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Posts Tagged ‘Guid.NewGuid()’

Random in Linq

Posted by Viral Sarvaiya on July 12, 2012


In sql query if we want to get one random row form the whole set of data we get from NEWID() in select statement’s order by clouse as like below.

Select top 1 * from Customers where IsActive = 1 order by newid()

What if we are using ORM like linq?

We can do this at the database, by using a fake UDF; in a partial class, add a method to the data context

partial class MyDataContext {
    [Function(Name="NEWID", IsComposable=true)]
    public Guid Random()
    { // to prove not used by our C# code...
        throw new NotImplementedException();
    }
 }

Then just order by ctx.Random(); this will do a random ordering at the SQL-Server courtesy of NEWID(). i.e.

var cust = (from row in ctx.Customers
   .where row.IsActive // your filter
   .orderby ctx.Random()
   select row).FirstOrDefault();

Note that this is only suitable for small-to-mid-size tables; for huge tables, it will have a performance impact at the server, and it will be more efficient to find the number of rows (Count), then pick one at random (Skip/First).

var qry = from row in ctx.Customers select row;

int count = qry.Count(); // 1st round-trip
int index = new Random().Next(count);

Customer cust = qry.Skip(index).FirstOrDefault(); // 2nd round-trip

We can also do woth Guid class

var cust = ctx.Customers
 .Where(x => x.IsActive)
 .OrderBy(x => Guid.NewGuid())
 .FirstOrDefault();

Hope this will helps you.

Thank you.

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