Question

我正在创建一个模拟数据源，我希望能够在SortExpressions列表中传递。

public SortExpression(string name, SortDirection direction)
{
     this.name = name;
     this.direction = direction;
}

使用Jon Skeet的代码以及整个班级

更新。 GetData（）只是用x个记录填充对象。

public class Data
{

public int Id { get; set; }
public Guid gId { get; set; }
public string Name { get; set; }
public string Phone { get; set; }
public string Address { get; set; }
public DateTime Created { get; set; }
public string SortMe { get; set; }
public static List<Data> GetFakeData(int start, int numberToFetch, IList<SortExpression> sortExpressions, IList<FilterExpression> filterExpressions, out int totalRecords)
{
    DataCollection items = GetData();
    IEnumerable<Data> query = from item in items select item;

    bool sortExpressionsExist = sortExpressions != null;
    if (sortExpressionsExist)
    {
        // Won't be read in the first iteration; will be written to
        IOrderedEnumerable<Data> orderedQuery = null;
        for (int i = 0; i < sortExpressions.Count; i++)
        {
            // Avoid single variable being captured: capture one per iteration.
            // Evil bug which would be really hard to find :)
            int copyOfI = i;
            // Tailor "object" depending on what GetProperty returns.
            Func<Data, object> expression = item =>
                  item.GetType().GetProperty(sortExpressions[copyOfI].Name);

            if (sortExpressions[i].Direction == SortDirection.Ascending)
            {
                orderedQuery = (i == 0) ? query.OrderBy(expression)
                                        : orderedQuery.ThenBy(expression);
            }
            else
            {
                orderedQuery = (i == 0) ? query.OrderByDescending(expression)
                                        : orderedQuery.ThenByDescending(expression);
            }
        }
        query = orderedQuery;
    }

    bool filterExpressionsExist = filterExpressions != null;
    if (filterExpressionsExist)
    {
        foreach (var filterExpression in filterExpressions)
        {
            query.Where(item => item.GetType().GetProperty(filterExpression.ColumnName).GetValue(item, null).ToString().Contains(filterExpression.Text));
        }
    }
    totalRecords = query.Count();


       return query.Skip(start).Take(numberToFetch).ToList<Data>();
    }
}

似乎没有做任何事情。编译，没有错误，只是没有排序。有什么想法吗？

Answer 1

有两个问题。第一个是其他人提到的 - 你需要使用OrderBy等返回的值。第二个是每次调用OrderBy时，都会添加一个新的“主要”排序。在第一次订购之后，你真的想要ThenBy。不幸的是，这让它非常丑陋。重构后仍然非常丑陋，但太不好......

IEnumerable<Data> query = from item in items select item;
if (sortExpressionsExist)
{
    // Won't be read in the first iteration; will be written to
    IOrderedEnumerable<Data> orderedQuery = null;
    for (int i = 0; i < sortExpressions.Count; i++)
    {
        // Avoid single variable being captured: capture one per iteration.
        // Evil bug which would be really hard to find :)
        int copyOfI = i;
        // Tailor "object" depending on what GetProperty returns.
        Func<Data, object> expression = item => 
              item.GetType()
                  .GetProperty(sortExpressions[copyOfI].Name)
                  .GetValue(item, null);

        if (sortExpressions[i].Direction == SortDirection.Ascending)
        {
            orderedQuery = (i == 0) ? query.OrderBy(expression)
                                    : orderedQuery.ThenBy(expression);
        }
        else
        {
            orderedQuery = (i == 0) ? query.OrderByDescending(expression)
                                    : orderedQuery.ThenByDescending(expression);
        }
    }
    query = orderedQuery;
}

Answer 2

OrderBy返回一个新的IEnumerable，所以你需要做类似的事情：

IEnumerable<Data> results 
    = query.OrderBy(item => item.GetType().GetProperty(sortExpressions[i].Name));

Answer 3

OrderBy / OrderByDescending'运算符'就像String.ToUpper（）一样工作，即他们接受你调用它的东西，并产生一个具有你要求的“副本”。

换句话说，而不是说：

query.Orderby(item->item.X)

你应该做

query = query.Orderby(item->item.X)

或

sortedResult = query.Orderby(item->item.X)

[正如Jon Skeet指出的那样，在答案中使用ThenBy / ThenByDescending]

Answer 4

查询不可变，因此OrderBy返回一个新对象。您需要拨打同一个电话，但在开头添加“query =”。

query = query.OrderBy(item => item.GetType().GetProperty(sortExpressions[i].Name));

Answer 5

OrderBy on IEnumerable返回一个IOrderedEnumerable。它没有对它们进行排序。所以从.OrderBy获得返回值，你会没事的。

Answer 6

这将有效：

YourCollection.Orderby(item => item.Property1).ThenBy(item => item.Property2);

如何使用linq按多个字段排序？

6 个答案: