Complex join conditions and composite-key parent relations

[gwynne]

This release includes significant feature additions, cleanups, and improvements:

• More complex conditions are now supported when using .join() in queries; the != operator is now supported, and conditions may be combined using &&.
• The new @CompositeParent property type may be used to reference a model which uses @CompositeID as the parent of another model.
• ModelAlias now works in most cases that were previously broken; among other cases, it is now possible to alias models which specify a space.
• The poorly-considered "duplicate" SQLList type previously available in FluentSQL is now deprecated; use SQLKit's version instead.
• Various code cleanups and minor performance improvements.
• Fields and ModelAlias now have detailed code documentation.
• A new type, SomeCodingKey, is now available, providing a complete implementation of CodingKey for convenience in various cases when arbitrary string or integer keys are desired.
• The SQL generated by FluentKit queries should now be slightly more consistent.

[codecov-commenter]

Codecov Report

Merging #547 (ea0d409) into main (a2fe755) will decrease coverage by 0.13%. The diff coverage is 43.84%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #547 +/- ## ========================================== - Coverage 45.82% 45.70% -0.13% ========================================== Files 101 103 +2 Lines 5724 5842 +118 ========================================== + Hits 2623 2670 +47 - Misses 3101 3172 +71 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `45.70% <43.84%> (-0.13%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/FluentKit/Database/DatabaseInput.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvRGF0YWJhc2UvRGF0YWJhc2VJbnB1dC5zd2lmdA==) | `0.00% <0.00%> (ø)` | | | [Sources/FluentKit/FluentError.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvRmx1ZW50RXJyb3Iuc3dpZnQ=) | `25.58% <0.00%> (-5.85%)` | :arrow_down: | | [Sources/FluentKit/Model/ModelAlias.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvTW9kZWwvTW9kZWxBbGlhcy5zd2lmdA==) | `0.00% <0.00%> (ø)` | | | [Sources/FluentKit/Operators/FieldOperators.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvT3BlcmF0b3JzL0ZpZWxkT3BlcmF0b3JzLnN3aWZ0) | `0.00% <0.00%> (ø)` | | | [Sources/FluentKit/Properties/CompositeParent.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9Db21wb3NpdGVQYXJlbnQuc3dpZnQ=) | `0.00% <0.00%> (ø)` | | | [Sources/FluentKit/Properties/Parent.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9QYXJlbnQuc3dpZnQ=) | `32.22% <0.00%> (ø)` | | | [Sources/FluentKit/Properties/Property.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9Qcm9wZXJ0eS5zd2lmdA==) | `76.92% <ø> (ø)` | | | [Sources/FluentKit/Properties/Relation.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUHJvcGVydGllcy9SZWxhdGlvbi5zd2lmdA==) | `75.00% <ø> (ø)` | | | [.../FluentKit/Query/Database/DatabaseQuery+Join.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvUXVlcnkvRGF0YWJhc2UvRGF0YWJhc2VRdWVyeStKb2luLnN3aWZ0) | `0.00% <0.00%> (ø)` | | | [Sources/FluentSQL/SQLList+Deprecated.swift](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRTUUwvU1FMTGlzdCtEZXByZWNhdGVkLnN3aWZ0) | `0.00% <0.00%> (ø)` | | | ... and [24 more](https://codecov.io/gh/vapor/fluent-kit/pull/547?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | |

[VaporBot]

These changes are now available in 1.37.0