feat: Add YawnComparison enum to yawn-api by chinhtrung · Pull Request #125 · Faire/yawn

chinhtrung · 2026-03-25T16:04:37Z

Follow up from this backend PR, we want to create a way to pass a typesafe comparison operators (EQ, LT, LE, GT, GE) as a parameter in Kotlin.

Summary

Adds a YawnComparison enum to the com.faire.yawn.query package in yawn-api. This provides a type-safe way to pass comparison operators (EQ, LT, LE, GT, GE) as a parameter, working around Kotlin's lack of higher-rank polymorphism on function types.

Motivation

When writing helper functions that apply the same comparison operator to multiple columns with different generic types (e.g. ColumnDef<DateTime> and ColumnDef<DateTime?>), you can't pass YawnRestrictions::le directly as a function parameter because ColumnDef<F> is invariant in F and Kotlin function types require F to be fixed. An enum with a generic compare method solves this — F is resolved independently at each call site.

Changes

New file: yawn-api/src/main/kotlin/com/faire/yawn/query/YawnComparison.kt
- enum class YawnComparison with variants EQ, LT, LE, GT, GE
- Generic compare method that delegates to the corresponding YawnRestrictions method
- Placed in the same package as YawnRestrictions and YawnQueryCriterion
- Public API for consumers of yawn-api
New file: yawn-api/src/test/kotlin/com/faire/yawn/query/YawnComparisonTest.kt
- Unit tests demonstrating the realistic use case: a helper function that applies the same comparison to columns of different generic types (Int, String, Long)
- Each column's restriction type is asserted separately for readability
- Verifies switching the comparison variant changes all generated restrictions
- Verifies each variant maps to the correct restriction type
- Verifies all five variants are present
New file: yawn-database-test/src/test/kotlin/com/faire/yawn/database/YawnComparisonDatabaseTest.kt
- Database integration tests using H2 with the BookFixtures dataset
- Tests each comparison variant (LT, LE, GT, EQ) against real queries
- Tests applying a single YawnComparison to columns of different types (Long and String) in the same query via a shared helper function
- Tests that switching the comparison variant changes query results

Adds a type-safe enum for comparison operators (LT, LE, GT, GE) with a generic compare method that delegates to YawnRestrictions. This works around Kotlin's lack of higher-rank polymorphism on function types when passing comparison operators as parameters to helper functions that apply the same operator to columns with different generic types. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

- Add YawnComparisonTest with 6 tests covering all enum variants - Fix compare() parameter from 'value: F' to 'value: F & Any' to match the YawnRestrictions method signatures Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

Include equality comparison alongside the ordering comparisons, delegating to YawnRestrictions.eq. Add corresponding test. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

Replace mechanical delegation tests with tests that demonstrate the actual use case: a helper function that applies the same comparison operator to columns of different generic types (Int, String, Long). This is the pattern that Kotlin function references cannot express due to invariance of the type parameter F. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

…ottom - Destructure results into named variables (amountCriterion, etc.) and assert each column's restriction type individually - Move private buildOrderCriteria helper to the bottom of the class - Return Triple instead of List to enable destructuring Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

Put each argument on its own line with named parameters to satisfy the ArgumentListWrapping lint rule. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

yawn-api/src/main/kotlin/com/faire/yawn/query/YawnComparison.kt

yawn-api/src/test/kotlin/com/faire/yawn/query/YawnComparisonTest.kt

Test YawnComparison against a real H2 database using the existing BookFixtures data. Includes tests for each comparison variant (LT, LE, GT, EQ) and two tests demonstrating the core use case: applying a single YawnComparison to columns of different types (Long and String) in the same query via a helper function. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

yawn-api/src/main/kotlin/com/faire/yawn/query/YawnComparison.kt

chinhtrung · 2026-03-26T13:46:36Z

/poke 🙇‍♂️

faire-pr-bot · 2026-03-26T13:46:39Z

/poke 🙇‍♂️

Sorry, I didn't understand that.

chinhtrung · 2026-03-26T13:46:49Z

/poke

faire-pr-bot · 2026-03-26T13:46:53Z

/poke

Poked 1 reviewers for PR

QuinnB73

Overall, this LGTM. However, I'm not sure that this should be part of Yawn's contract or if it should remain internal to our own usage of Yawn 🤔

I.e. are we adding too many ways to do things? Curious for your thoughts (and @luanpotter's as well of course!)

QuinnB73 · 2026-03-26T16:38:09Z

yawn-api/src/test/kotlin/com/faire/yawn/query/YawnComparisonTest.kt

+    }
+
+    @Test
+    fun `all comparison variants are present`() {


I don't think this test is all that valuable, it's subsumed by the restriction type test

luanpotter · 2026-03-26T16:54:36Z

@QuinnB73 I think it is worth if there is a good use case. I think the use case here is to provide generic functions that take an operator and do multiple operations using Yawn. but I guess my question is can't it just take the restriction lambda (ie YawnRestrictions.le) instead of an enum? is iterativability a concern? or the ability of having a function of shape fn(criteira, operation, ...). and could that be already solved with the existing api

QuinnB73 · 2026-03-26T16:56:34Z

@QuinnB73 I think it is worth if there is a good use case. I think the use case here is to provide generic functions that take an operator and do multiple operations using Yawn. but I guess my question is can't it just take the restriction lambda (ie YawnRestrictions.le) instead of an enum? is iterativability a concern? or the ability of having a function of shape fn(criteira, operation, ...). and could that be already solved with the existing api

Yeah that makes sense, worth trying @chinhtrung !

chinhtrung · 2026-03-26T17:24:59Z

@QuinnB73 I think it is worth if there is a good use case. I think the use case here is to provide generic functions that take an operator and do multiple operations using Yawn. but I guess my question is can't it just take the restriction lambda (ie YawnRestrictions.le) instead of an enum? is iterativability a concern? or the ability of having a function of shape fn(criteira, operation, ...). and could that be already solved with the existing api

Yeah that makes sense, worth trying @chinhtrung !

@QuinnB73 @luanpotter yeah, I gave that a try in this backend PR, but I think we couldn't just pass the operation YawnRestrictions.le as a param.

QuinnB73 · 2026-03-26T17:25:27Z

@QuinnB73 I think it is worth if there is a good use case. I think the use case here is to provide generic functions that take an operator and do multiple operations using Yawn. but I guess my question is can't it just take the restriction lambda (ie YawnRestrictions.le) instead of an enum? is iterativability a concern? or the ability of having a function of shape fn(criteira, operation, ...). and could that be already solved with the existing api

Yeah that makes sense, worth trying @chinhtrung !

@QuinnB73 @luanpotter yeah, I gave that a try in this backend PR, but I think we couldn't just pass the operation YawnRestrictions.le as a param.

I think Luan is saying that you can pass a lambda as a param

chinhtrung · 2026-03-26T17:36:05Z

I think Luan is saying that you can pass a lambda as a param

@QuinnB73 @luanpotter, yes I got the idea of passing a lambda as a param too. However, I couldn't get to that solution because of the type checking in Kotlin. I also attempt with ai agent but it seems to mention similar things. Can you give it a try in this case? 🙏

luanpotter · 2026-03-26T17:39:57Z

could you do <F: DateTime?> ?

faire-pr-bot-app bot added ai-coauthored cursor labels Mar 25, 2026

cursor bot changed the title ~~Add YawnComparison enum to yawn-api~~ feat: Add YawnComparison enum to yawn-api Mar 25, 2026

cursoragent and others added 5 commits March 25, 2026 18:10

Add EQ variant to YawnComparison enum

a96746d

Include equality comparison alongside the ordering comparisons, delegating to YawnRestrictions.eq. Add corresponding test. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

Fix detekt ArgumentListWrapping violations in test

304fca2

Put each argument on its own line with named parameters to satisfy the ArgumentListWrapping lint rule. Co-authored-by: Nguyen Chinh Trung <chinhtrung596@gmail.com>

chinhtrung marked this pull request as ready for review March 25, 2026 19:09

chinhtrung requested a review from luanpotter March 25, 2026 19:10

luanpotter reviewed Mar 25, 2026

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chinhtrung commented Mar 25, 2026

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chinhtrung requested a review from luanpotter March 25, 2026 19:45

luanpotter requested a review from a team March 26, 2026 14:06

QuinnB73 reviewed Mar 26, 2026

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chinhtrung closed this Mar 27, 2026

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chinhtrung commented Mar 25, 2026 •

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