How to Dynamically Order LINQ Results Using OrderBy?

Use OrderBy to dynamically sort LINQ results

Question:

How to dynamically specify the parameters passed to the OrderBy method based on the parameters?

Details:

Suppose you have a list of students and want to sort them by a specific attribute. The current implementation uses hardcoded property names, but how do I pass property names as parameters?

Example:

<code class="language-C#">string param = "City";
List<student> orderByAddress = existingStudents.OrderByDescending(c => param).ToList();</code>

Solution:

The solution involves dynamically building expression trees using reflection. An extension method can be created as follows:

<code class="language-C#">public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty,
                          bool desc) 
{
     string command = desc ? "OrderByDescending" : "OrderBy";
     var type = typeof(TEntity);
     var property = type.GetProperty(orderByProperty);
     var parameter = Expression.Parameter(type, "p");
     var propertyAccess = Expression.MakeMemberAccess(parameter, property);
     var orderByExpression = Expression.Lambda(propertyAccess, parameter);
     var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },
                                   source.Expression, Expression.Quote(orderByExpression));
     return source.Provider.CreateQuery<TEntity>(resultExpression);
}</code>

The

orderByProperty parameter represents the attribute name, and desc determines the sorting order.

Usage:

You can now sort your student list dynamically:

<code class="language-C#">existingStudents.OrderBy("City", true); // 按城市降序排序
existingStudents.OrderBy("City", false); // 按城市升序排序</code>

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