#33953: RenameModel breaking change in 4.1 with ManyToManyField
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Reporter: Timothy Thomas | Owner: nobody
Type: Uncategorized | Status: new
Component: Migrations | Version: 4.1
Severity: Normal | Keywords: RenameModel
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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Steps:
1) Create model with a ManyToManyField and a db_table in the Meta.
2) Rename model and keep db_table the same as before
The generated db schema generated from generating migrations would change
the columns on the ManyToMany relationship table to match the model name.
This matched the generated sql for interacting with this model as well.
It is possible the db_table not changing is not required.
Example:
{{{
class Publication(models.Model):
title = models.CharField(max_length=30)
class Article(models.Model):
class Meta:
db_table = "article"
headline = models.CharField(max_length=100)
publications = models.ManyToManyField(Publication)
}}}
Changed to:
{{{
class OtherArticle(models.Model):
class Meta:
db_table = "article"
headline = models.CharField(max_length=100)
publications = models.ManyToManyField(Publication)
}}}
with the corresponding migration:
{{{
operations = [
migrations.RenameModel(
old_name="Article",
new_name="OtherArticle",
),
]
}}}
Previous behavior (4.0.6):
The corresponding (functional) SQL gets generated:
{{{
'SELECT COUNT(*) AS "__count" FROM "publication" INNER JOIN
"article_publications" ON ("article"."id" =
"article_publications"."publication_id") WHERE
"article_publications"."otherarticle_id" = %s'
}}}
Current behavior (4.1):
**The same SQL gets generated but fails**. The schema that is now
generated from running the same set of migrations on a fresh db would
require:
{{{
'SELECT COUNT(*) AS "__count" FROM "publication" INNER JOIN
"article_publications" ON ("article"."id" =
"article_publications"."publication_id") WHERE
"article_publications"."article_id" = %s'
}}}
as the column now matches the old model name. However, running that SQL
would fail against our existing DB as it has ended up in a state that does
not match the behavior of the existing migrations in the current version.
--
Ticket URL: <https://code.djangoproject.com/ticket/33953>
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