使用LINQ进行反射而无需for或foreach

Question

I'm trying to filter a list of objects based on specific properties via reflection. The problem is I can't find a way to do it without a for or foreach loop. Not that there's anything wrong with that, but I'd like to use LINQ to capture the object I'm filtering for instead.

string prop = 'SortOrder';
string propVal = '1';
PropertyInfo result;
//StackObject is passed in and can contain over a million objects
var objList = (StackObject as IEnumerable).Cast<object>().ToList();

foreach (var obj in objList)
{
    PropertyInfo filterProperty = obj.GetType().GetProperty(prop);

    if (filterProperty.GetValue(obj, null).ToString() == propVal)
    {
        result = (PropertyInfo)obj;
        return result;
    }
}

I have tried this:

var objList = (StackObject as IEnumerable).Cast<object>().ToList();
PropertyInfo desiredObject = (PropertyInfo)objList.Where(o => o.GetType().GetProperty(prop).GetValue(o, null).ToString() == propVal);

But I keep getting a list of objects or null instead of the specific object. The end goal is to be more performant (as the list of objects can grow quite large at times) and filter appropriately for a given property.

Answer 1

You would want to use Select to get your initial property info along with the object. You can then filter to all of the matches with Where , or to the first match with FirstOrDefault .

Something like this should work:

var result = (StackObject as IEnumerable)
    .Cast<object>()
    .Select(obj => (Obj: obj, Prop: obj.GetType().GetProperty(prop)))
    .FirstOrDefault(tup => tup.Prop?.GetValue(tup.Obj, null)?.ToString() == propVal)
    ?.Prop;

This is utilizing a tuple of the object and the property within the select syntax so that your later filtering has access to both. The same predicate in the FirstOrDefault should work for a Where should you want to get all matches.

As an alternative to tuples, you could use an anonymous object. With an anonymous object, you may get something like this:

var result = (StackObject as IEnumerable)
    .Cast<object>()
    .Select(obj => new { Obj = obj, Prop = obj.GetType().GetProperty(prop)} )
    .FirstOrDefault(item => item.Prop?.GetValue(item.Obj, null)?.ToString() == propVal)
    ?.Prop;

If you wanted to use Where , you would need an additional Select to get the item => item.Prop values from the filtered enumerable.