是否可以通过命名多个参数而不是将多个参数传递给NSPredicate %@
例如，我有一个directly-passed参数me和you。
public static func ConversationByUserId( userId : String ) -> [Message] {
// Either Created By me and sent to you.
// Or, created by you and sent to me
let me = UserRepo.GetLoggedInUser()?.id
var format = "( createdBy == '" + me! + "' && createdTo == '" + userId + "') "
format += " || ( createdBy == '" + userId + "' && createdTo == '" + me! + "') "
print(format)
//prints: ( createdBy == '1' && createdTo == '5') || ( createdBy == '5' && createdTo == '1')
let predicate = NSPredicate(format: format)
return Filter(predicate);
}
注意：Filter(predicate)执行操作并返回结果。到目前为止，一切都很好。我得到了预期的结果。我猜这可能会带来诸如SQL攻击之类的问题。
我可以做以下事情吗：如果可以，怎么办？
var format = "( createdBy == @me && createdTo == @you ) "
format += " || ( createdBy == @you && createdTo == @me ) "
let predicate = NSPredicate(format: format, [ "me" : me, "you" : you ])
到目前为止，我已经实现了：
format = "( createdBy == %@ && createdTo == %@ ) "
format += " || ( createdBy == %@ && createdTo == %@ ) "
let predicate = NSPredicate(format: format, me!, you, me!, you)
您可以使用NSPredicate的predicateWithSubstitutionVariables（请参阅Apple Docs）。照常创建谓词，使用“ $ variable”代替要替换的值：
var format = "( createdBy == $me && createdTo == $you ) "
format += " || ( createdBy == $you && createdTo == $me ) "
let predicate = NSPredicate(format: format)
然后使用变量名和要传递的值创建一个字典：
let subVars = ["me" : me!, "you" : you!]
最后创建谓词，将变量名替换为您的值：
let finalPredicate = predicate.predicateWithSubstitutionVariables(subVars)
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