# Catalog - 系統目錄
`src/catalog/`
## 模組結構
| `mod.rs` | 模組入口 |
| `catalog.rs` | 目錄管理 |
| `meta.rs` | 中繼資料定義 |
## Catalog
```rust
pub struct Catalog {
tables: HashMap<String, TableSchema>,
indices: HashMap<String, IndexDef>,
}
```
### 主要方法
```rust
impl Catalog {
pub fn new() -> Self;
pub fn get_table(&self, name: &str) -> Option<&TableSchema>;
pub fn add_table(&mut self, schema: TableSchema);
pub fn drop_table(&mut self, name: &str);
pub fn get_index(&self, name: &str) -> Option<&IndexDef>;
pub fn add_index(&mut self, idx: IndexDef);
pub fn drop_index(&mut self, name: &str);
}
```
## TableSchema 表格結構
```rust
pub struct TableSchema {
pub name: String,
pub columns: Vec<ColumnDef>,
pub rowid_column: Option<String>,
pub foreign_keys: Vec<ForeignKey>,
pub constraints: Vec<TableConstraint>,
}
```
## ColumnDef 欄位定義
```rust
pub struct ColumnDef {
pub name: String,
pub data_type: SqlType,
pub not_null: bool,
pub primary_key: bool,
pub default: Option<Expr>,
pub autoincrement: bool,
}
```
## IndexDef 索引定義
```rust
pub struct IndexDef {
pub name: String,
pub table: String,
pub columns: Vec<String>,
pub unique: bool,
}
```
## 系統目錄表
SQLite 風格的系統表：
| `sqlite_master` | 主目錄表 |
| `sqlite_schema` | 結構描述資訊 |
| `sqlite_sequence` | AUTOINCREMENT 計數器 |
## 測試
```bash
cargo test catalog
```