是否存在LINQ查询中的where子句过滤序列的默认顺序

Question

public IQueryable<CarVersion> GetCar(int carIdToSearch)
{
    return _Dbcontext.CarVersion.Include("CarFactory").
            .Where(x => x.carId== carIdToSearch);
}

I have CarVersion table, which has two columns version and carId . Version column is primary key. There can be multiple version for single carId. CarFactory table has foreign key version from carVersion table. So I'm trying to understand, when I execute above query will it always give me results which are ordered in ascending order. Or will it be based on primary key? Or it can be guaranteed? I looked at MS documentation but it does not say anything about ordering.

Answer 1

The result you will get depends on the LINQ-provider. If it's Linq-To-Objects the order is stable(read below). It means it will be the same as it was in the source sequence. If it's a database driven LINQ provider like Linq-To-Entities the order is not predetermined.

You need an ORDER BY in sql to ensure a certain order. So you need an OrderBy in LINQ:

return _Dbcontext.CarVersion.Include("CarFactory").
    .Where(x => x.carId== carIdToSearch)
    .OrderBy(x => x.Version);

• However, even in Linq-To-Objects it's not guaranteed that the order will always be the same. It also depends on the type of the sequence. Set based collections like a Dictionary or HashSet also don't guarantee that the order stays the same as you can read here and here .