Entity Framework Ordering Includes

Question

I am trying to get something like the following to work:

_dbmsParentSections = FactoryTools.Factory.PdfSections
                        .Include(x => x.Children.OrderBy(y => y.Order).ToList())
                        .Include(x => x.Hint).Include(x => x.Fields)
                        .Where(x => x.FormId == FormId && x.Parent == null)
                        .OrderBy(o => o.Order)
                        .ToList();

The part that causes the exception is:

.Include(x => x.Children.OrderBy(y => y.Order).ToList())

EDIT:

Upon further observation,

_dbmsParentSections.ForEach(x => x.Children = x.Children.OrderBy(y => y.Order).ToList());

did the job for me (after the initial Factory call and without the Children.OrderBy).

Answer 1

Generally if you're using a bunch of includes, it's because you need to access child properties in a view. What I do is order the child collection when I need to access it in a view.

For example, I might build some Include statements for a master/detail form. There's no sense ordering this at the initial EF query. Instead, why not order these child records at the view level when you're actually accessing them?

I might have a survey with multiple survey questions. If I want to present the questions in a particular order at do it at the partial view level when I'm passing the model child collection to the partial view.

@Html.Partial("_ResponsesPartial",Model.SurveyResponses.OrderBy(x => 
x.QuestionId))

Answer 2

This will never gona work. EF include is try to understand and translate everything to SQL, but you want to much from this. Load all entities without sorting and .ToList()-ing, and write an extension method for IEnumerable to get an ordered result.

Answer 3

You should not convert an IQueryable type to IEnumerable and call Include because Include is not supported by IEnumerable type.

In short, never call Include after ToList

IQueryable = server side call (SQL)
IEnumerable = client side (loaded in memory)

Answer 4

It seems you cannot sort the children collection in your query. Either sort after the query or load the children in a second query.

Similar question and answer here

Answer 5

The extension method Includeis a mere wrapper around DbQuery.Include. Internally it does not execute the expressions but only parses them, i.e. it takes their member expressions and converts them to a path as string. The path is used as input for DbQuery.Include.

It has been requested before to enhance the functionality of Include, e.g. to allow partly loaded collections by including a Where clause. Ordering could be another change request. But as you see, because of the internal working of Include the whole mechanism will have to be re-engineered to implement such enhancements. I don't see it on the current road map so it may take a while...

Answer 6

I use this code por order the include, using a select and a function to order the collection. Is not the best but work fine if subcollection is small

   // GET: api/Tareas
    [HttpGet]
    public IEnumerable<Tarea> GetTareas()
    {
        var result = _context.Tareas
            .Include(p => p.SubTareas)
            .Select(p => SortInclude(p));
        return result;
    }

    private Tarea SortInclude(Tarea p)
    {
        p.SubTareas = (p.SubTareas as HashSet<SubTarea>)?
            .OrderBy(s => s.Position)
            .ToHashSet<SubTarea>();
        return p;
    }