Fix DBT converter round-trip losses entity issue

[MonkeyCanCode]

Summary

Currently a primary, unique, and foreign entity whose expression differs from its name is silently lost on MSI → OSI → MSI conversion. This is due to the following:

From converters/dbt/src/ossie_dbt/msi_to_osi.py, we have following:

    @staticmethod
    def _extract_keys(entities: Sequence[Entity]) -> Tuple[Optional[List[str]], List[List[str]]]:
        primary_key: Optional[List[str]] = None
        unique_keys: List[List[str]] = []

        for entity in entities:
            col = entity.expr if entity.expr is not None else entity.name
            if entity.type is EntityType.PRIMARY:
                primary_key = [col]
            elif entity.type is EntityType.UNIQUE:
                unique_keys.append([col])

        return primary_key, unique_keys

However, from converters/dbt/src/ossie_dbt/osi_to_msi.py following:

        if field.name in primary_key_cols:
            entities.append(
                PydanticEntity(
                    name=field.name,
                    type=EntityType.PRIMARY,
                    expr=expr_or_none,
                    description=field.description,
                    label=field.label,
                    role=None,
                    config=None,
                )
            )
            return
        if field.name in unique_key_cols:
            entities.append(
                PydanticEntity(
                    name=field.name,
                    type=EntityType.UNIQUE,
                    expr=expr_or_none,
                    description=field.description,
                    label=field.label,
                    role=None,
                    config=None,
                )
            )
            return
        if field.name in foreign_key_cols:
            entities.append(
                PydanticEntity(
                    name=field.name,
                    type=EntityType.FOREIGN,
                    expr=expr_or_none,
                    description=field.description,
                    label=field.label,
                    role=None,
                    config=None,
                )
            )
            return

Here is the local test result with the fixed code and newly added test:

➜  dbt git:(fix_dbt_roundtrip) ✗ uv run pytest
========================================================================== test session starts ==========================================================================
platform darwin -- Python 3.11.13, pytest-9.1.1, pluggy-1.6.0
rootdir: /Users/yong/Desktop/GitHome/ossie/converters/dbt
configfile: pyproject.toml
testpaths: tests
plugins: syrupy-5.5.3
collected 100 items

tests/test_msi_to_osi.py ..................................................................                                                                       [ 66%]
tests/test_osi_to_msi.py ..................................                                                                                                       [100%]

------------------------------------------------------------------------ snapshot report summary ------------------------------------------------------------------------
5 snapshots passed.
========================================================================== 100 passed in 0.34s ==========================================================================

Related Issues

Checklist

Specification

• Spec changes are included in core-spec/ and follow the existing structure
• Spec changes have been discussed on the mailing list or in a linked issue
• Breaking changes to the spec are clearly called out in the summary

Ontology

• Ontology changes in ontology/ are consistent with spec changes
• New or modified terms are defined and documented

Converters

• Converter logic in converters/ is updated to reflect spec or ontology changes
• New converters include tests under the converter's test directory

Validation

• Validation rules in validation/ are updated if the spec changed
• New validation cases are covered by tests

Documentation

• docs/ is updated to reflect any user-facing changes
• New features or behaviors are documented with examples where appropriate
• CONTRIBUTING.md is updated if the contribution process changed

Examples

• examples/ are added or updated for any new spec constructs or converter support

Tests

• All existing tests pass (pytest / CI green)
• New functionality is covered by tests

Compliance

• ASF license headers are present on all new source files
• No third-party dependencies are added without PMC/IPMC approval

[MonkeyCanCode]

@QMalcolm mind take a look?