How Can I Dynamically Specify the OrderBy Property in LINQ?

Dynamicly specify LINQ OrderBy parameters

In C#, LINQ’s OrderBy method allows sorting data based on specified properties or expressions. But how do we dynamically specify the property or expression to sort by?

Question:

Given a parameter, we want to sort the list of students based on the specified attribute, but currently, the attribute name in the OrderBy call is hardcoded.

Example:

<code class="language-csharp">List<Student> existingStudents = new List<Student> { new Student { ... }, new Student { ... } };
List<Student> orderByAddress = existingStudents.OrderBy(c => c.Address).ToList();</code>

Target:

We want to take the property name as parameter instead of using static property name in OrderBy.

Example:

<code class="language-csharp">string param = "City";
List<Student> orderByCity = existingStudents.OrderBy(c => c.City).ToList(); //仍然需要明确指定属性</code>

Solution:

Using reflection, we can dynamically construct an OrderBy expression:

<code class="language-csharp">public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string orderByProperty, bool desc)
{
    // ...  (反射代码构建表达式树) ...
    return source.Provider.CreateQuery<T>(resultExpression);
}</code>

You can then dynamically sort by specified attributes:

<code class="language-csharp">existingStudents.OrderBy("City", true); // 降序
existingStudents.OrderBy("City", false); // 升序</code>

(Note: The complete reflection code implementation is more complicated and is omitted here. You need to use the System.Linq.Expressions namespace to build the expression tree and handle possible exceptions, such as attributes that do not exist.) This solution provides the idea of ​​dynamic sorting. The complete implementation requires writing more robust code according to the actual situation. Using c => param directly is a mistake, as this will only sort the parameter string itself, not the properties of the student object. Reflection must be used to dynamically obtain properties and build the correct expression tree.

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