Fixed #35438 --Failed to insert an model instance into db that utilizes a UUID as its primary key and incorporates a GeneratedField.

[zshongyi]

Trac ticket number

ticket-35438

Branch description

I have defined a model that employs a UUIDField as its primary key, accompanied by a JSONField and several GeneratedFields, which are intended for indexing the JSONFields. However, when attempting to load data via loaddata from a JSON fixture, the process fails during the execution of the execute_sql method within django/db/models/SQL/compiler.py. The problematic code snippet is as follows:

def execute_sql(self, returning_fields=None):
    ....
            if not self.returning_fields:
                return []
   ....
            else:
                cols = [opts.pk.get_col(opts.db_table)]
                rows = [
                    (
                        self.connection.ops.last_insert_id(
                            cursor,
                            opts.db_table,
                            opts.pk.column,
                        ),
                    )
                ]
        converters = self.get_converters(cols)
        if converters:
            rows = list(self.apply_converters(rows, converters))
        return rows

Here, returning_fields comprises GeneratedFields, thereby preventing the method from directly returning an empty list at the outset of its logical execution. Moreover, since the model's primary key is not an AUTO_INCREMENT column (it's a UUID), last_insert_id() erroneously returns 0. This subsequently triggers an error within self.apply_converters(rows, converters) as it attempts to treat 0 as a UUID.

To address this issue, the else block logic requires adjustment to accommodate the presence of GeneratedField. Alternatively, within django/db/models/base.py's _save_table method, one could exclude GeneratedField from returning_fields. A modified approach might resemble:

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• I have attached screenshots in both light and dark modes for any UI changes.

[github-actions]

Hello! Thank you for your contribution 💪

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[sarahboyce]

Hi @zshongyi, this will need a test to be accepted 👍