How to Implement a Generic Extension Method for Dynamic Sorting on IQueryable Using String Column Names?

Generic extension method for dynamically sorting IQueryable using string column names

This article explores how to implement a generic extension method ApplySortFilter that allows dynamic sorting of a IQueryable collection using string column names. The core problem is how to specify the correct type for the OrderBy method at runtime.

Initial attempt

The original implementation attempts to infer the type of the sortExpression expression from OrderBy as follows:

<code>var sortExpression = Expression.Lambda<Func<T, TSortColumn>>(body, param);</code>

However, TSortColumn can only be determined dynamically, making this approach unfeasible.

A feasible solution

In a similar LINQ to SQL project, a solution was found:

<code class="language-csharp">public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string ordering, params object[] values)
{
    // 声明变量
    var type = typeof(T);
    var property = type.GetProperty(ordering);
    var parameter = Expression.Parameter(type, "p");

    // 创建表达式树
    var propertyAccess = Expression.MakeMemberAccess(parameter, property);
    var orderByExp = Expression.Lambda(propertyAccess, parameter);
    MethodCallExpression resultExp;

    // 确定排序方向
    if (ordering.StartsWith("-"))
    {
        resultExp = Expression.Call(typeof(Queryable), "OrderByDescending", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
    }
    else
    {
        resultExp = Expression.Call(typeof(Queryable), "OrderBy", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
    }

    // 创建并返回查询
    return source.Provider.CreateQuery<T>(resultExp);
}</code>

How to use

To use this method, you specify the column name to be sorted as a string:

<code class="language-csharp">IQueryable<MyEntity> query = db.MyEntities.OrderBy("Name");</code>

This will generate a query sorted by the Name column in ascending order.

This revised output provides a more concise and technically accurate description of the code and its purpose, while maintaining the original image. The formatting is also improved for readability.

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