ios - CloudKit 仅获取第一条记录

Question

我想知道如何从 CloudKit 表中获取第一条记录。例如，我有一个“类”表，我只想获取最后修改的类，而不是像现在这样获取所有类:

let pred = NSPredicate(format: "Students CONTAINS %@", studentRecord)
var query = CKQuery(recordType: "Class", predicate: pred)
publicDB.performQuery(query, inZoneWithID: nil) {
    records, error in
    if error != nil {
        println("\(error)")
    } else {
        if records.count > 0 {
            for record in records {
                println("\(record)")
            }
        }
    }
}

Answer 1

嗯，对于您的特定场景，您需要两件事。

1. 在“已修改”上添加排序，这是 Apple 在每条记录上生成的字段。
2. 您需要使用 CKQueryOperation 对您的 CKQuery 施加 LIMIT。

您的代码应如下所示:

let pred = NSPredicate(format: "Students CONTAINS %@", studentRecord)
var query = CKQuery(recordType: "Class", predicate: pred)
let sort = NSSortDescriptor(key: "Modified", ascending: false)
query.sortDescriptors = [sort]
var queryOperation = CKQueryOperation (query: query)
queryOperation.resultsLimit = 1
queryOperation.recordFetchedBlock = {
    record in
    println("\(record)")
}
queryOperation.queryCompletionBlock = {
    queryCursor, error in
    if error != nil {
        println("\(error)")
    }
}
publicDB.addOperation(queryOperation)