C# MVC2 Jqgrid - what is the correct way to do server side paging?

Question

I have a jqgrid where the database table has a few thousand rows, but the jqrid shows only 15 at a time.

It should be displaying very quickly (it doesnt take long to query 15 rows). But instead it takes 10 - 20 seconds, which indicates to that it is retrieving the entire table each time.

The grid is defined like this:

$("#Products").jqGrid({
url: url, mtype: "get", datatype: "json", jsonReader: {
    root: "Rows", page: "Page", total: "Total", records: "Records", repeatitems: false,
    userdata: "UserData",id: "Id"},
colNames: ["Product Id","Product Code", ... etc ],
colModel: [{ name: "Id", ... etc}],
viewrecords: true, height: 400, width: 800, pager: $("#jqgPager"),
rowNum: 15, rowList: [50, 100, 200], 
autowidth: true, multiselect: false

And the server side (MVC2 action) does this:

var model = (from p in products
    select new
    {
    p.Id, p.ProductCode, p.ProductDescription,
    AllocatedQty = p.WarehouseProducts.Sum(wp => wp.AllocatedQuantity),
    QtyOnHand = p.WarehouseProducts.Sum(wp => wp.OnHandQuantity)
    }).AsQueryable();

    JsonResult json = Json(model.ToGridData(
        page, rows, orderBy, "", 
        new[] { "Id", "ProductCode", "ProductDescription", "AllocatedQty", "QtyOnHand" }),
            JsonRequestBehavior.AllowGet);

And finally the model.ToGridData extension method does this:

var data =_service.GetAll(); 
var page = data.Skip((index) * pageSize).Take(pageSize);
list.Add(page.AsEnumerable);

And I'm a bit lost as to where the problem lies:

• Have I set the jqgrid paging options incorrectly?
• Have I written bad Linq that pulls all rows regardless? eg does the Sum() cause all rows to be read?
• Have I done the .Skip().Take() incorrectly?
• Have I missed something else entirely?

EDIT

When comparing my code to the example posted by Oleg I can see that I do things in this order:

1. getAll
2. select model fields
3. page

Wheras Olegs sample seems to be in this order:

1. getAll
2. page
3. select model fields

So I've changed to this much simpler implementation:

public ActionResult GetProductList(int page, int rows, string sidx, string sord, 
string searchOper, string searchField, string searchString)
{
        List<Product> products = _productService.GetAllProducts();
        int totalRecords = products.Count();

        var pagedData = products.Skip((page > 0 ? page - 1 : 0) * rows).Take(rows);

        var model = (from p in pagedData
                    select new
                    {
                        p.Id, p.ProductCode, p.ProductDescription,
                        Barcode = string.Empty, UnitOfMeasure = string.Empty,
                        p.PackSize, AllocatedQty = string.Empty,
                        QtyOnHand = string.Empty }).ToList();

        var jsonData = new
        {
            total = page, records = totalRecords,
            page = (totalRecords + rows - 1) / rows, rows = model
        };

        return Json(jsonData, JsonRequestBehavior.AllowGet);
}

However this has a new problem:

A circular reference was detected while serializing an object of type
'System.Data.Entity.DynamicProxies.Product_FA935D3899E2...

The only difference I can see now with Oleg's sample is that his getAll returns IQueryable where mine is just List.

Answer 1

You should post more full code. The model.ToGridData is not defined in the current code for example. How you caclulate index from the imput patrameters and so on are also unclear. Only having model.ToGridData() one can say whether the output which your program produce are correspond to the jsonReader which you define.

I recommend you to look this old answer, where both paging and sorting are used. In one more answer you will find more references to code examples.