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将Swift数组的Realm对象转换回Realm结果(Convert Swift Array of Realm Objects Back to Realm Results)

 我有一个Entry类，其中包含FieldValue对象列表：  
class Entry: Object{
  let fieldValues = List<FieldValue>()
  //...
}

class FieldValue: Object{
  dynamic var total = 0
  //...
}
 
 我对查询中的一些条目进行了大量过滤，如下所示：  
var entryObjects = realm.objects(Entry.self).filter(...)
 
 我现在想要sum我过滤的entryObjects仍然存在的所有fieldValues entryObjects 。 因此，如果我遍历所有条目，我可以构建一个FieldValue对象数组，如下所示：  
var fieldValues = [FieldValue]()
for entry in entryObjects{
  fieldValues += entry.fieldValues  
}
 
 我现在有[FieldValue]类型的fieldValues 。 但是为了对其total属性进行sum ，它必须是Results<FieldValue>类型：  
let total:Int = fieldValues.sum(ofProperty: "total") <-- /// Error! ///
 
 如何将我的[FieldValue]数组转换回Results<FieldValue>以便我可以对它进行聚合操作？ 

I have an Entry class that has a list of FieldValue objects within it: 
class Entry: Object{
  let fieldValues = List<FieldValue>()
  //...
}

class FieldValue: Object{
  dynamic var total = 0
  //...
}
 
I do a bunch of filtering on some entries in a query like this: 
var entryObjects = realm.objects(Entry.self).filter(...)
 
I now want to sum the total values for all the fieldValues still present in my filtered entryObjects. So if I iterate through all my entries, I can build an array of FieldValue objects like this: 
var fieldValues = [FieldValue]()
for entry in entryObjects{
  fieldValues += entry.fieldValues  
}
 
I now have fieldValues of type [FieldValue]. But in order to do a sum on its total property, it has to be of type Results<FieldValue>: 
let total:Int = fieldValues.sum(ofProperty: "total") <-- /// Error! ///
 
How do I convert my [FieldValue] array back to Results<FieldValue> so I can do aggregate operations on it?

原文：https://stackoverflow.com/questions/40185315

更新时间：2023-10-31 12:10

最满意答案

 升级到Java 8，其中SecretKey和RSAPrivateKey实现Destroyable 。 但是，快速测试表明，这不适用于AES密钥，也不适用于本地生成的RSA私钥。  
 以下代码确实有效，但它仅在第二个init（！）之后失败，因此请注意可以缓存密钥信息（AES需要子密钥派生，因此子密钥可能会延续）。 在使用后使用单独的（零）密钥重新初始化任何密码可能是个好主意。 此外，它不能防止VM本身复制数据，例如在垃圾收集后的内存压缩期间。  
MyAESKey myAESKey = new MyAESKey(new byte[16]);
Cipher aes = Cipher.getInstance("AES");
aes.init(Cipher.ENCRYPT_MODE, myAESKey);
aes.doFinal("owlstead".getBytes());
myAESKey.destroy();
aes.doFinal("owlstead".getBytes());
aes.init(Cipher.ENCRYPT_MODE, myAESKey);
aes.doFinal("owlstead".getBytes());
 
 MyAESKey实现SecretKey和Destroyable 。 不要忘记销毁MyAESKey的输入。 当然，您可以使用与Java 7及更低版本的MyDestroyable接口类似的方法。  
 我所知道的唯一其他方法是使用使用安全令牌（HSM / TPM /智能卡等）的提供商，其中密钥不会离开设备。 在这种情况下，密钥也可能不会被破坏，但它至少不可用。  
 使用本机代码（使用正确类型的内存）的提供程序也可能允许销毁关键数据。 但即使在VM之外，也许很难确保密钥数据不会留在RAM或（交换）磁盘中的任何位置。 

Upgrade to Java 8 where SecretKey and RSAPrivateKey implements Destroyable. However, a quick test shows that this doesn't work for AES keys nor RSA private keys generated locally. 
The following code does work, but it fails only after the second init (!) so beware that key information may be cached (AES requires sub-key derivation, so the sub keys may linger on). It may be a good idea to re-init any cipher with a separate (zero) key after use. Furthermore, it does not protect against copying of the data by the VM itself, e.g. during memory compaction after garbage collection. 
MyAESKey myAESKey = new MyAESKey(new byte[16]);
Cipher aes = Cipher.getInstance("AES");
aes.init(Cipher.ENCRYPT_MODE, myAESKey);
aes.doFinal("owlstead".getBytes());
myAESKey.destroy();
aes.doFinal("owlstead".getBytes());
aes.init(Cipher.ENCRYPT_MODE, myAESKey);
aes.doFinal("owlstead".getBytes());
 
where MyAESKey implements both SecretKey and Destroyable. Don't forget to destroy the input to the MyAESKey as well though. You could of course use a similar approach with your own MyDestroyable interface for Java 7 and below. 
The only other method that I know of is to use a provider that uses a security token (HSM / TPM / smart card etc.) where the key does not leave the device. In that case the key may not be destroyed either, but it is at least not available. 
Providers that use native code (which uses the right kind of memory) may also allow for destruction of key data. But even outside the VM it may be hard to ensure that the key data is not left anywhere in RAM or (swap) disk.

将Swift数组的Realm对象转换回Realm结果(Convert Swift Array of Realm Objects Back to Realm Results)

最满意答案

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