how to filter records in c#

There are two approaches

1. Make query to db each time the search text box changes using ajax, and apply the filter in db using like '%searchstring%'

OR

2. Get all data to UI/Service/Business layer using EF/SP/DataReader ... and filter data using .Contains clause in LINQ

When you say records, I am assuming Database table record selection here. Have you checked your SQL Queries (Where clause, Joins etc)??

try this

if ( ddlsearchby.SelectedItem.Text == "All")
 {
 DataTable dt = new DataTable();
 SqlDataAdapter da = new SqlDataAdapter("Select * from tbl ", con);
 SqlCommandBuilder cmd = new SqlCommandBuilder(da);
 da.Fill(dt);
 dgvitemDetails.DataSource = dt;
 }
 else
 {
 DataTable dt = new DataTable();
 SqlDataAdapter da = new SqlDataAdapter("Select * from tbl where " +  ddlsearchby.SelectedItem.text + " = '" + txtSearch.Text + "'", con);
 SqlCommandBuilder cmd = new SqlCommandBuilder(da);
 da.Fill(dt);
 dgvitemDetails.DataSource = dt;
}

complete example then visit link

http://hightechnology.in/how-to-filter-gridview-records-with-dropdownlist-selection/[^]

I guess you're looking for this,
A Shopping Cart Application Built with AngularJS[^]

Just for the reference[^]

-KR