Entity Framework Performance Tip - Be a Minimalist
Only get the data you need! This not only applies to Entity Framework query performance, but just about every situation were code interacts with data. It is a simple rule to follow, but yet I see it broken all the time. Breaking this rule is one of the top three reasons I’ve seen for slow Entity Framework query performance. I may discuss the other two in later posts …
Bad
private static IEnumerable<string> GetNames()
{
using (var dc = new MyDataContext())
{
// This is bad news!
// This will return alot of columns
// that won't even be used.
var userNames = from u in dc.UserSet
select u;
// SQL Server Profiler will show you that all the
// columns are fetched when you call "ToList()".
return userNames.ToList().Select(u => u.Name);
}
}Good
private static IEnumerable<string> GetNames()
{
using (var dc = new MyDataContext ())
{
// Just get the Name.
// Don't waste database and network resources!
var userNames = from u in dc.UserSet
select u.Name;
return userNames.ToList();
}
}Posted by Bill Simpkins on August 19, 2009