如何使用Parse解决Swift中“没有结果与查询匹配”的错误

Question

I try to add (detailsObj) into username_list if a product (title in the code) already exist in the class of "grouped_products"; otherwise, I would add a product into my class and (detailsObj) as well. Everything works well, but the error of "no results matched the query" showed. It makes sense to me because if no results matched the query, I will add a product into my class. But, I don't know is there any way I can solve this error?

let detailsObj = PFObject(className: "products")
let title = 1 <<==(example)

 ........
let query = PFQuery(className: "grouped_products")
query.whereKey("title", equalTo: title)
query.getFirstObjectInBackgroundWithBlock{ (titleInParse: PFObject?, error:NSError?) -> Void in
    if titleInParse != nil{
        titleInParse!.addObjectsFromArray([detailsObj], forKey: "username_list")
        titleInParse?.saveInBackgroundWithBlock({ (success: Bool?, error:NSError?) -> Void in
            loadingNotification.hide(true)
            if (error != nil){
                self.appDelegate.displayMyAlertMessage(error!.localizedDescription, userVI: self)
                return
            } else {
                self.appDelegate.displayMyAlertMessage("Sent", userVI: self)
            }
        })
    } else if titleInParse == nil {
        let grouped_product = PFObject(className: "grouped_products")
        grouped_product["title"] = title
        grouped_product.addUniqueObject(detailsObj, forKey: "username_list")
        grouped_product.saveInBackgroundWithBlock({ (success: Bool?, error:NSError?) -> Void in
            if (error != nil){
                self.appDelegate.displayMyAlertMessage(error!.localizedDescription, userVI: self)
                return
            } else {
                self.appDelegate.displayMyAlertMessage("Sent", userVI: self)
            }
        })
    } else {
    }
}

Answer 1

The PFQuery documentation for getFirstObjectInBackgroundWithBlock: states

The block to execute. It should have the following argument signature: ^(PFObject *object, NSError *error). result will be nil if error is set OR no object was found matching the query. error will be nil if result is set OR if the query succeeded, but found no results.

Apparently that documentation is at least partly wrong in regards to the error being nil for no found results.

Therefore you should probably use findObjectsInBackgroundWithBlock: instead because if no match is found, the array will simply be empty but no error will be present (it will be nil ).

If you still want to limit the results to just one you specify a limit of 1 .