>From the Python documentation:
When you use the App Engine datastore, every attempt to create,
update, or delete an entity happens in a transaction.
This means, I think, that GAE will perform/create a transaction for
you, in the API, if the put() code is not already inside a
transaction.
So you don't need to code a transaction to create a child object, GAE
will do that for you.
# no need for a transaction here.
Grok(parent=myFoo).put() # python syntax
Code the transaction yourself if you need to modify multiple objects
in the entity group.
2011/1/13 Stephen Johnson <[email protected]>:
> From the documentation:
> While an app is applying changes to entities in an entity group, all other
> attempts to update any entity in the group fail at commit time. Because of
> this design, using entity groups limits the number of concurrent writes you
> can do on any entity in that group. When a transaction starts, App Engine
> uses optimistic concurrency control by checking the last update time for the
> entity group. Upon commiting a transaction for an entity group, App Engine
> again checks the last update time for the entity group. If it has changed
> since our initial check, we throw an exception. For an explanation of entity
> groups, see Entity Groups.
>
>
> On Thu, Jan 13, 2011 at 10:48 AM, Mark <[email protected]> wrote:
>>
>> Hi,
>>
>> Let's say we have an entity group hierarchy like this:
>>
>> Foo
>> |
>> --- Grok
>>
>> Foo is the entity parent. Any time I add a Grok instance to the
>> datastore, does the parent Foo instance have to be locked? Example:
>>
>> Transaction tx = pm.currentTransaction();
>> try {
>> tx.begin();
>>
>> Grok grok = new Grok();
>> pm.makePersistent(grok);
>>
>> tx.commit(); // will a parent Foo get locked now?
>> }
>> finally {
>> if (tx.isActive()) {
>> tx.rollback();
>> }
>>
>> I guess the same question then - if I'm performing a transaction on
>> the parent Foo, will all its Grok instances be locked?
>>
>> Thanks
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