# Error Logging Implementation Summary

## Overview

This document summarizes the implementation of the error logging functionality in NoETL, which allows for capturing and storing detailed information about template rendering errors and other errors that occur during workflow execution.

## Problem Statement

Previously, when template rendering errors occurred in NoETL, they were only logged to the console/log file with limited information (error message and template). This made it difficult to debug template rendering errors, especially in production environments where access to logs might be limited or where errors might occur intermittently.

The requirement was to create a new `error_log` table in the NoETL meta schema to store comprehensive information about template rendering errors, including stack traces and input/output data related to the error.

## Implementation Details

### 1. Error Log Table Schema

A new `error_log` table was added to the NoETL meta schema with the following columns:

- `error_id`: A unique identifier for each error (SERIAL PRIMARY KEY)
- `timestamp`: When the error occurred (TIMESTAMP DEFAULT CURRENT_TIMESTAMP)
- `error_type`: The type of error (VARCHAR(50))
- `error_message`: The error message (TEXT)
- `execution_id`: The ID of the execution where the error occurred (VARCHAR)
- `step_id`: The ID of the step where the error occurred (VARCHAR)
- `step_name`: The name of the step where the error occurred (VARCHAR)
- `template_string`: The template that failed to render (TEXT)
- `context_data`: The context data used for rendering (JSONB)
- `stack_trace`: The stack trace of the error (TEXT)
- `input_data`: The input data related to the error (JSONB)
- `output_data`: The output data related to the error (JSONB)
- `severity`: The severity of the error (VARCHAR(20) DEFAULT 'error')
- `resolved`: Whether the error has been resolved (BOOLEAN DEFAULT FALSE)
- `resolution_notes`: Notes on how the error was resolved (TEXT)
- `resolution_timestamp`: When the error was resolved (TIMESTAMP)

Indexes were created on `timestamp`, `error_type`, `execution_id`, and `resolved` columns for efficient querying.

### 2. Helper Methods in DatabaseSchema Class

Three helper methods were added to the `DatabaseSchema` class in `schema.py`:

1. `log_error`: Logs an error to the `error_log` table
2. `mark_error_resolved`: Marks an error as resolved in the `error_log` table
3. `get_errors`: Retrieves errors from the `error_log` table with optional filtering

These methods provide a comprehensive API for working with the `error_log` table.

### 3. Error Logging in Render Module

The `render.py` module was updated to log template rendering errors to the `error_log` table:

1. Added imports for `traceback` and `DatabaseSchema`
2. Created a global instance of `DatabaseSchema` for error logging
3. Implemented a `log_template_error` helper function to encapsulate error logging logic
4. Updated error handling in `render_template` and `render_sql_template` to log errors to the database

### 4. Documentation

Comprehensive documentation was created in `error_logging.md` that explains:

1. The error logging functionality and its benefits
2. The schema of the `error_log` table
3. How to query errors and mark them as resolved
4. Best practices for using the error logging functionality
5. An example of debugging template rendering errors

## Files Modified

1. `noetl/schema.py`:
   - Added imports for `traceback` and additional type hints
   - Added the `error_log` table creation to `create_postgres_tables`
   - Added `log_error`, `mark_error_resolved`, and `get_errors` methods

2. `noetl/render.py`:
   - Added imports for `traceback` and `DatabaseSchema`
   - Added global `_db_schema` variable and `get_db_schema` function
   - Added `log_template_error` helper function
   - Updated error handling in `render_template` and `render_sql_template`

3. Added new documentation files:
   - `docs/error_logging.md`
   - `docs/error_logging_implementation_summary.md`

## Benefits

The implementation of the error logging functionality provides several benefits:

1. **Improved Debugging**: Comprehensive information about template rendering errors makes it easier to diagnose and fix issues.

2. **Historical Record**: A historical record of errors is maintained in the database, which can be useful for tracking recurring issues.

3. **Error Management**: Errors can be marked as resolved, which helps with tracking and managing issues.

4. **Filtering and Analysis**: Errors can be filtered by type, execution, and resolution status, which makes it easier to analyze patterns and trends.

5. **Context Preservation**: The context data and stack trace are preserved, which provides valuable information for debugging that might not be available in logs.

## Future Enhancements

Some potential future enhancements to the error logging functionality include:

1. **Error Notification**: Implement a notification system that alerts users when new errors occur.

2. **Error Dashboard**: Create a dashboard for visualizing and managing errors.

3. **Error Aggregation**: Implement error aggregation to group similar errors together.

4. **Automatic Resolution**: Implement automatic resolution of errors based on predefined rules.

5. **Error Archiving**: Implement a process to archive or delete old resolved errors to prevent the `error_log` table from growing too large.

6. **Additional Error Types**: Extend the error logging functionality to capture other types of errors beyond template rendering errors.

## Conclusion

The implementation of the error logging functionality in NoETL provides a powerful way to capture, store, and analyze errors that occur during template rendering and other operations. By using this functionality, users can more easily diagnose and fix errors, leading to more robust and reliable workflows.

The implementation follows best practices for database design, error handling, and code organization, and it provides a solid foundation for future enhancements to the error logging functionality.