Support more fields in GridView SortExpression

[holajan]

Change GridViewDataSet ApplySortingToQueryable method to support more fields in SortExpression separated by a comma.

Used for example like this:

<dot:GridViewTextColumn ValueBinding="{value: CeleJmeno}" AllowSorting="true" SortExpression="Prijmeni,Jmeno" HeaderText="Jméno zaměstnance" />

GridViewDataSet ApplySortingToQueryable method will be:

public virtual IQueryable<T> ApplySortingToQueryable(IQueryable<T> queryable)
{
    if (this.SortingOptions?.SortExpression == null)
    {
        return queryable;
    }

    var parameterExpression = Expression.Parameter(typeof(T), "p");
    Expression? sortExpression = null;

    foreach (string propertySortExpression in (this.SortingOptions.SortExpression ?? "").Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
    {
        Expression sortByExpression = parameterExpression;

        foreach (string prop in propertySortExpression.Trim().Split(new[] { '.' }, StringSplitOptions.RemoveEmptyEntries))
        {
            var property = sortByExpression.Type.GetTypeInfo().GetProperty(prop);
            if (property == null)
            {
                throw new Exception($"Could not sort by property '{prop}', since it does not exists.");
            }
            if (property.GetCustomAttribute<BindAttribute>() is BindAttribute bind && bind.Direction == Direction.None)
            {
                throw new Exception($"Cannot sort by an property '{prop}' that has [Bind(Direction.None)].");
            }
            if (property.GetCustomAttribute<ProtectAttribute>() is ProtectAttribute protect && protect.Settings == ProtectMode.EncryptData)
            {
                throw new Exception($"Cannot sort by an property '{prop}' that is encrypted.");
            }

            sortByExpression = Expression.Property(sortByExpression, property);
        }

        if (sortByExpression == parameterExpression)
        {
            continue;
        }

        var lambdaExpression = Expression.Lambda(sortByExpression, parameterExpression);
        var methodCallExpression = Expression.Call(typeof(Queryable), GetSortingMethodName(sortExpression == null),
            new[] { parameterExpression.Type, sortByExpression.Type },
            sortExpression ?? queryable.Expression,
            Expression.Quote(lambdaExpression));

        sortExpression = methodCallExpression;
    }

    if (sortExpression == null) //No sorting
    {
        return queryable;
    }

    return queryable.Provider.CreateQuery<T>(sortExpression);
}

private string GetSortingMethodName(bool isFirst)
{
    return isFirst ?
        this.SortingOptions.SortDescending ? "OrderByDescending" : "OrderBy" :
        this.SortingOptions.SortDescending ? "ThenByDescending" : "ThenBy";
}

[exyi]

This is planned for version 5. We already have a multi-criteria sorting implemented (https://github.com/riganti/dotvvm/blob/d57ecbb1613b37c2b2363264386d55b500412c6f/src/Framework/Core/Controls/Options/MultiCriteriaSortingOptions.cs), although it will have to be enabled specifically in each dataset. We didn't want to add more complex syntax to the SortExpression, since it then becomes nearly impossible to process client-side (flip direction, highlight sorted columns, ...)

We will let you know when we release a preview with this feature.