Weird Behavior of C# or is it a mistake i did?

Question

Can anyone explain why this action returns ZERO results when "0" is passed to "page" parameter:

[HttpPost]
public ActionResult SearchProperties(string id, string offerTypeID, string propertyTypeID, string page)
{
    int temp = 0;

    var props = from s in db.Properties
                    where s.Approved && s.Available
                    select s;

    if (!String.IsNullOrEmpty(id))
    {
        Int32.TryParse(id, out temp);
        props = from s in props
                    where s.PropertyType.PropertyTypeCategoryID == temp
                    select s;

    }

    if (!String.IsNullOrEmpty(offerTypeID))
    {
        Int32.TryParse(offerTypeID, out temp);
        props = from s in props
                    where s.OfferTypeID == temp
                    select s;
    }

    if (!String.IsNullOrEmpty(propertyTypeID))
    {
        Int32.TryParse(propertyTypeID, out temp);
        props = from s in props
                    where s.PropertyTypeID == temp
                    select s;
    }

    props = props.OrderBy(s => s.PropertyID);

    int i = 0, skip = 0;
    if (!String.IsNullOrEmpty(page))
    {
          Int32.TryParse(page, out temp);
          skip = temp * 10;
    }
    else
    {
         skip = 0;
    }

    props = props.Skip(skip).Take(10);


    var marks = (from s in props.ToList()
                         select s);
    return Json(new { markers = marks });
}

Is it because i am re-using the temp variable to tryparse?
Please enlighten me because this piece of code doesnt throw any exception or caution but just returns zero records...

Answer 1

Your code is more complex that it needs to be. Simplifying it should result in a correct result or, at least, make it easier to debug. Let the framework do the conversion to int for you. If the parameters aren't required, make them nullable.

[HttpPost]
public ActionResult SearchProperties(int? id, int? offerTypeID, int? propertyTypeID, int? page)
{

    var props = from s in db.Properties
                    where s.Approved && s.Available
                    select s;

    if (id.HasValue)
    {
        props = from s in props
                    where s.PropertyType.PropertyTypeCategoryID == id.Value
                    select s;
    }

    if (offerTypeID.HasValue)
    {
        props = from s in props
                    where s.OfferTypeID == offerTypeID.Value
                    select s;
    }

    if (propertyTypeID.HasValue)
    {
        props = from s in props
                    where s.PropertyTypeID == propertyTypeID.Value
                    select s;
    }

    props = props.OrderBy(s => s.PropertyID);

    // use null coalescing operator to default to 0
    page = page ?? 0;

    int skip = page * 10;

    props = props.Skip(skip).Take(10);


    var marks = (from s in props.ToList()
                         select s);
    return Json(new { markers = marks });
}

Answer 2

More than likely it relates to reusing the temp variable in TryParse, without really utilizing TryParse properly. If any of the parameters are non-null, non-empty, then no matter what it will still try to further limit your props query whether the TryParse succeeded or not.

What you should be doing is having the TryParse in a conditional statement any time you call it.

if(Int32.TryParse(propertyTypeID, out temp))
{
    props = ...
}

You can also short-circuit the evaluation into the initial conditional too, since you require BOTH that it be non-null or empty AND succeed with the parse:

if(!String.IsNullOrEmpty(id) && Int32.TryParse(id, out temp))
{
    props = ...
}

So if it fails in parsing the string to an integer, then it won't bother with the conditional statement.