Bee Eee Blog

There are four different string comparisons for handling string fields with linq to sql.  They are as follows:

The exact macth

DataContext dc = new DataContext(...)
var results =
  from row in dc.table
  where row.string_column == "Exact Match"
  select row;

Begins With:

DataContext dc = new DataContext(...)
var results =
  from row in dc.table
  where row.string_column.StartsWith("Ex")
  select row;

produces an sql match string “Ex%”

Contains

DataContext dc = new DataContext(...)
var results =
  from row in dc.table
  where row.string_column.Contains("Ex")
  select row;

Which is equivalent to “%Ex%”

Ends With

DataContext dc = new DataContext(...)
var results =
  from row in dc.table
  where row.string_column.EndsWith("Ex")
  select row;

Which is equivalent to “%Ex”

I’ve recently been writing an application that builds a linq to sql query dynamically.  For instance:

MyDataContext dc() = new MyDataContext;
var query = dc.MyTables;
query = query.Where( t=>t.id > 10);

and so I want to order it by a certain column:

query = query.OrderBy( t=>t.id )

but the problem is the order direction isn’t know before hand so at first I was stuck with the following:

if ( descending )
    query = query.OrderByDescending( t=>t.id);
else
    query = query.OrderBy(t=>t.id);

Now if there is only a few possible columns to sort against it isn’t too bad.  But when you have 10 different possible columns it really makes a lot of extra work just to control to sort direction.  So I made a little helper class that allows the following.  It works with linq and linq to sql:

query = query.OrderByAscDec( t=>t.id, descending );

here’s the static class that implments the OrderByAscDec function:

static class VPLinqExtensions
{
	public static IOrderedQueryable<TSource> OrderByAscDes<TSource, TKey>(
		this IQueryable<TSource> source,
		System.Linq.Expressions.Expression<Func<TSource,
		TKey>> keySelector, bool IsDescending)
	{
		if (IsDescending)
			return source.OrderByDescending(keySelector);
		else
			return source.OrderBy(keySelector);
	}
}