Question

我在存储过程中进行了分页分页。但是现在，我需要在LINQ中为以下对象做同样的事情。在以下场景中，用于实现排序和分页的最可读 LINQ查询是什么？

CODE

static  List<Employee> GetMyData(int pageIndex, int pageSize, out int itemCount, string sortField, string sortDirection )
{

    Employee e1= new Employee(){EmpID = 1, EmpName = "E1"};
    Employee e2= new Employee(){EmpID = 2, EmpName = "E2"};
    Employee e3= new Employee(){EmpID = 3, EmpName = "E3"};
    Employee e4= new Employee(){EmpID = 4, EmpName = "E4"};
    Employee e5= new Employee(){EmpID = 5, EmpName = "E5"};
    Employee e6= new Employee(){EmpID = 6, EmpName = "E6"};

    List<Employee> employees = new List<Employee>();
    employees.Add(e1);
    employees.Add(e2);
    employees.Add(e3);
    employees.Add(e4);
    employees.Add(e5);
    employees.Add(e6);

    itemCount = employees.Count;

    //Get subset of employees based on paging and sorting parameters
    //Sorting can be based on EmpID or EmpName
    List<Employee> currentPageEmployees = null;
    return currentPageEmployees;
}

调用方法

        int count = 0;
        List<Employee> e = GetMyData(0, 2, out count, "EmpID", "descending");

Answer 1

按任何字段排序只能使用动态linq http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

进行AFAIK

排序：

if (sortDirection == "ASC") 
    employees = employees.OrderBy(sortField).ToList();
else 
   employees = employees.OrderByDesceding(sortField).ToList();

寻呼：

var currentPageEmployees = sorted.Skip(pageindex*pageSize).Take(pageSize)

编辑：使用sortField和sortDirection更新代码

Answer 2

您可以使用自定义选择器将sortField解析为Employee类型的相应属性。然后，对于排序方向，我假设sortDirection是升序还是降序 - 如果是，那么bool可能更好？

鉴于这是一个例子：

var selector = new Func<Employee, object>(e => e.GetType().GetProperty(sortField).GetValue(e, null));
var query = sortDirection.Equals("descending", StringComparison.OrdinalIgnoreCase)
                ? employees.OrderByDescending(selector)
                : employees.OrderBy(selector);

List<Employee> currentPageEmployees = query
    .Skip(pageIndex * pageSize)
    .Take(pageSize)
    .ToList();

动态Linq扩展可能会使事情变得更加可读。

编辑：已删除投射

Answer 3

对于sorting，您可以使用linq的orderby方法指定要应用排序的参数。

 var result = employess.OrderBy(x=>x.Name);
 ar result = employess.OrderByDescending(x=>x.Name);

paging您可以像这样使用SKip和Take方法

 var queryResultPage = employess
                      .Skip(numberOfObjectsPerPage * pageNumber)
                      .Take(numberOfObjectsPerPage);

Answer 4

试试这个

List<Employee> currentPageEmployees = employees.OrderBy(p => ((sortField == "EmpID") ? p.EmpID : (((sortField == "EmpName") ? p.EmpName : (p.EmpID))))).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();

<强> refrence

Answer 5

其他人使用Skip和Take，这是可以的，但我们也可以使用Where：

enum SortDirection {
    Ascending,
    Descending
}

static  List<Employee> GetMyData(int pageIndex, int pageSize, out int itemCount, string sortField, SortDirection sortDirection )
{

    //.........
    //.........  

    int startIndex = pageIndex * pageSize; //pageIndex is Zero-based
    int endIndex = startIndex + pageSize;

    //Get subset of employees based on paging and sorting parameters
    //Sorting can be based on EmpID or EmpName <-- this is why I can use the ? below
    List<Employee> currentPageEmployees = 
          sortDirection == SortDirection.Ascending ? 
          employees.OrderBy(e=>sortField=="EmpID" ? e.EmpID : e.EmpName)
                   .Where((e,i)=>i>=startIndex&&i<endIndex)
          :
          employees.OrderByDescending(e=>sortField=="EmpID" ? e.EmpID : e.EmpName)
                   .Where((e,i)=>i>=startIndex&&i<endIndex);
    return currentPageEmployees;
}

根据参数获取员工子集

CODE

5 个答案: