如何使用linq按多个字段排序?

本文介绍了如何使用linq按多个字段排序?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在创建一个模拟数据源，希望能够在该数据源上传递SortExpressions列表.

I'm creating a mock data source that I want to be able to pass in a list of SortExpressions on.

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

更新，其中包含Jon Skeet的代码以及整个类. GetData()只是用x条记录填充对象.

Update with Jon Skeet's code and also the entire class. GetData() is just populating the object with x number of records.

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>(); } }

似乎什么也没做.编译，没有错误，只是没有排序.有什么想法吗?

Doesn't seem to be doing anything. Compiles, no errors, just no sort. Any ideas?

推荐答案

有两个问题.第一个是其他人提到的-您需要使用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"顺序.第一次订购后，您真的想要ThenBy.不幸的是，这使它变得非常丑陋.重构后仍然很丑陋，但太还不错...

There are two problems. The first is the one others have alluded to - you need to use the value returned by OrderBy etc. The second is that each time you call OrderBy, that's adding a new "primary" ordering. You really want ThenBy after the first ordering has been applied. That makes it pretty ugly, unfortunately. It's still pretty ugly after a refactoring, but not too bad...

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; }