Question

I have a web service that returns a JSON object when the web service is queried and a match is found, an example of a successful return is below:

{"terms":[{"term":{"termName":"Focus Puller","definition":"A focus puller or 1st assistant camera..."}}]}

If the query does not produce a match it returns:

Errant query: SELECT termName, definition FROM terms WHERE termID = xxx

Now, when I access this through my Win 8 Metro app I parson the JSON notation object using the following code to get a JS object:

var searchTerm = JSON.parse(Result.responseText)

I then have code that processes searchTerm and binds the returned values to the app page control. If I enter in a successful query that finds match in the DB everything works great.

What I can’t work out is a way of validating a bad query. I want to test the value that is returned by var searchTerm = JSON.parse(Result.responseText) and continue doing what I’m doing now if it is a successful result, but then handle the result differently on failure. What check should I make to test this? I am happy to implement additional validation either in my app or in the web service, any advice is appreciated.

Thanks!

Answer 1

There are a couple of different ways to approach this.

One approach would be to utilize the HTTP response headers to relay information about the query (i.e. HTTP 200 status for a found record, 404 for a record that is not found, 400 for a bad request, etc.). You could then inspect the response code to determine what you need to do. The pro of this approach is that this would not require any change to the response message format. The con might be that you then have to modify the headers being returned. This is more typical of the approach used with true RESTful services.

Another approach might be to return success/error messaging as part of the structured JSON response. Such that your JSON might look like:

{
    "result":"found",
    "message":
        {
            "terms":[{"term":{"termName":"Focus Puller","definition":"A focus puller or 1st assistant camera..."}}]}
        }
}

You could obviously change the value of result in the data to return an error and place the error message in message.

The pros here is that you don’t have to worry about header modification, and that your returned data would always be parse-able via JSON.parse(). The con is that now you have extra verbosity in your response messaging.