Question

I’ve created a dropdown with some column names in a table in my db. When a user selects a column name i want to add a where clause to the query to use this filter.

What i’m trying to do is:

Dim objQuery = (From wc In _dbBellen.dealer_telefonies Order By wc.Bedrijfsnaam Select wc)

'if dropdown has value...

objQuery = objQuery.Where(Function(wc) wc.DynamicColumnName < txtFilterValue1.Text)

The wc.DynamicColumnName has to be replaced by for example wc.Price.

—

The code what i’m tried now after some replies is:

    Dim objQuery = (From wc In _dbBellen.dealer_telefonies Order By wc.Bedrijfsnaam Select wc)

        If ddlFilterColumn1.SelectedValue <> "" And ddlFilterOperator1.SelectedValue <> "" And txtFilterValue1.Text <> "" Then

            Select Case ddlFilterOperator1.SelectedValue
                Case "..%"
                    objQuery = objQuery.Where(Function(wc) wc.WHMCSClient_id Like txtFilterValue1.Text & "%")
                Case "%.."
                    objQuery = objQuery.Where(Function(wc) wc.WHMCSClient_id Like "%" & txtFilterValue1.Text)
                Case Else '< > = <>
                    'objQuery = objQuery.Where(Function(wc) wc.WHMCSClient_id < txtFilterValue1.Text)
                    'objQuery = objQuery.Where(Function(wc) "wc." + ddlFilterColumn1.SelectedValue.ToString + " < " + txtFilterValue1.Text)
                    objQuery = objQuery.Where(Function(wc) "wc.WHMCSClient_id < 500")
            End Select

        End If

    Response.Write(objQuery.ToString())

But i am getting the following error (original error is in dutch but it said as follow):
The conversion from string wc.WHMCSClient_id < 500 to type Boolean is invalid.

Answer 1

This is quite an old article, but I think it’s still viable

Scott Gu posted about the Dynamic LINQ library a while back which essentially allows you to use strings to query collections in a “LINQ”-type format., i.e. something like this:

Dim objQuery = (From wc In _dbBellen.dealer_telefonies Order By wc.Bedrijfsnaam Select wc)

// if dropdown has value...
Dim result = objQuery.Where("MyColumnName < " + txtFilterValue1.Text);

Here’s a link to the full article: Dynamic LINQ (Part 1: Using the LINQ Dynamic Query Library)