使用 LINQ-to-Entities 选择父对象时对子对象进行排序

Question

Imagine you've got some Entity Framework entities that look like this (obviously not these specific classes, but the autogenerated ones with all the Entity Framework plumbing; these are just for illustration):

public class Parent
{
    public int ID { get; set; }
    public List<Child> Children { get; set; }
}

public class Child
{
    public int ID { get; set; }
    public Parent Parent { get; set; }
    public int Number { get; set; }
}

I have a LINQ query that looks like this:

from parent in context.Parents.Include("Child")
select parent

However, this returns a list of Parents where the children are in ID order. I want the children to be sorted by their Number property within their Parent. How can this be done?

Edit: A clarification: the idea is to have the query hidden behind a method call (in the layer facade) that simply returns an IList<Parent> . This makes using solutions like anonymous class queries and manual sorting painful (compared to some panacea solution where you can just do it in the query or something).

Answer 1

Alex James discusses this issue in this tip .

Essentially, relationships are considered as unordered, per standard relational modeling. So you can't get them sorted. But you can project onto other collections, which can be sorted.

Answer 2

Take a look at this post . You could try something like this:

var query = ((from parent in context.Parents
              from child in parent.Child
              orderby child.Number ascending
              select parent) as ObjectQuery<Parent>
            ).Include("Child");

Answer 3

One option is executing the query and sorting in memory (eg on output).

var parents = context.Parents.Include("Child").ToList(); //note that ToList is here just to execute the query and get the objects in memory

foreach (var p in parents)
{
   //do something with parent item
   foreach (var c in p.Child.OrderBy(c => c.Number))
   {
      /do something with the child item
   }
}

There are two other options that also seem to work with their own pros and cons:

LINQ ".Include" orderby in subquery

LINQ OrderBy Name ThenBy ChildrenCollection.Name

Answer 4

here is something that I have done:

var query = from parent in context.Parents 
            select new 
            {
                 parent,
                 childs = from child in context.Child
                            orderby child.ID ascending
                            select new
                            {
                                 child
                            }
            }

I implememented something like this and it worked very well for me