[collerek]

Part of #137. ForeignKey(..., primary_key=True) lets a foreign key be (part of) the primary key — link tables keyed by their foreign keys and shared primary keys — with key values holding the referenced values (enrollment.pk == (student.id, course.id)). ForeignKey(..., to_field="iso_code") references a unique non-pk column, and db_constraint=False skips the database FOREIGN KEY. Relations to models keyed by a foreign key, bulk writes, QuerySet.update, flattened pydantic models and key-only models all use the referenced value; pk ordering and Model.pk filters from phase 2 work on these keys too. Multi-column foreign keys follow in phase 3b.

• Changing a key that contains a relation (enrollment.pk = (...)) updates the relation itself.
• Model.load() of a model without a key raises NoMatch without querying.
• The tests/cross_check.py safety net now keeps forward relations on its detached copies, so reverse select_related into models keyed by a foreign key is cross-checked too instead of being switched off.

[codecov-commenter]

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[codspeed]

Merging this PR will degrade performance by 6.48%

3 warnings, 1 note

⚠️ 112 benchmarks are dominated by system calls

System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.

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⚠️ 3 benchmarks with a significant change ran on different hardware

Their base and head results were measured on machines with a different CPU, core count or memory, so the changes might not come from the code. Run base and head on the same runner type.

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⚠️ 3 benchmarks with a significant change ran in a different software environment

Their base and head results were measured with a different OS or toolchain, such as compiler, runtime or library versions, so the changes might come from this difference rather than from the code. Open an affected benchmark to see what changed.

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ℹ️ 126 benchmarks have no flamegraph

The flamegraph wasn't generated: the symbols of the profiling trace could not be resolved, because no information about the language frames was collected.

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⚡ 1 improved benchmark
❌ 2 (👁 2) regressed benchmarks
✅ 123 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_get_one_wide_model[250]	11 ms	10 ms	+10.45%
👁	test_get_one[500]	4.4 ms	5 ms	-12.07%
👁	test_first[1000]	5.8 ms	6.9 ms	-15.78%

Tip

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_{Comparing feat/relation-keys-phase-3a (1493cfd) with master (123bc9a)}