Add and get new component in the same session doesn't work

[Remus Avram]

Hi all,

we need to add and get a component for a AssetVersion in the same session.

Ex:

unmanaged_location = session.query('Location where name is "ftrack.unmanaged"').one()
version = session.query("AssetVersion where id is 87912656-5d89-11e6-a165-005056a76761").first()
path = '/path/to/a/file'
new_com_name = 'test_component'

print len(version['components'])

version.create_component(
                                         path,
                                         data={'name': new_com_name},
                                         location=unmanaged_location
                         )
session.commit()

print len(version['components'])

Result:

1

1

Only if we reopen the session we can get the new component.

Cheers!

[Lucas Correia]

Hi,

The result of version['components'] is cached and will not be re-fetched from the server the second time you print the amount of components in the version.

To address the issue, you can add the component to the collection manually:

component = version.create_component(...)
if component not in version['components']:
    version['components'].append(component)

I'll look into if we should do this automatically within in the create_component helper method.

Regards,
Lucas

[Remus Avram]

Hi Lucas,

thanks for your answer!

Unfortunately, it doesn't help to much for us. We keep the session opened for a very long time.

At some point we query again for the components of the version. We can not have the version variable globally.

Cheers,

Remus

[Lucas Correia]

Hmm, I think I misunderstood the situation somewhat.

You should be able to "refetch" a version's components by querying it again. For example:

version = session.query(
    'select components from AssetVersion where id is "{}"'.format(
        version['id']
    )
).one()

However, there seems to be a bug which is preventing this from working properly. I've added a ticket which we'll take a look at soon.

Regards,
Lucas

[Remus Avram]

Hi Lucas,

yes, we query the versions again at some point and it doesn't fetch all the data.

Dirty fix for now:

session.reset()

Thanks for your support!

[Martin Pengelly-Phillips]

TLDR; You should be able to also do:

del version["components"]
session.populate(version, "components")

This is most likely to do with how collection references are currently managed in the API and the way Python works.

Behind every attribute are actually two data stores: local and remote. 

Remote holds values fetched from the server, whilst local is intended to track local uncommitted changes (which can be discarded client side without committing).

For simple scalar attributes this works well:

>>> user = session.query("User").first()
>>> print user.attributes.get("username")
<ftrack_api.attribute.ScalarAttribute(username) object at 63763984>
>>> print user.attributes.get("username").get_remote_value(user)
NOT_SET
>>> print user.attributes.get("username").get_local_value(user)
NOT_SET
>>> print user["username"] # Populates remote value from server as not set.
anthonyf
>>> print user.attributes.get("username").get_remote_value(user)
anthonyf
>>> print user.attributes.get("username").get_local_value(user)
NOT_SET
>>> user["username"] = "martinpp"  # Sets local value only. 
>>> print user.attributes.get("username").get_remote_value(user)
anthonyf
>>> print user.attributes.get("username").get_local_value(user)
martinpp
>>> print user["username"]  # Uses local value.
martinpp
>>> del user["username"]  # Odd syntax, but clears local value only.
>>> print user.attributes.get("username").get_remote_value(user)
anthonyf
>>> print user.attributes.get("username").get_local_value(user)
NOT_SET
>>> print user["username"]  # Uses remote value (does not refetch from server).
anthonyf

However, for Collections (list like structures in Python), the local value has to be populated whenever the remote is, so that you can modify the list at all (list.append etc). This is because remote values are always immutable.

>>> print user.attributes.get("timelogs")
<ftrack_api.attribute.CollectionAttribute(timelogs) object at 60467472>
>>> print user.attributes.get("timelogs").get_local_value(user)
NOT_SET
>>> print user.attributes.get("timelogs").get_remote_value(user)
NOT_SET
>>> print user["timelogs"]  # Fetches and populates remote value from server, but also populates the local value for modification.
<ftrack_api.collection.Collection object at 0x3b21610>
>>> print user.attributes.get("timelogs").get_local_value(user)
<ftrack_api.collection.Collection object at 0x3b21610>
>>> print user.attributes.get("timelogs").get_remote_value(user)
<ftrack_api.collection.Collection object at 0x3b24d50>

This means that you will always see the local value (even when you didn't modify it) unless you explicitly clear it and let it repopulate from the remote value on next access. If you have an updated server value to fetch you should be able to do the following which is less heavy handed than session.reset:

del user["timelogs"]
session.populate(user, "timelogs")

@ftrack-support - Might be worth adding something like this to the documentation for clarity (until the issue resolved).

ps. How do you get Python syntax highlighting in this forum? I can't see an option...

[Remus Avram]

Hi Martin,

thanks for the explanation! Really useful!

Cheers!

[Lucas Correia]

Martin, thanks for clarifying the situation with the detailed response. Much appreciated!

I'll discuss this with rest of the team.

I checked on Python highlighting, but it doesn't look like it is supported. You can use "C" highlighting to get some highlighting (e.g. strings).

Regards,
Lucas

[Remus Avram]

Hi Lucas,

any updates regarding this bug?

Unfortunately, resetting the session doesn't work very well for us. One time we reset the session, all the data which we fetched before is lost and we got 'Symbol(NOT_SET)'.

Cheers!

[Lucas Correia]

Hi Remus,

There hasn't been any updates regarding this.

Did you try the workaround @Martin suggested?

del version["components"]
session.populate(version, "components")

Regards,
Lucas

[Remus Avram]

Hi Lucas,

the workaround which Martin suggested works, but we have to check everywhere where we are using components that we delete and populate them again, which makes it difficult and sometime confusing.

Cheers!