I had hoped it would be. I tried stuff as the following, but failed miserably:

     cbWohndresse.DataSource = ((IEnumerable<DataSet>)ds)
            .Where(x => x.Tables["Adresse"].Select("AdrLabel LIKE '%TEST%'"));
        cbWohndresse.DisplayMember = "Adresse.AdrLabel";
        cbWohndresse.ValueMember = "Adresse.adress_id";

ds is the DataSet which I would like to use as filtered DataSource. "Adresse" is one DataTable in this DataSet. It contains a DataColumn "AdrLabel". Now I would like to display only those "AdrLabel", which contain the string from the user input. (Currently, %TEST% replaces the textbox.text.)

The above code fails because the lambda expression does not return Bool. But I am sure, there are also other problems (which type should I use for IEnumerable? Now it's DataSet, but Darin used String. But how could I convert a DataSet to a string?

Yes, I am as much newbyish as it gets, my experience is "void", and publicly so. So please forgive me my rather stupid questions.

Your help is greatly appreciated, because I can't solve this on my own (tried hard already).

Thank you very much!

Pesche

P.S. I am only using Linq to achieve an uncomplicated filter for the ComboBox (avoiding a View). The rest is not based on Linq, but on oldstyle Ado.NET (ds is filled by an SqlDataAdapter), if that's of any importance.

Answer 1

LINQ does not seem, to me, like an obvious solution here. Your data is already loaded into a DataSet structure, so you should be able to do something like this:

var adresse = ds.Tables["Adresse"];
adresse.DefaultView.RowFilter = "AdrLabel LIKE '%TEST%'";

cbWohndresse.DataSource = adresse;
cbWohndresse.DisplayMember = "AdrLabel";
cbWohndresse.ValueMember = "adress_id"
cbWohndresse.DataBind();

To address the actual problems in your current code:

1. If ds is of type DataSet, casting it to IEnumerable<DataSet> will fail.
2. DataTable.Select returns an array of rows, not a boolean.
3. Ignoring #1 and #2, your Where() call would return zero, one or more DataSet instances which each have a table named "Adresse" with at least one row matching the filter. Hence, you end up binding your presentational control to a set of DataSet instances, which is not what you need.

Answer 2

If you want to use LINQ, then you'll need to add a reference System.Data.DataSetExtensions. You can then query your DataSet in a "linqish" manner.

The blog post Querying DataSets – Introduction to LINQ to DataSet by Erick Thompson, a PM at Microsoft is a good introduction to LINQ to DataSets

Here's a very crude example:

XAML

<StackPanel>

    <TextBox x:Name="MyFilter" />

    <ComboBox x:Name="MyComboBox" 
              ItemsSource="{Binding}"
              DisplayMemberPath="AdrLabel" />

    <Button Click="OnFilterClick">Filter</Button>

</StackPanel>

Code Behind

public partial class FilteredDataSet : Window
{
    public FilteredDataSet()
    {
        InitializeComponent();

        CreateDataContext();
        MyComboBox.DataContext = MyDataSet.Tables[0];
    }

    private DataSet MyDataSet { get; set; }
    private void CreateDataContext()
    {
        var ds = new DataSet();
        var dt = new DataTable( "Adresse" );
        ds.Tables.Add( dt );

        var dc = new DataColumn( "AdrLabel" );
        dt.Columns.Add( dc );

        DataRow dr = dt.NewRow();
        dr[0] = "one";
        dt.Rows.Add( dr );

        dr = dt.NewRow();
        dr[0] = "honed";
        dt.Rows.Add( dr );

        dr = dt.NewRow();
        dr[0] = "obiwone";
        dt.Rows.Add( dr );

        dr = dt.NewRow();
        dr[0] = "won";
        dt.Rows.Add( dr );

        MyDataSet = ds;

    }
    private void OnFilterClick( object sender, RoutedEventArgs e )
    {
        string filter = MyFilter.Text;

        var context = MyDataSet.Tables[0].AsEnumerable()
            .Where( dr => dr.Field<string>( "AdrLabel" ).Contains( filter ) )
            .Select( dr => dr.Field<string>( "AdrLabel" ) );

        MyComboBox.DisplayMemberPath = string.Empty;

        MyComboBox.DataContext = context;
    }
}