我在字符串中有“按属性排序”的名称。我需要使用Lambda/Linq对对象列表进行排序。
Ex:
public class Employee
{
public string FirstName {set; get;}
public string LastName {set; get;}
public DateTime DOB {set; get;}
}
public void Sort(ref List<Employee> list, string sortBy, string sortDirection)
{
//Example data:
//sortBy = "FirstName"
//sortDirection = "ASC" or "DESC"
if (sortBy == "FirstName")
{
list = list.OrderBy(x => x.FirstName).toList();
}
}
与其使用一堆if来检查字段名(sortBy)，还有一种更干净的排序方式吗 排序是否知道数据类型?
当前回答
我是这样解决问题的:
List<User> list = GetAllUsers(); //Private Method
if (!sortAscending)
{
list = list
.OrderBy(r => r.GetType().GetProperty(sortBy).GetValue(r,null))
.ToList();
}
else
{
list = list
.OrderByDescending(r => r.GetType().GetProperty(sortBy).GetValue(r,null))
.ToList();
}
其他回答
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Linq.Expressions;
public static class EnumerableHelper
{
static MethodInfo orderBy = typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(x => x.Name == "OrderBy" && x.GetParameters().Length == 2).First();
public static IEnumerable<TSource> OrderBy<TSource>(this IEnumerable<TSource> source, string propertyName)
{
var pi = typeof(TSource).GetProperty(propertyName, BindingFlags.Public | BindingFlags.FlattenHierarchy | BindingFlags.Instance);
var selectorParam = Expression.Parameter(typeof(TSource), "keySelector");
var sourceParam = Expression.Parameter(typeof(IEnumerable<TSource>), "source");
return
Expression.Lambda<Func<IEnumerable<TSource>, IOrderedEnumerable<TSource>>>
(
Expression.Call
(
orderBy.MakeGenericMethod(typeof(TSource), pi.PropertyType),
sourceParam,
Expression.Lambda
(
typeof(Func<,>).MakeGenericType(typeof(TSource), pi.PropertyType),
Expression.Property(selectorParam, pi),
selectorParam
)
),
sourceParam
)
.Compile()(source);
}
public static IEnumerable<TSource> OrderBy<TSource>(this IEnumerable<TSource> source, string propertyName, bool ascending)
{
return ascending ? source.OrderBy(propertyName) : source.OrderBy(propertyName).Reverse();
}
}
另一个，这次是IQueryable:
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
public static class IQueryableHelper
{
static MethodInfo orderBy = typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(x => x.Name == "OrderBy" && x.GetParameters().Length == 2).First();
static MethodInfo orderByDescending = typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(x => x.Name == "OrderByDescending" && x.GetParameters().Length == 2).First();
public static IQueryable<TSource> OrderBy<TSource>(this IQueryable<TSource> source, params string[] sortDescriptors)
{
return sortDescriptors.Length > 0 ? source.OrderBy(sortDescriptors, 0) : source;
}
static IQueryable<TSource> OrderBy<TSource>(this IQueryable<TSource> source, string[] sortDescriptors, int index)
{
if (index < sortDescriptors.Length - 1) source = source.OrderBy(sortDescriptors, index + 1);
string[] splitted = sortDescriptors[index].Split(' ');
var pi = typeof(TSource).GetProperty(splitted[0], BindingFlags.Public | BindingFlags.FlattenHierarchy | BindingFlags.Instance | BindingFlags.IgnoreCase);
var selectorParam = Expression.Parameter(typeof(TSource), "keySelector");
return source.Provider.CreateQuery<TSource>(Expression.Call((splitted.Length > 1 && string.Compare(splitted[1], "desc", StringComparison.Ordinal) == 0 ? orderByDescending : orderBy).MakeGenericMethod(typeof(TSource), pi.PropertyType), source.Expression, Expression.Lambda(typeof(Func<,>).MakeGenericType(typeof(TSource), pi.PropertyType), Expression.Property(selectorParam, pi), selectorParam)));
}
}
你可以传递多个排序条件，像这样:
var q = dc.Felhasznalos.OrderBy(new string[] { "Email", "FelhasznaloID desc" });
您可以使用反射来访问该属性。
public List<Employee> Sort(List<Employee> list, String sortBy, String sortDirection)
{
PropertyInfo property = list.GetType().GetGenericArguments()[0].
GetType().GetProperty(sortBy);
if (sortDirection == "ASC")
{
return list.OrderBy(e => property.GetValue(e, null));
}
if (sortDirection == "DESC")
{
return list.OrderByDescending(e => property.GetValue(e, null));
}
else
{
throw new ArgumentOutOfRangeException();
}
}
笔记
你为什么要传阅这份名单? 您应该使用枚举作为排序方向。 如果传递一个lambda表达式，可以得到一个更简洁的解决方案 指定要排序的属性，而不是以字符串形式指定属性名。 在我的例子中，list == null将导致NullReferenceException，您应该捕获这种情况。
加上@Samuel和@bluish所做的。这要短得多，因为在这种情况下Enum是不必要的。当升位是期望的结果时，作为额外的奖励，您只能传递2个参数而不是3个参数，因为true是第三个参数的默认答案。
public void Sort<TKey>(ref List<Person> list, Func<Person, TKey> sorter, bool isAscending = true)
{
list = isAscending ? list.OrderBy(sorter) : list.OrderByDescending(sorter);
}
不幸的是，Rashack提供的解决方案不适用于值类型(int、enum等)。
对于任何类型的属性，这是我发现的解决方案:
public static Expression<Func<T, object>> GetLambdaExpressionFor<T>(this string sortColumn)
{
var type = typeof(T);
var parameterExpression = Expression.Parameter(type, "x");
var body = Expression.PropertyOrField(parameterExpression, sortColumn);
var convertedBody = Expression.MakeUnary(ExpressionType.Convert, body, typeof(object));
var expression = Expression.Lambda<Func<T, object>>(convertedBody, new[] { parameterExpression });
return expression;
}
Sort使用IComparable接口，如果该类型实现了该接口。 你可以通过实现一个自定义IComparer来避免if:
class EmpComp : IComparer<Employee>
{
string fieldName;
public EmpComp(string fieldName)
{
this.fieldName = fieldName;
}
public int Compare(Employee x, Employee y)
{
// compare x.fieldName and y.fieldName
}
}
然后
list.Sort(new EmpComp(sortBy));