#28193: Maximum length of Column in through table is not updated in migrations
-----------------------------------------+------------------------
Reporter: James Hiew | Owner: nobody
Type: Uncategorized | Status: new
Component: Migrations | Version: 1.11
Severity: Normal | 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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If you have a model `Foo`with a `CharField` primary key, and then another
model `Bar` which has a `ManyToManyField` relationship with `Foo`, any
changes to the `max_length` of `Foo`'s primary key is not reflected in the
max string length of the corresponding Bar-Foo m2m table column.
Starting with the below minimal example
```
from django.db import models
class Foo(models.Model):
code = models.CharField(max_length=15, primary_key=True, unique=True,
auto_created=False, editable=False)
name = models.CharField(max_length=100)
class Bar(models.Model):
foos = models.ManyToManyField(Foo)
```
Run `./manage.py makemigrations` then `./manage.py migrate`.
Change the `max_length` of `Foo.code` to a higher value e.g. 100
```
from django.db import models
class Foo(models.Model):
code = models.CharField(max_length=100, primary_key=True, unique=True,
auto_created=False, editable=False)
name = models.CharField(max_length=100)
class Bar(models.Model):
foos = models.ManyToManyField(Foo)
```
Run `./manage.py makemigrations` then `./manage.py migrate` once more.
The final `myapp_bar_foos` table DDL is:
```
CREATE TABLE "myapp_bar_foos" ("id" integer NOT NULL PRIMARY KEY
AUTOINCREMENT, "bar_id" integer NOT NULL REFERENCES "myapp_bar" ("id"),
"foo_id" varchar(15) NOT NULL REFERENCES "myapp_foo" ("code"));
CREATE UNIQUE INDEX "myapp_bar_foos_bar_id_foo_id_6037806e_uniq" ON
"myapp_bar_foos" ("bar_id", "foo_id");
CREATE INDEX "myapp_bar_foos_bar_id_f5103189" ON "myapp_bar_foos"
("bar_id");
CREATE INDEX "myapp_bar_foos_foo_id_84900b21" ON "myapp_bar_foos"
("foo_id")
```
The `foo_id` column should have been updated to type `varchar(100)` but it
remains as `varchar(15)`.
The problem is not noticeable when using SQLite (e.g. during local
development), as SQLite doesn't seem to enforce the varchar length
constraints, but Postgres does, so this issue is pernicious when moving to
production.
--
Ticket URL: <https://code.djangoproject.com/ticket/28193>
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