C# Linq query execution order

Question

Consider the following method:

public IEnumerable<Owner> GetOwners(OwnerParameters ownerParameters)
{
    return FindAll()
        .OrderBy(on => on.Name)
        .Skip((ownerParameters.PageNumber - 1) * ownerParameters.PageSize)
        .Take(ownerParameters.PageSize)
        .ToList();
}

Where FindAll() is a repository pattern method that returns IQueryable<Owner>. Does having .OrderBy() before .Skip() and .Take() methods mean that all the elements from the Owner data table will be retrieved and ordered, or, does Linq take into account that .Skip() and .Take() methods might narrow down the required Owner elements and only after having retrieved those will the ordering happen?

EDIT: Profiler log:

SELECT XXX
FROM [Owners] AS [a]
ORDER BY [a].[Name]
OFFSET @__p_0 ROWS FETCH NEXT @__p_1 ROWS ONLY',N'@__p_0 int,@__p_1 int',@__p_0=0,@__p_1=10

Answer 1

Ultimately, this depends on what FindAll() does and what it returns:

• if it returns IEnumerable<T>, then it is using LINQ-to-Objects, which mostly just does literally what it is told; if you sort then pages, then it sorts then pages; if you page then sort, then it pages then sorts
• however, if it returns IQueryable<T>, then the query is being composed - and only actually executed in ToList(), at which point the provider model gets a chance to inspect your query tree and build the most suitable implementation possible, which often means: writing a SQL query that includes an ORDER BY and some paging hints suitable for the specific RDBMS; if your code paged then sort (which is... unusual) then I would expect most providers to either write some kind of horrible sub-query to try to describe that, or just throw an exception (perhaps NotSupportedException) in disgust