如何通过Google App Engine中的ByteString字段查询过滤？

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) 

和这种类型的查询试图将urlHash解码为字符串，抛出异常

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

Answer 1

看起来它会工作，如果你明确地使散列成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

一种解决方案，我发现是手动编码为Base64

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

我注意到，除了例外的名称是UnicodeDecodeError，它也发生在编码上。