如何在 C# 中为 OrderBy 有条件地设置 LINQ OrderByDescending 中的列？

Question

如何使用 LINQ OrderBy 子句有条件地对列进行排序。

ex-我有一个属性 Filter.OrderBy 和 Filter.Order 。在OrderBy 中可能有很多 ex>姓名、地址、城市等，Order 将升序或降序，但我不确定如何使用条件列对其进行排序

请参考以下代码-

IQueryable<Filter> query;

PropertyInfo prop = typeof(Filter).GetProperty(Filter.OrderBy);  

if (Filter.Order ==" Ascending"){
  query = query.OrderBy ( x = > prop.GetValue(x,null));
}
else if (Filter.Order ==" Descending"){
  query = query.OrderByDescending ( x = > prop.GetValue(x,null));
}

但查询失败。我不确定是什么问题我可以使用反射看到 prop 属性 但表达式 prop.GetValue 不起作用。

请帮我解决这个问题

Answer 1

您可以使用库System.Linq.Dynamic.Core，它支持动态查询、选择和排序。

示例代码：

var q = new List<Person>
{
    new Person{Name = "C", Age = 30 },
    new Person{Name = "A", Age = 7 },
    new Person{Name = "B", Age = 5 }
}.AsQueryable();

var x1 = q.OrderBy("Name asc");

var a1 = q.OrderBy("Age desc");

有关完整的工作示例，请参阅dotnetfiddle

Answer 2

我创建了这个示例，也许它可以帮助你

IEnumerable<Person> q = new List<Person>
{
    new Person{Name = "C", Age = 3 },
    new Person{Name = "A", Age = 7 },
    new Person{Name = "B", Age = 5 }
};
var props = new[] { "Name", "Age" };
var orders = new[] { "Ascending", "Descending" };

foreach (var prop in props)
{
    var property = typeof(Person).GetProperty(prop);
    foreach (var order in orders)
    {
        IEnumerable<Person> q2 = null;
        if (order == "Ascending")
        { q2 = q.OrderBy(p => property.GetValue(p)); }
        else
        { q2 = q.OrderByDescending(p => property.GetValue(p)); }

        Console.WriteLine("Property: {0}, Order: {1}", prop, order);
        foreach (var p in q2)
        {
            Console.WriteLine("Name: {0}, Age: {1}", p.Name, p.Age);
        }
        Console.WriteLine();
    }
}

输出：

Property: Name, Order: Ascending
Name: A, Age: 7
Name: B, Age: 5
Name: C, Age: 3

Property: Name, Order: Descending
Name: C, Age: 3
Name: B, Age: 5
Name: A, Age: 7

Property: Age, Order: Ascending
Name: C, Age: 3
Name: B, Age: 5
Name: A, Age: 7

Property: Age, Order: Descending
Name: A, Age: 7
Name: B, Age: 5
Name: C, Age: 3

Answer 3

将属性设置为参数。 示例：

var param = "Address";    
var propertyInfo = typeof(Filter).GetProperty(param);    
var orderByAddress = items.OrderBy(x => propertyInfo.GetValue(x, null));

Answer 4

public static class LinqUtils
    {
        /// <summary>
        /// Orders the by.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">The source.</param>
        /// <param name="propertyName">Name of the property.</param>
        /// <param name="direction">The direction.</param>
        /// <returns></returns>
        public static IOrderedMongoQueryable<T> OrderBy<T>(this IMongoQueryable<T> source, string propertyName, OrderDirection direction)
        {
            switch (direction)
            {
                case OrderDirection.ASC:
                    return source.OrderBy(ToLambda<T>(propertyName));

                case OrderDirection.DESC:
                    return source.OrderByDescending(ToLambda<T>(propertyName));

                default:
                    return source.OrderBy(ToLambda<T>(propertyName));
            }

        }

        /// <summary>
        /// Orders the by.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">The source.</param>
        /// <param name="propertyName">Name of the property.</param>
        /// <param name="direction">The direction.</param>
        /// <returns></returns>
        public static IOrderedMongoQueryable<T> OrderBy<T>(this IMongoQueryable<T> source, string propertyName, int direction)
        {
            var dir = (OrderDirection)direction;

            switch (dir)
            {
                case OrderDirection.ASC:
                    return source.OrderBy(ToLambda<T>(propertyName));

                case OrderDirection.DESC:
                    return source.OrderByDescending(ToLambda<T>(propertyName));

                default:
                    return source.OrderBy(ToLambda<T>(propertyName));
            }

        }


        /// <summary>
        /// Orders the by.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">The source.</param>
        /// <param name="propertyName">Name of the property.</param>
        /// <returns></returns>
        public static IOrderedMongoQueryable<T> OrderBy<T>(this IMongoQueryable<T> source, string propertyName)
        {
            return source.OrderBy(ToLambda<T>(propertyName));
        }

        /// <summary>
        /// Orders the by descending.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">The source.</param>
        /// <param name="propertyName">Name of the property.</param>
        /// <returns></returns>
        public static IOrderedMongoQueryable<T> OrderByDescending<T>(this IMongoQueryable<T> source, string propertyName)
        {
            return source.OrderByDescending(ToLambda<T>(propertyName));
        }

        /// <summary>
        /// Wheres the specified property name.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source">The source.</param>
        /// <param name="propertyName">Name of the property.</param>
        /// <param name="stringToSource">The string to source.</param>
        /// <returns></returns>
        public static IMongoQueryable<T> Where<T>(this IMongoQueryable<T> source, string propertyName, string stringToSource)
        {
            return source.Where(ToLambdaWhere<T>(propertyName, stringToSource));
        }


        /// <summary>
        /// Wheres the text.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="query">The query.</param>
        /// <param name="field">The field.</param>
        /// <param name="search">The search.</param>
        /// <returns></returns>
        public static IMongoQueryable<T> WhereText<T>(this IMongoQueryable<T> query, Expression<Func<T, object>> field, string search)
        {

            search = Regex.Escape(search);
            var filter = Builders<T>.Filter.Text(search);
            var member = HelpersLinq.PropertyName<T>(field);

            var regexFilter = string.Format("^{0}.*", search);
            var filterRegex = Builders<T>.Filter.Regex(member, BsonRegularExpression.Create(new Regex(regexFilter, RegexOptions.IgnoreCase)));

            return query.Where(_ => filter.Inject() && filterRegex.Inject());
        }

        /// <summary>
        /// Converts to lambda.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="propertyName">Name of the property.</param>
        /// <returns></returns>
        private static Expression<Func<T, object>> ToLambda<T>(string propertyName)
        {
            var parameter = Expression.Parameter(typeof(T));
            var property = Expression.Property(parameter, propertyName);
            var propAsObject = Expression.Convert(property, typeof(object));

            return Expression.Lambda<Func<T, object>>(propAsObject, parameter);
        }

        /// <summary>
        /// Converts to lambdawhere.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="propertyName">Name of the property.</param>
        /// <param name="stringToSearch">The string to search.</param>
        /// <returns></returns>
        private static Expression<Func<T, bool>> ToLambdaWhere<T>(string propertyName, string stringToSearch)
        {
            //var parameter = Expression.Parameter(typeof(T));

            // Create a parameter to use for both of the expression bodies.
            var parameter = Expression.Parameter(typeof(T), "x");
            // Invoke each expression with the new parameter, and combine the expression bodies with OR.
            var predicate = Expression.Lambda<Func<T, bool>>(Expression.Call(Expression.PropertyOrField(parameter, propertyName), "Contains", null, Expression.Constant(stringToSearch)), parameter);

            return predicate;
        }
    }


    public static class HelpersLinq
    {
        public static string PropertyName<T>(Expression<Func<T, object>> expression)
        {
            var member = expression.Body as MemberExpression;
            if (member != null && member.Member is PropertyInfo)
                return member.Member.Name;

            throw new ArgumentException("Expression is not a Property", "expression");
        }
    }

public enum OrderDirection
{
    ASC = 1,
    DESC
}

所以你可以像这样使用它：

 initialQuery.OrderBy("Name", OrderDirection.ASC)

希望对你有帮助！