Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

`select_related` doesn't work: raises AttributeError

See original GitHub issue

Describe the bug If using select_related, it raises AttributeError

Seems like the error is related to one-to-many relation

To Reproduce short:

# query:
t: Tournament = await Tournament.filter(name=tournament_name).select_related("events").first()

# exception
  File "/opt/project/api/stuff.py", line 51, in run
    t: Tournament = await Tournament.filter(name=tournament_name).select_related("events").first()
    │                     │          │           └ 'tournament'
    │                     │          └ <classmethod object at 0x7f95e62e5df0>
    │                     └ <class '__main__.Tournament'>
    └ <Tournament: 1>

  File "/usr/local/lib/python3.8/site-packages/tortoise/queryset.py", line 797, in _execute
    instance_list = await self._db.executor_class(
                          │    └ <member '_db' of 'QuerySet' objects>
                          └ <tortoise.queryset.QuerySet object at 0x7f95e5349c70>
  File "/usr/local/lib/python3.8/site-packages/tortoise/backends/base/executor.py", line 149, in execute_select
    setattr(ins, model_name, obj)
            │    │           └ <Event: 1>
            │    └ 'events'
            └ <Tournament: 1>

AttributeError: can't set attribute

Expected behavior Don’t raise, just load selected relations

Additional context

Full example:

from tortoise import Tortoise, fields, run_async
from tortoise.models import Model


class Tournament(Model):
    id = fields.IntField(pk=True)
    name = fields.TextField()

    events: fields.ReverseRelation["Event"]

    def __str__(self):
        return self.name


class Event(Model):
    id = fields.IntField(pk=True)
    name = fields.TextField()
    tournament: fields.ForeignKeyRelation[Tournament] = fields.ForeignKeyField(
        "models.Tournament",
        related_name="events",
    )

    def __str__(self):
        return self.name


async def run():
    await Tortoise.init(db_url="sqlite://:memory:", modules={"models": ["__main__"]})
    await Tortoise.generate_schemas()

    tournament_name = "tournament"
    tournament = await Tournament.create(name=tournament_name)
    await Event.create(name="First", tournament=tournament)
    await Event.create(name="Second", tournament=tournament)

    t: Tournament = await Tournament.filter(name=tournament_name).first()
    print(t, t.events)
    # tournament <tortoise.fields.relational.ReverseRelation object at 0x7f7e4b693e50>

    t: Tournament = await Tournament.filter(name=tournament_name).prefetch_related("events").first()
    print(t, t.events, list(t.events))
    # tournament <tortoise.fields.relational.ReverseRelation object at 0x7f7e4b6b3760> [<Event: 1>, <Event: 2>]

    t: Tournament = await Tournament.filter(name=tournament_name).select_related("events").first()
    print(t, t.events, list(t.events))
    # Traceback (most recent call last):
    #   File "/opt/project/api/stuff.py", line 47, in <module>
    #     run_async(run())
    #   File "/usr/local/lib/python3.8/site-packages/tortoise/__init__.py", line 636, in run_async
    #     loop.run_until_complete(coro)
    #   File "/usr/local/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
    #     return future.result()
    #   File "/opt/project/api/stuff.py", line 42, in run
    #     t: Tournament = await Tournament.filter(name=tournament_name).select_related("events").first()
    #   File "/usr/local/lib/python3.8/site-packages/tortoise/queryset.py", line 797, in _execute
    #     instance_list = await self._db.executor_class(
    #   File "/usr/local/lib/python3.8/site-packages/tortoise/backends/base/executor.py", line 149, in execute_select
    #     setattr(ins, model_name, obj)
    # AttributeError: can't set attribute

if __name__ == "__main__":
    run_async(run())

relates to #500 and #501

Issue Analytics

State:
Created 3 years ago
Reactions:2
Comments:8 (3 by maintainers)

Top GitHub Comments

3reactions

mahenzoncommented, Oct 15, 2020

@DrJackilD I’m sorry, I don’t understand your point. What’s wrong with one-to-many relationship?

There’re two ways to do it: 1 - in two queries. at first query main objects, then collect their ids and then fetch related objects 2 - in one query, using join.

anyways in both cases we’ll have to create python objects and connect them together

Creating tables and a relation with foreign key:

CREATE TABLE authors (
	author_id serial PRIMARY KEY,
	username VARCHAR ( 50 ) UNIQUE NOT NULL
);

CREATE TABLE articles (
	article_id serial PRIMARY KEY,
	title VARCHAR ( 50 ) NOT NULL,
	body text NOT NULL,
	author_id INT NOT NULL,
    CONSTRAINT fk_author
      FOREIGN KEY(author_id)
	  REFERENCES authors(author_id)
);

INSERT INTO authors (username) VALUES ('john');
INSERT INTO authors (username) VALUES ('james');
INSERT INTO authors (username) VALUES ('sam');
INSERT INTO articles (title, body, author_id) VALUES ('python lesson', 'text body', 1);
INSERT INTO articles (title, body, author_id) VALUES ('tortoise lesson', 'another body', 1);
INSERT INTO articles (title, body, author_id) VALUES ('django lesson', 'some body text', 2);

Queries:

-- selecting author by article.author_id ( =1)
SELECT author_id, username
FROM authors
WHERE author_id = 1;

author_id	username
1	john

-- selecting all authored posts by author.author_id
SELECT article_id, title, body, author_id
FROM articles
WHERE articles.author_id = 1;

article_id	title	body	author_id
1	python lesson	text body	1
2	tortoise lesson	another body	1

SELECT au.author_id, au.username, ar.article_id, ar.title, ar.body
FROM authors au
LEFT OUTER JOIN articles ar on au.author_id = ar.author_id
WHERE username ILIKE 'j%';

author_id	username	article_id	title	body
1	john	1	python lesson	text body
1	john	2	tortoise lesson	another body
2	james	3	django lesson	some body text

-- selecting one selected author's articles
SELECT au.author_id, au.username, ar.article_id, ar.title, ar.body
FROM authors au
LEFT OUTER JOIN articles ar on au.author_id = ar.author_id
WHERE username = 'james';

author_id	username	article_id	title	body
2	james	3	django lesson	some body text

-- selecting some selected authors articles
SELECT au.author_id, au.username, ar.article_id, ar.title, ar.body
FROM authors au
LEFT OUTER JOIN articles ar on au.author_id = ar.author_id
WHERE username ILIKE '%a%';

author_id	username	article_id	title	body
2	james	3	django lesson	some body text
3	sam	NULL	NULL	NULL

-- all authors with their articles
SELECT au.author_id, au.username, ar.article_id, ar.title, ar.body
FROM authors au
LEFT OUTER JOIN articles ar on au.author_id = ar.author_id;

author_id	username	article_id	title	body
1	john	1	python lesson	text body
1	john	2	tortoise lesson	another body
2	james	3	django lesson	some body text
3	sam	NULL	NULL	NULL

1reaction

Rebbit13commented, Jul 30, 2022