# ADR-027: Standardized Naming Convention for AI and Database Types

**Date**: 2026-01-05

**Status**: Accepted

## Context

The application codebase primarily follows the standard TypeScript convention of `camelCase` for variable and property names. However, the PostgreSQL database uses `snake_case` for column names. Additionally, the AI prompts are designed to extract data that maps directly to these database columns.

Attempting to enforce `camelCase` strictly across the entire stack created friction and ambiguity, particularly in the background processing pipeline where data moves from the AI model directly to the database. Developers were unsure whether to transform keys immediately upon receipt (adding overhead) or keep them as-is.

## Decision

We will adopt a hybrid naming convention strategy to explicitly distinguish between internal application state and external/persisted data formats.

1. **Database and AI Types (`snake_case`)**:
   Interfaces, Type definitions, and Zod schemas that represent raw database rows or direct AI responses **MUST** use `snake_case`.
   - _Examples_: `AiFlyerDataSchema`, `ExtractedFlyerItemSchema`, `FlyerInsert`.
   - _Reasoning_: This avoids unnecessary mapping layers when inserting data into the database or parsing AI output. It serves as a visual cue that the data is "raw", "external", or destined for persistence.

2. **Internal Application Logic (`camelCase`)**:
   Variables, function arguments, and processed data structures used within the application logic (Service layer, UI components, utility functions) **MUST** use `camelCase`.
   - _Reasoning_: This adheres to standard JavaScript/TypeScript practices and maintains consistency with the rest of the ecosystem (React, etc.).

3. **Boundary Handling**:
   - For background jobs that primarily move data from AI to DB, preserving `snake_case` is preferred to minimize transformation logic.
   - For API responses sent to the frontend, data should generally be transformed to `camelCase` unless it is a direct dump of a database entity for a specific administrative view.

## Consequences

### Positive

- **Visual Distinction**: It is immediately obvious whether a variable holds raw data (`price_in_cents`) or processed application state (`priceInCents`).
- **Efficiency**: Reduces boilerplate code for mapping keys (e.g., `price_in_cents: data.priceInCents`) when performing bulk inserts or updates.
- **Simplicity**: AI prompts can request JSON keys that match the database schema 1:1, reducing the risk of mapping errors.

### Negative

- **Context Switching**: Developers must be mindful of the casing context.
- **Linter Configuration**: May require specific overrides or `// eslint-disable-next-line` comments if the linter is configured to strictly enforce `camelCase` everywhere.
