我正在尝试为NSPredicate编写一个子查询。我的问题是我手边没有查询SUBQUERY的谓词部分。有没有一种方法可以将NSPredicate嵌套在SUBQUERY中?
例如,这就是我尝试过的:
let ordersPredicate = NSPredicate()//some predicate passed in
//how do I use the ordersPredicate inside the subquery??
let subQueryPredicate = NSPredicate(format: "SUBQUERY(orders, $x,'%@').@count > 0", ordersPredicate.predicateFormat)
更新:我现在必须通过执行第一个谓词并执行ANY IN查询来做一个肮脏的解决方法。它的la脚:(因为我正在其他地方以及在管道的稍后执行ordersPredicate。
let fetchRequest = NSFetchRequest()//blah
fetchRequest.predicate = orderPredicate
let orders = //execute fetch
let subQueryPredicate = NSPredicate(format: "SUBQUERY(orders, $x, ANY $x in %@).@count > 0", orders)
感谢@Willeke的一些指导,我得以提出一个解决方案。
public extension NSPredicate{
public func stringForSubQuery(prefix:String) -> String{
var predicateString = ""
if let predicate = self as? NSCompoundPredicate{
for (index, subPredicate) in predicate.subpredicates.enumerate(){
if let subPredicate = subPredicate as? NSComparisonPredicate{
predicateString = "\(predicateString) \(prefix)\(subPredicate.predicateFormat)"
}
else if let subPredicate = subPredicate as? NSCompoundPredicate{
predicateString = "\(predicateString) (\(subPredicate.stringForSubQuery(prefix)))"
}
//if its not the last predicate then append the operator string
if index < predicate.subpredicates.count - 1 {
predicateString = "\(predicateString) \(getPredicateOperatorString(predicate.compoundPredicateType))"
}
}
}
return predicateString
}
private func getPredicateOperatorString(predicateType: NSCompoundPredicateType) -> String{
switch(predicateType){
case .NotPredicateType: return "!"
case .AndPredicateType: return "&&"
case .OrPredicateType: return "||"
}
}
}
这是用法
let ordersPredicate = NSPredicate()//some predicate passed in
let ordersPredicateFormat = orderPredicate.stringForSubQuery("$x.")
let subQueryPredicate = NSPredicate(format: "SUBQUERY(orders, $x, \(ordersPredicateFormat)).@count > 0")
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