Do not validate when loading from the db

[henadzit]

Description

• Remove validate calls from Field.to_python_value, effectively, removing validation of objects when they are loaded from the database
• The side effect of this changes is that it is going to fix Problem with Sum with F and Field validator MinValue #1502

Motivation and Context

None of the ORMs that I checked validate records when loading them from the database:

• Django doesn't do it
• SQLAlchemy doesn't do it
• Active Record of Ruby does not do it

I do not see a reason why validating the record on loading should be a default behavior. I can see that you might want to do it in some cases but you can always call .validate explicitly. But I can imagine the issue where you add a new validator, run a data migration to fix the data but while the migration is being run, the reads are failing.

I also ran a benchmark where I was loading 100 testmodels.ValidatorModel records from the database and on average not running validation is ~5% faster for a model with many validators. I do not think at all that this is a decisive argument but something to keep in mind.

How Has This Been Tested?

• Added tests
• Ran a benchmark
• Tested on a snippet from Problem with Sum with F and Field validator MinValue #1502:

from tortoise import Tortoise, fields, run_async
from tortoise.functions import Sum
from tortoise.models import Model
from tortoise.expressions import F, Q
from tortoise.validators import MinValueValidator

class Deal(Model):
    test = fields.IntField()
    broker_payed_money = fields.FloatField(default=0, validators=[MinValueValidator(0)])

    broker_commission = fields.FloatField(null=False)

    developer_payed_money = fields.FloatField(
        null=False, default=0, validators=[MinValueValidator(0)]
    )


async def main():
    # Initializing Tortoise and creating the schema

    await Tortoise.init(  # type: ignore
        db_url="sqlite://:memory:",
        modules={"models": ["__main__"]},
    )
    await Tortoise.generate_schemas()

    await Deal.create(
        test=1, broker_payed_money=10, broker_commission=0.1, developer_payed_money=20
    )

    result = await Deal.annotate(
        balance=Sum(F("developer_payed_money") * F("broker_commission") - F("broker_payed_money")),
    ).values_list("balance")
    print("res", result)


run_async(main())

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.

[coveralls]

Pull Request Test Coverage Report for Build 11540154248

Details

• 5 of 6 (83.33%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 89.008%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/backends/sqlite/executor.py	3	4	75.0%

Files with Coverage Reduction	New Missed Lines	%
tortoise/backends/sqlite/executor.py	1	77.14%

Totals
Change from base Build 11529966516:	-0.02%
Covered Lines:	5974
Relevant Lines:	6598

---

💛 - Coveralls

[henadzit]

@abondar, would love to hear your feedback on this one!