LINQ can be used effectively to filter out a set of
objects from a List of objects, in todays post we shall see on how to
accomplish object filtering using LINQ.
To know more about binding a List object to a DropDownList
refer to the post, Binding a List <T> object to a DropDownList control
First let us create a class whoose objects will be stored
in the List <T> here
is the code for the class.
public class clsCountry
{
public string _CountryCode;
public string _CountryName;
//
public
clsCountry(string strCode, string strName)
{
this._CountryCode
= strCode;
this._CountryName
= strName;
}
//
public string CountryCode
{
get {return _CountryCode;}
set
{_CountryCode = value;}
}
//
public string CountryName
{
get { return _CountryName; }
set {
_CountryName = value; }
}
}
Next, let us create a list of objects
based on our class clsCountry and store them in a List <T> object. Here is the code
for the List
<T>
List<clsCountry>
lstCountry = new List<clsCountry>();
lstCountry.Add(new clsCountry("USA", "United
States"));
lstCountry.Add(new clsCountry("UK", "United
Kingdom"));
lstCountry.Add(new clsCountry("IND", "India"));
Next, we shall bind the List <T> object lstCountry to a DropDownList
control.
Here the code to bind the data.
drpCountry.DataSource = lstCountry;
drpCountry.DataValueField
= "CountryCode";
drpCountry.DataTextField
= "CountryName";
drpCountry.DataBind();
Notice that the DataValueField and
DataTextField property of the DropDownList control are mapped to the Properties
of the class CountryCode and CountryName, hence make sure to create properties
for every member of the class so that they can be used while binding the data
to controls.
Finally, we shall use LINQ to filter
data from the lstCountry object and bind the filtered list to the
dropdown control drpCountry. Here is the code to filter
the List <T> using LINQ
var filteredCountries = from c in lstCountry
where c.CountryName.StartsWith("U")
select c;
drpCountry.DataSource
= filteredCountries;
drpCountry.DataValueField
= "CountryCode";
drpCountry.DataTextField
= "CountryName";
drpCountry.DataBind();
Now the dropdown control will have only
2 items
United States
United Kingdom
Here we are using c.CountryName.StartsWith("U") which works like
CountryName LIKE 'U%'
We can use c.CountryName.Contains("U"), method to make the filter work like
CountryName LIKE '%U%'
i.e, it will filter out all objects which have the character U anywhere in
the CountryName property of the
object.
That’s it we have filtered a List <T> and bound
the contents of the filtered List <T> to a DropDownList control.
