CODEWITHSUNDEEP
c#asp.net-mvclist
Willy
Willy

Reputation: 1729

how to keep order of data in list

I have a dropdown with checkboxes in it. Lets say I've the following data displayed in the dropdown:

<select multiple="multiple" name="Products" id="Products">
    <option value="1">A</option>
    <option value="2">B</option>
    <option value="3">C</option>
    <option value="4">D</option>
</select>

Then I checked record no 4, 2, 3 and submit the page. In the controller I change the int[] arrIDs into List<int> listIDs to collect the Products from the database.

List<Product> products = db.Product
    .Where(d => listIDs.Contains(d.ProductID))
    .ToList();

But I've got the products is sorted in the following sequence 2, 3, 4. I want to keep the sequence based on the records that I've selected in the page 4, 2, 3. How to solve it?

Upvotes: 1

Views: 441

Answers (3)

devuxer
devuxer

Reputation: 42354

You need to do a GroupJoin:

List<Product> products = listIDs
    .GroupJoin(
        db.Product,
        x => x,
        y => y.ProductID,
        (x, ys) => ys.First())
    .ToList();

This performs the equivalent of a "left outer join", which maintains the values of listIDs in their original order, then matches each listID with the corresponding product in the table.

Note: this code assumes there is always a single matching ProductID in the database.

Upvotes: 0

Ken Clubok
Ken Clubok

Reputation: 1238

The multiple select box does not preserve the order of clicks.

You'll need to use Javascript to watch the clicks, and record the order into a hidden field, which will be submitted with the form. Or give up on the multiple select box, and use a component like this one. (That's not a .NET component, but I suspect that similar ones exist.)

Upvotes: 1

Tim Schmelter
Tim Schmelter

Reputation: 460108

You can use List.IndexOf to get the index for the order:

List<Product> products = db.Product
    .Where(d => listIDs.Contains(d.ProductID))
    .AsEnumerable()
    .OrderBy(d => listIDs.IndexOf(d.ProductID))
    .ToList();

Upvotes: 3

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