Picking random record from Entity Framework database without OrderBy

Question

I try to get random record from database:

 personToCall = db.Persons.Skip(toSkip).Take(1).First();

but I get exception which tells me:

{"The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'."}

Can I do it without OrderBy? Sorting data structure (O(nlogn)) to pick random element(which should be constant) doesn't look wise.

EDIT: I use Entity Framework 6.1.1.

Answer 1

You can have something like :

personToCall = db.Persons.OrderBy(r => Guid.NewGuid()).Skip(toSkip).Take(1).First();

You should use FirstOrDefault to be mode defensive.

Here the dark lord teaching the force to yoda! what is the world coming to!

Answer 2

First you need to get the random number from 1 to max record, see this

Random rand = new Random();
int toSkip = rand.Next(0, db.Persons.Count());

db.Persons.Skip(toSkip).Take(1).First();

with order by you can use the Guid.NewGuid()

db.Persons.OrderBy(x=>x.Guid.NewGuid()).Skip(toSkip).Take(1).FirstOrDefault();

Answer 3

There is no way to do this without an ordering clause.

personToCall = db.Persons.OrderBy(r => Random.Next()).First();

That could be slow depending on the size of your Persons table, so if you wanted to make this fast, you'd have to add a column to Person, or join it to a dictionary of random numbers and Person keys, then order by that. But that is rarely a wise solution.

Better to ask a higher level question about the overall task at hand.