Net Core: Create Expression function for Sorting Multi column

Question

How do I convert the following answer into an expression function? I want to enable multi column sort.

How do I create an expression tree for run time sorting?

public override Expression> SpecExpression

public static class QueryableExtensions
{
    public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortProperty, ListSortDirection sortOrder)
    {
        var type = typeof(T);
        var property = type.GetProperty(sortProperty);
        var parameter = Expression.Parameter(type, "p");
        var propertyAccess = Expression.MakeMemberAccess(parameter, property);
        var orderByExp = Expression.Lambda(propertyAccess, parameter);
        var typeArguments = new Type[] { type, property.PropertyType };
        var methodName = sortOrder == ListSortDirection.Ascending ? "OrderBy" : "OrderByDescending";
        var resultExp = Expression.Call(typeof(Queryable), methodName, typeArguments, source.Expression, Expression.Quote(orderByExp));

        return source.Provider.CreateQuery<T>(resultExp);
    }
}


private void PrintVideoList(IEnumerable<string> sortColumns, ListSortDirection sortOrder)
{
    var videos = this.GetVideos();
    var sortedVideos = videos.AsQueryable();

    foreach (var sortColumn in sortColumns.Reverse())
    {
        sortedVideos = sortedVideos.OrderBy(sortColumn, sortOrder);
    }

    // Test the results
    foreach (var video in sortedVideos)
    {
        Console.WriteLine(video.Title);
    }
}

score 0 · Answer 1 · answered Aug 26 '19 at 07:26

It looks like the problem lies in the way you call following order methods. Normally to do multisort in LINQ you do collection.OrderBy([...]).ThenBy([...]), so you need to pick different method if collection is already sorted. For example:

    public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortProperty, ListSortDirection sortOrder)
    {
        var methodCallExpression = source.Expression as MethodCallExpression;
        var isOrdered = methodCallExpression != null 
                        && (methodCallExpression.Method.Name == "OrderBy" 
                            || methodCallExpression.Method.Name == "OrderByDescending" 
                            || methodCallExpression.Method.Name == "ThenBy" 
                            || methodCallExpression.Method.Name == "ThenByDescending");

        var type = typeof(T);
        var property = type.GetProperty(sortProperty);
        var parameter = Expression.Parameter(type, "p");
        var propertyAccess = Expression.MakeMemberAccess(parameter, property);
        var orderByExp = Expression.Lambda(propertyAccess, parameter);
        var typeArguments = new Type[] { type, property.PropertyType };
        var methodName = isOrdered
            ? (sortOrder == ListSortDirection.Ascending ? "ThenBy" : "ThenByDescending")
            : (sortOrder == ListSortDirection.Ascending ? "OrderBy" : "OrderByDescending");
        var resultExp = Expression.Call(typeof(Queryable), methodName, typeArguments, source.Expression, Expression.Quote(orderByExp));

        return source.Provider.CreateQuery<T>(resultExp);
    }

Net Core: Create Expression function for Sorting Multi column

1 Answers1