# Module: Azaion.Common.Database.AzaionDbSchemaHolder

## Purpose
Static holder for the linq2db `MappingSchema` that maps C# entities to PostgreSQL table/column naming conventions and handles custom type conversions.

## Public Interface

| Member | Type | Description |
|--------|------|-------------|
| `MappingSchema` | `static readonly MappingSchema` | Pre-built schema with column name and type mappings |

## Internal Logic
Static constructor:
1. Creates a `MappingSchema` with a global callback that converts all column names to snake_case via `StringExtensions.ToSnakeCase`.
2. Uses `FluentMappingBuilder` to configure the `User` entity:
   - Table name: `"users"`
   - `Id`: primary key, `DataType.Guid`
   - `Role`: stored as text, with custom conversion to/from `RoleEnum` via `Enum.Parse`
   - `UserConfig`: stored as nullable JSON text, serialized/deserialized via `Newtonsoft.Json`

## Dependencies
- `User`, `RoleEnum` entities
- `StringExtensions.ToSnakeCase`
- linq2db `MappingSchema`, `FluentMappingBuilder`
- `Newtonsoft.Json`

## Consumers
- `DbFactory.LoadOptions` — passes `MappingSchema` to `DataOptions.UseMappingSchema()`

## Data Models
Defines the ORM mapping for the `users` table.

## Configuration
None — all mappings are compile-time.

## External Integrations
None directly; mappings are used when queries execute against PostgreSQL.

## Security
None.

## Tests
None.