#29500: SQLite functions crashes on NULL values
-------------------------------------+-------------------------------------
Reporter: Sergey Fedoseev | Owner: Srinivas
| Reddy Thatiparthy
Type: Bug | Status: assigned
Component: Database layer | Version: 2.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Nick Pope):
We need to be careful how we handle this to ensure that the behaviour
mirrors other backends.
I've checked PostgreSQL and when any one of the arguments to `POWER()`.
`LPAD()` or `RPAD()` is `NULL` they return `NULL`.
We should ensure that we check whether any one of the arguments is `None`
and, if so, return `None`.
We must not catch exceptions such as `TypeError` or `ValueError` to do
this as has been done in the initial version of the
[https://github.com/django/django/pull/10121 PR].
If we were to pass a string to `_sqlite_power()` we would expect a
`TypeError` which should blow up, not return `None`. Compare to
PostgreSQL:
{{{
postgres=# select power(2, 'abc');
ERROR: invalid input syntax for type double precision: "abc"
LINE 1: select power(2, 'abc');
^
}}}
The second part of the problem here is that the sqlite backend suppresses
the error message and returns a different exception:
{{{
OperationalError: user-defined function raised exception
}}}
Obviously this is not particularly helpful, but a quick search and I found
the following on Stack Overflow: https://stackoverflow.com/a/45834923
It points to the documentation for
[https://docs.python.org/3/library/sqlite3.html#sqlite3.enable_callback_tracebacks
sqlite3.enable_callback_tracebacks()].
I would recommend the following:
1. Creation of a decorator to check for `None` passed into any of the
arguments which returns `None` or calls the function as appropriate.
2. Enabling callbacks on tracebacks for sqlite3 (always / when debug
enabled / documentation change to give instruction).
Note that the outcome of this pull request will affect
[https://github.com/django/django/pull/9622 PR/9622] which I am reviewing,
particular with respect to my
[https://github.com/django/django/pull/9622#discussion_r165360894
comment].
--
Ticket URL: <https://code.djangoproject.com/ticket/29500#comment:6>
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