#30108: Include FK constraints when adding columns in PostgreSQL
-------------------------------------+-------------------------------------
Reporter: Dan Tao | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Migrations | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Dan Tao):
I've taken a look at the code already, and I believe it's ''almost''
there.
The `BaseDatabaseSchemaEditor` class includes the attribute
`sql_create_inline_fk`, `None` by default, which is appended to a column
definition when creating a table. It is not included when adding a field,
but as far as I can tell that is simply an oversight.
Somewhat surprisingly, this attribute is ''only'' defined on the sqlite3
backend. (Why there was any need to optimize this particular backend, I
couldn't say.)
I attempted to make the following changes:
1. Update the logic in `BaseDatabaseSchemaEditor.add_field` to append
`sql_create_inline_fk` (if defined) to the column definition.
2. Add the `sql_create_inline_fk` attribute to the postgresql backend
class.
Unfortunately this ended up causing test failures because there are
[https://github.com/django/django/blob/master/tests/mutually_referential/models.py
test models] defined with a cyclic dependency. It seems that SQLite
doesn't mind if you create a table with a foreign key to another table
that doesn't exist yet, but PostgreSQL does.
{{{
psycopg2.ProgrammingError: relation "mutually_referential_child" does not
exist
}}}
I'm not sure what the solution is. Perhaps the code could be refactored so
that the postgresql backend ''only'' applies the `sql_create_inline_fk`
optimization in `add_field` (which is when this scenario can occur) and
not in `create_model` (when it shouldn't matter, because a table scan on
an empty table is not problematic).
--
Ticket URL: <https://code.djangoproject.com/ticket/30108#comment:1>
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