C# linq and sorting

Question

对于linq，我想将order by与特定列一起使用，但我需要两个开关，因为我不知道如何在一个中使用desc或asc

public class CustomersRepository : RepositoryBase<Customers>
{
public List<Customers> GetAll(CustomersProperties property, SortEnum sortEnum, int page, int limit)
{
var query = _context.Set<Customers>();
switch (sortEnum)
{
case SortEnum.Ascending:
switch (property)
{
case CustomersProperties.Name:
query = query.OrderBy(x => x.Name);
break;
case CustomersProperties.Surname:
query = query.OrderBy(x => x.Lastname);
break;
default:
throw new ArgumentOutOfRangeException("property");
}
break;
case SortEnum.Descending:
break;
default:
throw new ArgumentOutOfRangeException("sortEnum");
}
return query.Skip(page * limit)
.Take(limit).ToList();
}
}

没有两个开关箱可能吗？

Answer 1

请注意，query.OrderBy(x => x.Name);不会做任何事情，因为排序的集合是从OrderBy返回的，并且您没有捕获该返回。

也就是说，林克没有办法"动态"选择方向。然而，条件开关将是一个小清洁器。另一种选择是捕获变量中的排序表达式：

Expreccion<Func<Customers, string>> propExp;
switch (property)
{
case CustomersProperties.Name:
propExp = ((Customers)x => x.Name)            
break;
case CustomersProperties.Surname:
propExp = ((Customers)x => x.Lastname);
break;
default:
throw new ArgumentOutOfRangeException("property");
}
query = sortEnum == SortEnum.Ascending 
? query.OrderBy(propExp);
: query.OrderByDescending(propExp);

Answer 2

您可以自己进行过载，如下所示：

public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(
this IQueryable<TSource> source,
Expression<Func<TSource, TKey>> keySelector, SortEnum sort) {
switch (sort) {
case SortEnum.Ascending:
return source.OrderBy(keySelector);
case SortEnum.Descending:
return source.OrderByDescending(keySelector);
default:
throw new ArgumentOutOfRangeException("sort");
}
}

// later on..
query = query.OrderBy(x => x.LastName, sortEnum);

Answer 3

您可以先准备sortProperty表达式，然后将其与OrderBy或OrderByDescending:一起使用

public List<Customers> GetAll(CustomersProperties property, SortEnum sortEnum, int page, int limit)
{
var query = _context.Set<Customers>();
Expression<Func<Customers, string>> sortProperty;
switch (property)
{
case CustomersProperties.Name:
sortProperty = x => x.Name;
break;
case CustomersProperties.Surname:
sortProperty = x => x.Lastname;
break;
default:
throw new ArgumentOutOfRangeException("property");
}
switch (sortEnum)
{
case SortEnum.Ascending:
query = query.OrderBy(sortProperty);
break;
case SortEnum.Descending:
query = query.OrderByDescending(sortProperty);
break;
default:
throw new ArgumentOutOfRangeException("sortEnum");
}
return query.Skip(page * limit)
.Take(limit).ToList();
}