Fix JSON path operators: Use schema-based detection and correct table.column handling

[richardwooding]

Summary

Fixes two critical issues with JSON path operator generation:

Issue #59: Incorrect operator usage - was applying ->> to table names
Issue #20: Hardcoded JSON field names causing maintainability and security issues

Problem

Issue #59: Wrong SQL Generated

-- CEL: obj.metadata.user_name == "test"
-- Generated (WRONG): obj->>'metadata'->>'user_name' = 'test'
-- Should be:         obj.metadata->>'user_name' = 'test'

The code was treating obj (the table name) as something that needs JSON operators, when it should recognize obj.metadata as a regular table.column reference.

Issue #20: Hardcoded Field Names

JSON field detection relied on hardcoded lists in 7+ locations:

• Inconsistent across functions
• No way for users to specify their own JSON columns
• Security risk if fields missed
• Maintenance burden

Solution

1. Schema-Based Type Detection

• Added IsJSON bool field to pg.FieldSchema
• Created ConvertWithSchemas(ast, schemas) function
• Converter now checks schema information to determine if a field is JSON/JSONB
• Falls back to hardcoded lists for backward compatibility

2. Fixed table.column Handling

• Added getTableAndFieldFromSelectChain() to identify direct table.column access
• Updated buildJSONPathInternal() to render table.column correctly before applying JSON operators
• Now properly distinguishes between table references and JSON paths

Changes

Core Changes

• cel2sql.go: Added ConvertWithSchemas(), schema lookup methods, and schemas field to converter
• json.go: Fixed shouldUseJSONPath() and buildJSONPathInternal() to use schema information
• pg/provider.go: Added IsJSON field to FieldSchema, GetSchemas() method to interface

Testing

• json_operator_validation_test.go: Validates correct operator usage with real PostgreSQL
• json_integration_validation_test.go: Verifies generated SQL executes correctly
• Updated all JSON tests to use ConvertWithSchemas() and set IsJSON: true

PostgreSQL Validation

Created integration tests using testcontainers with PostgreSQL 17:

✅ Correct SQL that works:

obj.metadata->>'user_name' = 'test'
obj.metadata->'settings'->>'theme' = 'dark'

❌ Wrong SQL that fails:

obj->>'metadata'->>'user_name' = 'test'  
-- ERROR: operator does not exist: obj ->> unknown

Backward Compatibility

• Convert(ast) still works without schema information
• Falls back to hardcoded field lists when schemas not provided
• All existing tests pass with minimal changes

Test Results

All tests pass:

make test
# All tests: PASS
make lint  
# 0 issues

Closes

Closes #59
Addresses #20

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com