jQuery DataTable和MVC服务器端处理

Question

So I have implemented Server-Side processing in MVC for jQuery Datatables, I am Showing 1 to 10 of 8,037 entries (with pagination). However when I navigate to the page with the table the first load takes far to long (5 to 10 seconds). In my controller I set it to only take 10 records (iDisplayLength) :

        var displayedProviders = filteredProviders
            .Skip(param.iDisplayStart)
            .Take(param.iDisplayLength);

So when I first navigate to the page with the table or I use pagination it should only load 10 records at a time.

Can anyone guide me to why the first load is taking such a long time? My fear is that its loading the entire table into the Json Request which is slowing it down at first. This wasnt what I had in mind when implementing server side processing. Is there a way around this? If I implement:

    var model = _db.CareProviders
.OrderBy(row => row.ProviderId).Skip((pageNumber - 1) * pageResults)
    .Take(pageResults).ToList();

This will only show 10 results and no more?

Model:

    public class jQueryDataTableParamModel
    {
        /// <summary>
        /// Request sequence number sent by DataTable,
        /// same value must be returned in response
        /// </summary>       
        public string sEcho { get; set; }

        /// <summary>
        /// Text used for filtering
        /// </summary>
        public string sSearch { get; set; }

        /// <summary>
        /// Number of records that should be shown in table
        /// </summary>
        public int iDisplayLength { get; set; }

        /// <summary>
        /// First record that should be shown(used for paging)
        /// </summary>
        public int iDisplayStart { get; set; }

        /// <summary>
        /// Number of columns in table
        /// </summary>
        public int iColumns { get; set; }

        /// <summary>
        /// Number of columns that are used in sorting
        /// </summary>
        public int iSortingCols { get; set; }

        /// <summary>
        /// Comma separated list of column names
        /// </summary>
        public string sColumns { get; set; }
    }
}

Controller:

    public ActionResult AjaxHandler(jQueryDataTableParamModel param)
    {
        var allProviders = _db.CareProviders.ToList();
        IEnumerable<CareProvider> filteredProviders;

        if (!string.IsNullOrEmpty(param.sSearch))
        {
            filteredProviders = _db.CareProviders.ToList()
                     .Where(c => c.ProviderId.Contains(param.sSearch)
                                 ||
                      c.CareServiceType.Contains(param.sSearch)
                                 ||
                                 c.CareServiceName.Contains(param.sSearch));
        }
        else
        {
            filteredProviders = allProviders;
        }
        var displayedProviders = filteredProviders
            .Skip(param.iDisplayStart)
            .Take(param.iDisplayLength);

        var result = from c in displayedProviders
                     select new[] { Convert.ToString(c.ProviderId), c.CareServiceType, c.CareServiceName, c.Email };
        return Json(new
        {
            sEcho = param.sEcho,
            iTotalRecords = allProviders.Count(),
            iTotalDisplayRecords = filteredProviders.Count(),
            aaData = result
        },
                         JsonRequestBehavior.AllowGet);

    }

Jquery DataTable Script:

<script type="text/javascript">
    $(function () {
        // Initialize Example 2
        // $('#example2').dataTable();
        $('#example2').dataTable({
            "bServerSide": true,
            "sAjaxSource": "AdminPanel/AjaxHandler",
            "bProcessing": true,
            "aoColumns": [
                            { "sName": "ProviderId" },
                            { "sName": "CareServiceType" },
                            { "sName": "CareServiceName" },
                            { "sName": "Email" }
            ]
        });
    });
</script>

Answer 1

I don't believe this is a datatables problem. In your code, the first line var allProviders = _db.CareProviders.ToList(); is immediately hitting your database and loading all of your providers into memory. Only after loading into memory are you then filtering with skip and take, so you are hitting the initial query execution overhead. To make things a little worse, if you have a filtering condition, you run filteredProviders = _db.CareProviders.ToList() which hits your database and does the whole thing over again.

Remember while linq employs deferred execution, calling ToList() tells it "OK, I want this now." It stops building your expression trees, hits your database, and dumps the result into your list, and any further filtering is done on the list itself.

Your initial premise is correct. running var model = _db.CareProviders .OrderBy(row => row.ProviderId).Skip((pageNumber - 1) * pageResults) .Take(pageResults).ToList(); will indeed only return the rows you want, as long as you are using a provider that understands skip and take (EF does).

Consolidate your allProviders and filteredProviders variables, and call ToList() only after you've applied all possible filters and your skip and take, and see if that improves your speed.

Answer 2

In the first line of the AjaxHandler method, there is var allProviders = _db.CareProviders.ToList(); which will load everything from the table. Is it the large one? ... If so, that is your problem.

Also the line filteredProviders = _db.CareProviders.ToList() will load everything from the table and materialize that. The Where will be executed on the materialized data and also the Take method later in the code will take the small portion from already materialized data (the same reason).

It is the selection from the DB and the materialization what is taking a long time.