Adding nullable TextField/JSONField with default fails on MySQL 8.0.13+.

[Omkar Deshpande]

Versions Involved:

Django: 3.2.4
Python: 3.8.7
MySQL: 8.0.19
OS: CentOS 7

---

Referenced:

Ticket: https://code.djangoproject.com/ticket/32503
PR: ​https://github.com/django/django/pull/14421
Commit: ​https://github.com/django/django/pull/14421/commits/5e04e84d67da8163f365e9f5fcd169e2630e2873

---

New project used for reproducing the error:

Project: ​https://github.com/omkar-dsd/almanac

---

Error:

django.db.utils.OperationalError: (1101, "BLOB, TEXT, GEOMETRY or JSON column 'new_txt' can't have a default value")

Occurred on migration:

migrations.AddField(
            model_name='nucleusdata',
            name='new_txt',
            field=models.TextField(blank=True, default='abc', null=True),
        )

---

How to reproduce:

1. Add new TextField or JSONField with default on pre-existing model, with Django < 3.2
2. Upgrade Django version to 3.2.4
3. Run migration which involves creation of of the new field added in step 1.

---

Details:

This occurs for all JSON and Text Fields with default value.

This occurred to me when I upgraded from Django 2.2.24 to 3.2.4 and ran migrations on fresh DB.
This error did not occur when upgraded from Django 2.2.24 to 3.1.12. And, it occurs for all 3.2.X till date.
New project was created to demonstrate the issue it available on the above GitHub link for reference.

[Omkar Deshpande]

Python Project Requirement

[Omkar Deshpande]

models.py

[Omkar Deshpande]

Initial Migration to Create the Table

[Omkar Deshpande]

Second Migration to Alter the fields

[Omkar Deshpande]

Third Migration to AddField with default value on which migration breaks

[Omkar Deshpande]

Full Error Traceback

[Mariusz Felisiak]

Regression in d4ac23bee1c84d8e4610350202ac068fc90f38c0.
Reproduced at fcd44b889f36c4be87910745614a0a4c88d7a3d8.

We can consider backporting 5e04e84d67da8163f365e9f5fcd169e2630e2873 and fix it with:

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index c409464eca..77c5ce1629 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -900,7 +900,7 @@ class BaseDatabaseSchemaEditor:
 
         new_db_params = new_field.db_parameters(connection=self.connection)
         if drop:
-            if new_field.null:
+            if new_field.null and not self.skip_default_on_alter(new_field):
                 sql = self.sql_alter_column_no_default_null
             else:
                 sql = self.sql_alter_column_no_default

[Mariusz Felisiak]

Omkar, thanks for the detailed report!

[Mariusz Felisiak]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In fa0433d0:

Fixed #32832 -- Fixed adding BLOB/TEXT nullable field with default on MySQL 8.0.13+.

Regression in d4ac23bee1c84d8e4610350202ac068fc90f38c0.

Thanks Omkar Deshpande for the report.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 826a1659:

[3.2.x] Fixed #32832 -- Fixed adding BLOB/TEXT nullable field with default on MySQL 8.0.13+.

Regression in d4ac23bee1c84d8e4610350202ac068fc90f38c0.

Thanks Omkar Deshpande for the report.

Backport of fa0433d05f213afe4c67055006320f7aba4c8108 from main