JSON.NET use empty string when data is not available

Question

I'm querying the Google Books API, and I'm parsing the books into a custom object like this:

foreach (JToken item in items)
{
    try
    {
        FoundBookViewModel viewModel = new FoundBookViewModel
        {
            Title = item.SelectToken("volumeInfo.title").ToString(),
            Isbn13 = item.SelectToken("volumeInfo.industryIdentifiers[1].identifier").ToString(),
            Authors = item.SelectToken("volumeInfo.authors").Select(x => x.ToString()).ToList().Aggregate((i, j) => i + ", " + j),
            Pages = item.SelectToken("volumeInfo.pageCount").ToString(),
            ImageUri = item.SelectToken("volumeInfo.imageLinks.smallThumbnail").ToString()
        };

        newList.Add(viewModel);
    }
    catch (Exception)
    {
        newList.Add(new FoundBookViewModel());
    }
}

However, sometimes not all data is available. Sometimes there is no 'pageCount', sometimes there is no 'ISBN13', etc. In those cases an exception is thrown at the ToString() part.

So what I want is this: when an exception is thrown for one of the properties, I just want it to be an empty string. But I don't know a clean way to accomplish this.

I tried multiple things:

I wrapped the whole thing inside a try catch, but then I don't know what property was empty, so I can't 'fill' it with an empty string.
I tried using safe casting ('as string') but that operation is not available on SelectToken().
Couple of other things that didn't work anyway.

Of course I could put every operation inside its own try catch, but that will result in 5 try catch blocks in this situation, so that's not what I'm looking for.

Who knows a clean way to solve this? Btw. I choose to use LINQ to JSON instead of materializing it directly because the Google Books API doesn't neatly map to simple entities (the JSON contains lots of nesting).

Alexei Levenkov · Accepted Answer · 2012-05-15 00:11:02Z

5

If you don't want to throw exception - don't...

I.e. you can change item.SelectToken("volumeInfo.pageCount").ToString() into:

item.SelectToken("volumeInfo.pageCount") == null? 
   String.Empty : item.SelectToken("volumeInfo.pageCount").ToString()

answered May 15, 2012 at 0:11

Alexei Levenkov

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5 Comments

Leon Cullens Over a year ago

Ah, the ternary operator. I already played around with that (but I didn't mention it), but I did it like this: item.SelectToken("volumeInfo.industryIdentifiers[1].identifier").ToString() ? blabla : blabla;, which is (of course) not going to work. Stupid of me. Btw, is there any way to avoid duplication of the 'item.SelectToken' part?

Alexei Levenkov Over a year ago

You can create a a function like ValueAsStringOrDefault(valueThatCanBeNull, "some default for null"). If you make it extension on string code will be very compact.

Leon Cullens Over a year ago

Thanks, I just came up with another solution: (item.SelectToken("volumeInfo.title") ?? string.Empty).ToString(). Works like a charm now :)

Alexei Levenkov Over a year ago

Yes, if SelectToken already returns string you don't even need last .ToString() (I assumed SelectToken returns some sort of non-trivial object as result)

Leon Cullens Over a year ago

It does :-) That's what the last ToString() is for.

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