如何通過Google App Engine中的ByteString字段查詢過濾？

Question

我有

class Map(db.Model): 
    urlHash= db.ByteStringProperty() 

hasher = hashlib.sha256() 
hasher.update(staticMapUrl) 
urlHash = hasher.digest() 
query = db.Query(models.Map) 
query = query.filter('urlHash =', urlHash) 
results = query.fetch(1) 

和這種類型的查詢試圖將urlHash解碼爲字符串，拋出異常

UnicodeDecodeError: 'ascii' codec can't decode byte 0xfe in position 0: ordinal not in range(128)

Answer 1

看起來它會工作，如果你明確地使散列成ByteString：

from google.appengine.api.datastore_types import ByteString 

hasher = hashlib.sha256() 
hasher.update('http://www.google.com/') 
urlHash = hasher.digest() 
bs = ByteString(urlHash) 

m = Map(urlHash=bs).put() 

query = db.Query(Map) 
query = query.filter('urlHash =', bs) 
results = query.fetch(1) 

Answer 2

一種解決方案，我發現是手動編碼爲Base64

urlHash = hasher.digest().encode('base64') 

我注意到，除了例外的名稱是UnicodeDecodeError，它也發生在編碼上。