Question

我正在尝试编写一个linq to sql方法来处理ajax网格的排序，分页和过滤。我创建了一个具有TotalRecordCount的部分类Employee，因为我需要将其传递给javascript来设置寻呼机。问题是它不会构建，因为我无法设置AnonymousType＃1.TotalRecordCount，它是只读的。然而，如果我“选择新的员工”，那么它将抛出异常 - “不允许在查询中明确构造实体类型'InVision.Data.Employee'。”。

这是代码......

public string GetPageJSON(string sortColumn, string sortDirection, int pageNumber, int pageSize, EmployeeSearch search)
        {
            var query = from e in db.Employees
                        select new
                        {
                            EmployeeID = e.EmployeeID,
                            FirstName = e.FirstName,
                            LastName = e.LastName,
                            LoginName = e.LoginName,
                            IsLockedOut = e.IsLockedOut,
                            TotalRecordCount = e.TotalRecordCount
                        };
            //searching.
            if (search.FirstName.Length > 0) query = query.Where(e => e.FirstName.Contains(search.FirstName));
            if (search.LastName.Length > 0) query = query.Where(e => e.LastName.Contains(search.LastName));
            if (search.LoginName.Length > 0) query = query.Where(e => e.LoginName.Contains(search.LoginName));
            if (search.Status.Length > 0) query = query.Where(e => (search.Status == "Active" && !e.IsLockedOut) 
                || (search.Status == "Inactive" && e.IsLockedOut));
            //sorting.
            query = query.OrderBy(sortColumn, sortDirection);
            //get total record count.
            int totalRecordCount = query.Count();
            //paging.
            query = query.Skip((pageNumber - 1) * pageSize).Take(pageSize);
            //set total record count.
            var list = query.ToList();
            if (list.Count > 0)
            {
                list[0].TotalRecordCount = totalRecordCount; //throws exception
            }
            //return json.
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            return serializer.Serialize(list);
        }

Answer 1

您需要选择原始对象，而不是将它们映射到新对象（无论是相同类型还是匿名类型）。

替换它：

var query = from e in db.Employees
                        select new
                        {
                            EmployeeID = e.EmployeeID,
                            FirstName = e.FirstName,
                            LastName = e.LastName,
                            LoginName = e.LoginName,
                            IsLockedOut = e.IsLockedOut,
                            TotalRecordCount = e.TotalRecordCount
                        };

有了这个：

var query = db.Employees.AsQueryable();

然后稍后更换：

var list = query.ToList();
if (list.Count > 0)
{
    list[0].TotalRecordCount = totalRecordCount;
}

有了这个：

var list = from e in query
           select new
           {
               EmployeeID = e.EmployeeID,
               FirstName = e.FirstName,
               LastName = e.LastName,
               LoginName = e.LoginName,
               IsActive = !e.IsLockedOut,
               TotalRecordCount = totalRecordCount
           };

我认为这应该是一切。如果JavaScriptSerializer需要List，请确保您按照以下方式使用return serializer.Serialize(list.ToList());

Answer 2

我最终使用自定义视图类来实现此功能......

partial class EmployeeView
    {
        public int EmployeeID { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string LoginName { get; set; }
        public bool IsActive { get; set; }
        public int TotalRecordCount { get; set; }
    }

public string GetPageJSON(string sortColumn, string sortDirection, int pageNumber, int pageSize, EmployeeSearch search)
        {
            var query = from e in db.Employees
                        select new EmployeeView
                        {
                            EmployeeID = e.EmployeeID,
                            FirstName = e.FirstName,
                            LastName = e.LastName,
                            LoginName = e.LoginName,
                            IsActive = !e.IsLockedOut,
                            TotalRecordCount = 0
                        };
            //searching.
            if (search.FirstName.Length > 0) query = query.Where(e => e.FirstName.Contains(search.FirstName));
            if (search.LastName.Length > 0) query = query.Where(e => e.LastName.Contains(search.LastName));
            if (search.LoginName.Length > 0) query = query.Where(e => e.LoginName.Contains(search.LoginName));
            if (search.Status.Length > 0) query = query.Where(e => (search.Status == "Active" && e.IsActive) 
                || (search.Status == "Inactive" && !e.IsActive));
            //sorting.
            query = query.OrderBy(sortColumn, sortDirection);
            //get total record count.
            int totalRecordCount = query.Count();
            //paging.
            query = query.Skip((pageNumber - 1) * pageSize).Take(pageSize);
            //set total record count.
            var list = query.ToList();
            if (list.Count > 0)
            {
                list[0].TotalRecordCount = totalRecordCount;
            }
            //return json.
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            return serializer.Serialize(list);
        }

Linq to SQL问题 - 指定列然后修改列

2 个答案: