解析Swift查询

Question

I am building an app that will handle voting for a talent show. I want to run a query that runs against a Parse database, and return the "Total". Here's what I have:

 var query = PFQuery(className:"points")
    query.whereKey("Act", equalTo:"Act 1")
    query.findObjectsInBackgroundWithBlock {
        (objects: [AnyObject]!, error: NSError!) -> Void in
        if error == nil
        {
            // The find succeeded.
            var test = objects["Total"]
            println(test)

            // Do something with the found objects
        } else {
            // Log details of the failure
            println("nope")
        }
    }

However when I run it, the console prints "Optional 3". Any advice?

Answer 1

Querying a dictionary always returns an optional, to handle the case when a key doesn't exist.

What you can do is apply the forced unwrapping operator ! :

var test = objects["Total"]!

but that generates a runtime exception if the key is not found. A better way is using optional binding:

if let test = objects["Total"] {
    println(test)
}

The difference is that it is safer, and the if branch is executed only if objects["Total"] is not nil