many-to-many nullable columns with through

[nikelborm]

such code:

...
class TickerCollection(ormar.Model):
  class Meta(BaseMeta):
    tablename = "ticker_collection"

  id: int = ormar.Integer(name="ticker_collection_id", nullable=False, primary_key=True, autoincrement=True)

  createdByUser: Optional[User] = ormar.ForeignKey(User, name="created_by_user_id", nullable=True, unique=False)
  isPublic: bool                = ormar.Boolean(         name="is_public",          nullable=False, default=False)
  name: str                     = ormar.Text(            name="name",               nullable=False)
  description: str              = ormar.Text(            name="description",        nullable=True)
  tickers: Optional[List[Ticker]] = ormar.ManyToMany(
    to=Ticker,
    through=TickerToTickerCollection,
    related_name="tickerCollections",
    through_relation_name="ticker_collection_id",
    through_reverse_relation_name="ticker_id",
    # is_through_relation_column_nullable=False,
    # is_through_reverse_relation_column_nullable=False,
  )
...

cause such migration:

...
op.create_table('ticker_to_ticker_collection',
    sa.Column('id', sa.Integer(), nullable=False),
    sa.Column('ticker_id', sa.Integer(), nullable=True),
    sa.Column('ticker_collection_id', sa.Integer(), nullable=True),
    sa.ForeignKeyConstraint(['ticker_collection_id'], ['ticker_collection.ticker_collection_id'], name='asd1', onupdate='CASCADE', ondelete='CASCADE'),
    sa.ForeignKeyConstraint(['ticker_id'], ['ticker.ticker_id'], name='asd2', onupdate='CASCADE', ondelete='CASCADE'),
    sa.PrimaryKeyConstraint('id')
    )
...

Here ticker_id and ticker_collection_id are nullable by default, and there is no built-in way to set them non nullable.
I tried to set sql_nullable and nullable in arguments of ormar.ManyToMany but looks like it affects only typing information.
So then I added these two parameters, that will allow to override nullability of both through columns.

[collerek]

Can you rename it to shorter names: through_relation_nullable and through_reverse_relation_nullable

[collerek]

Can you add missing tests for setting that column settings nullable/ not nullable and different expected behavior?

[collerek]

Sorry for the long review time!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7f3149d) to head (ccbd159).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #852   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          204       204           
  Lines        14845     14847    +2     
=========================================
+ Hits         14845     14847    +2     

Files	Coverage Δ
ormar/fields/many_to_many.py	100.00% <100.00%> (ø)
ormar/models/helpers/sqlalchemy.py	100.00% <ø> (ø)

[codspeed-hq]

CodSpeed Performance Report

Merging #852 will degrade performances by 12.33%

_{Comparing nikelborm:many-to-many-nullable-columns (ccbd159) with master (7f3149d)}

Summary

❌ 1 regressions
✅ 83 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	master	nikelborm:many-to-many-nullable-columns	Change
❌	test_deleting_individually[10]	8.6 ms	9.8 ms	-12.33%

[nikelborm]

Hi @collerek
Since I wrote this PR, long time passed. At the time I wasn't much experienced in python\ormar and didn't have much time, so I wasn't able to properly write tests on this PR and fix your reviews, but now I hope I'm soon will be able to finish it