I'm in the process of moving from ADO.NET to Linq. The application is a directory search program to look people up. The users are allowed to type the search criteria into a single textbox. They can separate each term with a space, or wrap a phrase in quotes such as "park place" to indicate that it is one term.

Behind the scenes the data comes from a XML file that has about 90,000 records in it and is about 65 megs. I load the data into a DataTable and then use the .Select method with a SQL query to perform the searches. The query I pass is built from the search terms the user passed. I split the string from the textbox into an array using a regular expression that will split everything into a separate element that has a space in it. However if there are quotes around a phrase, that becomes it's own element in the array. I then end up with a single dimension array with x number of elements, which I iterate over to build a long query.

I then build the search expression below:

      query = query & _
    "((userid LIKE '" & tempstr & "%') OR " & _
    "(nickname LIKE '" & tempstr & "%') OR " & _
    "(lastname LIKE '" & tempstr & "%') OR " & _
    "(firstname LIKE '" & tempstr & "%') OR " & _
    "(department LIKE '" & tempstr & "%') OR " & _
    "(telephoneNumber LIKE '" & tempstr & "%') OR " & _
    "(email LIKE '" & tempstr & "%') OR " & _
    "(Office LIKE '" & tempstr & "%'))"

Each term will have a set of the above query. If there is more than one term, I put an AND in between, and build another query like above with the next term. I'm not sure how to do this in Linq. So far, I've got the XML file loading correctly. I'm able to search it with specific criteria, but I'm not sure how to best implement the search over multiple terms.

'this works but far too simple to get the job done
    Dim results = From c In m_DataSet...<Users> _
    Where c.<userid>.Value = "XXXX" _
    Select c    

The above code also doesn't use the LIKE operator either. So partial matches don't work. It looks like what I'd want to use is the .Startswith but that appears to be only in Linq2SQL. Any guidance would be appreciated. I'm new to Linq, so I might be missing a simple way to do this.

The XML file looks like so:

<?xml version="1.0" standalone="yes"?>
<theusers>

<Users>
<userid>person1</userid>
<nickname></nickname>
<lastname></lastname>
<firstname></firstname>
<department></department>
<telephoneNumber></telephoneNumber>
<email></email>
</Users>

<Users>
<userid>person2</userid>
<nickname></nickname>
<lastname></lastname>
<firstname></firstname>
<department></department>
<telephoneNumber></telephoneNumber>
<email></email>
</Users>