Fix MySQL charset collation conflicts in database operations

[Bkm016]

Fix MySQL charset/collation conflicts that occur when using the inside operator with utf8_general_ci collation.

Changes

• Add useUnicode=true and connectionCollation=utf8mb4_unicode_ci to MySQL connection flags
• Add insideBinary operator for explicit binary collation when needed

Fixes

Fixes #603

Generated with Claude Code

[claude]

Claude finished @Bkm016's task —— View job

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PR Review: Fix MySQL charset collation conflicts

Reviewing the merged PR for code quality, bugs, performance, security, and test coverage.

Todo List:

• Read and analyze changed files (Filterable.kt and HostSQL.kt)
• Review MySQL connection configuration changes
• Analyze the new insideBinary operator implementation
• Assess code quality and best practices
• Check for potential bugs or issues
• Evaluate performance considerations
• Review security implications
• Assess test coverage
• Provide comprehensive feedback

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Review Summary

This PR addresses a legitimate MySQL charset/collation conflict issue. The changes are well-implemented and follow good practices. Here's my detailed analysis:

✅ Positive Aspects

1. Problem-Solution Alignment

• The fix directly addresses MySQL charset conflicts with utf8_general_ci collation
• Two complementary approaches: connection-level configuration + query-level control

2. Code Quality

• Clean, readable implementation following existing code patterns
• Proper documentation with Chinese comments matching the codebase style
• Consistent naming conventions (insideBinary follows the pattern of existing operators)

3. Connection Configuration (HostSQL.kt:16)

val flags = arrayListOf(..., "useUnicode=true", "connectionCollation=utf8mb4_unicode_ci")

• Upgrades to utf8mb4_unicode_ci which is more robust than utf8_general_ci
• Good comment explaining the purpose
• Non-breaking change - existing functionality preserved

4. Query-Level Solution (Filterable.kt:77-81)

infix fun String.insideBinary(value: Array<Any>): Criteria {
    // ...
    return Criteria("${asFormattedColumnName()} COLLATE utf8mb4_bin IN (...)", el)
}

• Provides explicit control when connection-level changes aren't sufficient
• Uses utf8mb4_bin for binary collation (case-sensitive, no locale-specific rules)

⚠️ Areas for Consideration

1. Documentation

• Could benefit from usage examples in code comments
• The relationship between connection collation and query collation could be clearer

2. Potential Edge Cases

• insideBinary is hardcoded to utf8mb4_bin - might not be suitable for all use cases
• No validation that the connection actually supports the specified collation

3. Test Coverage ⚠️

• No visible tests for the new insideBinary operator
• Connection string changes should ideally have integration tests
• Consider testing both collation scenarios to ensure they work as expected

🔒 Security Assessment

• No security concerns identified
• Changes don't introduce SQL injection vulnerabilities
• Collation changes are configuration-level, not user-input dependent

🚀 Performance Impact

• Minimal performance impact
• Connection flags are set once during connection establishment
• Query-level collation has negligible overhead
• utf8mb4_unicode_ci is generally as performant as utf8_general_ci

📋 Recommendations

1. Add tests for the new insideBinary operator
2. Consider making collation configurable in insideBinary for flexibility:

   infix fun String.insideBinary(value: Array<Any>, collation: String = "utf8mb4_bin"): Criteria

3. Add usage documentation showing when to use inside vs insideBinary

Overall Assessment: ✅ Approved

This is a solid, well-targeted fix for a real MySQL charset issue. The implementation is clean, follows existing patterns, and addresses the problem effectively without breaking changes. The only notable gap is test coverage.

Score: 8.5/10 - Excellent implementation, minor improvements suggested for documentation and testing.

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