MySQL索引长度限制为3072字节,复合索引包含长字符串字段时会超限。
**错误信息**:
```
Specified key was too long; max key length is 3072 bytes
```
**必须设置字符串字段长度限制**:
```rust
department: string_field(Some(100), Some(1), None).required(),
position: string_field(Some(100), Some(1), None).required(),
```
**避免在复合索引中使用过多长字符串字段**:
```rust
// ❌ 错误
indexes = [
]
```