public static IQueryable <T> OrderBy <T>(this IQueryable <T> query, string orderBySpec, IDictionary <string, string> nameMapping = null)
{
if (string.IsNullOrWhiteSpace(orderBySpec))
{
return(query);
}
var memberInfos = typeof(T).GetAllProperties();
string propRef;
bool isDesc;
var segments = orderBySpec.SplitNames();
foreach (var segm in segments)
{
if (string.IsNullOrWhiteSpace(segm))
{
continue;
}
var arr = segm.SplitNames(':', '-'); // '-' is better for URLs, ':' is a special symbol, must be escaped
if (arr.Length < 2)
{
propRef = segm;
isDesc = false;
}
else
{
propRef = arr[0];
var ascDesc = arr[1].Trim().ToUpper();
if (!string.IsNullOrEmpty(ascDesc))
{
Util.Check(ascDesc == "ASC" || ascDesc == "DESC", "Invalid OrderBy spec, ASC/DESC flag: '{0}'", ascDesc);
}
isDesc = ascDesc == "DESC";
}
Util.Check(!string.IsNullOrWhiteSpace(propRef), "Invalid OrderBy spec, empty property ref: '{0}'", orderBySpec);
//Build expression ent => ent.Prop
string mappedName;
if (nameMapping != null && nameMapping.TryGetValue(propRef, out mappedName))
{
propRef = mappedName;
}
//propRef might be a chain of reads: User.Person.FirstName; let's unpack it and build expression
var prm = Expression.Parameter(typeof(T), "@ent");
var memberGet = ExpressionHelper.BuildChainedPropReader(prm, propRef);
var lambda = Expression.Lambda <Func <T, object> >(memberGet, prm);
// Note: we might need to use ThenBy and ThenByDescending here for all clauses after first.
// But it looks like it works OK, at least in SQL, the ORDER BY clause is correct
query = isDesc ? query.OrderByDescending(lambda) : query.OrderBy(lambda);
}
return(query);
}//method
