Error LINQ to Entities does not recognize the meth

问题:

This question already has an answer here:

• Why LINQ to Entities does not recognize the method 'System.String ToString()? 8 answers

I am working with MVC4 , Entityframewor and Jqgrid, when am fetching data from Database , i stucked with this error.Many of you said populate the id field to anothe var , but i a not getting where exactly to write it, and my Id field in Database is of Integer. so please do help me. u.Id is a Id field which i am accessing from EF, It showing this error. what is the alternate way, and where to put the new code. My Controller looks like

public JsonResult GetUserDetails(string sidx="Id", string sord="asc", int page=1, int rows=5)
{

    int pageIndex = Convert.ToInt32(page) - 1;
    int pageSize = rows;
    int totalRecords = db.Users.Count();
    int totalPages = (int)Math.Ceiling((float)totalRecords / (float)pageSize);
    var userdata = db.Users.OrderBy(sidx + " " + sord).Skip(pageIndex * pageSize).Take(pageSize);

    var jsonData = new
    {
        total = totalPages,
        page,
        records = totalRecords,

        rows = (from u in userdata
                select new
                {
                    i = u.Id,
                    cell = new string[]{**u.Id.ToString()**, u.Name,u.Designation,u.City}
                    //cell = new string[] { "", "", "", "" }
                }).ToArray()
    };
    return Json(jsonData);
}

I am Working this from past a day, and not getting relief from this .

回答1:

Method ToString() cannot be translated to SQL query. So you have several options:

1. You can get full entity userdata from db and map it to string array in .net code:

   var userdata = db.Users.OrderBy(sidx + " " + sord).Skip(pageIndex * pageSize).Take(pageSize).AsEnumerable();
   
   var jsonData = new
   {
   
       total = totalPages,
       page,
       records = totalRecords,
   
       rows = (
           from u in userdata
           select new
           {
               i = u.Id,
               cell = new string[]{**u.Id.ToString()**, u.Name,u.Designation,u.City}
               //cell = new string[] { "", "", "", "" }
           }).ToArray()
   };
   

2.You can use two Select(), first to get data from db, second to map it to your string array:

var userdata = db.Users.OrderBy(sidx + " " + sord).Skip(pageIndex * pageSize).Take(pageSize).Select(u=>new{u.Id, u.Name, u.Designation, u.City});

var jsonData = new
{

    total = totalPages,
    page,
    records = totalRecords,

    rows = (
        from u in userdata.AsEnumerable()
        select new
        {
            i = u.Id,
            cell = new string[]{u.Id.ToString(), u.Name,u.Designation,u.City}
        }).ToArray()
};