How do you sort an EntitySet

问题

The MSDN documentation states that an EntitySet implements IBindingList

(see 'Binding to EntitySets' at http://msdn.microsoft.com/en-us/library/bb546190.aspx)

However, it can be clearly seen that an EntitySet does not implement this interface!

So how do I sort?

For context, I'm binding this set to a WPF ListView.

For wider context of problem I'm trying to solve please see this post.

回答1:

EntitySet<T> doesn't implement IBindingList...it provides a method to get an IBindingList. You need to call .GetNewBindingList() to get an instance of EntitySetBindingList<T>, which derives from SortableBindingList<T>, which is a BindingList<T>. EntitySetBindingList is just a wrapper around the original EntitySet<T> it was created from, so any modifications to it are modifications to the original EntitySet.

EDIT: Sorting with BindingList:

To sort with a BindingList, you need to expose some kind of interface to allow sorting. Sorting is supported within the BindingList<T> class, but its through protected properties and methods. It should be possible to expose an expressive sort method with a wrapper:

public class EntitySetBindingWrapper<T>: BindingList<T>
{
    public EntitySetBindingWrapper(BindingList<T> root) : base(root)
    {
    }

    public void Sort(Expression<Func<T, P>> expr, ListSortDirection direction)
    {
        if (expr == null)
            base.RemoveSortCore();

        MemberExpression propExpr = expr as MemberExpression;
        if (propExpr == null) throw new ArgumentException("You must provide a property", "expr");

        PropertyDescriptorCollection descriptorCol = TypeDescriptor.GetProperties(typeof(T));
        IEnumerable<PropertyDescriptor> descriptors = descriptorCol.Cast<PropertyDescriptor>();
        PropertyDescriptor descriptor = descriptors.First(pd => pd.Name == propExpr.Member.Name);

        base.ApplySortCore(descriptor, direction);
    }
}

You should then be able to sort like so:

var bindingWrapper = new EntitySetBindingWrapper(myEntitySet.GetNewBindingList());
bindingWrapper.Sort(e => e.MyProperty, ListSortDirection.Ascending);

listView.DataSource = bindingWrapper;

There might be additional implementation for the EntitySetBindingWrapper class...such as fortwarding any normally public methods on BindingList<T> to the one provided to the constructor.

回答2:

OrderByDecending!

var tags = objContext.Tags;
gvTester.DataSource = tags.OrderByDescending(x => x.TagID); ;
gvTester.DataBind();

回答3:

Could you do .ToList().OrderBy(x=>x.FieldToSortBy) ?

回答4:

Hainesy - judging by your comment on Vinny's post, I think you're missing his point... [I'm not presenting this as an answer to your question directly, I'm just elaborating on Vinny's point to clear up any possible confusion regarding that.]

Consider this object:

public class Person
{
    public string FirstName;
    public string MiddleInitial;
    public string LastName;

    public DateTime DateOfBirth { get; set; }

    public int Age
    {
        get
        {
            return (int)DateTime.Today.Subtract(DateOfBirth).TotalDays / 365;
        }
    }
}

now, assume I've got a list of Person set up called People

var people = new List<Person>();

And I've got a whole bunch of people in my list.

var sortedByLastName = people.OrderBy(o => o.LastName);
var sortedByFirstName = people.OrderBy(o => o.FirstName);
var sortedByAge = people.OrderBy(o => o.Age);
var sortedByAgeDesc = people.OrderByDescending(o => o.Age);
var sortedByLastThenFirst = people.OrderBy(o => o.LastName).ThenBy(o => o.FirstName);

That's for complex objects. If we've got a list of some primitive type, like a string:

var strings = new List<string>();

I want to sort them based on themselves - i.e. not by some property of my object

var sorted = strings.OrderBy(s => s);

This will sort on the object. You can also use the same idea if you're sorting complex objects that implement IComparable to sort by their default comparer.

An EntitySet can be sorted in a similar fashion, whether for a primitive type, or a complex object.

来源：https://stackoverflow.com/questions/925567/how-do-you-sort-an-entitysett

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