correct way to use .alter to update element event.Event datatype

[trose-neuro]

Hi all,

As discussed on slack, I’m currently facing a quantization issue with the old Elements event.Event schema: the event_start_time and event_end_time attributes are quantized to ~10 ms for times exceeding 1000s because the datatype is float.

I see that decimal(10,4) was introduced in a later version of event.py.

We therefore have to change the datatype safely post-hoc in our rather large database. However, running on test data, I fail to get the .alter method to run.

What’s the correct way to use .alter() here? event_start_time is a primary key.

thanks,
Tobias

---

What I tried

I changed the event.Event schema definition from float to decimal(10,4):

@schema
class Event(dj.Imported):
    definition = """
    -> BehaviorRecording
    -> EventType
    event_start_time          : decimal(10, 4)
    ---
    event_end_time=null       : float
    """

Then loaded an old test database

schema = dj.Schema('tobiasrext_event')
schema.spawn_missing_classes()

Event.describe() shows float as it should:
'-> BehaviorRecording\n-> EventType\nevent_start_time : float # (second) relative to recording start\n---\nevent_end_time=null : float # (second) relative to recording start\n'

However, restarting the kernel and then using Event.alter() yields

---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
Cell In[9], [line 1](vscode-notebook-cell:?execution_count=9&line=1)
----> [1](vscode-notebook-cell:?execution_count=9&line=1) Event.alter()

File ~/miniconda3/envs/datajoint/lib/python3.8/site-packages/datajoint/table.py:135, in Table.alter(self, prompt, context)
    133     del frame
    134 old_definition = self.describe(context=context)
--> [135](https://vscode-remote+ssh-002dremote-002b7b22686f73744e616d65223a22425554227d.vscode-resource.vscode-cdn.net/home/backup_user/adamacs/notebooks/~/miniconda3/envs/datajoint/lib/python3.8/site-packages/datajoint/table.py:135) sql, external_stores = alter(self.definition, old_definition, context)
    136 if not sql:
    137     if prompt:

File ~/miniconda3/envs/datajoint/lib/python3.8/site-packages/datajoint/user_tables.py:105, in UserTable.definition(self)
    100 @property
    101 def definition(self):
    102     """
    103     :return: a string containing the table definition using the DataJoint DDL.
    104     """
--> [105](https://vscode-remote+ssh-002dremote-002b7b22686f73744e616d65223a22425554227d.vscode-resource.vscode-cdn.net/home/backup_user/adamacs/notebooks/~/miniconda3/envs/datajoint/lib/python3.8/site-packages/datajoint/user_tables.py:105)     raise NotImplementedError(
    106         'Subclasses of Table must implement the property "definition"'
    107     )

NotImplementedError: Subclasses of Table must implement the property "definition"