Question

I have a database table that holds parent and child records much like a Categories table. The ParentID field of this table holds the ID of that record’s parent record…

My table columns are: SectionID, Title, Number, ParentID, Active

I only plan to allow my parent to child relationship go two levels deep. So I have a section and a sub section and that it.

I need to output this data into my MVC view page in an outline fashion like so…

1. Section 1
   • Sub-Section 1 of 1
   • Sub-Section 2 of 1
   • Sub-Section 3 of 1
2. Section 2
   • Sub-Section 1 of 2
   • Sub-Section 2 of 2
   • Sub-Section 3 of 2
3. Section 3

I am using Entity Framework 4.0 and MVC 2.0 and have never tried something like this with LINQ. I have a FK set up on the section table mapping the ParentID back to the SectionID hoping EF would create a complex “Section” type with the Sub-Sections as a property of type list of Sections but maybe I did not set things up correctly.

So I am guessing I can still get the end result using a LINQ query. Can someone point me to some sample code that could provide a solution or possibly a hint in the right direction?

Update:

I was able to straighten out my EDMX so that I can get the sub-sections for each section as a property of type list, but now I realize I need to sort the related entities.

var sections = from section in dataContext.Sections
                       where section.Active == true && section.ParentID == 0
                       orderby section.Number
                       select new Section
                       { 
                        SectionID = section.SectionID,
                        Title = section.Title,
                        Number = section.Number,
                        ParentID = section.ParentID,
                        Timestamp = section.Timestamp,
                        Active = section.Active,
                        Children = section.Children.OrderBy(c => c.Number)
                       };

produces the following error.
Cannot implicitly convert type ‘System.Linq.IOrderedEnumerable’ to ‘System.Data.Objects.DataClasses.EntityCollection’

Answer 1

Your model has two navigation properties Sections1 and Section1. Rename the first one to Children and the second one to Parent.

Depending on whether you have a root Section or perhaps have each top-level section parented to itself (or instead make parent nullable?), your query might look something like:-

  // assume top sections are ones where parent == self
  var topSections = context.Sections.Where(section => section.ParentId == SectionId);

  // now put them in order (might have multiple orderings depending on input, pick one)
  topSections = topSections.OrderBy(section => section.Title);

  // now get the children in order using an anonymous type for the projection
  var result = topSections.Select(section => new {top = section, children = section.Children.OrderBy(child => child.Title)});