#31731: Dead code in the sequence_reset_sql for postgres and oracle
-------------------------------------+-------------------------------------
Reporter: axil | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: sql sequence reset | Triage Stage:
postgres oracle | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by axil:
Old description:
> In the definition of `sequence_reset_sql` function in
> `django/db/backends/postgresql/operations.py` and
> `django/db/backends/oracle/operations.py` files
>
> {{{
> def sequence_reset_sql(self, style, model_list):
> from django.db import models
> output = []
> qn = self.quote_name
>
> for model in model_list:
> # Use `coalesce` to set the sequence for each model to the
> max pk value if there are records,
> # or 1 if there are none. Set the `is_called` property (the
> third argument to `setval`) to true
> # if there are records (as the max pk value is already in
> use), otherwise set it to false.
> # Use pg_get_serial_sequence to get the underlying sequence
> name from the table name
> # and column name (available since PostgreSQL 8)
>
> for f in model._meta.local_fields:
> if isinstance(f, models.AutoField):
> output.append(
> "%s setval(pg_get_serial_sequence('%s','%s'), "
> "coalesce(max(%s), 1), max(%s) %s null) %s %s;" %
> (
> style.SQL_KEYWORD('SELECT'),
> style.SQL_TABLE(qn(model._meta.db_table)),
> style.SQL_FIELD(f.column),
> style.SQL_FIELD(qn(f.column)),
> style.SQL_FIELD(qn(f.column)),
> style.SQL_KEYWORD('IS NOT'),
> style.SQL_KEYWORD('FROM'),
> style.SQL_TABLE(qn(model._meta.db_table)),
> )
> )
> break # Only one AutoField is allowed per model, so
> don't bother continuing.
> for f in model._meta.many_to_many:
> if not f.remote_field.through:
> ## output.append(
> ## "%s setval(pg_get_serial_sequence('%s','%s'), "
> ## "coalesce(max(%s), 1), max(%s) %s null) %s %s;"
> % (
> ## style.SQL_KEYWORD('SELECT'),
> ## style.SQL_TABLE(qn(f.m2m_db_table())),
> ## style.SQL_FIELD('id'),
> ## style.SQL_FIELD(qn('id')),
> ## style.SQL_FIELD(qn('id')),
> ## style.SQL_KEYWORD('IS NOT'),
> ## style.SQL_KEYWORD('FROM'),
> ## style.SQL_TABLE(qn(f.m2m_db_table()))
> ## )
> ## )
> return output
> }}}
>
> The statement marked with ## never executes.
>
> 11 years ago when this code was written (ticket #11107) this `if not
> f.remote_field.through:` was a valid way to check if the
> `ManyToManyField` uses the user-provided intermediate `through` table or
> not. Nowadays `bool(f.remote_field.through)` always evaluates to `True`,
> no matter if it is a user-provided or an automatic table.
>
> But actually it is not necessary anymore. This function is used in three
> places in django code:
>
> 1) `manage.py sqlsequencereset` uses
> {{{
> models = app_config.get_models(include_auto_created=True)
> }}}
> instead of the original
> {{{
> models = app_config.get_models()
> }}}
> which was there when this ticket 11107 was merged. So now it fetches both
> automatic and user-defined intermediate tables at the ealier stage,
> before going.
>
> 2) loaddata is unaffected by this branch of execution because it needs to
> reset the sequences solely of the models that are being loaded and not of
> any others. To be 100% sure I included the fixture from ticket 11107 as
> the testcase and it passes without entering into that execution branch.
>
> 3) `django.contrib.sites.management.create_default_site` applies it to
> the Site model
> {{{
> sequence_sql = connections[using].ops.sequence_reset_sql(no_style(),
> [Site])
> }}}
> which has no manytomany keys, so it is unaffected.
>
> I would suggest to remove the code marked with "##" and check for other
> usages of `f.remote_field.through` for similar issues.
New description:
In the definition of `sequence_reset_sql` function in
`django/db/backends/postgresql/operations.py` and
`django/db/backends/oracle/operations.py` files
{{{
def sequence_reset_sql(self, style, model_list):
from django.db import models
output = []
qn = self.quote_name
for model in model_list:
# Use `coalesce` to set the sequence for each model to the max
pk value if there are records,
# or 1 if there are none. Set the `is_called` property (the
third argument to `setval`) to true
# if there are records (as the max pk value is already in
use), otherwise set it to false.
# Use pg_get_serial_sequence to get the underlying sequence
name from the table name
# and column name (available since PostgreSQL 8)
for f in model._meta.local_fields:
if isinstance(f, models.AutoField):
output.append(
"%s setval(pg_get_serial_sequence('%s','%s'), "
"coalesce(max(%s), 1), max(%s) %s null) %s %s;" %
(
style.SQL_KEYWORD('SELECT'),
style.SQL_TABLE(qn(model._meta.db_table)),
style.SQL_FIELD(f.column),
style.SQL_FIELD(qn(f.column)),
style.SQL_FIELD(qn(f.column)),
style.SQL_KEYWORD('IS NOT'),
style.SQL_KEYWORD('FROM'),
style.SQL_TABLE(qn(model._meta.db_table)),
)
)
break # Only one AutoField is allowed per model, so
don't bother continuing.
for f in model._meta.many_to_many:
if not f.remote_field.through:
## output.append(
## "%s setval(pg_get_serial_sequence('%s','%s'), "
## "coalesce(max(%s), 1), max(%s) %s null) %s %s;"
% (
## style.SQL_KEYWORD('SELECT'),
## style.SQL_TABLE(qn(f.m2m_db_table())),
## style.SQL_FIELD('id'),
## style.SQL_FIELD(qn('id')),
## style.SQL_FIELD(qn('id')),
## style.SQL_KEYWORD('IS NOT'),
## style.SQL_KEYWORD('FROM'),
## style.SQL_TABLE(qn(f.m2m_db_table()))
## )
## )
return output
}}}
The statement marked with ## never executes.
11 years ago when this code was written (ticket #11107) this `if not
f.remote_field.through:` was a valid way to check if the `ManyToManyField`
uses the user-provided intermediate `through` table or not. Nowadays
`bool(f.remote_field.through)` always evaluates to `True`, no matter if it
is a user-provided or an automatic table.
But actually it is not necessary anymore. This function is used in three
places in django code:
1) `manage.py sqlsequencereset` uses
{{{
models = app_config.get_models(include_auto_created=True)
}}}
instead of the original
{{{
models = app_config.get_models()
}}}
which was there when this ticket 11107 was merged. So now it fetches both
automatic and user-defined intermediate tables at the ealier stage, before
going.
2) loaddata is unaffected by this branch of execution because it needs to
reset the sequences solely of the models that are being loaded and not of
any others. To be 100% sure I created a project reproduced the models.py
from 11107 and loaded the fixture provided there with `manage.py loaddata`
- it succeeded without entering into that execution branch.
3) `django.contrib.sites.management.create_default_site` applies it to the
Site model
{{{
sequence_sql = connections[using].ops.sequence_reset_sql(no_style(),
[Site])
}}}
which has no manytomany keys, so it is unaffected.
I would suggest to remove the code marked with "##" and check for other
usages of `f.remote_field.through` for similar issues.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/31731#comment:1>
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