How to change orderby on postback for LINQ to SQL query

Question

I have a drop down list set to auto post back which needs to return a list of products in the specified order. I thought I could just put that query in its own method and use a parameter to specify the orderby, but I cannot get it to work.

Here is an example:

protected void Show_Products(int item)
    {
        using (storeDataContext db = new storeDataContext())
        {
           string query = "";
            switch (item)
            {
                case 1:
                    query ="x.Name";
                    break;
                case 2:
                    query = "x.MSRP";
                    break;
                default:
                    break;
            }
            var q = db.Items.OrderBy(x=> query).Select(x => x);
            foreach(var n in q)
             {
               Do work
             }
           }
       }

And the drop down list method that gets called on postback:

protected void ddlSortBy_SelectedIndexChanged(object sender, EventArgs e)
    {
        int value =int.Parse(ddlSortBy.SelectedValue);
        Show_Products(value);
    }

How about posting what you tried that didn't work? It's not clear what you were trying to do. — Adam Robinson, Feb 10 '11 at 03:25
User clicks drop down, chooses price and the query above dynamically changes. Putting x.MSRP in a string and passing that variable in place of x.Name doesn't work. — The Muffin Man, Feb 10 '11 at 03:31
in that case, a duplicate of [Dynamic LINQ OrderBy ](http://stackoverflow.com/questions/41244/dynamic-linq-orderby) — Kirk Woll, Feb 10 '11 at 03:42

score 1 · Answer 1 · answered Feb 10 '11 at 04:00

I took one look at that book of code someone linked and knew there was a way to do it. Low and behold I was right.

protected void Show_Products(int item)
{
    using (storeDataContext db = new storeDataContext())
    {
       var q = db.Items.OrderBy(x=> x.Name).Select(x => x);
        switch (item)
        {
            case 1:
                var q = db.Items.OrderBy(x=> x.Name).Select(x => x);
                break;
            case 2:
                q = db.Items.OrderBy(x => x.MSRP).Select(x => x);
                break;
            default:
                break;
        }

        foreach(var n in q)
         {
           Do work
         }
       }
   }

I initially set var q to a query for initialization, but it doesn't matter because this method will be passed a parameter which will change it.

It may not be the most elegant way, but for only a few options I think it is doable.

you can go `var q = db.Items;` then in Switch `q = q.OrderBy(x ...` — PostMan, Feb 10 '11 at 04:05

score 1 · Accepted Answer · answered Feb 10 '11 at 04:09

1

var q = from p in db.Items
        select q;

switch(item)
{
    case 1:
        q.OrderBy(x=> x.Name);
        break;
    case 2:
        q.OrderBy(x=> x.MSRP);
        break;
    default:
        break;

}

foreach(var n in q)
{
    // Do work
}

answered Feb 10 '11 at 04:09

Brettski

19,351
15
74
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This is interesting, I didn't think about doing it this way. – The Muffin Man Feb 10 '11 at 05:27

Shekhar_Pro · Answer 3 · 2011-02-10T03:56:41.833

0

Sorry, but what you are trying to do is using a Literal "x.Name" and "x.MSRP" to access methods.. you don't do it unless you are using Reflection to get Method and Properties.

edited Feb 10 '11 at 03:56

answered Feb 10 '11 at 03:44

Shekhar_Pro

18,056
9
55
79

How to change orderby on postback for LINQ to SQL query

3 Answers3