#10320: CursorDebugWrapper should allow using iterators/generators for
executemany().
-------------------------------------+-------------------------------------
Reporter: MockSoul | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 1.0
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Design
Keywords: | decision needed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by aaugustin):
* ui_ux: => 0
* easy: => 0
Comment:
Strictly speaking, PEP 249 defines `executemany(operation,
seq_of_parameters)`, where `seq_of_parameters` is a
[http://docs.python.org/library/stdtypes.html#sequence-types-str-unicode-
list-tuple-bytearray-buffer-xrange sequence], and `len` is always
available on sequences.
However, three out of four database backends support calling
`Cursor.executemany` with an iterator as second argument:
- The built-in `sqlite3` module
[http://docs.python.org/library/sqlite3#sqlite3.Cursor.executemany also
allows] using an iterator yielding parameters instead of a sequence.
- It's clear from the source of pyscopg2, in `cursor_type.c`, that
`psycopg.Cursor.executemany` accepts iterators, and if it receives a non-
iterable, it actually converts it to an iterator -- `if
(!PyIter_Check(vars)) { vars = iter = PyObject_GetIter(vars); ... }`.
- `MySQLdb.Cursor.executemany` is implemented in Python, and the two
possible code paths use `for row in args`, which clearly works with
iterators.
- Only `cx_Oracle.Cursor.executemany` fails to accept an iterator as
argument: in `Cursor.c`, `Cursor_ExecuteMany` does `numRows =
PyList_GET_SIZE(listOfArguments);`
So, it would be a good idea to support iterators in `CursorDebugWrapper`.
Note that the performance argument is irrelevant for `CursorDebugWrapper`
itself, since it's only used when `DEBUG=True`. The real reason for the
fix is that `CursorDebugWrapper` shouldn't be more restrictive than
regular cursors.
NB: `django.db.backends.oracle.base.FormatStylePlaceholderCursor` also
relies on `params` not being a iterator, since it tries to access
`params[0]`. But that could be fixed by adding something along the lines
of `if params is not None: params = list(params)`.
--
Ticket URL: <https://code.djangoproject.com/ticket/10320#comment:6>
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