feat: foreignkey to model class

[waketzheng]

Description

• Before this PR:

from tortoise import Model, fields

class Group(Model):
    name = fields.CharField(20)

class Role(Model):
    name = fields.CharField(20)

class User(Model):
    group = fields.ForeignkeyField('models.Group')
    roles = fields.ManyToManyField('models.Role')

• After this PR merged:

from tortoise import Model, fields

class Group(Model):
    name = fields.CharField(20)

class Role(Model):
    name = fields.CharField(20)

class User(Model):
    group = fields.ForeignkeyField(Group)
    roles = fields.ManyToManyField(Role)

Motivation and Context

To support Django style foreignkey/o2o/m2m

How Has This Been Tested?

make ci

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed-hq]

CodSpeed Performance Report

Merging #2027 will not alter performance

_{Comparing waketzheng:feat-foreignkey-to-model (01a9de2) with develop (a725917)}

Summary

✅ 16 untouched

[coveralls]

Pull Request Test Coverage Report for Build 20420146382

Details

• 23 of 29 (79.31%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.07%) to 90.677%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/init.py	8	9	88.89%
tortoise/fields/relational.py	15	20	75.0%

Totals
Change from base Build 20418916800:	-0.07%
Covered Lines:	6648
Relevant Lines:	7216

---

💛 - Coveralls

[henadzit]

Looks like a great addition!

Does it actually work though? Can you please add tests with "self" and classes passed to relations. Thanks!

[henadzit]

You can check for that more precisely:

issubclass(child_type, parent_type)

[waketzheng]

parent_type is tortoise.models.Model, which will cause a import cycle if I use issubclass