Freeze a linq IQueryable (as a ToList().AsQueryable() would do)

Question

Is there a way to freeze an IQueryable so that no additional joins will be added to the query when hitting the database? For example, I could do a .ToList() to freeze the query, but that has performance impacts because any filtering I do is on the middle layer and I don't have any performance gains from pre-filtering on the db server?

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Edit for clarity:

I have an OData service which returns an IQueryable that the client can filter/sort/project as needed. I just want to prevent them from pulling more data out. I could do that by doing ToList().AsQueryable(), but that loses the advantage of lazyLoading, and with it, the whole purpose of allowing the client to filter the request.

One option that I looked at was to set: EnableQueryAttribute.AllowedQueryOptions to exclude Expand, however even if my initial Query had been expanded, the client is still prevented from selecting those parts.

Answer 1

Im assuming that you actually have an IQueryable<T> instead of a IQueryable.

If you don't want your client having access to all IQueryable<T> methods, don't return an IQueryable<T>. Since you want them to be able to only filter/sort/project, create a object witch contains an IQueryable<T> but only expose the desired methods, and use that:

public interface IDataResult<T>
{
    IDataResult<T> FilterBy(Expression<Func<T, bool>> predicate);

    IDataResult<TResult> ProjectTo<TResult>(Expression<Func<T, TResult>> predicate);

    IDataResult<T> SortBy<TKey>(Expression<Func<T, TKey>> keySelector);

    IDataResult<T> SortByDescending<TKey>(Expression<Func<T, TKey>> keySelector);

    List<T> ToList();

    IEnumerable<T> AsEnumerable();
}

public class DataResult<T> : IDataResult<T>
{
    private IQueryable<T> Query { get; set; }

    public DataResult(IQueryable<T> originalQuery)
    {
        this.Query = originalQuery;
    }

    public IDataResult<T> FilterBy(Expression<Func<T, bool>> predicate)
    {
        return new DataResult<T>(this.Query.Where(predicate));
    }

    public IDataResult<T> SortBy<TKey>(Expression<Func<T, TKey>> keySelector)
    {
        return new DataResult<T>(this.Query.OrderBy(keySelector));
    }

    public IDataResult<T> SortByDescending<TKey>(Expression<Func<T, TKey>> keySelector)
    {
        return new DataResult<T>(this.Query.OrderByDescending(keySelector));
    }

    public IDataResult<TResult> ProjectTo<TResult>(Expression<Func<T, TResult>> predicate)
    {
        return new DataResult<TResult>(this.Query.Select(predicate));
    }

    public List<T> ToList()
    {
        return this.Query.ToList();
    }

    public IEnumerable<T> AsEnumerable()
    {
        return this.Query.AsEnumerable();
    }
} 

That way you can also prevent EF and DB related dependencies creeping up on your application. Any change on IQueryable<T> methods will be contained within this class, instead of spread all over the place.