ios - 解析: retrieving the last object

Question

我试图通过 desc 字段“createdAt”检索选择订单的最后一个对象:在 SQL 中是这样的:

SELECT *   
FROM Message
ORDER BY createdAt DESC
LIMIT 1

我尝试了这个，但不起作用。结果是第一个对象:

let query = PFQuery(className: "Message")

query.orderByDescending("createdAt")
query.limit = 1

var lastMessage = "..."

if let objects = query.findObjects() as [AnyObject]?
{
    for object in objects
    {
        //Execute one time only and don't return the row that i want
        lastMessage = object["Text"] as! String
    }
}

通过这个懒惰的代码，我得到了我想要的，但我必须循环所有对象:

let query = PFQuery(className: "Message")

var lastMessage = "..."

if let objects = query.findObjects() as [AnyObject]?
{
    for object in objects
    {
        //Execute many times and return the row that i want int the last
        lastMessage = object["Text"] as! Strin
    }
}

Answer 1

var lastMessage = "..."        

let query = PFQuery(className: "Message", predicate: predicate)

query.orderByDescending("createdAt")

if let object = query.getFirstObject() as PFObject?
{
    lastMessage = object["Text"] as! String
}