# Migration Guide: Repository Queries
This guide helps migrate from id-based repository methods to the new filter-oriented QueryRepository API.
## What changed
- Added QueryRepository<T> with associated types:
- type Filter
- type SortKey
- methods: find_one, find, exists, count, delete_where
- Legacy methods on Repository<T> are deprecated (but available):
- find_by_id, find_all, delete(id)
## Minimal migration steps
1. Define domain-owned filter and sort key types for each aggregate you query.
```rust
#[derive(Clone, Debug)]
pub enum UserFilter { ById(String), ByEmail(String), All }
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum UserSortKey { CreatedAt, Email }
```
2. Implement QueryRepository for your adapters.
```rust
impl QueryRepository<User> for InMemoryUserRepository {
type Filter = UserFilter;
type SortKey = UserSortKey;
fn find_one(&self, f: &Self::Filter) -> HexResult<Option<User>> { /* match filter */ }
fn find(&self, f: &Self::Filter, opts: FindOptions<Self::SortKey>) -> HexResult<Vec<User>> { /* filter + sort + page */ }
}
```
3. Replace usages:
- find_by_id(id) -> find_one(&Filter::ById(id))
- find_all() -> find(&Filter::All, FindOptions::default())
- Add pagination/sorting with FindOptions { sort, limit, offset }
4. Optional: delete by filter
- Replace delete(id) with delete_where(&Filter::ById(id)) when appropriate.
## Tips
- Keep filters small and composable; avoid storage-specific DSLs
- Use exists and count for efficient UIs without fetching full pages
- Maintain legacy methods temporarily while refactoring call sites
See hex/README.md for a full example and tutorials/04-cqrs-basics for CQRS usage.