迭代整个数据存储并将默认值设置为修改后的架构的最有效方法？
我有一个现有架构：
class Example (db.Model) :
row_num = db.IntegerProperty(required=True)
updated = db.IntegerProperty()
...
...
我现在已将其更新为：
class Example (db.Model) :
row_num = db.IntegerProperty(required=True)
updated = db.IntegerProperty(default=0)
...
...
但是，数据存储区中有超过 200 万个实体默认情况下没有设置 update = 0。
做到这一点最简单的方法是什么？这可以通过管理终端的单个命令来完成吗？
I have an existing schema:
class Example (db.Model) :
row_num = db.IntegerProperty(required=True)
updated = db.IntegerProperty()
...
...
I have now updated this to :
class Example (db.Model) :
row_num = db.IntegerProperty(required=True)
updated = db.IntegerProperty(default=0)
...
...
However, there are over 2 million entities in the Datastore which do not have update = 0 set by default.
What is the easiest way to do this? Can this by done by a single command from the admin terminal?
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您需要编写一个脚本来迭代对象、抓取它们（一次最多 1000 个）、更新它们的属性值，然后将它们保存回来。
不，相对于执行同类操作的标准 SQL DB（您可以只发出单个
UPDATE）而言，这并不是真正高效，但 BigTable（GAE 数据存储背后的支持技术）却不是SQL 关系数据库 - 它是一个完全不同的架构，旨在擅长不同的事情，并且没有针对一次更新数百万行中的单个字段进行优化 - 这就是为什么 GQL 语法 没有UPDATE语句的概念。编辑：
正如 David 在评论中善意指出的那样，Google 最近发布了 Mapper API 可以用来帮助实现这一点。
You'll need to write a script that iterates through the objects, grabbing them (up to 1000 at a time), updating their property value, and then saving them back.
No, this is not really efficient relative to a standard SQL DB doing the same kind of thing (where you could just issue a single
UPDATE), but BigTable (the backing technology behind the GAE Datastore) is not a SQL relational database - it's an entirely different architecture designed to be good at different things and not optimized for updating a single field across millions of rows at a time - hence why GQL syntax has no notion of anUPDATEstatement.Edit:
As David kindly pointed out in comments, Google recently released the Mapper API which can be used to assist with this.