linq to sql case query

Im having problems building a query with the linq to sql data query expression in c#.

What I'm trying to ultimately do is based on this pseudo-code expression.

public IQueryable<CTest> searchRecords(string category, string searchString, DateTime startDate, DateTime endDate, int searchType, int searchType2)
        {
            //-Search All Records
            //-From the information table
            //-By the category column containing a specific search
            //-Also by
            //  ~if both a startDate and endDate are entered (not (0000,00,00) OR null) then get records
            //  by this expression
            //  ~else then don't worry about this statement
            //-Also by
            //  ~if a searchType is equal zero(0) then search for records from the 
            //  search_type table equal to zero(0)
            //  ~if a searchType is equal one(1) then search for records from the 
            //  search_type table equal to one(1)
            //  ~else then don't worry about this statement
            //-Also by
            //  ~if a searchType2 is equal zero(0) then search for records from the 
            //  search_type table equal to zero(0)
            //  ~if a searchType2 is equal one(1) then search for records from the 
            //  search_type table equal to one(1)
            //  ~else then don't worry about this statement

            //Here is my attempt at it
            /*  
                var table = db.table1;

                switch (category)
                {
                case "_category1":
                    var records =
                        from c in table
                        where c.column1.ToString().Contains(searchString)
                        select new CTest
                        {
                            test_id = c.id,
                            test_name = c.name,
                            test_number = c.number,
                            date = ((startDate != null) && (endDate != null)) ? ((c.test_date >= startDate) && (c.test_date <= endDate)) :
                                         c.test_date),
                            test_type = (searchType == 0 ? (c.searchType = 0) :
                                        searchType == 1 ? (c.searchType = 1) :
                                        c.searchType),
                            test_type2 = (searchType2 == 0 ? (c.searchType2 = 0) :
                                        searchType2 == 1 ? (c.searchType2 = 1) :
                                        c.searchType2)
                        };
                    break;
                default:
                    break;
                }
             */
        }

Thanks in advance.

This would be easier to do with extension methods than LINQ syntax:

 var records = context.Table
                      .Where( c => c.column1.Contains( searchString ) );
 if (startDate != null && endDate != null)
 {
     records = records.Where( c => c.test_date >= startDate
                                    && c.test_date <= endDate );
 }

 ...

This will build up the LINQ expression as you go along. The evaluation is delayed until you actually invoke some extension that requires the selection to be performed, like Count() or ToList(), or enumerate the elements of the result.